Stanislaus County Almond Pest Management Alliance Project 

2001 Final Report

Roger Duncan, UCCE Farm Advisor, Stanislaus County; Walt Bentley, IPM Advisor, UC Kearney Agricultural Center, Parlier; Cara Cross & Clinton Bowman, Field Technicians, Stanislaus County UCCE; Merlyn Garber, grower; Art Bowman, pest control advisor, Salida Ag Chem  

Objectives of the Stanislaus County Almond Pest Management Alliance project:

·        To scientifically evaluate the long-term effectiveness and economic viability of less broadly toxic pest management programs.

·        To extend gained information to the almond industry.

·        To demonstrate IPM monitoring techniques and decision-making processes.

We have completed our third season in the Stanislaus County PMA trial.  The original three pest management regimes were maintained similar to the first two years (grower’s standard practice and two “reduced risk” treatments).  Because reject levels have been very low for all three pest management regimes during the first two years, a fourth, “untreated” program was added in 2001.  Each pest management program is replicated three times within a 120 acre Nonpareil: Carmel orchard west of Modesto.  Each plot is approximately 13.5 acres in size.  The treatments are:

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

¨       A dormant application of Asana^® (a pyrethroid), 6 gallons of oil, & 8 lb. Kocide^®.

¨       A May spray with an organophosphate (Lorsban).

¨       Omite^® if needed for mites.

¨       Lorsban for ant control.

2)                  Soft Program #1:

¨       A dormant application of copper & oil (no insecticide).

¨       A “bloom” spray of Success^® at ~ 30% PTB emergence (piggy-backed with fungicides).

¨       A May spray of Confirm^®.

¨       Savey^® for mites if monitoring deems necessary.

¨       Clinch^® (Abamectin) bait for ants if monitoring deems necessary.

3)                  Soft program #2:

¨       A dormant application with oil only.

¨       Two “bloom” applications of Bt (@ ~20% PTB emergence & ~ 80% emergence).

¨       Two May sprays of Bt (300-350 & 450-500 DD after biofix).

¨       Potassium nitrate & oil for mites if monitoring deems necessary.

¨       Esteem^® bait for ants if monitoring deems necessary.

4)                  “Untreated”:  only mites and ants are controlled if necessary. 

¨       No dormant copper, oil, or insecticide application.

¨       No bloom Bt applications.

¨       No May or hull split sprays.

¨       Potassium nitrate & oil for mites if monitoring deems necessary.

¨       Esteem^® bait for ants if monitoring deems necessary.

Overwintering nuts (“mummies”) were removed and destroyed in all treatments to reduce overwintering naval orangeworm.  Cover crop management, fertilization, and fungicide treatments were the same for all treatments other than no dormant copper was applied in “soft program #2” and the “untreated” areas.

Monitoring:

Each plot had two PTB pheromone traps, two San Jose Scale pheromone traps, four sticky tape traps for S.J. scale crawlers, and two NOW egg traps for a total of 120 traps in the trial.  Peach twig borer and naval orangeworm traps were checked twice weekly while San Jose scale pheromone and sticky traps were monitored weekly throughout the season (March through October).  In addition, mites and mite predators were monitored bi-weekly with the presence / absence leaf sampling technique.  Ants were monitored periodically using hotdog bait traps.  In the dormant period, spurs were sampled to monitor San Jose scale populations.

Results:

Peach Twig Borer.  Early in the season, peach twig borer moth catches were roughly half as high in areas treated with Asana or Success compared to “untreated” or Bt treated areas.  Most of the difference was due to a peak of moths caught May 9 in the Bt treated and untreated areas.  After May, PTB moth catches were very similar for all treatments (Fig. 1).  By the end of the season, cumulative moth catches were also very similar for all treatments and showed no clear advantage to dormant and in-season spraying (Fig. 2).

Mites.  Brown almond mite (BAM) feeding damage was most severe early in the year and mostly restricted to individual trees within the orchard.  In this trial, brown almond mite numbers were highest in untreated areas (Fig. 3).  On the first date of mite monitoring using the presence / absence method (May 22), about 15% of leaves sampled from untreated trees had BAM.  The dormant oil and Bt treated trees had approximately 7% infestation while the dormant oil & Success or Asana treatments each had approximately 2% infestation.  By mid-July, BAM numbers were similar for all programs.  By the end of August, no BAM were found on sampled leaves.  Very few European red mites were found in the trial.

