Impact assessment is central to the evolution and evaluation of our 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 or 24c 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.

Powdery mildew on lettuce is caused by the fungus Golovinomyces cichoracearum (Erysiphe cichoracearum). The disease is favored by moderate to warm temperatures and relatively dry weather conditions. Several fungicides were evaluated for their ability to suppress development of powdery mildew on lettuce in 2006. Powdery mildew was first detected Jan 26 in this trial. The data in the accompanying table illustrate the degree of control obtained by applications of the various materials tested in this trial. Among treatments, the degree of powdery mildew suppression ranged from virtually complete to minimal; however, all treatments significantly reduced the severity of both mildew diseases compared to nontreated plants. This trial was initiated as a combined downy and powdery mildew trial; therefore, some of the products were placed in the test specifically for downy mildew. Due to low humidity levels and no rainfall during the trial, no downy mildew developed.

Sclerotinia drop on lettuce is caused by two soil-borne fungi, Sclerotinia minor and S. sclerotiorum. This disease is favored by moist soil and moderate temperatures. 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 2006-2007. Sclerotia of each pathogen were incorporated into plots after lettuce thinning and just before the first application of test compounds. In plots infested with S. minor, Sclerotinia drop was reduced most effectively by some of the treatments containing boscalid, (Endura), fluazinam (Omega), Coniothyrium minitans (Contans), potassium silicate (Silmatrix), and polyoxin D (Endorse), where disease reduction compared to untreated plants ranged from 34 to 53%.. In plots infested with S. sclerotiorum, disease was reduced most effectively by application of iprodione (Rovral) and Omega followed by cyprodinil+fludioxonil (Switch), where Sclerotinia drop reduction compared to untreated plants ranged from 40 to 52%. Several other treatments provided significant but lessor degrees of disease control in the presence of S. minor and S. sclerotiorum. Two applications of the biopesticide Contans significantly reduced disease in plots infested with either S. minor or S. sclerotiorum. There was no statistical difference in disease control for either pathogen between application of Endura at 50 or 100 gal/acre. Two applications of Endura resulted in significantly higher disease control compared to one application of this product for plots infested with S. sclerotiorum; however, there was no difference in plots containing S. minor. 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 an accurate picture of the relative efficacy of tested compounds for control of Sclerotinia drop. Fungicides are not the only tools available to growers to manage Sclerotinia drop. Cultural methods, such as soil solarization or soil flooding in the summer, as well as crop rotation, can greatly reduce the number of viable sclerotia in an infested field. Use of these cultural methods alone or in combination with fungicide treatments can result in dramatic reductions in the incidence of Sclerotinia drop of lettuce.

Powdery mildew, caused by the fungus Golovinomyces cichoracearum (formerly known as Erysiphe cichoracearum), can develop rapidly in spring lettuce during March and April in western Arizona, as the crop nears maturity, when moderate to warm temperatures and dry environmental conditions prevail. The first signs of disease can occur as early as December or January. Successful chemical control of powdery mildew requires the presence of an effective fungicide on plants before disease onset, followed by successive applications of materials to maintain disease control until harvest. A field trial was conducted in 2007 to test and compare the efficacy of some registered as well as new fungicides, applied alone or in a rotational treatment program, for management of powdery mildew. Foliar applications of treatments were made Jan 24, Feb 1, Feb 16 and Feb 28, 2007. Among treatments, the degree of powdery mildew control ranged from virtually complete to minimal; however, all treatments significantly reduced disease severity compared to untreated plants. Treatments that reduced the severity of powdery mildew more than 90% compared to untreated plants included Procure alternated with Quintec, Quintec, Microthiol Disperss, and Procure alternated with Microthiol Disperss. Yield loss due to rejected lettuce heads usually would begin to occur when the powdery mildew disease rating exceeds 2.0. Fungicide treatments that kept disease severity below this level (in addition to the treatments already listed) include V-10118, Procure alternated with Quadris, Procure, Switch, Forum + Cabrio, Endorse, Maneb + Reason, and Endura. This trial was initiated as a combined downy and powdery mildew trial; therefore, some of the products were placed in the test specifically for downy mildew. Due to low humidity levels and no rainfall during the trial, no downy mildew developed; however, some of these downy mildew fungicides, such as Forum, Maneb, and Reason, significantly suppressed powdery mildew. Phytotoxicity symptoms were not noted on lettuce for any of the materials tested.

