Several studies were conducted in the spring and fall 2001 to evaluate a number of neonicotinoid compounds (Admire, Calypso, Actara, Platinum and dinotefuron) for whitefly control in spring and fall melons. The results of these studies demonstrate that several insecticide products are being developed that offer melon growers management alternatives for controlling whiteflies. The new foliar neonicotinoid Calypso (thiacloprid), shows excellent promise as a foliar, post-planting spray with 14-21 day residual. Further, no consistent negative interaction was detected between Platinum and fertilizer, 10-34-0 and UN 32, applied together as at-planting or side dress soil treatments. These treatments provided good whitefly control, but further research is needed to replicate these effects as Platinum has been labeled at lower rates than the manufacturer initially anticipated. At planting applications of Platinum at 8 oz (current labeled rate) did however provide acceptable residual control of whiteflies on fall melons under heavy population pressure.

Small plot studies were conducted from 1999-2001 to examine the population abundance and control of the lettuce aphid on winter and spring head lettuce crops. In each year, Seven, 0.25 acre planting of head lettuce were established beginning in Sep-Oct with final harvest occurring in April. Replicated plots within several planting were treated with an Admire treatment at planting, a side dress application of Platinum post-planting or allowed to remain untreated. Lettuce aphids were first detected in our experimental area in December in PD 3 in 2001, but in 2002 first occurred in lettuce almost 2 months later (Feb 21). Similarly, lettuce aphid abundance was much greater in 2001 than in 2002, probably a result of temperature difference. Temperature had an important influence upon lettuce aphid development based on our field observations. Population appeared to increase in early March when the average daily temperature was about 65 E F. We observed a sharp decline in population abundance in April where daytime highs exceeded 90E F. Insecticide treatments also influenced seasonal abundance. Under heavy aphid pressure in 2001, lettuce treated with Admire in the early planting dates appeared to prevent lettuce aphids from significantly infesting lettuce heads at harvest. However, lettuce aphids in the last 3 planting dates were able to colonize plants and infest a larger proportion of heads at levels not considered commercially acceptable. Under lighter pressure in 2002, lettuce aphids did not significantly colonize Admire treated lettuce. Green peach aphid, potato aphid and foxglove aphids were also present in both years, but seldom reached economic levels, and where completely controlled in plots treated with soil, systemic insecticides.

Three separate field trials over two years were conducted to evaluate the comparative knockdown and residual efficacy of several conventional, Reduced risk and biopesticide compounds against western flower thrips in romaine lettuce. These trials consistently demonstrated that both Lannate-pyrethroid combinations and Success provided significant knockdown and residual control of thrips adults and larvae when compared to the other spray biopesticide treatments. Unfortunately, the biopesticide alternatives at best provided poor to marginal efficacy against western flower thrips. The implication of these results on desert lettuce production and resistance management programs is discussed.

Success®, Proclaim®, and Confirm® treated lettuce exhibited no beet armyworm (BAW) larvae at 3 days after treatment (DAT). Avaunt®, Intrepid®, and S-1812 (Valent) treated lettuce had no medium-sized larvae but 0.3 to 0.5 small larvae were observed. At 7 and 10 DAT, BAW populations diminished significantly in all of the lettuce and no larvae or eggs were observed in any lettuce.

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.