It is very difficult to draw conclusions from the spider mite data.  Due to lengthy pre-harvest interval and re-entry restrictions, miticides can be applied no later than about one month before harvest.  Even though two-spotted mite numbers in 2001 were higher than the previous two years, none of the treatment areas had reached economic thresholds by the time mite sprays had to be applied.  Despite leaf infestation levels of only about 12%, all areas were treated for mites on July 19 & 20 (treatment threshold is approximately 33% infestation).  The “untreated” areas were sprayed a second time with potassium nitrate and oil on August 3.  Despite spraying, spider mite levels exceeded the treatment threshold on August 21in all but “Soft” program #1 (Fig. 4).  Areas treated with a dormant applied pyrethroid did not develop higher mite numbers than areas that did not receive dormant or in-season insecticide sprays.  However, each area was treated with different in-season miticides with differing efficacies and residual effectiveness, making it difficult to draw sound conclusions.  In the future, all areas will be treated with the same in-season miticide to alleviate this problem.

San Jose scale and scale parasitoids.  In general, San Jose scale numbers were very low in this trial.  Untreated areas (areas not sprayed with oil or an insecticide) had higher pheromone trap catches than areas sprayed with dormant oil.  Cumulative season totals for the grower’s standard, soft program #1, soft program #2, and “untreated” areas were 92, 30, 33, and 320 scale caught per trap.  As in previous seasons, approximately twice the number of scale parasitoids were caught in areas that were not sprayed with dormant Asana and in-season Lorsban (Fig. 5).  The vast majority of parasitoids caught was Encarsia sp. although Aphytis sp. was also present in the orchard.  Ratios of parasitoids to scale were very high (70:1) in the two treatments that received dormant oil sprays but no dormant or in-season insecticides.  Although the ‘untreated” areas had high numbers of parasitoids, these areas also had the highest scale numbers resulting in a less favorable parasitoid to scale ratio (6:1).  Observations over future seasons will determine if high parasitoid numbers in untreated areas can maintain scale levels below economic thresholds without the use of oils.

Spur samples collected after the 1999 and 2000 growing seasons showed almost no San Jose scale present in any of the treatments.  Samples will be collected in January 2002 to determine scale numbers overwintering from the 2001 season.

Ants.  Bait materials (Esteem and Clinch) were applied approximately five weeks prior to harvest (July 19) in the two “soft” treatments and in “untreated” areas.  No ant treatment was applied in the grower’s standard treatment.  Ants were monitored on July 17 (prior to treatment) and again just after harvest.  Twenty vials containing pieces of hot dog were placed throughout each replication in early morning and collected after 3-4 hours.  Vials were transported back to the lab and put into a freezer.  After 24 hours, frozen ants were identified and counted under a dissecting microscope.  Almost all ants collected were identified as black pavement ants with only an occasional southern fire ant captured. Just after Nonpareil harvest, ants were again collected and counted.  Fewer ants were caught in the reduced risk program areas in the pretreatment samples (Fig. 6).  This may have been due to a carry over effect from bait materials used the previous season.  By harvest, there were very few ants in any of the treatments.

Harvest Evaluation:

At harvest, 500 almonds were randomly collected from each replication (1500 per treatment) and examined for insect damage.  Reject levels for all treatments were very low.  There were no differences between treatments from damage due to NOW or PTB (Table 2).  The grower’s standard treatment had high ant damage in one of the three replications, resulting in an average of 1.8% ant damage over all.  Areas treated with Clinch or Esteem baits had 0.1 – 0.2% ant damage.

*Costs do not include ant treatments because the grower’s standard treatment was not treated for ants.

Conclusions:

After 3 years of intensive monitoring, we have not seen an increase in any pest in the two “soft” treatment programs compared to the standard grower’s practices.  There also have not been any differences in rejects due to PTB, NOW or ants at harvest.  In 2001 we added an “untreated” program where no sprays are applied to control NOW, PTB or San Jose scale.  This program does allow for mite management with potassium nitrate and oil and for ant control with bait.  After one year, there is no indication of increased populations of NOW, PTB or ants in these untreated areas.  Harvest reject levels were also very low and similar to treated areas.

