Task 4:

Stanislaus County

Objectives:

1. 1. To scientifically evaluate the success and profitability of managing arthropod pests with less broadly toxic pesticides in a commercial almond orchard.
   2. To demonstrate and facilitate adoption of integrated pest management monitoring techniques and decision-making processes to growers and pest control advisors.

This report summarizes our progress as we approach the end of the second season of a 4-year project. The trial is being conducted in a 120-acre Nonpareil orchard west of Modesto. Three insect pest management programs are replicated three times within the trial. Each plot is approximately 13.5 acres in size. The treatments are:

Grower’s Standard Practice (common in the Northern San Joaquin Valley):

• A dormant application of 8 oz. Asana XL (a pyrethroid), 8 lb. copper (Kocide DF), and 6 gallons of oil (Gavicide 440).
• A May spray of 4 pints Lorsban 4E (an organophosphate).
• Omite for mite control.
• Lorsban @ 4 pints for ant control if shown necessary through monitoring.

"Soft" Program #1: In these areas, "reduced risk" pesticides are used:

• A dormant application of 6 oz SuccessÒ , 8 lb. copper (Kocide DF), and 6 gallons of oil.
• A May PTB spray of 6 oz SuccessÒ
• Agri-Mek 0.15 EC @ 10 oz & Gavicide 440 oil @ 1 gallon for mite control
• Abamectin bait (Clinch) @ 1.5 pounds for ant control if shown necessary through monitoring.

"Soft" program #2: This program utilizes Bt in lieu of traditional dormant and in-season sprays:

• A dormant application of oil only (Gavicide 440 @ 6 gallons).
• Two spring applications of Bt (Dipel DF @ 1 lb.). These were tank mixed with normally scheduled fungicide and foliar nutrient applications and therefore did not necessitate additional application costs.
• Two May sprays of Bt (Dipel DF @ 1 lb.) timed for 300-350 & 450-500 degree days after biofix of peach twig borer.
• Potassium nitrate & oil for mite control
• Abamectin bait (Clinch) @ 1.5 pounds for ant control if necessary.

Dormant sprays were applied on January 12-13 in 100 gallons of water per acre. Mummies were removed and destroyed in all treatments. Mummy counts averaged 1.9 mummies per tree throughout the trial. This falls just below the established UC threshold of less than two mummies per tree.

We attempted to time the two spring Bt sprays with 20-40% and 80% peach twig borer emergence from their hibernacula. In an attempt to prevent additional application costs and to mimic what most growers do, we applied these sprays with regularly scheduled fungicide and foliar nutrient sprays. Unfortunately, the first spray was probably applied too early at about 5% emergence. The second application went on at about 60-70% emergence. Due to the cold spring, PTB emergence was prolonged. Three Bt applications were probably necessary to adequately cover PTB emergence this year.

Monitoring:

This trial is extensively monitored for peach twig borer, naval orangeworm, web spinning mites, San Jose scale adult males and crawlers, and San Jose scale parasitoids (Encarsia and Aphytis) from March through October. In addition, brown almond mite, European red mite and San Jose scale are monitored in the dormant season. In each treatment replication there are two PTB pheromone traps, two S.J. scale pheromone traps, eight S.J. scale crawler sticky tape traps, and two NOW egg traps for a total of 126 traps in the trial. PTB and NOW traps are checked twice each week. San Jose scale pheromone and sticky tape traps are checked weekly. Beginning in May, plots are monitored weekly for mites using the presence / absence sampling technique. Ants were monitored four times using the hot dog baiting method.

PTB pheromone traps were hung March 16 and checked every other day to establish the first biofix. Biofix for the overwintering generation of PTB was established on March 30. The first naval orangeworm egg was detected on March 20. Trap catches and the degree-day phenology model were used to determine application timings for May PTB sprays.

Cumulative trap catches through October 2, 2000 for PTB, SJS scale males, Encarsia, Aphytis and NOW eggs are listed below for the three treatments.

As in the first year of the trial, we have seen approximately twice as many Encarsia scale parasitoids in the "soft" programs verses the program with the dormant pyrethroid treatment. Male San Jose scale adult numbers are very low in all treatments. In Stanislaus County, it is rare to find an orchard with a San Jose scale problem due to the high parasitoid populations in the area. Time will tell if the higher scale parasite numbers in the "soft" treatments will keep the San Jose scale under control as well or better than the grower’s standard practice.

PTB pressure has been moderate in this orchard this season. It does not appear that there will be significant differences in peach twig borer populations between treatments. Naval orangeworm egg laying was low through the season and there will be no differences between treatments.

