• Comparative Efficacy of Fungicides for Management of Downy Mildew of Broccoli in 2004

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2004-09)
      Downy mildew of broccoli, cauliflower and cabbage is caused by the oomycete pathogen Peronospora parasitica. Cool moist environmental conditions favor the development of downy mildew on these crops. Several fungicides were evaluated individually or combined with another material (applied as a mixture or in a rotational program) for control of this disease on broccoli in 2004. A moderate level of disease had developed by crop maturity. Tanos+maneb provided the best reduction in disease among treatments. Other treatments that performed well included Tanos alternated with Maneb, Actigard, Reason alternated with Aliette, Reason alternated with Maneb, Maneb, and Serenade+Sonata.
    • Comparison of Products for Management of Powdery Mildew on Cantaloupe in 2003

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2004-09)
      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. 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.
    • Evaluation of Products to Manage Sclerotinia Drop of Lettuce in 2004

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2004-09)
      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 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.
    • Field Evaluations of Lettuce Cultivars for Resistance to Fusarium Wilt: 2-Year Summary

      Matheron, Michael E.; Tickes, Barry R.; Porchas, Martin; Ford, Kevin P.; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2004-09)
      Fusarium wilt of lettuce was first recognized in Arizona in 2001. The pathogen, Fusarium oxysporum f. sp. lactucae, has been recovered from infected lettuce plants in 27 different fields during the last three years. This fungus is a soil-borne pathogen that can remain viable in soil for many years. Historically, control of Fusarium wilt on crops other than lettuce, such as tomatoes and melons, has been achieved by planting cultivars resistant to the fungal pathogen. Large scale field trials were conducted during the 2002-03 and 2003-04 production seasons to evaluate existing lettuce cultivars for their relative susceptibility to Fusarium wilt. Among virtually all tested lettuce cultivars, the severity of disease in the first planting (early September) was much higher than that observed in the second planting (mid October), which in turn was higher than that observed in the third planting (early December). Soil temperatures differed considerably among plantings. In 2002-03 (or 2003-04) the average daily soil temperature at the 4-inch depth ranged from 65 to 85°F (70 to 94°F), 55 to 74°F (47 to 78°F), and 48 to 64°F (47 to 74°F) for the first, second and third plantings, respectively. In all three plantings, differences in disease severity were detected among the different types of lettuce, with head lettuce cultivars as a group being most susceptible and romaine cultivars collectively demonstrating the highest level of tolerance. Disease tolerance for specific cultivars was dependent on disease pressure. This is reflected in the comparative disease severity recorded in 2003-04 for specific cultivars (such as Beacon, Buccaneer, Coyote, Desert Heat, Lighthouse, Monolith, Red Tide, Sharpshooter, Sniper and Two Star) planted at each of the three different planting dates. Disease development began as early as the seedling stage and continued up to plant maturity, demonstrating the benefit of evaluating lettuce resistance in the field compared to greenhouse studies where plants are usually not carried to maturity before final disease ratings are performed. Data from these cultivar evaluation studies suggest that proper selection of planting date and cultivar would allow successful production of lettuce in fields infested with Fusarium oxysporum f. sp. lactucae.
    • Fungicide Performance for Management of Powdery Mildew on Lettuce in 2004

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2004-09)
      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 2004. Powdery mildew appeared in our plots by January 15 and reached high levels by plant maturity (March 10). Compared to nontreated plants, all treatments significantly reduced the final severity of powdery mildew on lettuce. No powdery mildew was observed in plots treated with Cabrio, Quinoxyfen, Pristine, and Procure. High levels of disease suppression were evident in plots treated with Serenade+Sonata alternated with Quadris, Sonata, Actigard, Serenade+Sonata, and Quadris.
    • Management of Powdery Mildew on Cantaloupe in 2004

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2004-09)
      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 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 2004 at the Yuma Valley Agricultural Center. A high level of disease had developed by the time this trial was terminated (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 top of leaves differed from that on the underside of leaves. The better treatments among all tested fungicides included Bravo Ultrex, Cabrio, Cabrio alternated with Procure, Flint alternated with Bravo, Microthiol Disperss, Procure, Procure alternated with Quinoxyfen, Quinoxyfen, Quinoxyfen alternated with Topsin M, Rally, Topsin M+Microthiol Disperss, and Topsin M alternated with Cabrio. 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 is important to minimize the development of insensitivity by the pathogen to one or more of these active ingredients.