Phytophthora blight of peppers (Capsicum annuum) is caused by the oomycete pathogen Phytophthora capsici. In Arizona, the root and crown rot phase of the disease initially can appear on plants early in the growing season in areas of the field where soil remains saturated with water after an irrigation or rainfall event. Disease severity can increase dramatically due to summer rains during July and August in the southeastern Arizona production area. Fungicides are an important component of a Phytophthora disease management system, when used in combination with other management practices such as crop rotation, raised beds, and water management. The efficacy of the systemic fungicide mefenoxam (Ridomil Gold) for control of Phytophthora blight on pepper has been documented; however, in many pepper production regions, populations of the pathogen insensitive to this fungicide have developed. Other chemistries, including dimethomorph (Acrobat) as well as some new fungicides in development, have activity on some species of Phytophthora and associated diseases on crops other than pepper. The objective of the following study was to evaluate these additional chemistries for efficacy in suppressing development of root and crown rot on pepper plants grown in soil naturally infested with Phytophthora capsici in a greenhouse environment. The mean duration of survival for Aristotle bell pepper plants in untreated soil infested with P. capsici was 29 days. On the other hand, a significant increase in pepper plant survival was achieved when soil was treated with Reason (fenamidone) + Previcur Flex (propamocarb), SA-110201, Ranman (cyazofamid), Omega (fluazinam), Ridomil Gold (mefenoxam), V-10161(fluopicolide), Forum (dimethomorph), NOA-446510 (mandipropamid), IR-6141 (kiralaxyl), and Maestro (captan). The data from this study suggest that several fungicides currently not registered for use on peppers may be effective components of a management program for Phytophthora crown and root rot. The data is promising; however, additional studies in field soil naturally infested with P. capsici are needed to confirm these preliminary findings as well as to determine the optimal application rate and timing for each new chemistry.

Impact assessment is central to the evolution and evaluation of our 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 cantaloupes and watermelons 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 or 24c 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 melon industry by showing the importance of cost-effective management of insect pests in desert production.

Several large plot field studies were conducted in the spring of 2006 and 2007 to evaluate and compare the efficacy of several insecticides (used alone and in combinations) for knockdown and residual control of adult whiteflies in cantaloupes. Treatments were initiated when adult whitefly populations exceeded action threshold of 2 adults/ leaf. Evaluations of adult and immature control were made a various intervals following each application. The results of this study demonstrate that the synergized pyrethroid still provides the most significant knockdown activity on whitefly adults among registered alternatives in melons. In most cases, the addition of endosulfan (Thionex) with bifenthrinin provided 7-14 days of adult suppression below the action threshold. Residual control of adults was less effective following a second sequential application. Other alternative tank-mix partners with Capture were less effective, but might be useful to use in rotation with the Capture+Thionex treatments to provide adult knockdown. As we anticipated, adult and immature whitefly control did not differ among the bifenthrin formulations (Capture vs. generics). Finally, because of the risk of whitefly resistance and the heavy reliance on pyrethoids in all vegetable crops grown in the desert, new alternatives for adult whitefly control are needed.

