• Assessment of Fungicide Performance for Management of Downy and Powdery Mildew on Lettuce in 2005

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      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.
    • Comparative Evaluation of Products to Manage Sclerotinia Drop of Lettuce in 2005

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      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.
    • Effect of Fungicides on Development of Root and Crown Rot on Chile Pepper Plants Grown in Field Soil Naturally Infested with Phytophthora capsici

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      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. 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 mefenoxem (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 two new fungicides in development (Ranman and TM-459) have activity on some species of Phytophthora and associated diseases on crops other than pepper. The objective of the following trials was to evaluate and compare the effects of soil drench treatments with Ridomil, Acrobat, Ranman and TM-459 alone, as well as in combination treatments on subsequent development of root and crown rot on chile pepper plants grown in soil naturally infested with P. capsici. Three separate trials were conducted in the greenhouse. Usually, the top fresh weight of plants treated with an appropriate amount of Ranman, TM-459, or Acrobat did not differ from plants grown in sterilized soil. On the other hand, the top fresh weight of plants treated with Ridomil Gold often was not significantly different from plants grown in untreated infested soil, implying that this soil contained a population of Phytophthora capsici that is insensitive to this fungicide. These trials suggest that soil application of Ranman and TM-459 could effectively inhibit the development of Phytophthora root and crown rot on chile peppers grown in soil infested with Phytophthora capsici.
    • Effectiveness of Contans and Serenade Within a Biologically Intensive Integrated Pest Management System for Sclerotinia Drop on Lettuce: 2005 Study

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      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.
    • Efficacy of Fungicides for Management of Powdery Mildew on Cantaloupe in 2005

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      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.
    • Evaluation of Management Tools for Fusarium Wilt 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), 2005-12)
      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.
    • Management of Downy Mildew of Broccoli in 2005

      Matheron, Michael E.; Porchas, Martin; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      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 the 2004- 05 growing season. Several treatments provided the most efficacious degree of disease control, including Maneb, Reason+Bond alternated with Aliette, Ranman+Maneb+Silwet L-77, Ranman+Silwet L-77, Forum+Maneb, Forum+Penetrator Plus, Reason+Bond alternated with Maneb, PREV-AM +Formula 1, Ranman+Aliette+Silwet L-77, Acrobat+Maneb, Aliette and Phostrol.