• 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.
    • Effects of Foliar Applied Fertilizers on Yield and Quality of Late Spring Cantaloupes and Honeydews

      Rethwisch, Michael D.; Perez, Rogellio; Morrison, Steven; Parker, Larry; Juan, Julio; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      A number of foliar fertilizers were evaluated for their effects on yield and quality of both cantaloupes and honeydews. None of the treatments or treatment combinations resulted in statistical increases or decreases for numbers of cantaloupes or honeydews when compared with the untreated check. A highly significant increase of one treatment regimen (which contained calcium) was noted for cantaloupe weights when compared with the untreated check. Statistical differences were not noted for honeydew weights for this treatment although it also resulted in highest calculated weights of honeydew/area of treatments evaluated. All treatments resulted in numerically higher brix for cantaloupes than the untreated check, thought to be a response to pounds of melons/unit area as the untreated check had the least cantaloupe weight. No differences were noted for cantaloupe seed cavity diameters.
    • 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 a New Harpin Product on Microbial Quality and Shelf Life of Minimally Processed Lettuce

      Fonseca, Jorge; Kline, Wesley L.; Wyenandt, Christian A.; Hoque, Mushidul; Ajwa, Husein; Byrne, David N.; Baciewicz, Patti; The University of Arizona - Yuma Agricultural Center; Rutgers Cooperative Extension - Bridgeton, NJ; University of California, Davis /USDA-ARS, Salinas CA (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      The effect of pre-harvest application of Extend®, a newly developed second generation harpin product, on shelf life of fresh-cut lettuce was investigated. The lettuces were grown in locations A: Watsonville, CA; B: Cedarville, NJ; and C: Yuma, AZ, and treated five days before harvest at 30, 60 and 90 ppm (2,4 and 6 oz/acre in 50 gal/acre). Lettuce processed and bagged was stored at 34-37°F and evaluated for quality for 20 days. Lettuce from trial A treated with 60-90 ppm harpin consistently had a better overall quality and lower microbial population than the control. Results from trial B showed no differences among treatments. In trial C, microbial population was lower and visual quality higher in lettuce treated at 60 ppm than the control during early stages of storage. Overall results are mixed but it was revealed that a field application of harpin can improve quality of fresh-cut lettuce under conditions that need to be determined.
    • Evaluation of AuxiGro® WP on Cantaloupe Production in the Low Desert

      Rethwisch, Michael D.; Reay, Mark; Grudovich, Jessica L.; Wellman, Jessica J.; Ramos, David M.; Hawpe, Erica; Berger, Lois; Byrne, David N.; Baciewicz, Patti (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      AuxiGro® WP was applied to three cantaloupe fields in the Palo Verde Valley of far eastern California in the spring of 2004. One field utilized evaluated high rates (3.4x higher than other fields for each rate) of AuxiGro® WP for the purposes of phytotoxicity observations, while either a single application or two applications of varying rates of AuxiGro® WP were applied in the other two fields respectively. No visual symptoms of phytotoxicity were noted for AuxiGro® WP in any of the fields where applied, including two honeydew fields in the fall of 2003. Applications of any rate of AuxiGro® WP did not result in a statistical increase in numbers of melons from either a single or a double application on either variety (Ranger, Topmark respectively) used for yield data in this experiment. Data indicated that statistical differences existed for some melon parameters between treatments means in the hybrid variety (Ranger) but these statistical differences were not present for most fruit parameters in the open pollinated variety (Topmark), although some of the same trends were noted. These differences may be due to differing lengths of time from application to harvest. Of only the four rates of AuxiGro® WP evaluated, the heaviest melons were noted in the 4 oz./acre rate followed by the 8 oz./acre rate in both cantaloupe varieties, with this rate resulting in slightly heavier cantaloupes than the untreated check in both varieties. The one oz./acre rate of AuxiGro® WP also resulted in slightly shorter and lighter melons for both varieties than did application of only Solar™, but brix was numerically higher for this rate of AuxiGro® WP than for the Solar™ treatment. The two lowest mean brix were noted from in both cantaloupe varieties treated by Solar™ treatment alone and the 4 oz./acre rate of AuxiGro® WP + CalMax treatment, with these means being statistically less than the untreated check in 'Ranger' cantaloupes. CalMax by itself resulted in slightly smaller melons than the untreated check in both melon varieties. The AuxiGro® WP + CalMax treatment resulted in the largest melons (both longest and widest) of any treatment in the 'Ranger' cantaloupe field, with the difference in length being statistically greater than CalMax alone. Although larger melons would normally be thought to ripen earlier and therefore have higher brix readings, usage of AuxiGro® WP in combination with CalMax is thought to reduce stress as plants are still quite actively growing, hence the lower brix readings.
    • 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.
    • Evaluation of the Effect of Cytokinin Products on Yield of Head Lettuce

