White Clover

Images of White Clover

Summary

(Dutch White Clover, New Zealand White Clover, Ladino Clover)
Trifolium repens
Perennial legume
Many forms; small-leafed form is called "wild white"; large-leafed forms do not tolerate as wide a range of environmental conditions
Flowers virtually all year, but mainly from April to December
Height 8-10"
Biomass production per year is about 11,100-22,200 lb/acre
N content 2%
Eastern Mediterranean region
Less drought tolerant than birdsfoot trefoil
In some prune and peach orchards, used in mixes with strawberry clover (Trifolium fragiferum),
birdsfoot trefoil (Lotus corniculatus), and creeping red fescue (Festuca rubra)
More shade tolerant than strawberry clover, but less heat tolerant
Harbors high densities of pocket gophers
Flowers attract lygus bugs
Uses more water than do winter-annual cover crops

Common Name

White clover and Ladino clover (Duke, 1981).

Scientific Name

Trifolium repens L. (Duke, 1981).

Cultivar

White clover cultivars are classified arbitrarily by size of the plants, as small, intermediate, and large. Small varieties frequently include the words "Wild White" in their names. Most common are the intermediate-sized white clovers, which behave as annuals when stressed. Large type white clovers do well where climatic and soil conditions are optimal but do not have as wide environmental tolerances as the smaller types (Carlson et al., 1985). Of the three types, small is considered a weedy type (Miller, 1984c).

Ladino clover is a variety of white clover (McLeod, 1982); intermediate types of white clover are more tolerant of heat than are ladino-type white clovers (Miller, 1984c). There are Canadian varieties of white clover that tolerate soil pH as low as 4.5. (Miller, 1984c).

Seed Description

Seeds ovoid-truncate, ca 1.5 mm long and wide, surface smooth, usually entirely yellowish, sometimes reddish; 1,764,000 seeds per kg (Duke, 1981). White clover seed are small (1,764,000/kg, 77 kg/hl) (Gibson and Cope, 1985).

Seedling Description

White clover shows strong seedling vigor (Finch & Sharp, 1983). Seedlings are epigeal, and germination occurs at the soil surface (Gibson and Cope, 1985).

Mature Plant Description

Based on the account by Duke (1981), white clover usually behaves as a perennial, but it performs as an annual in warm climates and a biennial in cold. Stolons glabrous, solid, creeping, 1-4 dm long, leaves long-petioled; leaflets cuneate-obovate to broadly oblong, emarginate to obtuse, 1-3 cm long, 0.75-2.5 cm broad, solid dull green or occasionally marked with a white "V" and sometimes with dark red flecks, denticulate; stipules pale except for the conspicuous nerves, abruptly narrowed to a point; peduncles scapiform, usually very elongate; heads subglobose in fruit, rather loose, 1.5-2.0 cm in diameter; flowers 20-40 (100); bracts membranous, at first equaling the pedicels but much exceeded by them as the latter elongate; pedicels often sparsely puberulent, elongating and recurving in age, the inner longer than the outer; flowers 6-10 mm long, fragrant; calyx-teeth unequal, the upper slightly shorter than the tube, the lower two-thirds its length; corolla white or rose tinged, becoming brown, 8 mm long, twice the length of the calyx; pods sessile, linear, exserted, usually 3- to 4-seeded, with 75-100 seeds per head.

As a perennial legume, this species spreads by stolons (Slayback, pers. comm.).

Leaves, stems, and flower heads of Ladino clover generally are from two to four times as large as common white clover. In shape, color and markings, the leaves and flower heads look like common white clover (Miller et al., 1951).

White clover can develop a taproot 1 m deep, but it dies at the end of the first year, and secondary roots developing from the stolon become the main root system. The roots of white clover are mainly shallow (Miller, 1984c).

Temperature

Duke (1981) related that white clover tolerates mean annual temperatures of 4.3-21.8 C, with the mean of 101 cases being 11.6.

White clover grows best under cool, moist conditions (Carlson, et al., 1985) and is about as hardy as Red Clover or Alfalfa (McLeod, 1982). Hofstetter (1988) termed it extremely winter-hardy.

Miller et al. (1951) advised that in districts subject to severe frosts, clover-seed fields should enter winter with at least 6 to 8 inches of growth. Such growth protects the stand against excessive frost damage. With mild climates, the grazing can continue into winter without serious damage ensuing.

Heritability of frost tolerance in white clover is high (0.75-0.93), suggesting that incorporation of frost tolerance into agronomically-suitable, but frost-sensitive cultivars could be successful (Caradus, et al., 1990).

As heat tolerance is concerned, intermediate types of white clover are more resistant than ladino types (Miller, 1984c). Hot dry periods during the summer reduce growth of white clover, but plants will usually survive (McLeod, 1982)

Geographic Range

According to Duke (1981), white clover probably originated in the eastern Mediterranean region of Asia Minor, and was spread to other continents by colonists; it ranges from the Boreal Moist to Wet through Subtropical Dry to Rain Forest Life Zones. Munz (1973) listed it as naturalized to wet places in California, especially in the mountains and in northern parts of the state. Based on the account by Duke (1981), the species grows in a wide range of habitats, including dry meadows, mudflats, rarely on saline meadows, wood margins, open woods, banks of rivers and brooks, plains, semi-desert regions, and mountains up to the subalpine meadows. It is a frequent weed on roadsides and in barrens. Miller et al.(1951) noted that seed production is largely confined to irrigated areas in California, Oregon, and Idaho, where weather is favorable. Seed can probably be produced in most of California at elevations under 3,000 feet, except where summer heat is excessive. High winds at harvest (July, August, and September) can be a problem. Excessively fog or rain and snow at harvest may disrupt harvest and reduce seed quality.

Water

White Clover grows best under cool, moist conditons (Carlson, et al., 1985) and is less drought tolerant than trefoil (Finch & Sharp, 1983).

Miller et al. (1951) wrote that seed production usually necessitates irrigation about every 7 to 10 days during summer. With frequent irrigations, to produce good seed on open soils may require from 2 to 3 times that needed on heavier type soils. On heavy clay soils the irrigation interval may range from ten to twenty-one days.

