The effect of three different release rates (1x, 10x, and 20x the recommended rate of 10,000/acre) of Eretmocerus eremicus, a whitefly parasitoid, on sweet potato whitefly populations in cantaloupe were evaluated against populations in untreated control plots. Parasitoids were released from a point source in the center of each of nine treatment plots. All stages of whitefly development were monitored within a 10-m annulus surrounding each release point in all 12 plots, as were rates of parasitism. This occurred over a 52-d period from July 21 through September 11, 2001. The rates of sweet potato whitefly population increase during this time were equivalent and independent of the parasitoid release rate. Whitefly densities were not controlled in any of our treatment plots, nor in the controls. Moreover, rates of parasitism did not increase with time in any of the treatment plots and did not differ among the three release rates (22.0 ± 16.2%). Hence, Eretmocerus eremicus, by itself, is not efficient as a means to control whitefly populations in melon crops in the Southwest US. The ineffectiveness of E. eremicus to control whitefly populations in the field may be due to its propensity to dispersal at low host densities.

Studies were conducted in the field and laboratory to investigate how the addition of spray adjuvants to Success affected its insecticidal activity against leafminers, thrips and lepidopterous larvae. Studies were also designed to evaluate the knockdown and residual mortality of Success against worms when applied with a buffer to produce an acidic spray solution. Results indicated that Success applied without an adjuvant appeared to provide the most consistent adult mortality of Liriomyza leafminers. In contrast, the addition of a penetrating surfactant (crop oil concentrate) resulted in significantly greater larval mortality consistent with the leafminer feeding behavior. Efficacy of Success against lepidopterous larvae and western flower thrips was not improved using a spray surfactant. However, addition of buffering agents to Success spray solutions significantly affected efficacy against beet armyworm and cabbage looper. Lab bioassays and field studies showed that knockdown mortality was not affected, but residual efficacy was significantly reduced when Success was applied in an acidic (pH 4.2) spray environment.

Studies to examine lettuce aphid population growth on resistant head and butter lettuce cultivars were conducted in small filed plots at the Yuma Agricultural Center. By artificially infesting plants on several lettuce plantings during the spring, the influence of the resistant lettuce plants were evaluated for their capability of preventing lettuce aphid populations from colonizing plants. Results of five field trials showed that several varieties of head and butter lettuce have been developed that almost completely prevent lettuce aphids from surviving and reproducing on plants during the spring. Although the cultivars tested did not posses marketable characteristic for harvests, they do provide germplasm for breeding new varieties suited for desert production. In addition, these studies also support conclusions drawn from the past several seasons that suggest lettuce aphid population growth is greatest when ambient temperatures average between 65-70 °F.

A two year study was conducted from 2000-2002 to evaluate the use of overhead sprinkler irrigation for suppressing thrips populations in romaine lettuce. Specifically we looked at how the duration and frequency of sprinkler irrigation use reduced adult and larval populations following various irrigation applications employed specifically for thrips suppression. We also evaluated combinations of insecticide spray regimes, used in association with sprinkler irrigation runs, for suppressing thrips populations in both fall and spring seasons. The results of the study demonstrated that overhead sprinkler irrigation has the ability to suppress thrips populations in romaine lettuce. At best, we experienced about 50% population reduction using only sprinkler irrigation compared with the untreated control during these trials. Sprinkler ruins of durations of > 4 hrs and more than 4 cm of water appeared to provide the minimal necessary for suppression. Furthermore, sprinkle runs of 2 or 3 times weekly appeared to provide the most consistent suppression. In contrast, insecticide sprays consistently provided >80% suppression and provided higher yielding and better quality lettuce than sprinklers. The use of sprinkler irrigation, in addition to insecticide sprays did not significantly improve thrips suppression or yields. However, sprinkler irrigation is being used season long in some romaine fields and in organic production and should be of benefit for thrips suppression, particularly in organic systems where effective insecticide alternatives are not currently available.

Studies were replicated over 2 years to further evaluate the residual efficacy of several selective, reduced-risk compounds that are now registered for use in head lettuce. In most cases, the Success, Proclaim, Avaunt and Intrepid provided excellent seasonal efficacy against beet armyworm and cabbage looper larvae. Their performance at stand establishment and harvest were also examined. Based on the results of these studies and additional trials conducted over the past several years, we now have sufficient information for optimizing their uses in our lettuce pest management program. Because they are uniquely different insecticide chemistries, they can be rotated throughout the season to prevent the rapid buildup of resistance. A table was constructed that offers suggested uses for each compound throughout the season. The results are ultimately are aimed at assisting growers and PCA’s in making sound decisions on choosing compounds for use in controlling beet armyworm and cabbage looper in head lettuce.

