Stanislaus County Almond PMA Project

Year-end Summary 1999

Walt Bentley, IPM Advisor, Kearney Agricultural Center, Parlier

Roger Duncan, UCCE Farm Advisor, Stanislaus County

Lonnie Hendricks, UCCE Farm Advisor, Merced County

Cara Cross, Field Technician, Stanislaus County UCCE

Merlyn Garber, grower

Art Bowman, pest control advisor

The Stanislaus County PMA site is a research trial as well as a demonstration. The trial is being conducted in a uniform 120-acre orchard (Nonpareil:Carmel) west of Modesto. Three insect pest management program treatments are fully replicated three times within the 120-acre orchard. Each plot is approximately 13.5 acres in size. The treatments are:

Grower’s Standard Practice: This pest management program is fairly common in the Northern San Joaquin Valley. While most growers in this area apply a hull split spray for naval orangeworm control, our cooperator elects to target peach twig borer with a May spray. Specifically, pesticide treatments included:

• A dormant application (1-21-99) of Asana XL (a pyrethroid) @ 8 oz, Kocide DF @ 8 lb, and Gavicide Super 90 @ 6 gallons (6%).
• A May spray (5-20-99) of Lorsban 4E (an organophosphate) @ 4 pints + 12.8 oz Nu-film 17.
• Omite was applied to the northwest corner (approximately four acres) of Replication 1 on 7-12 due to an increase of Pacific mites (an area historically prone to mite buildup). On August 5 the entire replication (13 acres) was treated with Omite as mites were beginning to build and the cooperator was concerned about the 30-day pre-harvest interval.

Intermediate Program: In these areas, "reduced risk" pesticides are used. Specifically, pesticide treatments included:

• A dormant application (1-21-99) of Success @ 6.4 oz, Kocide DF @ 8 lb, and Gavicide Super 90 @ 5 gallons (5%).
• A May PTB spray (5-21-99) of Success @ 6.4 oz.
• Agri-Mek 0.15 EC @ 10 oz & Gavicide Super 90 @ 1 gallon were included in the May spray because mite populations were beginning to build in Replication 1 only.

Soft program: Pesticide treatments included:

• A dormant application (1-21-99) with oil only (Gavicide Super 90 @ 6 gallons).
• Two bloom applications of Bt (Dipel DF @ 1.5 lb on 3-2 and 3-16). These coincided with normal fungicide applications and therefore did not necessitate additional application costs.
• Two May PTB sprays of Bt (Dipel DF @ 1.5 lb on 5-14 and 5-24).
• Agri-Mek 0.15 EC @ 10 oz & Gavicide Super 90 @ 1 gallon for Replication 1 only (5-24).

All dormant and in-season sprays were applied in approximately 100 gallons of water per acre. Mummies were removed and destroyed in all treatments. Mummy counts were recorded on February 12 & 15, 1999 and averaged 0.4 mummies per tree. There were no differences between treatments. Cover crop management (periodic mowing of native vegetation), fertilization, and fungicide treatments did not differ between treatments. A nutrient buffer product (10-12-0) was included in the May sprays for all treatments.

Monitoring:

Peach twig borer hibernacula were examined in the spring to determine appropriate "bloom-time" Bt sprays for overwintering PTB. The first Bt application was made when approximately 20% of the overwintering PTB larvae had emerged. The second Bt application was applied at approximately 90% emergence. Both of these applications coincided with the normal bloom-time fungicide applications. PTB pheromone traps were hung March 29 and checked every other day to establish the first biofix. The first biofix for PTB was April 17.

In each treatment replication there were two PTB pheromone traps, two S.J. scale pheromone traps, four S.J. scale crawler sticky tape traps, and two NOW egg traps for a total of 90 traps in the trial. The orchard was monitored twice weekly through the season for PTB and NOW. Trap catches and the degree-day phenology model were used to determine application timings for the May PTB spray. San Jose scale pheromone and sticky tape traps were checked weekly. Each plot was also monitored weekly for mites using the presence / absence sampling technique. In addition, ants were monitored occasionally using the hot dog baiting method.

Figure 1 shows the seasonal dynamics of the peach twig borer flight in this trial.

During the first half of the season there tended to be fewer peach twig borer in the Grower’s Standard treatment. There did not appear to be differences between the intermediate and soft programs. After 21 June, PTB flights appeared very similar for all three pest management programs.

Flights of San Jose scale were very low through most of the season in all pest management programs. By the first of September, male scale catches increased substantially. Trap catches were lowest in the Grower’s Standard treatment. Seasonal population dynamics for the San Jose scale flight are shown in Figure 2.

Dynamics of the Encarsia (Prospaltella) flight are shown in Figure 3 below. We began catching Encarsia in mid-April and continued catching high numbers through June. Peak populations reached approximately 300 Encarsia per week in the soft and intermediate pest management programs. Parasite populations were substantially lower in the Grower’s Standard treatment.

