• Assessment of Fungicide Performance on Control of Downy Mildew of Broccoli in 1998

      Matheron, Michael E.; Porchas, Martin; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1999-02)
      Peronospora parasitica is the pathogen responsible for causing downy mildew of broccoli, cabbage and cauliflower. Cool moist environmental conditions favor the development of downy mildew on these crops. Several potential new fungicides were evaluated for control of this disease on broccoli in 1998. The final severity of downy mildew in this trial was moderately high. Significant reduction in disease severity compared to nontreated plants was achieved by application of standard compounds such as Aliette, Bravo, maneb and Trilogy as well as the new fungicides Actigard, an Unknown, Curzate, Quadris, RH-7281, BAS 490, Acrobat and BAS 500. Broccoli yield was significantly increased compared to nontreated plots by treatments with Bravo, Curzate, Acrobat, BAS 500, Quadris, maneb, Actigard, BAS 490, an Unknown, RH-7281 and Aliette. The future registration and subsequent availability of one or more of these new chemistries for broccoli and related crops could help minimize the risk of development of resistance to fungicides used to manage downy mildew.
    • Comparison of New Fungicides for Management of Powdery Mildew of Cantaloupe in 1997

      Matheron, Michael E.; Porchas, Martin; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1999-02)
      Powdery mildew of cucurbits, which include cantaloupe, honeydew and watermelon as well as cucumbers and squash, occurs every year in Arizona. Moderate temperatures and relative humidity, succulent plant growth and reduced light intensity are factors that favor the development of powdery mildew, which is caused by the pathogenic fungus Sphaerotheca fuliginea Potential new fungicides were evaluated and compared to existing chemicals for control of powdery mildew of cantaloupe in a field trial conducted in the spring of 1997 at the Yuma Agricultural Center. The top performer in this study for disease control as well as reduction in culled fruit was a combination of Topsin-M + Trilogy. Other effective materials included BAS 490, Quadris, Procure, Benlate, Microthiol Special and Rally. Bayleton significantly reduced the amount of culled fruit, but did not significantly reduce the severity of powdery mildew. Compared to nontreated plots, a gain of up to $973 per acre could have been realized due to the reduction in amount of culled fruit in plots treated with fungicides. The potential availability of new chemistries for management of powdery mildew of cantaloupe and other cucurbits could help in the implementation of fungicide resistance management strategies, which strive to minimize the risk of resistance development by the pathogen to these compounds.
    • Evaluation of New Fungicides for Management of Downy and Powdery Mildew of Lettuce in 1998

      Matheron, Michael E.; Porchas, Martin; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1999-02)
      Bremia lactucae and Erysiphe cichoracearum, respectively, cause downy and powdery mildew of lettuce. Cool moist environmental conditions favor the development of downy mildew, whereas warm and dry weather is conducive for powdery mildew. Several potential new fungicides were evaluated for control of these diseases of lettuce in 1998. The final severity of downy mildew in this trial was low. In addition to the standard compounds maneb, Aliette and Trilogy, several fungicides currently in development significantly reduced the severity of downy mildew compared to nontreated plants. These chemistries included Acrobat, RH -7281, an Unknown, Actigard, EF1295, Curzate, Quadris, BAS 500, QST 153, BAS 505 and BAS 490. Untreated lettuce plants were heavily infected with powdery mildew. In addition to the standard materials Microthiol Special and Trilogy, powdery mildew was significantly reduced on plants treated with BAS 490, BAS 505, EF1295, BAS 500 and Quadris. The possible availability of one or more of these chemistries under development for lettuce could help in efforts to develop and maintain a fungicide resistance management program for plant medicines of importance for this crop.
    • New Fungicides Evaluated for Control of Sclerotinia Leaf Drop of Lettuce in 1997 and 1998

      Matheron, Michael E.; Porchas, Martin; Oebker, Norman F. (College of Agriculture, University of Arizona (Tucson, AZ), 1999-02)
      Sclerotinia leaf drop of lettuce is caused by two different species of this fungal pathogen, Sclerotinia minor and S. sclerotiorum. Cool and moist environmental conditions favor this disease. Some new fungicides in development were evaluated for control of leaf drop on lettuce during the winter vegetable growing seasons of 1996-97 and 1997-98. Sclerotia of each pathogen were applied to plots after thinning and just before the first of two applications of test compounds. The final severity of leaf drop in these trials was high. Significant reduction in disease or increase in marketable heads compared to nontreated plants was usually achieved by application of the standard compounds Ronilan and Rovral as well as the new fungicides BAS 500 and an "unidentified" material. The future registration and subsequent availability of one or both of these new chemistries for lettuce could provide equivalent disease control to that of the current standard materials with 0.2 to 0.25 lb active ingredient (a.i.) per acre instead of the current 1.0 lb a.i. per acre required with the standard compounds.