Impact assessment is central to the evolution and evaluation of our local Insect Pest Management (IPM) programs. Quantifiable metrics on insecticide use patterns, costs, targets, and frequency, crop losses due to all stressors of yield and quality, and other real world economic data (e.g., crop value) are our most objective tools for assessing change in our systems. We recently initiated a project to measure the impact of insect losses and insecticide uses in head lettuce grown in Yuma, AZ and the Bard-Winterhaven area of Imperial County, CA. The data generated in this report is useful for responding to pesticide information requests generated by EPA, and can provide a basis for regulatory processes such as Section 18 requests, as well as for evaluating the impact of our extension programs on risk reduction to growers. This information also confirms the value of PCAs to the lettuce industry by showing the importance of cost-effective management of insect pests in desert lettuce production.

Field experiments were conducted with the objective of developing a general New Mexico chile type plant (Capsicum annuum L.) phenological model as a function of heat units accumulated after planting (HUAP). Field experiments were conducted from 2003 through 2005 in the Sulfur Springs Valley of Arizona, near Sunsites in Cochise County, Arizona (31° 56" N, 109° 52" W, about 4,000 feet elevation) on a Borderline fine sandy loam (coarse-loamy, mixed, superactive thermic Typic Calcigypsids) and in the Animas Valley, New Mexico (31° 57" N, 109° 48" W, about 4,400 feet elevation), on a Vekol fine sandy clay loam (fine, mixed, thermic, Typic Haplargids). Plant measurements were collected routinely and important phenological stages that corresponded to first bloom, early bloom, peak bloom, physiological maturity, and red harvest were identified and recorded. Results indicate that within locations, all varieties performed similarly in relation to HU accumulation patterns. A general New Mexico chile type plant phenological model as a function of HUAP for all sites and varieties was obtained. First bloom occurred at 954 ± 254 HUAP, early bloom at 1349 ± 306 HUAP, peak bloom at 1810 ± 261 HUAP, physiological maturity at 2393 ± 215 HUAP, and red chile harvest was identified to occur at 3159 ± 220 HUAP. The purpose of this phenological baseline or model is to provide a crop management tool for growers for predicting and identifying critical stages of growth. Further development and validation of this model is a continued objective of this research program.

Field experiments were conducted in 2007 to evaluate a cantaloupe (Cucumis melo L.) plant development model as a function of heat units accumulated after planting (HUAP). Field experiments were conducted in 2007 in the Yuma Valley, Arizona (32° 42' N, 114° 42' W), about 150 feet (~ 32 m) elevation in four commercial cantaloupe fields managed by a cooperator-grower using four varieties. Plant measurements were made on regular 14-day intervals and the following growth stages were identified in relation to plant measurement data collection: pre-bloom, early fruit set, early netting, and physiological maturity (harvest). The model was evaluated by comparing the observed HUAP versus the predicted HUAP values using a repeated measures design. Mean differences within each sampling stage were separated using the Fishers’ protected least significance difference (LSD) test at P≤ 0.01. In addition, regression models were performed for all in-season data collected and the accuracy of the model was evaluated on the basis of the R² values with a specified level significance (α = 0.01). No statistical differences were found between the observed phenological data and the predicted values from the model throughout the study period. Also, the model presented an overall accuracy of 54 ± 37 HUAP (2 ± 1 day) in predicting cantaloupe-harvesting time. It can be concluded that the model can be used as a useful tool to assist cantaloupe growers in predicting and identifying critical stages of growth for irrigated spring cantaloupe crops in Arizona and the desert Southwest.

Several small-plot studies were conducted in the spring of 2004 to compare the residual efficacy of several new reduced risk insecticides against aphids infesting desert head lettuce. In 4 head lettuce trials and one broccoli trial, economic aphid control was consistently achieved following foliar applications with flonicamid and Assail. These compounds provided good knockdown of aphids when applied relatively early in lettuce plant development and aphid population growth. Fulfill was less consistent and performance was reliant on correct spray timing. Collectively, the chemical attributes and biological activities of Fulfill, Assail and flonicamid make them extremely attractive for implementation into an aphid management program.

The influence of planting dates on aphid population growth in head lettuce was measured over a 5 year period to identify planting windows during the season when lettuce is at risk from aphid infestations. Small, untreated 0.2 acre plantings of head lettuce were established beginning in October with final harvest occurring in April. Plant samples were conducted weekly to estimate the numbers of aphid per plant. Based on these studies, planting date and temperature likely has a strong influence on seasonal abundance and damage caused by aphids. Green peach aphid was the least abundant aphid during the 5 year period, and foxglove aphids appear to be increasing in abundance over the past 3 years. All aphid species have the potential to economically contaminate lettuce, particularly in the November and December planting windows.

Insect pest populations seemed to be exceptionally abundant on our desert vegetable crops this past growing season. It is difficult to explain why some insect populations occurred in larger numbers this year, but the weather we experienced may have had a significant role. Hot, dry weather in the early fall and spring, coupled with moderate winter temperatures provided ideal conditions for some insect pests.

