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 2004-2005. 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, most materials tested at an appropriate rate significantly reduced disease. In plots infested with S. minor, the best treatments included Endura, Endura followed by Rovral, Botran, and Endura + Contans. For plots containing S. sclerotiorum, the best treatments included Endura + Contans, Endura followed by Rovral, and Contans. One of the products tested, Contans, is a biological control material. 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.

Sclerotinia drop of lettuce, caused by the pathogenic fungi Sclerotinia minor and S. sclerotiorum, is a serious disease in most regions where this crop is grown. Conventional fungicides, such as Rovral (iprodione) and Endura (boscalid), are usually applied after lettuce is thinned and once more 2 to 3 weeks later. Two biological products, Contans (Coniothyrium minitans) and Serenade (Bacillus subtilis), are also available. In earlier field trials conducted from 2001 to 2003 in the presence of S. sclerotiorum, the mean reduction in disease by Contans, Serenade and Endura was 69, 18 and 41%, respectively. The objective of the current study was to determine the efficacy of the biological products Contans and Serenade, applied alone or in combination with each other or the conventional fungicide Endura, within a biologically intensive integrated pest management system for Sclerotinia drop on lettuce. The study was conducted at The University of Arizona, Yuma Valley Agricultural Center. Sclerotia of Sclerotinia sclerotiorum were produced in the laboratory. Lettuce ‘Winterhaven’ was seeded and sclerotia were applied to the plots on November 8, 2004. Disease assessment was performed three times, including plant maturity (February 24), by recording the number of dead plants in each plot. Lettuce drop caused by Sclerotinia sclerotiorum was significantly reduced by the biofungicides Contans and Serenade as well as the conventional fungicide Endura. At plant maturity, the highest level of disease control among all treatments was provided by one or two applications of the biofungicide Contans as well as application of Contans at seeding following by either Serenade or Endura after thinning. Also, two applications of the other tested biofungicide, Serenade, controlled Sclerotinia drop as well as two applications of the conventional fungicide, Endura. The results of this study suggest that the biological products Contans and Serenade, used either alone or with the conventional fungicide Endura, can provide effective levels of control of lettuce drop caused by S. sclerotiorum. Although encouraging, the results from this initial field trial will need to be confirmed by additional studies. Funding for this research project was provided, in part, by the IR-4 project under a cooperative agreement with the U.S. Environmental Protection Agency.

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. 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 2005 at the University of Arizona Yuma Valley Agricultural Center. A high level of disease had developed by the time disease severity data was recorded (June 10). 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. Relative performance of treatments on the upper leaf surface differed from that on the underside of leaves. The best treatments among all tested fungicides included Quintec, Pristine, BAS517, Procure and Topsin M + Microthiol Disperss. Good levels of disease control were also achieved by Rubigan and Cabrio. The number of marketable cantaloupes was significantly higher in plots where powdery mildew was well controlled compared to untreated plots. Among tested products, several are registered for use in Arizona for control of powdery mildew on melons. Using a mixture of products or rotating among efficacious fungicides with different modes of action is important to minimize the development of insensitivity by the pathogen population to one or more of these active ingredients.

Fusarium wilt of lettuce was first recognized in Arizona in 2001. Since this first discovery, the pathogen, Fusarium oxysporum f.sp. lactucae (Fol), has been recovered from infected lettuce plants from approximately 30 different fields. This fungus is a soil-borne pathogen that can remain viable in soil for many years. Cultural disease control measures, such as extended soil flooding and soil solarization, have shown promise in managing Fusarium wilt in other cropping systems. The specific objectives of this research were to repeat preliminary soil solarization and flooding experiments conducted last year and to evaluate the effect of preplant treatment of planting beds with either Vapam or soil solarization on the subsequent incidence of Fusarium wilt on lettuce. In a microplot study, soil naturally infested with Fol was flooded or solarized for 15, 30, 45 and 60 days, then bioassayed by transplanting and growing lettuce plants in samples of treated soil as well as nontreated soil. In field studies, plots were solarized for 40 days or treated with Vapam before planting to lettuce. In the microplot experiment, the severity of Fusarium wilt on lettuce grown in previously flooded or solarized soil was significantly less than that in nontreated soil. Additionally, there was no difference between flooding and solarization with respect to disease severity, as lettuce plants in both cases had virtually no symptoms of Fusarium wilt. Weight of the tops of lettuce plants was significantly greater for plants grown in flooded or solarized soil compared to that in nontreated soil. Furthermore, top growth in solarized soil was sometimes significantly greater than that in flooded soil. Compared to nontreated soil, root growth in solarized soil was significantly greater. In contrast, root growth in flooded soil was not significantly different than that recorded in nontreated soil. In the field studies, the incidence of lettuce plants with foliar symptoms of Fusarium wilt was reduced by an average of 42% when grown on solarized beds compared to nonsolarized beds. Preplant application of Vapam at rates of 30, 45 and 60 gallons of product per acre resulted in reductions in the incidence of Fusarium wilt of 38, 50, and 45%, respectively. Further work is needed to attempt to increase the reduction of disease recorded this past year. Refinements in our solarization technique as well as application methods for Vapam may increase the efficacy of these tools in reducing the incidence and severity of Fusarium wilt of lettuce.