Miller et al. (1951) recommended the strip-check system of land preparation and irrigation. A modified version of the contour check system of irrigation, was also successful for irrigated pastures but was rarely used for Ladino seed production. Immediate and complete drainage following the irrigation is essential to avoid seed damage through germination and drowning of plants. Sprinklers may be used where land cannot be leveled. Clover-seed fields require frequent irrigation, so land preparation should be calculated to minimize labor costs.

Madson (1951) suggested that white clover should be irrigated when leaves begin to cup together. This may occur in sandy or hard spots at first. Field condition in general should be considered. Do not withhold irrigation until the entire field is wilting.

Irrigation should replenish the soil moisture to the depth of the white clover roots. Examine the soil to ascertain the depth of soil and the root zone. From 1 to 3 inches of water per irrigation will usually suffice. Larger applications will be wasteful and perhaps harmful. Ponding in hot weather can drown plants (Miller et al., 1951).

It is customary to withhold water for 4 to 10 days before a field is cut for seed. Miller et al. (1951), however, advised not intentionally drying up a field which has a good developing seed crop, because this would reduce seed yield, cause much seed to shrivel, and reduce germination. Whereas Ladino clover requires frequent irrigation, its annual requirement usually does not exceed that of alfalfa. In most of California, Ladino requires from 3 to 5 acre-feet of water per acre annually. In the interior valleys on open, permeable soils 6 to 9 acre-feet year may be needed.

If water is withheld before harvest, irrigate immediately afterward, to minimize drought damage. This can also increase fall pasturage. Irrigations should be given frequently in the fall until the seasonal rains begin (Miller et al., 1951).

White clover can grow on clays to silty loams if water is available all year (Gibson and Cope, 1985). Ladino clover does well on soils with a high water table or with poor drainage (Miller, 1984c), but it is not suited to dry, swampy, high-alkaline, or highly-saline sites (Gibson and Cope, 1985).

Mixtures of grasses and white clover are difficult to maintain because grasses may shade the clover and because the clover requires high soil moisture levels. If soil nitrogen is high, grasses will tend to predominate, whereas the clover will dominate if nitrogen is low (Miller, 1984c).

Nutrients

White clover may require the equivalent of 300-600 kg/ha of 20% superphosphate and 60-250 kg/ha of muriate of potash (Duke, 1981). It is a poor competitor with grass for soil P (Mackay et al., 1990). 112 white clover cultivars and 7 breeding lines from 25 countries were evaluated for response to added P. Cultivars that responded to low levels of added P were all from countries with cold winters. 119 cultivars and lines of white clover were originally evaluated for response to P addition. Based on principal components analysis, these were assigned to 8 groups. 26 of the varieties were selected to represent the 8 groups. The varieties that absorbed the most P also accumulated the most N (Mackay et al., 1990). Caradus et al. (1990) wrote that in New Zealand, the large-leaved white clover cultivar 'Grasslands Kopu' showed better growth response to P and higher yields than did 'Barbian', 'Grasslands Tahora', or 'Grasslands Huia.' Maximum yield of 'Grasslands Kopu' was also attained at a lower level of added P.

White clover responds well to addition of gypsum or flowers of sulfur as sulfur sources. It showed a 63% increase in dry matter production following application to a 2-year-old stand (Bowdler and Pigott, 1990).

Kanyama-Phiri et al., (1990) wrote that in strawberry clover - white clover - perennial ryegrass - orchardgrass mixtures, the clovers were most productive with 60 kg/ha of N added. Strawberry clover and ladino clover are similar in morphology and growth habit but differ in response to different nutrient and grazing regimes. In strawberry clover - white clover - perennial ryegrass - orchardgrass mixtures, with no added nitrogen, ladino clover peaked in dry matter production in October, then fell off during November. Strawberry clover peaked in November. By contrast, when nitrogen was added (60, 120, and 180 kg/ha of N added), these situations were reversed.

Soil pH

Duke (1981) wrote that white clover tolerates soil pH of 4.5-8.2, with the mean of 89 cases being 6.3, and stated that the species or cultivars thereof show tolerance to both high and low pH. The species is said not to grow well in alkaline soil, and the best pH range is 6.0 to 6.5 (McLeod, 1982), 6 to 7 (Carlson et al., 1985), or 6.5 to 7.0 (Hofstetter, 1988), with the optimal pH for white clover said to be 6.5 (Duke, 1981; Gibson and Cope, 1985).

Some Canadian varieties of white clover can tolerate soil pH as low as 4.5 (Miller, 1984c), but acid soil should be limed to a pH of 6.0-6.5 before seeding white clover (Carlson et al., 1985).

White clover is not suited to dry, swampy, high-alkaline, or highly-saline sites (Gibson and Cope, 1985).

Soil Type

Duke (1981) wrote that white clover or varieties thereof tolerate aluminum, drought, heavy soil, high ph, low pH, poor soil, and salt. The species does better on clay or loam soils than on sandy soils. White clover grows best on well-drained loam or clay soils of high fertility (Carlson et al., 1985). McLeod (1982) advised that heavy, moist, well-drained, highly fertile soils are best and stated that with abundant rainfall, white clover will grow on sandier soil, but not reliably.

Ladino clover does well on soils with a high water table or with poor drainage (Miller, 1984c), but it is not suited to dry, swampy, high-alkaline, or highly-saline sites (Gibson and Cope, 1985). White clover can grow on clays to silty loams if water is available all year (Gibson and Cope, 1985).

When grown for seed production, heavier clay or loam soils are best. White clover does well on shallow soil underlain by a tight clay layer or a hardpan, even if this is 18 inches or slightly less of the surface. On deep, open, friable, fertile soils, seed production seldom is good because plants do not produce abundant seed heads. Luxuriant vegetative growth, sparse production of seed heads, and excessive water losses combine to reduce seed production (Miller et al., 1951).

Shade Tolerance

In California, white clover is often included in mixtures with strawberry clover because the former is shade tolerant and the latter tolerates heat. Thus, in an orchard understory with dappled shade and sun, the two species complement one another (Bugg, pers. comm.). White clover is shade tolerant and does well in mature, irrigated, swampy pecan orchards in southern Georgia (Bugg, pers. comm.).