Several studies were conducted on spring cantaloupes from 2002-2004 to evaluate a new insecticide, Oberon (spiromesifen) for whitefly control in spring melons. These studies demonstrate that this IGR-like insecticide offers melon growers management alternatives for effectively controlling whiteflies. The results strongly suggest that Oberon has good potential for controlling whiteflies in spring melon crops similar to what can be expected from Courier. Oberon provided 21-28 days of residual control of whiteflies under spring growing conditions when applied early in whitefly population growth. Our studies also indicate that spray timing is important for cost-effective control with both Oberon and Courier. They also suggest that action thresholds based on adult abundance and nymph densities differ for these two compounds depending on whether Admire has been applied at planting.

"Whitefly resistance to insecticides is a constant threat to successful management of sticky cotton resulting from inadequate control of Bemisia whiteflies. A three-stage resistance management program was implemented in Arizona cotton following a severe whitefly resistance crisis in 1995. This program has been highly successful for eight years. Success has been fostered by intensive investments into improved whitefly sampling and treatment decisions, coupled with conservation of natural enemies. This latter component has hinged on limited, strategic use of two insect growth regulators in cotton, use of the neonicotinoid insecticide, imidacloprid, in vegetables and melons, and tactical deployment of non-pyrethroid and pyrethroid chemicals. Statewide monitoring of whitefly resistance to insecticides in cotton, melons and greenhouse crops has permitted annual assessments of the status of whitefly resistance management in Arizona. In this paper we summarize susceptibility of whitefly collecions made in cotton in the 2002 and 2003 seasons and discuss longer term trends in resistance development. No major problems regarding field performance of insecticides against whiteflies were observed or reported in 2002 or 2003. However, monitoring confirmed the early stages of evolution of resistance to pyriproxyfen (Knack®) and showed that whiteflies possessing this resistance could be detected in all cotton-producing areas of the state. Susceptibility to buprofezin (Applaud®/Courier®) has not changed significantly since 1997. Mean susceptibility to synergized pyrethroids (e.g., Danitol® + Orthene®) has increased strikingly on a statewide basis since 1995. However, 50 and 25% of cotton fields sampled in 2002 and 2003, respectively, had resistance levels expected to result in inadequate performance of synergized pyrethroid treatments. Whiteflies from throughout Arizona were highly susceptible to imidacloprid (Admire®/Provado®) and two other neonicotinoid insecticides, acetamiprid (Intruder®) and thiamethoxam (Actara®/Centric®/Platinum®)."

Powdery mildew occurs annually on melons in Arizona. Podosphaera xanthii (Sphaerotheca fuliginea) is the plant pathogenic fungus that causes powdery mildew on cucurbits, such as cantaloupe, honeydew, watermelon, cucumber and squash. When environmental conditions are favorable, disease incidence and severity can reach economically significant levels. Development of powdery mildew on melons is favored by moderate temperatures and relative humidity, succulent plant growth and reduced light intensity brought about by a dense plant canopy. Existing products as well as some materials under development were evaluated and compared for efficacy in management of powdery mildew on cantaloupe in a field trial conducted during the spring of 2003 at the Yuma Agricultural Center. A moderately high level of disease had developed by crop maturity (June 17) on untreated plants. Among treatments, the degree of powdery mildew suppression ranged from modest to essentially complete control. All treatments significantly reduced the severity of powdery mildew compared to untreated plants. The best performer among all treatments in this trial was Procure at 0.25 lb a.i., which completely inhibited disease development. Several other treatments resulted in a low mean disease severity rating (1 to 5 mildew colonies per leaf), including Quinoxyfen+Actigard, Rally+Actigard, Flint alternated with Bravo, Microthiol Disperss, Bravo, Quinoxyfen, Rally, Flint alternated with Bravo, Flint+Reason+Bond, Topsin M, Quadris+Latron B-1956, Flint+Actigard, Flint, Topsin+Trilogy, Kaligreen+No Foam A, Quadris+Latron B-1956 alternated with Actigard, Quadris+Latron B-1956+Actigard, and Pristine. Multiple applications of a single compound are included in these trials to gather information on the relative efficacy of each separate chemistry over a multi-year period. Among tested products, several are registered for use in Arizona for control of powdery mildew on melons. The use of a mixture or rotation among efficacious chemistries with different modes of action will help to inhibit the development of insensitivity by the pathogen to one or more of these active ingredients.

Sclerotinia drop on lettuce is caused by two soil-borne fungi, Sclerotinia minor and S. sclerotiorum. Moist soil and moderate temperatures favor this disease. Some registered products as well as new chemistries in development were compared for their ability to suppress Sclerotinia drop on lettuce during the winter vegetable growing season in 2003-2004. Sclerotia of each pathogen were incorporated into plots after lettuce thinning and just before the first application of test compounds. In plots infested with either Sclerotinia minor or S. sclerotiorum, all materials tested at an appropriate rate significantly reduced disease. In plots infested with S. minor, the best treatments included Endura, Fluazinam, and Contans alternated with Endura. For plots containing S. sclerotiorum, the best treatments included Fluazinam, Contans, Switch, Endura, and Contans alternated with Endura. Two of the products tested, Contans and Serenade, are biological control materials. For a valid comparison of products for control of Sclerotinia drop of lettuce, it is important to compare the results obtained from more than one field study. The reader is urged to review previous studies in addition to this report to get a true picture of the relative efficacy of tested compounds for control of Sclerotinia drop.