• Assessment of Fungicide Performance for Management of Powdery Mildew on Cantaloupe in 2006

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2006-09)
      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 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 2006 at the Yuma Valley Agricultural Center. A high level of disease had developed when disease severity data was recorded at crop maturity (Jun 15). Among treatments, the degree of powdery mildew control ranged from 0 to 100%. 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 in the pathogen population to one or more of these active ingredients.
    • Comparison of Products to Manage Sclerotinia Drop of Lettuce in 2006

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2006-09)
      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.
    • Efficacy of Fungicides for Management of Powdery Mildew on Lettuce in 2006

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2006-09)
      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.
    • Evaluation of a Biologically Intensive Integrated Pest Management System for Sclerotinia Drop on Lettuce: 2006 Study

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2006-09)
      Sclerotinia drop of lettuce, caused by the pathogenic fungi Sclerotinia minor and S. sclerotiorum, is a serious disease in most regions were 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 2004 in the presence of S. minor, the mean reduction in disease by Contans, Serenade and Endura was 36, 21 and 51%, respectively. The main 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 caused by S. minor. The study was conducted at the The University of Arizona, Yuma Valley Agricultural Center. Sclerotia of Sclerotinia minor were produced in the laboratory. Lettuce ‘Winterhaven’ was seeded and sclerotia were applied to the plots on Nov 14, 2005 and the final disease assessment at plant maturity was made Mar 13, 2006. There was a high degree of variability among the replicate plots for each treatment in this trial, as well as an overall low disease incidence, which made statistical comparisons of data difficult. The only treatment in this trial that significantly lowered disease incidence compared to nontreated plots was an initial application of Contans at seeding followed by Endura at thinning. This study was established in a field containing well-draining loam soil, which combined with the lack of any rainfall and the use of furrow irrigations in January and February, which kept the tops of beds dry, likely contributed to the excessive variability and low incidence of disease.
    • Evaluation of Fungicides as Potential Management Tools for Phytophthora Crown Rot on Pepper Plants

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2006-09)
      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. 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 additional chemistries for efficacy in suppressing development of root and crown rot on pepper plants grown in soil naturally infested with Phytophthora capsici. In the first trial, nontreated pepper plants were all dead after an average elapsed time of 5 days in soil infested with P. capsici. In the same trial, no plants died after 66 days when the soil was treated with Ranman (cyazofamid), V-10161 (fluopicolide), and Reason (fenamidone) + Previcur Flex (propamocarb). Additionally, only one out of five pepper plants died when treated with Omega (fluazinam), NOA-446510 (mandipropamid) and AgriFos (mono- and di-potassium salts of phosphorous acid). For all of these treatments, the duration of plant survival and fresh weight of plant shoots and roots did not differ significantly from plants grown in sterilized soil. Similar results were obtained in the second trial. The results from these trials suggest that several fungicides currently not registered for use on peppers may be effective components of a management program for Phytophthora root and crown rot. The data is promising; however, additional studies in field soil naturally infested with P. capsici are needed to confirm the preliminary findings of these initial experiments.
    • Examination of Soil Solarization as a Management Tool for Fusarium Wilt of Lettuce: 2005 Field Trial

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2006-09)
      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 research objective during the 2005 growing season was to further evaluate the effect of preplant solarization of planting beds on subsequent development of Fusarium wilt on lettuce. There was no significant difference between the short (28 days) and long (56 days) solarization period in the subsequent number of diseased lettuce plants; therefore, the disease incidence values for both solarization periods were combined and compared to nonsolarized plots. At each data collection date, the number of lettuce plants showing symptoms of Fusarium wilt was significantly lower in solarized beds compared to nonsolarized beds. At plant maturity (Nov 18), Fusarium wilt had claimed virtually all lettuce plants of the cultivar 'Lighthouse' growing in nonsolarized soil; however, only 19% of lettuce plants of the same cultivar growing in solarized soil showed disease symptoms. This equates to an 81% reduction in diseased plants in solarized soil compared to nonsolarized soil. The results of this field trial suggest that a 30-day summer solarization treatment of lettuce beds can significantly reduce the inoculum of Fusarium oxysporum f. sp. lactucae to levels that would allow substantial growth of a susceptible lettuce cultivar. Additional field studies are needed to refine the solarization process to potentially achieve further increases in efficiency of destroying propagules of Fusarium oxysporum f. sp. lactucae in infested fields.