Evaluation of Medicago Species as Self Reseeding
Cover Crops for Vineyards
Peter Christensen1 and Walter Graves1Kearney
Ag. Center, 9240 S Riverbend Ave, Parlier CA 93648
Naturalized bur medic (M. polymorpha) has been recognized as a very adaptable economical cover crop by many San Joaquin Valley vineyardists. Its advantages include early spring growth which facilitates weed competition, mowing for frost protection, and minimal irrigation requirements. The potential for high seed protection for self-reseeding is probably the most important reason for its popularity and success with individual growers. Raisin growers, in particular, have used bur medic because of its low cost and high seed production. The high seed production is needed for self-reseeding because of grower practice of deep tillage to prepare for raisin drying which buries a high proportion of seed. Its relatively high production of hard seed also assures re-seeding in successive years. Some raisin growers were using bur medic as an IPM management tool as far back as the 1950's and 1960's. They were particularly interested in Pacific mite suppression by reducing dust and providing cover for spider mite predator buildup in the vineyard. However, the biggest problem with bur medic has been the lack of commercial seed availability. Consequently, it is often ignored in cover crop trials and by seed companies and is unknown to many growers.
We initiated a replicated trial at the Kearney Agricultural Center on November 19, 1993 to evaluate bur medic species and selections under San Joaquin Valley vineyard conditions. Four Medicago spp. --polymorpha (bur), scutellata (snail), truncatula (barrel) and orbicularis (button) -- are represented in the 17 sections under test. Thirteen of the selections are spiny or smooth bur medics, most of which are ecotypes collected in Northern and Baja California or are foreign introductions from the USDA germplasm collection at UC Riverside. The plots have been rated for plant density and blooming dates; they will also be evaluated for biomass and seed production. Their ability to regenerate will be evaluated in 1995. Plans are also underway to further compare some of the better performing medics, particularly the naturalized California bur medics and the Australian varieties of Serena, Santiago, and Circle Valley. We will also investigate management strategies such as seeding date and mowing, as well as nitrogen contribution and pest interactions.
The ultimate goal is to make bur medic an effective cover crop
for vineyards, including commercial availability. A group of raisin
growers is expected to implement bur medic demonstration sites
in 1995 in conjunction with an industry IPM program.
Cover Crop Research and Education Summaries