Maxwell Norton

Plant Protection Quarterly 7(1):4-6. 1997

Reprinted with permission.

Codling moth [Cydia (Laspeyresia) pomonella] (CM) is the most important insect pest of apples in California. In the San Joaquin Valley, there are between three and four generations per year which can cause extensive damage if uncontrolled. Traditional control programs include three to four organophosphate or carbamate insecticide sprays per year.

In an effort to reduce environmental impact and preserve beneficial arthropods, many growers have been incorporating Bacillus thuringiensis (Bt), a biological control agent, as an alternate material for insect control. As use of Bt has become commonplace in many tree crops, there has been some concern over the development of resistance, through only one such case been reported so far. The primary weakness of Bt is its short residual.

There is also considerable interest in using mating disruption (MD) to control CM, and to supplement this technology with Bt which would be applied two or more times to control other lepidopteran pests such as leafrollers and fruitworms. It is presumed that some secondary CM control results from the Bt.

These two trials tested the efficacy of Spinosad, the common name for a [biological control] product derived from Saccharopolyspora spinosa. Spinosad has similar beneficial attributes to Bt. It is active against a wide variety of insect pests and it is considered to have low toxicity to beneficial organisms.

Materials and Methods

In the first trial we used a mature Granny Smith apple orchard that had a conventional insecticide program for several years. The trees were irrigated with overhead sprinklers. Weeds were controlled with herbicides in the tree row and were mowed in the middles. Diseases were controlled with a conventional fungicide program.

There were three treatments: 1) 1.5 lb/a Lorsban 50W, 2) 0.9 oz Spinosad per acre and 3) untreated check. Treatment dates are as follows: 1) 19 April–emergence of first brood, 2) 6 May–3 weeks later as a bracket spray, and 3) 13 June–emergence of second brood.

The plot consisted of six, single-tree replications in a randomized complete block design. Each tree and half of each adjacent tree was sprayed with a hand-gun sprayer to the point of run-off in such a matter that all foliage and fruit were thoroughly wetted. The surrounding trees were treated with 1.5 lb/a Lorsban.

On 29 June, 100 fruit were picked from the center tree of each replication and examined for insect damage of any type. The leaves were randomly sampled and examined for leafminer damage. The number of fruit with CM strikes were recorded. On 14 August 200 fruit were sampled in the same way.

The second trial was conducted in a similar block of Granny Smith that utilized MD as the primary control for CM during the last two seasons. There were three treatments: 1) 1 lb/a Dipel 2X [a Bt product], 2) 2.88 oz/a Spinosad, and 3) untreated check. Both materials were applied on 4 April and 12 April 1996 for the control of miscellaneous lepidopteran pests other than CM. CM control was to be achieved with Consep mating disruption dispensers which were applied 18 March, 16 May, and 18 July.

We used a randomized complete block design with four replications that were five rows wide and 20 trees long. The treatments were applied at 100 gallons per acre with a commercial air blast sprayer.

On 29 June, 200 fruit were picked from the center row of each replication and examined for insect damage of any type. The leaves were randomly sampled and examined for leafminer damage. The number of fruit with CM strikes were recorded. On 14 August the block was re-sampled in the same way except that the fourth replication was not sampled.

Results and Discussion

In the conventional orchard there was significant damage from CM. The average number of fruit with CM strikes is presented below. There was no appreciable damage from the leafminer or lepidopteran pests other than CM. There was a small amount of mice damage

The data shows that Lorsban and Spinosad significantly reduced CM damage below that of the check. Spinosad clearly shows promise as a control agent for CM in apples and warrants further testing under commercial conditions.

In the disruption orchard there was no appreciable damage from the leafminer nor lepidpoteran pests other than CM. There was significant damage from CM. The average number of fruit with CM strikes is presented below.

In the June sampling, both the Dipel and the Spinosad treatments had damage levels significantly lower than the check. In the August sampling, there was no significant differences among the treatments.

While our original intent was to evaluate control of pests other than CM, we observed a difference in CM control among the treatments. In this trial, under these conditions, the Spinosad and Dipel provided control of CM that was significantly better than the check.

For more information: Maxwell Norton, UC Cooperative Extension, 2145 W. Wardrobe Ave., Merced, CA 95340.

(DEC.546) Contributed by Maxwell Norton