Salinity Tolerance

Duke (1981) ascribed salt tolerance to white clover or cultivars thereof, but the species is not suited to highly-saline sites, according to Gibson and Cope (1985). This confirms the finding by Miller et al. (1951), who wrote that the species does not do well on very saline soils.

Rogers et al. (1993) rated cultivars of white clover for salinity tolerance as follows: 'Haifa' and 'Irrigation' > 'Tamar' and 'Ladino'. With moderate salinity, highest yields occurred with cultivars that yield the most under non-saline conditions. Varieties that showed little decline with increased salinity yielded poorly in non-saline conditions.

Herbicide Sensitivity

Duke (1981) reported that the cultivar 'Regal Ladino' was selected for tolerance to the herbicides 2,4-D, 2,4-DB, and 2,4,5-T. The herbicide 2,4-DB does not injure grass or white clover (Miller, 1984c). Also, the herbicides propyzamide and carbetamide can be useful in suppressing incumbent grasses during the establishment phase of slot-seeded white clover (Standell, 1990).

Life Cycle

Based on the account by Duke (1981), white clover usually behaves as a perennial but performs as an annual in warm climates and a biennial in cold. Stands regenerate themselves by reseeding and by vegetative (clonal) growth; both processes operate in the same stands (Gibson and Cope, 1985). Perenniation is by continual reestablishment of seedlings or rooting of new stolons (Miller, 1984c). Flowering and fruiting can occur nearly year-round in some areas, and spring to fall in the North (Duke, 1981). White clover flowers develop once days lengthen to 14 hours and 15 minutes. (Miller, 1984c). Flowers are insect pollinated, and abundant bees are essential to cross pollination and high seed production (Duke, 1981). White clover seedlings are epigeal; germination occurs at the soil surface (Gibson and Cope, 1985).

Seeding Rate

Proposed seeding rates are variable: 0.45-5 kg/ha (Duke, 1981); 4 kg/ha (Gibson and Cope, 1985); 5 lb/acre (Finch & Sharp, 1983; Miller, 1988); 4 to 6 lb/acre (Hofstetter, 1988); 4 lbs/acre by ground or aerial application; or 5 or 6 lbs/acre (Miller et al., 1951).

Seeding Depth

White clover seed should be sown at or near the soil surface, or at a depth of no more than 4 mm (Duke, 1981) or 5 mm (Gibson and Cope, 1985).

Seeding Method

Drilling is the preferred method, but broadcasting will suffice (Slayback, pers. comm.). Miller et al. (1951) advised that, in preparing to seed white clover for seed production, it is desirable to have a fine, firm seedbed with a firm, moist bottom covered by two to three inches of moist, soil free of fine tilth. Cultipack the soil before seeding. Loose, cloddy seedbeds filled with air pockets may lead to patchy, poor stands. Before planting, an irrigation settles and fills, revealing irregularities that can be corrected and provides moisture for germinating seed. After the irrigation, level the field if irregular settling has occurred, then harrow and seed.

In establishing clover simultaneously with grass, drill grass seed in rows 40 to 50 cm apart, then broadcast white clover seed and cover them using a cultipacker (Gibson and Cope, 1985).

If establishing white clover amid preexisting warm-season grass sod, the clover should be seeded (possibly along with a cool-season grass such as ryegrass) in the fall when the grass is dormant. Mow or graze the grass closely, broadcast the inoculated clover seed, and use a roller to press it into the soil. If establishing the white clover during the spring, grass competition should be reduced by mowing or grazing closely, or by damaging strips of the grass by ploughing or banding herbicide (Gibson and Cope, 1985).

The herbicides propyzamide and carbetamide can be useful in suppressing incumbent grasses during the establishment phase of slot-seeded white clover (Standell, 1990).

Seeding Dates

Depending on local conditions, seeding should be done between September 15 and November 15. Planting in the early fall insures larger and more productive Ladino plants in the first crop year.

Spring seedings are preferable if fields are foul with winter weeds, although the chances of obtaining a satisfactory seed crop are fewer. In areas subject to severe winter frosts, planting should be completed early enough in the fall to insure seedling establishment before the first hard freeze (Miller et al., 1951).

Inoculation

White clover requires rhizobial inoculant type "B" (Nitragin Co.) (Burton and Martinez, 1980).

In reestablishing stands in warm regions, white clover seed should always be inoculated before sowing. In cool regions, rhizobia from the preexisting white clover crop will survive in the soil (Duke, 1981).

Seed Cost

Dutch white clover cost $2.80 per lb, New Zealand white clover $2.80, and ladino clover $3.33 retail in 1993 (Fred Thomas, pers comm.).

Seed Availability

Seed availability for white clover is good (Slayback, pers. comm.). The Southern Seedsmen's Association 41st Edition 1990-91 Directory and Buyers' Guide lists 25 suppliers of white clover seed.

Days to Flowering

Munz (1973) listed the flowering period in California as April through December. According to Duke (1981), flowering can be nearly year round in some areas and is from spring to fall in the North. White clover shows a series of flowering periods or seed sets, which mature successively. Blooming periods may be 12 to 20 days apart and often overlap. Maximum bloom usually occurs 4 to 6 weeks after the last spring grazing or cutting (Miller et al., 1951).

Days to Maturity

Seed ripens in July and August in the Central Valley (Miller et al., 1951).

Seed Production

White clover seed is produced mainly in irrigated areas of the West (Gibson and Cope, 1985). Duke (1981) summarized seed yields as being 30-200 kg/ha in humid climates and 150-600 kg/ha in th West. First-season seed yields of 100-350 lbs/acre may result from early fall planting (Miller et al., 1951). Bees are important in pollination and seed production, and should be protected (Miller et al., 1951).

Animal manures, unless known to be weed-seed free, should not be used on seed fields (Miller et al., 1951).

For seed formation, Ladino clover flowers must be cross-pollinated. 1 to 1.5 beehives per acre is sufficient for complete pollination. Bees should be moved in when blossoming starts, usually 2 to 3 weeks after the spring grazing or cutting is finished. In California, bees are usually moved in about May 10, and are retained through the blooming period, i.e., until late August or September (Miller et al., 1951).

