Susceptibility to spinosad (Success®/Tracer®) of beet armyworm (Spodoptera exigua) from the southern U.S.A. and Southeast Asia was determined through exposure of third instar larvae to dipped cotton leaves. LC₅₀ values of field populations ranged from 0.6 to 14 μg spinosad/ml. Field populations were 3.0 to 70-fold less susceptible to spinosad than was a susceptible reference population. The least susceptible population was collected from Thailand. We hypothesized that this population was resistant to spinosad because: (1) it was significantly less susceptible to spinosad than all other populations evaluated and than any other reports in the literature; (2) it regained susceptibility while in culture; (3) it was collected from a region of very intensive insecticide use and severe insect resistance problems; and (4) it exhibited significant survivorship on field-treated cabbage leaves. Piperonyl butoxide (PBO), diethyl maleate (DEM), and S,S,S tributyl-phosphorothiolate (DEF) failed to synergize spinosad in this resistant Thailand population, and PBO failed to do so in the least susceptible domestic population evaluated, the Parker, AZ, field strain. However, the synergist and field residue studies were conducted using a Thailand population that had levels of resistance that declined while in laboratory culture.

During the past 5 years, the efficacy and field performance of several new insecticides for control of Lepidopterous insects on desert lettuce crops has been investigated in small plot trials at the Yuma Agricultural Center and in produce fields with commercial cooperators. The objective has been to determine how these new chemistries will fit into pest management programs in Arizona. Thus, research programs have been focused on studies to define use patterns for these insecticides chemicals that can be integrated into our local management programs in the most cost-effective way possible. This report was created to provide an overview of the new chemistries being developed, their field activity and characteristics, and guidelines for use in head lettuce. In addition, an approach for sustaining the long-term efficacy of these products is discussed.

The Western Growers Association and Arizona Cotton Growers Association worked cooperatively with a group of University of Arizona scientists, Arizona Department of Agriculture officials and regional pest control advisors to develop general guidelines for managing whiteflies and specific recommendations for Applaud and Admire use. This was achieved by identifying differences in crop production, insecticide use, and whitefly population dynamics on key host crops within three distinct growing regions in Arizona. Data was compiled that when graphically illustrated identified important, multidimensional interactions within cropping systems. Based on the patterns resulting from our analysis, initial recommendations have been formulated to harmonize chemical use across commodities by restricting Applaud use to only once per crop season in use windows, with additional guidelines for reducing the possibility of exposing successive whitefly generations to the same mode of action. The diversification and limitation of Admire and other active ingredients, and the employment of cultural practices are also be considered. Should this model of cooperation be successful, valuable and scarce modes of action may also be shared in the future within diverse, integrated use systems.

Whitefly populations in the Yuma area have been reduced to levels that growers can cost-effectively manage. Data from our studies suggest that these declines in pest populations are largely attributed to the use of Admire 2F (imidacloprid) soil treatments. Relative to the outbreaks in 1993-1994, whitefly populations during the past four growing seasons have remained at sub-economic levels on lettuce crops throughout the growing areas in Yuma This chemical has provided excellent control of whiteflies on fall lettuce, and aphids on spring lettuce. After 6 years of evaluation in commercial fields, the product appears to remain highly efficacious, maintaining good residual activity. Studies in 1998 on fall broccoli and melons crops further support this conclusion. Factors responsible for this sustained efficacy of Admire are discussed.

Spinosad (Success7), chlorfenapyr (Alert7), DPX-MP062 (DuPont), thiodicarb (Larvin7), and cryolite (Kryocide7) progressively reduced the total number of Plutella xylostella (diamondback moth, DBM) following each of three applications. Success treated cabbage had the fewest number of small-sized DBM larvae after the first application and maintained very low numbers following subsequent applications. Relative performance of the insecticides based on efficacy indicated by a seasonal average of total DBM larvae showed that Success was highly effective followed by methomyl (Lannate) and Larvin. Emamectin-benzoate (Proclaim7), Alert, and DPX-MP062 performed comparably and tebufenozide (Confirm7) and Kryocide were less effective.

Cantaloupe leaf damage from leafminer activity was minimal to non-existent when evaluated at 6 days after treatment (DAT) following each of the first four weekly application dates. At 13 DAT-4, the number of mined leaves increased tremendously over the previous observation date. The untreated cantaloupes showed an increase from 30.8 to 81.8 mined leaves compared to the previous week. Agri-mek and the alternation treatment of Trigard, Success7, and Agri-mek applied on cantaloupes showed the fewest number of mined leaves at about 22 mined leaves. Trigard and Success treated cantaloupes had increased number of mined leaves ranging from 44 to 56.8. Agri-mek and the alternation treatment consistently had the fewest number of mined leaves during the course of the test period. Trigard and Success treatments performed similarly and reduced the number of mined leaves relative to the untreated cantaloupes. Success at the higher rate appeared to be slightly more active by showing numerically fewer mined leaves than the lower rate of application. Success treated melons yielded nearly twice as much compared to the other treatments and the untreated. Success treated melons also offered a higher number of marketable fruit at better than 80% compared to about 60% for the other treatments. Less stickiness was observed on the Success treated cantaloupes. There appeared to be an effect from Success applications on whitefly to reduce the honeydew stickiness.