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 the two “soft” programs where oil was applied in the dormant period, extremely low levels of scale were caught in-season and very high numbers of Encarsia scale parasitoids were present.  In these areas, 70 Encarsia parasitoids were caught for every 1 San Jose scale, a very high ratio of parasitoids to the pest.  In the grower’s standard practice treatment, San Jose scale numbers were also low but parasitoid numbers were only half as high as in the other three programs, leading to a ratio of 12 parasitoids to 1 scale.  In the northern San Joaquin Valley, 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.  In the untreated program where no dormant oil was applied, high parasitoid numbers were present but San Jose scale numbers were significantly higher than the other treatment programs (a ratio of only 6:1).  Although scale numbers were still too low to cause concern, these areas will need to be watched closely in the future to determine if natural predation will be enough to keep San Jose scale under control.

Brown almond mite numbers were highest in the “untreated” areas.  This could be expected because dormant oil can kill mite eggs.  However, BAM numbers were not serious and obvious feeding injury was limited to a few isolated trees.  Even this amount of feeding could not be expected to cause economic levels of damage. 

There was no clear relationship between pest management program and spider mite numbers.  It has been shown in other experiments that the use of broad-spectrum insecticides, primarily pyrethroids, can lead to large increases in spider mites.  This has not been observed in the three-year duration of this trial.  However, miticides have been applied each year before mite levels have reached established threshold levels.  This is largely because conventional miticides have lengthy re-entry and pre-harvest intervals (Omite is 28 days).  This leads many growers to apply these materials for “insurance” even when mites are present in low levels.  If a miticide is not applied and then mites build shortly before harvest, growers are unable to treat and thus risk defoliation.  In addition, the use of different miticide materials with different efficacies and residual levels makes it even more difficult to interpret the effects of dormant and in-season sprays on mites.  Beginning in 2002, one miticide with the shortest pre-harvest interval will be used in all treatment programs.

Very few ants were captured on the harvest sampling date even though no treatment for ant control was applied in the grower’s standard program.  This orchard had a moderate infestation of Fuller’s rose beetle which lays its eggs in microsprinklers and clogs them.  The entire trial area was sprayed with Lorsban shortly before harvest to control this pest.  It is certain that this spray substantially reduced ant numbers in all treatments.  It will be valuable to observe if the bait products hold ant populations down into the 2002 season.

In the spring, areas treated with and without dormant copper were examined for brown rot and shot hole diseases.  No brown rot strikes were observed in any treatment.  In addition, very few shot hole lesions were observed on the fruit and no treatment differences were detected.  It is doubtful that dormant applied copper has a significant effect on brown rot or shot hole if a strong bloom-time fungicide program is maintained.

We have shown over the past three years that almonds can be farmed with less broadly toxic insecticides and still have very low damage to the crop, at least in cases where pest pressure is low.  In addition, using only dormant oil and in-season sprays that do not harm scale parasitoids may better control San Jose scale than a “conventional” program.  However, programs that utilize newer, less broadly toxic materials are often more expensive than using pyrethroids and organophosphate insecticides.  In our trial, the “soft” program #1 using Success, Confirm and Savey was the most expensive program, a cost increase of 22% over the grower’s normal practice.  Soft program #2 utilizing Bt and Savey cost 9% more than the grower’s normal practice.  The cost increase in the Bt program was largely due to increased labor and equipment costs where two applications at bloom and in May were required instead of the normal single application required with more conventional insecticides.  Under present economic conditions, almond growers cannot afford to adopt practices that increase their costs.  The “untreated” program was the least expensive by far in this trial (only 13% of the grower’s standard program).  However, leaving orchards completely untreated increases the risk of experiencing periodic economic damage.  Although there was very little insect feeding in the untreated areas in 2001, more years of observation are necessary to evaluate the long-term consequences of this practice.  Better monitoring techniques to determine treatment thresholds for PTB and San Jose scale need to be developed before almond growers can reduce pesticide usage with confidence.