The average production of Ladino clover seed in California is about 100 lbs/acre. Seed yields vary tremendously depending upon management and age of stand. Early fall-planted, well-managed stands may produce 100 to 300 lbs or more of seed per acre the first season. Some spring-planted stands do not produce any seed at all the first year. Second-year stands give peak seed production, and may yield 250 to 5000 lbs per acre. After the third year, seed yields usually decline rapidly, and there is seldom production after the fifth year. Weeds such as ryegrass cause declining seed yields from the third year on (Miller et al., 1951).

Seed Storage

No information is available in this database on this topic.

Growth Habit

Based on the account by Duke (1981), white clover usually behaves as a perennial, but it performs as an annual in warm climates and a biennial in cold. The primary axis seldom lasts more than 2 years, but plants persist by forming new growth centers through rooted stolons and their apical meristems. The plants are shallow rooted and spread by stolons that root at the nodes. The species acts as a winter annual under adverse conditions, as in the southern United States.

The species is low growing with prostrate stems (McLeod, 1982).

White clover grows rapidly, and is a long-lived, true clover, spreading by creeping stems called stolons. These elongate rapidly and root at the joints if soil is moist. Thus, sparse stands may thicken by the end of the first year (Miller et al., 1951).

As related by Turkington (1989), Trifolium repens can reproduce either vegetatively or by seed. In a permanent pasture, the species may display phenotypic plasticity allowing a clone to respond to local conditions (fine-grained environmental variability), and genotypic variability allowing different genets to respond differentially to coarse-grained environmental variability.

Maximum Height

Height has been variously reported as 8-10 inches on good sites (Finch & Sharp, 1983) or 5-30 cm (Munz, 1973). Mixed stands of strawberry and white clovers attained height of 33.0 +/- 3.3 cm (mean +/- SEM) (Bugg, R.L., pers. comm.) in early May, following October seeding in Mendocino County, California.

Root System

White clover is relatively shallow rooted, with most roots in the top 20 cm of soil, although some roots extend to a depth of 1 m or more; clones expand through the adventitious rooting of stolons (Gibson and Cope, 1985). Miller (1984c) confirmed that the roots of white clover are mainly shallow; it can develop a taproot 1 m deep, but it dies at the end of the first year, and secondary roots developing from the stolon become the main root system.

Miller et al. (1951) wrote that white clover plants have most roots in the upper 18 to 24 inches of soil. Therefore, Ladino clover does well on soils too shallow for deep-rooted crops like alfalfa, sugar beets, or tree crops. On deep, open soils, roots extend to four or five feet.

White clover taproot can extend to a depth of 1-3 ft (Brinton, 1989).

Kutschera (1960) reported that white clover generally roots to a depth of 61-76 cm.

Establishment

Ladino is slow to establish. Keep surface soil moist during germination. Early fall and late spring seedings require frequent light irrigations timed to keep the surface soil moist, preventing crusting and enabling emergence. Fall seeding is favored because rains may help establishment. Do not allow the soil surface to remain dry more than two days until clover plants have at least four true leaves (Miller et al., 1951).

As noted by Gibson and Cope (1985), white clover clones expand through the adventitious rooting of stolons; nonetheless, establishment is crucial. A good initial stand of white clover outperforms poor stands even after 3 years.

The herbicides propyzamide and carbetamide can be useful in suppressing incumbent grasses during the establishment phase of slot-seeded white clover (Standell, 1990).

Maintenance

White clover behaves as a perennial by continual reestablishment of seedlings or rooting of new stolons (Miller, 1984c). White clover stands regenerate themselves by reseeding and by vegetative (clonal) growth; both processes operate in the same stands (Gibson and Cope, 1985). White clover clones expand through the adventitious rooting of stolons; nonetheless, establishment is crucial, and a good initial stand of white clover outperforms poor stands even after 3 years (Gibson and Cope, 1985).

Young or thin stands can thicken rapidly. When foliage is removed by grazing or clipping, recovery occurs in from 21 to 28 days (Miller et al., 1951).

White clover performs best under regimes of heavy grazing or mowing (Gibson and Cope, 1985). Heavy accumulation of vegetation is deleterious to white clover because light is reduced, soil moisture may be depleted, and the microclimate predisposes for disease and insect problems. Under such a regime, white clover is prone to have very succulent growth, and is unlikely to survive the microclimatic change that would result from sudden heavy mowing or grazing.

In managing mixed stands, grass height must be controlled to allow white clover to do well (Carlson et al., 1985).

In mixtures of white clover and bermuda grass or another warm- season grass, nitrogen should be applied in the late spring or summer, if the desire is to encourage the grass. If the desire is to encourage cool-season grasses, the nitrogen should be applied in the fall or early spring (Miller, 1984c).

In Austria, Danso et al. (1991) conducted a 2-year trial in a triple-species mixed sward of white clover (cv 'Zapican'), birdsfoot trefoil (Lotus corniculatus cv 'Gabriel') and fescue (Festuca arundinacea cv 'Tacuabe'). White clover showed good production for the first harvest of the first year; thereafter, birdsfoot trefoil dominated. In the first year, both legumes contribute about equally to the approximately 130 kg N/ha fixed in the sward. In the second year, white clover only contributed 5% of the 46 kg N/ha fixed in the last two harvests. Mixtures including the two legumes have an advantage because the early production by white clover is complemented by later production and better persistence by birdsfoot trefoil. Stands with multiple legumes often show better livestock weight gains.

Kanyama-Phiri et al. (1990) reported that in strawberry clover - white clover - perennial ryegrass - orchardgrass mixtures, close mowing alternating with 30-31 day regrowth periods apparently favored the two clovers and the perennial ryegrass.

Kanyama-Phiri et al. (1990) asserted that Strawberry clover and ladino clover are similar in morphology and growth habit but differ in response to different nutrient and grazing regimes. In strawberry clover - white clover - perennial ryegrass - orchardgrass mixtures, with no added nitrogen, ladino clover peaked in dry matter production in October, then fell off during November. Strawberry clover peaked in November. By contrast, when nitrogen was added (60, 120, and 180 kg/ha of N added), these situations were reversed.

As related by Turkington (1989), Trifolium repens can reproduce either vegetatively or by seed. In a permanent pasture, the species may display phenotypic plasticity allowing a clone to respond to local conditions (fine-grained environmental variability), and genotypic variability allowing different genes to respond differentially to coarse-grained environmental variability.