AuxiGro® WP was applied to three cantaloupe fields in the Palo Verde Valley of far eastern California in the spring of 2004. One field utilized evaluated high rates (3.4x higher than other fields for each rate) of AuxiGro® WP for the purposes of phytotoxicity observations, while either a single application or two applications of varying rates of AuxiGro® WP were applied in the other two fields respectively. No visual symptoms of phytotoxicity were noted for AuxiGro® WP in any of the fields where applied, including two honeydew fields in the fall of 2003. Applications of any rate of AuxiGro® WP did not result in a statistical increase in numbers of melons from either a single or a double application on either variety (Ranger, Topmark respectively) used for yield data in this experiment. Data indicated that statistical differences existed for some melon parameters between treatments means in the hybrid variety (Ranger) but these statistical differences were not present for most fruit parameters in the open pollinated variety (Topmark), although some of the same trends were noted. These differences may be due to differing lengths of time from application to harvest. Of only the four rates of AuxiGro® WP evaluated, the heaviest melons were noted in the 4 oz./acre rate followed by the 8 oz./acre rate in both cantaloupe varieties, with this rate resulting in slightly heavier cantaloupes than the untreated check in both varieties. The one oz./acre rate of AuxiGro® WP also resulted in slightly shorter and lighter melons for both varieties than did application of only Solar™, but brix was numerically higher for this rate of AuxiGro® WP than for the Solar™ treatment. The two lowest mean brix were noted from in both cantaloupe varieties treated by Solar™ treatment alone and the 4 oz./acre rate of AuxiGro® WP + CalMax treatment, with these means being statistically less than the untreated check in 'Ranger' cantaloupes. CalMax by itself resulted in slightly smaller melons than the untreated check in both melon varieties. The AuxiGro® WP + CalMax treatment resulted in the largest melons (both longest and widest) of any treatment in the 'Ranger' cantaloupe field, with the difference in length being statistically greater than CalMax alone. Although larger melons would normally be thought to ripen earlier and therefore have higher brix readings, usage of AuxiGro® WP in combination with CalMax is thought to reduce stress as plants are still quite actively growing, hence the lower brix readings.

We report on susceptibility to insecticides of whiteflies (Bemisia tabaci) collected from cotton, melons and ornamental plants during the 2004 season. No major problems with field performance of insecticides against whiteflies were observed or reported in 2004 in Arizona cotton, vegetables, or melons. However, monitoring revealed further statewide reduction in susceptibility to pyriproxyfen (Knack®) and showed that whiteflies possessing pyriproxyfen resistance could be detected in all low desert 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 though highly resistant whiteflies were detected in some collections from cotton, melons and ornamentals. Whiteflies from throughout Arizona continued to be highly susceptible to imidacloprid (Admire®/Provado®). However, susceptibility to the related neonicotinoid insecticide, acetamiprid (Intruder®) varied widely and was lowest in collections from melons and greenhouse plants. Whiteflies from cotton that were least susceptibile to acetamiprid were significantly less susceptible to a second neonicotinoid, thiamethoxam (Actara®/Centric®/Platinum®). The most worrisome findings of our 2004 studies stemmed from detection of a strain of B. tabaci, at a retail nursery, that was essentially unaffected by pyriproxyfen in egg bioassays. It also possessed strikingly reduced susceptibility to acetamiprid, buprofezin, mixtures of fenpropathrin and acephate, imidacloprid, and thiamethoxam. This strain was found to be a biotype of B. tabaci previously undescribed in the US, the Q biotype. We cannot predict with accuracy the timecourse of future resistance problems or the spread and impact of this new whitefly biotype. However, our findings point to the need to formulate contingency plans for management of resistance, in order to insure that Arizona agriculture does not revisit the severe whitefly control problems experienced in the past.

Downy mildew, caused by the oomycete pathogen Bremia lactucae, usually can be found in some lettuce fields each year in Arizona. However, both the incidence and severity of the disease are governed by the frequency and duration of cool moist conditions required for disease development. Free moisture on the leaf surface is essential for spore germination and infection, but not growth of this pathogen within the leaf. Powdery mildew on lettuce is caused by the fungus Golovinomyces cichoracearum (Erysiphe cichoracearum). The disease is favored by moderate to warm temperatures and relatively dry weather conditions. Several fungicides were evaluated for their ability to suppress development of downy and powdery mildew on lettuce in 2005. Downy mildew was first observed in plots on February 7, whereas powdery mildew was first detected January 26. The data in the accompanying table illustrate the degree of control obtained by applications of the various materials tested in this trial. Among treatments, the degree of downy and powdery mildew suppression ranged from virtually complete to minimal; however, all treatments significantly reduced the severity of both mildew diseases compared to nontreated plants.