Mites:

Beginning May 4, mites have been monitored weekly using the presence / absence sampling method. When using the presence / absence method, leaves are examined for the presence of mites and mite eggs. If a leaf has one or more mites or mite eggs, it is rated as a (+). If no mites or eggs are present, then it is given a (–) rating. Mite predators are also noted. If mite predators are not present, a treatment threshold is reached if approximately 1/3 of examined leaves have mites or eggs. If predators are present, then the treatment threshold is increased to approximately 50% or more of sampled leaves with mites or eggs.

In this trial, ten leaves from ten trees per plot (100 leaves total) are sampled and examined for mites. Past trials have shown mites often build in areas treated with pyrethroids. Although spider mite numbers were greater in the pyrethroid treatment early in the season, mite numbers became similar between treatments by June. In general, spider mite populations remained fairly low in all treatments through the season. Hot spots of brown almond mite appeared in one block but were not related to treatment.

Agrimek was applied on June 12 to all three reps of Soft treatment #1. Agrimek must be applied while leaves are still soft to maximize absorption and residual effectiveness. Unfortunately this means the material is often applied unnecessarily. Omite was applied to hot spots in the standard practice treatment in early August. Although mite populations were not at treatable levels, Omite has a thirty-day pre-harvest interval and had to be applied as an insurance spray. Spider mite hot spots were treated with potassium nitrate and oil as they became evident in soft treatment #2.

Harvest Reject Levels

At harvest, 1000 almonds were randomly collected from each replication (300 per treatment) and examined for insect damage. Reject levels for all treatments were very low. There were no differences between treatments in percent damage due to NOW, PTB, or ants.

Conclusions:

After two years of intensive monitoring, we have not seen an increase in any pest in the "soft" treatments compared to the standard grower’s practices. There also have not been any differences in rejects due to PTB or NOW at harvest. It is clear San Jose scale parasitoids are significantly reduced in areas where a pyrethroid is applied in the dormant period and an organophosphate is applied in-season. In Stanislaus County, almond and stonefruit orchards rarely have significant damage from San Jose scale whether orchards are treated with insecticides or not. However, in areas where San Jose scale is a serious threat, growers should understand that the use of some insecticides could exacerbate their scale problems.

The cost of the Bt program is almost identical to the grower’s standard pesticide program. This includes the cost of two May sprays of Bt. No additional application costs are incurred during the bloom sprays if Bt can be applied with regularly scheduled fungicide or nutrient sprays. If Bt timing does not correspond well with other sprays or a third application is necessary, cost of the Bt program could be slightly higher than the standard program. However, if pyrethroid or organophosphate sprays facilitate the need of a mite spray, then a Bt program could prove more cost effective. The intermediate treatment is twice as expensive as the other two programs. The costs of Success and Agrimek far exceed their alternatives. In addition, Agrimek must be applied early in the season as a preventative treatment, often leading to unnecessary and expensive applications.

One should use caution when interpreting results from this trial. We are only halfway through a four-year study. In addition, this orchard appears to be in an area with fairly low pest pressure. It is possible damage would remain low in this orchard even if it remained completely untreated. A Bt program may prove less satisfactory in an orchard under high PTB pressure.

Stanislaus County Pesticide Summary

Despite rapid population growth in Stanislaus County throughout the past 10 years, the amount of harvested almond acreage has increased. Chart 4.1 shows the trend of harvested acreage in Stanislaus County.

Chart 4.1. Harvested Acreage in Stanislaus County 1990-1998.

Organophosphate use in Stanislaus County has decreased substantially from 1990 to 1998. From a high pounds applied per acre in 1993, organophosphate use has decreased substantially. As stated above, the information regarding harvest acreage was access from the California Agricultural Statistical Service (CASS) and the pesticide use was accessed via the World Wide Web www.ipm.ucdavis.edu. Chart 4.2 shows the trend of organophosphate use.

Chart 4.2. Organophosphate use in Stanislaus County 1990-1998.

Carbamates applied in Stanislaus County have fluctuated throughout the years but decreased in 1998. Chart 4.3 shows the trend of carbamates in Stanislaus County from 1990-1998.

Chart 4.3. Pounds of Carbamates applied per acre in Stanislaus County 1990-1998.

Pyrethroid applications per acre in Stanislaus County have risen since 1992 then the use per acre fluctuates every other year. Chart 4.4 shows the pyrethroid application trend in Stanislaus County.

Chart 4.4. Pyrethroid applications per acre in Stanislaus Co. 1990-1998.

Bt use per acre in Stanislaus County appears to have peaked in 1995 and then has shown a steady decline in use. Chart 4.5 shows the trend of Bt use per acre in Stanislaus County.

Chart 4.5. Bt use per acre in Stanislaus County from 1990-1998.