Mowing

White clover performs best under regimes of heavy grazing or mowing (Gibson and Cope, 1985). In tolerating close grazing (and, presumably, mowing) ladino white clover is exceeded only by birdsfoot trefoil and subterranean clover (Miller, 1984c). Heavy accumulation of vegetation is deleterious to white clover because light is reduced, soil moisture may be depleted, and the microclimate predisposes for disease and insect problems. Under such a regime, white clover is prone to have very succulent growth, and is unlikely to survive the microclimatic change that would result from sudden heavy mowing or grazing (Gibson and Cope, 1985).

In managing mixed stands of white clover and grasses, grass height must be controlled to allow white clover to do well (Carlson et al., 1985). Frequent mowing will encourage the clover (Miller, 1984c), which revives quickly when cut for hay, because stems are not cut (McLeod, 1982). Four or five cuttings per year, at 35-40 day intervals, can be harvested in some areas (McLeod, 1982).

Miller et al. (1951) advised that first-year stands should not be grazed, except near the end of the season; otherwise, severe injury to the stand can result. By contrast, spring grazing or mowing until mid-May is typical, helps in weed control weeds and promotes more uniform flowering and seed production (Miller et al., 1951).

According to Miller (1984c), white clover is subject to root damage by the fungi Sclerotium rolfsii and Sclerotinia trifoliorum. Root and stolon damage is caused by the fungi Rhizoctonia, Fusarium, Leptodiscus, Curvularia, and Colletotrichum. In the Southeast, the root-knot nematodes, Meloidogyne spp., damage white clover roots. Host plant resistance, crop rotation, soil fertility, and proper cutting schedules can aid in control of these pests.

As noted by Kanyama-Phiri et al., (1990), in strawberry clover - white clover - perennial ryegrass - orchardgrass mixtures, close mowing alternating with 30-31 day regrowth periods apparently favors the two clovers and the perennial ryegrass. Strawberry clover and ladino clover are similar in morphology and growth habit but differ in response to different nutrient and grazing regimes. In strawberry clover - white clover - perennial ryegrass - orchardgrass mixtures, with no added nitrogen, ladino clover peaked in dry matter production in October, then fell off during November. Strawberry clover peaked in November. By contrast, when nitrogen was added (60, 120, and 180 kg/ha of N added), these situations were reversed.

Incorporation

White clover is a perennial plant, and is seldom incorporated as a part of normal cultural practice (Bugg, pers. comm.). A good stand should provide 100 lb of N per acre when plowed at bud stage (Hofstetter, 1988).

Harvesting

Seed may be harvested by three methods: (1) direct combining, (2) combining from the windrow, or (3) stationary thresher (Miller et al., 1951).

Miller et al. (1951) recommended harvesting for seed when 90-95% of the visible heads are brown and the flower stems (seed stalks) have started to dry. In the Sacramento and San Joaquin Valleys, this would be in July and August. Withhold irrigation for 4 to 10 days prior to harvest. According to Duke (1981), seed should be harvested when most seed heads are light brown, about 25-30 days after peak blossoming. Mow and cure in swaths or in small windrows and retrieve using combines with pickup attachments. Each handling causes some shattering, so minimize the number of operation. Complete drying of seeds may require artificial means or spreading and turning the covered seed.

White clover revives quickly after mowing because stems are not cut. Four or five cuttings per year, at 35-40 day intervals, can be harvested in some areas (McLeod, 1982).

Equipment

Either rotary or flail mowers can be used to mow white clover. See other sections on harvesting, seeding, seed production, and mowing.

Uses

Duke (1981) regarded white clover as among the most nutritious and widely-used forage legumes, with a value difficult to estimate because of its tendency to volunteer; about half the irrigated or humid pasture in the U.S. contains some white clover. It is usually grown in mixes with grasses, it makes excellent feed, pasture, hay, and silage for livestock and poultry. Once established it serves excellently as a cover crop and in stabilizing soil and reducing erosion. The latter point was confirmed by Miller (1984c).

White clover is widely used as an irrigated pasture plant in California (Finch & Sharp, 1983) and is best adapted to rotational pasture management. As a cover crop, it is suitable in orchards where a perennial ground cover can be maintained (Miller, 1988) and in vineyards of the same description (Finch & Sharp, 1983).

Mixtures

White clover is usually grown in mixtures with grasses (Duke, 1981); the latter can be either temperate or tropical grasses (Bowdler and Pigott, 1990). Examples include Bermudagrass, bromegrass, dallisgrass, Kentucky bluegrass, orchardgrass, tall fescue, or timothy (Gibson and Cope, 1985). In mixtures with grasses, frequent mowing will encourage the white clover (Miller, 1984c).

Companion or nurse crops of barley or oat are not recommended for fall seedings, but may be used for spring-sown Ladino on tight soils which seal or cake. Nurse plants lead to better spring-sown stands by shading and reducing surface moisture loss. Therefore, white clover seedlings are better able to establish. Mow the nurse crop promptly once the clover has established, to reduce competition (Miller et al., 1951).

Gibson and Cope (1985) recommended that if establishing clover simultaneously with grass, one should drill grass seed in rows 40 to 50 cm apart, then broadcast white clover seed and cover them using a cultipacker. In establishing white clover amid preexisting warm-season grass sod, the clover should be seeded (possibly along with a cool-season grass such as ryegrass) in the fall when the grass is dormant. Mow or graze the grass closely, broadcast the inoculated clover seed, and use a roller to press it into the soil. If establishing the white clover during the spring, grass competition should be reduced by mowing or grazing closely, or by damaging strips of the grass by ploughing or banding herbicide.

The herbicides propyzamide and carbetamide can be useful in suppressing incumbent grasses during the establishment phase of slot-seeded white clover (Standell, 1990). By contrast, the herbicide 2,4-DB does not injure grass or white clover (Miller, 1984c).

In mixtures of white clover and bermuda grass or another warm-season grass, Gibson and Cope (1985) advised that nitrogen should be applied in the late spring or summer, if the desire is to encourage the grass. If the desire is to encourage cool-season grasses, the nitrogen should be applied in the fall or early spring.