Field experiments were conducted at four sites in 2005 in the Yuma Valley, AZ (approximately 150 ft. elevation) to evaluate the performance of CN9 fertilizer [a N-calcium (Ca) based fertilizer (9-0-0-11)] in comparison to a conventional N fertilizer source with irrigated melons/cantaloupes (Cucumis melo L.). Each field was divided into two equal (approximately 40 acres) sections. One section received the grower’s N fertilizer source (Conventional) while the other section received the CN9 fertilizer. Basic plant growth and development measurements, aboveground biomass, total and marketable yield, Sugar fruit content as well as total nutrient analysis were among the main variables analyzed. In general, all phenology variables responded similarly between conventional and CN9 treatments. Fresh weight yields ranging from 4,000 to 10,000 kg/ha were observed between conventional and CN9 treatments. Statistical analyses show that total yield between conventional and CN9 was statistically the same; with the exception of the Perriconi site. Similar results were observed for marketable yield. Brix values ranged from 10 to 14 percent, statistical differences for Brix values between the conventional and CN9 treatments were found on the Perriconi and Mason 80 sites where the conventional treatment had higher sugar content in the fruit. Overall, there were no differences in nutrient uptake and allocation patterns due to the addition of CN9 among experimental sites or sampling dates. Regarding the allocation of nutrients in the rind and flesh of melons, the same patterns between treatments at all sites were observed.

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.

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.

Action thresholds, based on the percentage of plants infested, for the aphid pest complex found in head lettuce were evaluated in October, November and December plantings in 2005 and 2006 at the Yuma Agricultural Center. Action thresholds were also evaluated for their compatibility with newly developed reduced-risk and conventional insecticides. Although all five common aphid species were present in both years of the study, foxglove aphids provided most of the pest pressure. Compared with the SAC threshold treatment (sprayed-at colonization; essentially sprayed weekly until new aphid colonies were not found), action thresholds of 10% and 30% plants infested with 5 or more aphids resulted in fewer insecticide applications, while maintaining varying levels of head contamination at harvest. Despite variable pest pressure between years and planting dates, the threshold based on 10% infested plants performed as well as the SAC but with half as many sprays and no significant head contamination. However, significant head contamination was experienced when the 10% action threshold was used exclusively with reduced-risk insecticides.

Studies were conducted on spring cantaloupes from 2004-2006 to evaluate two adult and nymph based thresholds used for timing the application of Oberon (spiromesifen) and Courier (buprofezin) in spring melons for controlling whiteflies. The results of these studies demonstrate that these selective insecticides offer melon growers effective foliar management alternatives for controlling whiteflies. Both Oberon and Courier provided economic control of whitefly nymphs and significantly prevented sooty mold contamination when applied after populations exceeded either an adult threshold of 2 adults per leaf or an immature threshold or 0.5 large nymph per 2 cm² leaf disc. Applied at these thresholds, both compounds provided consistent residual suppression of whitefly immature population growth for 21-28 days under spring growing conditions.

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 2005-2006. 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, a significant reduction in disease compared to untreated plots was achieved with Omega, Rovral, Endorse, Endura, and Switch. For plots containing S. sclerotiorum, disease was significantly reduced by Contans, Rovral, Omega and Endura. 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.