Naval Orangeworm:

Naval orangeworm egg laying was detected very infrequently on our eighteen almond press-cake egg traps. No egg laying was detected through the whole year in the soft and intermediate pest management blocks. Only thirty eggs were detected in the Grower’s Standard treatment, and these occurred during the first two weeks of sampling.

Cumulative trap catches through June 15 for PTB, SJ. scale males (pheromone traps), Encarsia, Aphytis and naval orangeworm are listed below for the three treatments.

The first half of the season, there were fewer PTB caught in the Grower’s Standard treatment and most in the intermediate treatment. By the end of the season, there were no significant differences in peach twig borer catches between the grower’s standard treatment and the two softer programs. However, the trend of fewer San Jose scale and scale parasites continued throughout the season.

Cumulative trap catches through September 30 for PTB, S. J. scale males (pheromone traps), Encarsia, Aphytis and naval orangeworm are listed below for the three treatments.

Mites:

The trial was sampled weekly for mites using the presence / absence sampling technique. Fifteen leaves each from three trees per plot were examined for presence of mites and mite predators. Numbers were compared to the chart in the University of California Almond IPM Manual to determine if mite treatments were necessary. In two of the three blocks (both irrigated with microsprinklers), mites never reached treatable levels according to our sampling technique. However, the grower grew concerned about increasing mite numbers on orchard edges and decided to treat these areas with ten pounds of potassium nitrate plus 2% oil on August 28. The higher mite numbers along orchard edges did not appear to be related to pest management treatments.

In the northern-most 40 acre block (Replication 1), Pacific mite numbers began building and exceeded threshold values by mid-May. As a result, Agri-Mek (avermectin) was included in the May PTB spray in replication 1 of the soft and intermediate programs. The Grower’s Standard treatment was not treated at this time because it was felt Omite could be applied later effectively if mite numbers continued to increase. Omite was eventually applied on July 12 to the edge of the Grower’s Standard treatment in replication 1 and finally to the entire plot on August 6. Mite counts remained very low in avermectin treated areas through the remainder of the season.

Ants:

Ant populations were monitored on July 29. Fifteen vials containing a 3-5 cm section of hotdog were placed throughout each plot. After three hours the vials were collected, taken back to the lab and frozen. Ants in each vial were counted. Ant populations were very low and were not at treatable levels. Ant counts for the three treatments are shown in Table 3 below.

Harvest:

At harvest, nuts were collected randomly from windrows in all plots. Five hundred Nonpareil kernels will be examined from each plot (1500 total per treatment) for presence or feeding damage from peach twig borer, naval orangeworm, and ants. As of the date of this report only 200 kernels per treatment have been examined.

As shown in Table 4, preliminary data show damage from all three insect pests was very low in all treatments. No statistical analyses have been performed on these data as yet.

Treatment Costs:

Costs associated with each pest management program are itemized below. Material costs reflect actual prices at the date of purchase from a local agricultural chemical supplier. Application costs reflect the price of labor to mix, load and apply materials, (including wages, workman’s comp., insurance, etc.), fuel costs, and equipment maintenance as calculated by the grower.

Discussion:

In general, pest populations and reject levels were similar and very acceptable for all three pest management programs this season. A pattern of reduced arthropod numbers (both pest and beneficial) was established in the Grower’s Standard treatment. However, pest pressure was generally low in all treatments and the low levels of damage at harvest reflected this. Over time, differences in pest and beneficial arthropod populations between treatments may become larger. It is uncertain whether reduced kill of San Jose scale in the softer treatments will lead to economically damaging levels or whether the increased numbers of scale parasites will keep this pest under control. More significant differences in other pest populations may also become apparent with time.

Costs to the grower were 15% and 26% higher than the grower’s standard treatment in the "soft" and intermediate programs, respectively. Higher costs in the "soft" program are associated with an extra in-season application for PTB control and the use of a more costly miticide. In the future, a cheaper "reduced risk" miticide may be used in this treatment. Increased costs in the intermediate program were associated with the use of Success and Agri-Mek, two relatively expensive materials.

Risk of increased losses due to higher reject levels and increased San Jose scale are arguably higher in the "soft" and intermediate programs. Increased costs of extra monitoring in softer pest management programs should be included in an analysis of these programs also.

One must be careful not to put too much emphasis on the preliminary results of this trial. It may take a few years before significant shifts in arthropod populations occur. This trial is conducted in an orchard with historically low reject levels in a year with unusually low pest pressure. It will be interesting to observe this trial over the next few years.

In the future, treatments may be modified slightly but the general idea of maintaining "standard", "intermediate", and "soft" management strategies will continue. It would be interesting to include a completely unsprayed or "oil only" treatment.