Woledge (1988) wrote that mixtures of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) yield less than heavily fertilized monocultures of the former. Addition of small amounts of nitrogen in the spring leads to reduction of the proportions of clover in the stand. The present study indicated that the relative growth rate of clover is as great as that of the grass when nitrogen is added, and greater when nitrogen is not added. There was no evidence that fertilized grass overtopped clover. Clover showed a smaller ratio of leaf area to total above-ground dry weight, but had a higher proportion of its lamina in the upper, well-lit strata.

In Austria, Danso et al. (1991) conducted a 2-year trial in a triple-species mixed sward of white clover (cv 'Zapican'), birdsfoot trefoil (Lotus corniculatus cv 'Gabriel') and fescue (Festuca arundinacea cv 'Tacuabe'). White clover showed good production for the first harvest of the first year; thereafter, birdsfoot trefoil dominated. In the first year, both legumes contributed about equally to the approximately 130 kg N/ha fixed in the sward. In the second year, white clover only contributed 5% of the 46 kg N/ha fixed in the last two harvests. Mixtures including the two legumes have an advantage because the early production by white clover is complemented by later production and better persistence by birdsfoot trefoil. Stands with multiple legumes often show better livestock weight gains.

Kanyama-Phiri et al. (1990) wrote that in strawberry clover - white clover - perennial ryegrass - orchardgrass mixtures, close mowing alternating with 30-31 day regrowth periods apparently favors the two clovers and the perennial ryegrass. The clovers were most productive with 60 kg/ha of N added. Strawberry clover and ladino clover are similar in morphology and growth habit but differ in response to different nutrient and grazing regimes. In strawberry clover - white clover - perennial ryegrass - orchardgrass mixtures, with no added nitrogen, ladino clover peaked in dry matter production in October, then fell off during November. Strawberry clover peaked in November. By contrast, when nitrogen was added (60, 120, and 180 kg/ha of N added), these situations were reversed.

Turkington (1989) reported that Trifolium repens in the same 1-ha old field will diverge genetically through time depending on the grass species with which it is associated. Reciprocal transplant experiments have demonstrated differential success of T. repens from areas dominated by the grasses Lolium perenne or Agrostis capillaris to areas dominated by the original grass or other perennial grasses. The results suggested that, even within a field, white clover clones are genetically adapted to perform better amid stands of particular grasses.

In replicated pot and field trials, Hartl, W. (1989) grew wheat with undersown white clover, black medic, Medicago lupulina L., Persian clover, Trifolium resupinatum L., and various associated weeds. In both pot and field trials, biomass of weeds alive at the time of harvest was reduced substantially (50% or more reduction). The field trials showed reduction of wheat yield, as well, for black medic and Persian clover, but a non-significantly-increased yield when white clover, Trifolium repens, was used.

Studies by McNeill and Wood (1990) in an environmental chamber with an atmosphere enriched by 15N indicated that white clover did not rapidly transfer nitrogen to associated ryegrass. The plants were mycorrhizal.

White and Scott (1991) in New York found that yield of cereal rye was less affected by living mulch of white clover, 'Ladino' clover, or red clover than of crown vetch, birdsfoot trefoil or alfalfa.

Biomass

The mean proportion of dry weight of white clover comprised by N is 0.04 (Hostetter, 1988); 225 kg N/ha added annually to pastures in the U.S. (Miller, 1984). Based on these assumptions, an annual biomass production of 5.9 Mg/ha can be projected (Bugg, pers. comm.). In New Zealand, with a 10-month growing period, the N figure can supposedly be doubled (Miller, 1984), and thus, presumably, so can the biomass figure. By contrast, if we assume the mean crude protein content of 22% given by Duke (1981) and 6.25% of the protein being N, the projection is 16.36 Mg/ha, which seems inordinately high (Bugg, pers. comm.).

Dry matter yield of white clover should equal or exceed that of red clover (1,500 to 2,000 lb/acre) (Hofstetter, 1988). In mid-May, a first-year stand of a fall-sown mixed stand of strawberry and white clover yielded an above-ground dry biomass of 3.9+/-0.9 Mg/ha (Mean +/- S.E.M.) in an organic vineyard in Mendocino County, California. This figure is significantly less than that of the standing biomass for various winter-annual vetches, clovers, and medics sown in the same trial. With weeds including, the corresponding figure is 6.8+/-1.2 Mg/ha (Bugg et al., 1996).

N Contribution

White clover may yield as much as 225 kg/ha of nitrogen per year, or up to double this in New Zealand, where a 10-month growing season prevails (Miller, 1984c).

In Austria, Danso et al. (1991) conducted a 2-year trial in a triple-species mixed sward of white clover (cv 'Zapican'), birdsfoot trefoil (Lotus corniculatus cv 'Gabriel') and fescue (Festuca arundinacea cv 'Tacuabe'). White clover showed good production for the first harvest of the first year; thereafter, birdsfoot trefoil dominated. In the first year, both legumes contributed about equally to the approximately 130 kg N/ha fixed in the sward. In the second year, white clover only contributed 5% of the 46 kg N/ha fixed in the last two harvests. Mixtures including the two legumes have an advantage because the early production by white clover is complemented by later production and better persistence by birdsfoot trefoil. Stands with multiple legumes often show better livestock weight gains.

First-year white clover mean nitrogen content is 81 lb/a, according to Brinton (1989). Nitrogen content of white clover averages 3.8%. A good stand should provide 100 lb of N per acre when plowed at bud stage (Hofstetter, 1988).

Haley and Hogue (1990) assessed influence of type of ground cover on apple aphid, Aphis pomi DeGeer (Homoptera: Aphididae), and its predators in a young apple orchard. Four ground cover regimes were compared: (1) fall cereal rye (Secale cereale), herbicided in spring and summer; (2) a mixture of white clover (Trifolium repens) and grass; (3) herbicided tree-row strips and grassed-in alleys; and (4) woven black-plastic strips in the tree row and grassed alleys. The trial was initiated at the beginning of the second year of the orchard. Few aphidophagous insects of interest (e.g., the predatory mirids Deraeocoris brevis and Campylomma verbasci, the predatory midge Aphidoletes aphidimyza, lady beetles, hover flies, or lacewings), were found in the ground covers. In the first year of the study, leaf nitrogen and aphid and predator densities were lower on trees with the white clover-grass mixture. These differences did not occur the second year. Terminal growth was particularly depressed for apple trees with understories of white clover and grass.