Several relative sampling techniques (direct visual counts, beat pans and sticky traps) were compared to absolute counts (plant wash) to determine sampling reliability for estimating western flower thrips population levels in lettuce. In numerous plantings of experimental plots of head lettuce, the relative sampling methods indicated similar thrips population trends throughout the season and all relative estimates of abundance were significantly correlated with absolute densities. However, both relative methods could only account for a proportion of the adult thrips infesting head lettuce plants, where they estimated about 30% of the actual absolute population. For larvae, beat pan sample estimated about 18-20% of the actual population density, whereas direct visual counts accounted for less than 10% of the thrips present. Comparison of sampling methods in insecticide efficacy trials indicated that beat pan and direct visual counts did not always accurately estimate treatment differences for adult. For densities of thrips larvae however, beat pan and visual counts methods did consistently provide accurate estimates of treatment differences in efficacy trials. Overall, both beat pan and direct visual count procedures are reliable thrips sampling methods that will generally provide precise estimates of thrips abundance necessary in lettuce pest management programs. Furthermore, these methods, and the beat pan in particular, also may serve as effective research tools that provide reliable estimates of treatment differences.

Studies were conducted in the spring of 2001 and 2002 to evaluate the interaction between starter and side dress fertilizer mixes with neonicotinoid insecticides and their performance against whiteflies in spring cantaloupes in Yuma, AZ. No incompatibility was observed between the fertilizers and the Admire and Platinum mixtures applied at planting and side dress, and both insecticides provided comparable control of whitefly populations regardless of fertilizer used. However, based on our experience in 2001, we suggest that growers use a dilute mixture with the final applied volume to avoid any potential "clumping" problems in the mix tank. In some cases the addition of the DuneUp® starter fertilizer appeared to improve plant growth, but was probably more due to the unique mixture of NPK rather than the combination with the insecticides. Based on the results of these studies growers should not hesitate to apply either Admire or Platinum with starter and side dress fertilizers in melon crops.

The effect of three different release rates (1x [label rate], 10x, and 20x the recommended rate of 10,120/acre) of the parasitoid Eretmocerus eremicus on sweet potato whitefly populations found in open fields of cantaloupe was evaluated against populations in untreated control plots. Parasitoids were released from a point source in the center of each of nine treatment plots. Whitefly population growth, encompassing all developmental stages, and rates of parasitism were monitored within a 33 ft radius surrounding the center point in all 12 plots over a 52-d period. The rates of sweet potato whitefly population increase during this time were equivalent regardless of the parasitoid release rate. Whitefly densities were not limited in any of our treatment plots when compared to those found in the control plots. Moreover, mean rates of parasitism did not increase with time nor did they differ among the three treatments or control plots (7.9 ± 6.5%). Finally, estimated rates of parasitism were density dependent responding positively to increasing host numbers. The ineffectiveness of this parasitoid in controlling whitefly populations in the field may be due to its high propensity to disperse at low host densities or to influxes of immigrating whiteflies. Hence, the use of E. eremicus alone is not an efficient means to reduce whitefly populations in melon crops in the southwestern United States.

Several small-plot studies were conducted in the spring of 2003 to compare the residual efficacy of several new reduced risk insecticides with a number of conventional aphicide compounds on head lettuce and romaine. Our efforts were primarily directed at determining efficacy against the foxglove aphid, a newly discovered pest in Yuma. In general, several new neonicotinoid foliar compounds provided good residual control of all aphid species including foxglove aphid. Other new compounds were less consistent. Admire, the standard soil systemic used in lettuce, was inconsistent against Foxglove aphid providing 85-90% control relative to >95% control against other aphid species present in the plots. Conventional aphid compound such as Capture, dimethoate, endosulfan, Orthene and MSR consistently provided good, economic control of Foxglove aphids in both head and romaine lettuce. Based on the results of these and previous studies, a sampling procedure and action threshold are recommended for foxglove aphid control in desert lettuce.

Replicated studies were conducted to examine aphid distribution and insecticidal control in a commercial cauliflower seed crop in 2001, and in large plots at the Yuma Agricultural Center in 2003. Results were generally consistent in both studies. The primary aphid species found colonizing pre-blooming crops were cabbage aphids, turnip aphids, and green peach aphids. During the bloom period (March-April), the population was almost exclusively cabbage aphid feeding on seed pods and extensions. During the pre-bloom growth period, green peach aphids tended to colonize plants slightly earlier and were found primarily on the older frame leaves low on the plant. In most cases, male and female plants were colonized to the same extent. Cabbage and turnip aphids did not appear to have a clear preference between older and younger leaves, and appeared to colonize males and females equally. Once the plant began to bloom and set seed, cabbage aphid was the primary species (>90%) found feeding on developing seed pods in both tests. These aphid populations were very susceptible to contact insecticides and quickly knocked down by both Capture and MSR. Of the selective, bee safe products, Pirimor provided the most consistent residual aphid control. Assail and Fulfill worked well against aphids on foliage, but did not provide comparable control on seed pods. Aphid densities were extremely high in the untreated check and resulted in almost complete loss of the crop in these plots. Seed yields were not taken due to heavy losses to Sclerotinia and bird damage.