McNeill and Wood (1990) conducting studies in an environmental chamber with an atmosphere enriched by 15N indicated that white clover did not rapidly transfer nitrogen to associated ryegrass. The plants were mycorrhizal.

Mackay et al. (1990) evaluated 119 cultivars and lines of white clover for response to P addition. Based on principal components analysis, these were assigned to 8 groups. 26 of the varieties were selected to represent the 8 groups. The varieties that absorbed the most P also accumulated the most N.

In a field study in Uruguay, Mallarino and Wedin (1990) found that N-fixation was more markedly depressed through the application of nitrogen fertilizer (100kg/ha) for birdsfoot trefoil than for white clover or red clover.

In combination with tall fescue (Festuca arundinacea), year diculture stands with birdsfoot trefoil, white clover, and red clover led to respective annual total N fixation of 70-223, 42-200, and 49-277 kg N/ha. White clover-tall fescue mixes did not require legume domination in order to maximize total N fixation. Red clover gave the greatest N fixation among the legumes tested (Mallarino et al., 1990).

In Sweden, Marstorp and Kirchmann (1991) reported the following values for stems and leaves of several legumes harvested from the field 100 days after emergence. and later used as green manure:

				% Of Dry Matter
Species 		Carbon		Nitrogen	Lignin C	C/N
		
Red Clover		45.9		2.61		 9.08		17.6
White Clover		39.5		3.10		10.26		12.7
Black Medic		42.9		3.12		10.88		13.8
Persian Clover		46.1		3.20		11.38		20.9
Berseem Clover		45.3		2.52		12.47		18.0
Subterranean Clover	42.6		3.02		 9.69		14.1

Non-N Nutrient Contribution

In the first year, white clover mean phosphorus content is 5 lb/a, and potassium content, 35 lb/a (Brinton, 1989).

Effects on Water

In Wales, Mytton et al. (1993) evaluated the differential effects on soil structure and water infiltration of monocultural swards of white clover and perennial ryegrass and a mixture of the two. The replicated study employed undisturbed soil cores (100 mm i.d. x 180 mm length; silt loam acid brown earth) extracted from the field and arranged in a greenhouse. White clover stands led to greater water infiltration, 43.1g/4h, vs. 32.9 for annual ryegrass, vs. 39.4 for mix. Apparent greater soil friability in the clover cores was not reflected in soil bulk density of % soil aggregates >2mm upon wet sieving. Total porosity was little changed, but air-filled (macroporosity) was as follows: clover > mix > perennial ryegrass.

Effects on Microclimate

No information is available in this database on this topic.

Effects on Soil

White clover is very good for soil conservation (Miller, 1984c) because stolons provide ground cover that stabilizes soil (Gibson and Cope, 1985).

Effects on Livestock

In Austria, Danso et al. (1991) conducted a 2-year trial in a triple-species mixed sward of white clover (cv 'Zapican'), birdsfoot trefoil (Lotus corniculatus cv 'Gabriel') and fescue (Festuca arundinacea cv 'Tacuabe'). White clover showed good production for the first harvest of the first year; thereafter, birdsfoot trefoil dominated. In the first year, both legumes contributed about equally to the approximately 130 kg N/ha fixed in the sward. In the second year, white clover only contributed 5% of the 46 kg N/ha fixed in the last two harvests. Mixtures including the two legumes have an advantage because the early production by white clover is complemented by later production and better persistence by birdsfoot trefoil. Stands with multiple legumes often show better livestock weight gains.

White clover is very palatable to livestock. In mixture with grasses and other legumes, it provides highly productive, nutritive pasture and is the basic legume in California's irrigated pasture (Miller et al., 1951).

Miller et al. (1951) wrote that cut Ladino clover dries slowly; it is usually ensiled rather than cured for hay. 70 to 80 lbs of cane molasses can be added per ton of green clippings going into the silo; this improves silage quality and feeding value.

Effects on Workers

No information is available in this database on this topic.

Pest Effects, Insects

Gibson and Cope (1985) noted that heavy accumulation of vegetation is deleterious to white clover because light is reduced, soil moisture may be depleted, and the microclimate predisposes for disease and insect problems. Under such a regime, white clover is prone to have very succulent growth and is unlikely to survive the microclimatic change that would result from sudden heavy mowing or grazing.

Avoid insecticides other than sulfur if bees are working seed-producing stands of white clover (Miller et al., 1951). Duke (1981) wrote that many arthropods attack white clover, including grasshoppers, clover leaf weevil (Hypera punctata), potato leafhopper (Empoasca fabae), meadow spittlebug (Philaenis spumarius), garden fleahopper (Halticus bractatus), spider mites, clover root curculio (Sitona hispidula), green june beetle (Cotinus nitida), lesser clover leaf weevil (Hypera nigrirostris), clover head weevil (Hypera meles), clover seed weevil (Microtrogus picirostris). white clover flower midge (Dasineura gentneri), lygus bugs, clover aphid (Nearctaphis bakeri), green cloverworm (Plathypena scabra), cutworms, lesser cornstalk borer (Elasmopalpus lignocellus), alfalfa weevil (Hypera postica), blister beetles (Epicauta spp.), and the fall armyworm (Spodoptera frugiperda).

Potato leafhopper (Empoasca fabae) is the most important insect pest of white clover. Other pests include meadow spittlebug, clover leaf weevil, alfalfa weevil, lygus bugs, clover seed weevil, and clover seed midge. Crop resistance, weed control, and crop rotation may be important in controlling some insect pests (Miller, 1984c).

Miller et al. (1951) wrote that four species of spider mite (called red spiders) can cause damage, beginning in early May. These include Atlantic mite, brown almond mite, Pacific mite, and the two-spotted mite. These mites are usually found on the undersides of the leaves, and infested leaves become cupped, yellowish and spotted. Heavily infested fields may appear dried-out and reddish-brown. Lygus bugs may build up rapidly in seed fields in late May, June, and July. These damage the flower parts and developing seed. Various grasshopper species may move into Ladino fields in great numbers. Infestations may originate in high, dry checks and borders, and fence rows within fields. Adjacent dry fields may be breeding grounds. Yellow-striped armyworm may damage seed fields,and in some cases may strip a field in 3 or 4 days.

Flexner et al. (1990) related their studies in southern Oregonian pear orchards. Certain understory weeds can harbor high densities of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). This mite is mainly a secondary pest and a creature of pesticide-disrupted or stressed agroecosystems. Among the plant species suitable for use as cover crops, white clover appeared particularly prone to outbreaks of the mite. Use of herbicides led to increased movement by mites into trees.

Haley and Hogue (1990) assessed the influence of type of ground cover on apple aphid, Aphis pomi DeGeer (Homoptera: Aphididae), and its predators in a young apple orchard. Four ground cover regimes were compared: (1) fall cereal rye (Secale cereale), herbicided in spring and summer; (2) a mixture of white clover (Trifolium repens) and grass; (3) herbicided tree-row strips and grassed-in alleys; and (4) woven black-plastic strips in the tree row and grassed alleys. The trial was initiated at the beginning of the second year of the orchard. Few aphidophagous insects of interest (e.g., the predatory mirids Deraeocoris brevis and Campylomma verbasci, the predatory midge Aphidoletes aphidimyza, lady beetles, hover flies, or lacewings) were found in the ground covers. In the first year of the study, leaf nitrogen and aphid and predator densities were lower on trees with the white clover-grass mixture. These differences did not occur the second year. Terminal growth was particularly depressed for apple trees with understories of white clover and grass.

White clover is used as a nectar source by Scolia sp. (Scoliidae) and Prionyx sp. (Sphecidae) wasps in pecan orchards of southern Georgia (Bugg, pers. comm.).

Grafton-Cardwell et al. (unpublished manuscript) found that pollen of bell bean, 'Austrian Winter' field pea, and New Zealand white clover sustained longevity and fecundity of the predatory mite Euseius tularensis (Acari: Phytoseiidae) as well as the standard diet of iceplant pollen. By contrast, reduced fecundity was observed for common vetch, woollypod vetch, and crimson clover, and E. tularensis did not survive more than one generation when fed pollen of rose clover or red clover. Inoculation with E. tularensis in early spring led to build-up of the mite by late spring in a cover crop of bell bean, field pea, and woollypod vetch. Most of the mites were found on the bell bean component of the mix. When the cover crop was mowed and the mowings placed in young citrus trees, significantly increased densities of the predatory mite were observed on the citrus foliage.

Pest Effects, Nematodes

Duke (1981) listed 41 species of nematodes as having been isolated from white clover, including several species each of Meloidogyne, Heterodera, and Pratylenchus.

In England, the nematode Tylenchorynchus dubius is known to damage white clover (Clements and Boag, 1990).

In the Southeast, the root-knot nematodes, Meloidogyne spp. damage white clover roots. Host plant resistance, crop rotation, soil fertility, and proper cutting schedules can aid in control of these pests (Miller, 1984c).

Pest Effects, Diseases

Sixty-two species of fungi have been recorded as attacking white clover, as is the bacterium Pseudomonas syringae and 14 types of virus (Duke, 1981). Miller (1984c) wrote that white clover is subject to root damage by the fungi Sclerotium rolfsii and Sclerotinia trifoliorum. Root and stolon damage is caused by the fungi Rhizoctonia, Fusarium, Leptodiscus, Curvularia, and Colletotrichum. Host plant resistance, crop rotation, soil fertility, and proper cutting schedules can aid in control of these pests.

White clover can be attacked by several foliar and root diseases, as well as clover mosaic virus. The latter cause more problems where white clover persists as a perennial and regenerates vegetatively than were it reseeds as an annual (Gibson and Cope, 1985).

Heavy accumulation of vegetation is deleterious to white clover because light is reduced, soil moisture may be depleted, and the microclimate predisposes for disease and insect problems. Under such a regime, white clover is prone to have very succulent growth and is unlikely to survive the microclimatic change that would result from sudden heavy mowing or grazing (Gibson and Cope, 1985).

As of 1951, no serious diseases of economic importance had affected the Ladino crop in California (Miller et al., 1951).

Interspecific hybrids between Trifolium repens and T. ambiguum show resistance to peanut stunt mosaic, clover yellow vein virus, and alfalfa mosaic virus. These resistances could prove valuable if they can be incorporated into adapted white clover varieties (Pederson and McLaughlin, 1989).

Pest Effects, Weeds

Mowing in early May of the first season can reduce weed problems; stands should be mowed before the weeds produce seed. Annual weeds such as ryegrass, burclover, canarygrass, etc., may preclude a satisfactory stand of white clover. Spring sowing of clover can circumvent this problem because the winter-germinated weeds can be destroyed during spring seedbed preparations (Miller et al., 1951).

For seed production, grazing or mowing by May 15 can reduce weeds. Grazed fields should be mowed thereafter to control weeds and equalize the stand (Miller et al., 1951).

Hartl, W. (1989) reported replicated pot and field trials in which wheat was grown with undersown white clover, black medic, Medicago lupulina L., Persian clover, Trifolium resupinatum L., and various associated weeds. In both pot and field trials, biomass of weeds alive at the time of harvest was reduced substantially (50% or more reduction). The field trials showed reduction of wheat yield, as well, for black medic and Persian clover, but a non-significantly-increased yield when white clover, Trifolium repens, was used.

Bugg et al. (1996) conducted a replicated study of various cover crops (r=4) at Blue Heron Vineyard (Fetzer Vineyards), Hopland, Mendocino County, California. Weed above-ground biomass data (dry) were taken in a replicated Cover crops were seeded in late October, 1990; harvest was on May 15-16, 1991. Dominant winter annual weeds were chickweed, shepherds purse, rattail fescue, and annual ryegrass. In plots sown to a mixture of white and strawberry clovers, weed biomass was 2.8+/-0.7 Mg/ha (Mean +/- S.E.M.). This was 57.5% of the value obtained in weedy control plots. Vegetational cover afforded by the clover mix was 77.50+/-3.23 % Vegetational Cover (Mean +/- S.E.M.).

Pest Effects, Vertebrates

Some Sacramento Valley seed producers used night lights to protect white clover stands against ducks in the winter. Airplanes were used to herd the ducks from their fields during the daytime. Otherwise, fields may be almost denuded in a few hours (Miller et al., 1951).

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