      Fonseca, Jorge; Byrne, David N.; Baciewicz, Patti; The University of Arizona – Yuma Agricultural Center, Yuma AZ (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      A series of replicated trials were conducted during the winter season of 2003 and 2004 to investigate the effect of pre-harvest applications of cytokinins on yield and postharvest quality of intact and fresh-cut lettuce. We report here only those results obtained at harvest. Cytokinins products were applied at different frequency and rates. The crops in the different trials were under different cultivation programs, including different nitrogen fertilization rates. Figures showing the performance of each individual cytokinin product versus the corresponding untreated controls are provided. Results obtained are mixed even for the same cytokinin product, however, some trends were observed. With the exception of products that also contain other plant growth regulators in their formula, high rates (or multiple applications) of the cytokinin products resulted in no effect or even in negative results. For example applications of Cytokin® did not improve yields as was the case with Cytoplex®, from the same manufacturer, under different conditions. The results from this study suggest that lettuce plants can respond to cytokinin applications, but factors to enhance positive response still need to be studied further. Single applications appear to be the most effective program for products containing only cytokinins, while products such as Cytoplex® can increase yield with multiple applications. A discussion addressing the different results obtained with nitrogen rates and the cytokinin products in yield and quality is included.
    • 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.
    • Microbial Quality of Iceberg Lettuce is Affected by Moisture at Harvest - 2nd Year Evaluation

      Fonseca, Jorge; Byrne, David N.; Baciewicz, Patti; The University of Arizona - Yuma Agricultural Center (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      In a continuing work, the effect of moisture conditions on yield and microbial quality of Iceberg lettuce was investigated. Iceberg lettuce cv. Sahara grown at the University of Arizona Yuma Agricultural Center was evaluated for yield, microbial population and postharvest quality either following different irrigation termination schedules or before/after a rainfall event. We report here microbial population data with treatments including early (16 days before harvest), middle (8 days before harvest) and late (4 days before harvest) irrigation termination. Lettuce receiving the last irrigation 4 days before harvest showed increased weight but had higher microbial population than other treatments. The effect of moisture prior to harvest on quality was further evaluated with lettuce harvested before and after a rainfall event. Increased aerobic bacteria population of over 1 log CFU/g for outer leaves and over 2 log CFU/g for head leaves was observed after rain. The results from this study suggest that managing moisture conditions at harvest is important to enhance quality of lettuce.
    • New Challenges to Management of Whitefly Resistance to Insecticides in Arizona

      Dennehy, Timothy J.; DeGain, Benjamin A.; Harpold, Virginia S.; Brown, Judith K.; Morin, Shai; Fabrick, Jeff A.; Byrne, Frank J.; Nichols, Robert L.; Byrne, David N.; Baciewicz, Patti; The University of Arizona, Tucson, AZ; University of California, Riverside, CA; University of California, Riverside, CA (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      We report on susceptibility to insecticides of whiteflies (Bemisia tabaci) collected from cotton, melons and ornamental plants during the 2004 season. No major problems with field performance of insecticides against whiteflies were observed or reported in 2004 in Arizona cotton, vegetables, or melons. However, monitoring revealed further statewide reduction in susceptibility to pyriproxyfen (Knack®) and showed that whiteflies possessing pyriproxyfen resistance could be detected in all low desert areas of the state. Susceptibility to buprofezin (Applaud®/Courier®) has not changed significantly since 1997. Mean susceptibility to synergized pyrethroids (e.g., Danitol® + Orthene®) has increased strikingly on a statewide basis since 1995 though highly resistant whiteflies were detected in some collections from cotton, melons and ornamentals. Whiteflies from throughout Arizona continued to be highly susceptible to imidacloprid (Admire®/Provado®). However, susceptibility to the related neonicotinoid insecticide, acetamiprid (Intruder®) varied widely and was lowest in collections from melons and greenhouse plants. Whiteflies from cotton that were least susceptibile to acetamiprid were significantly less susceptible to a second neonicotinoid, thiamethoxam (Actara®/Centric®/Platinum®). The most worrisome findings of our 2004 studies stemmed from detection of a strain of B. tabaci, at a retail nursery, that was essentially unaffected by pyriproxyfen in egg bioassays. It also possessed strikingly reduced susceptibility to acetamiprid, buprofezin, mixtures of fenpropathrin and acephate, imidacloprid, and thiamethoxam. This strain was found to be a biotype of B. tabaci previously undescribed in the US, the Q biotype. We cannot predict with accuracy the timecourse of future resistance problems or the spread and impact of this new whitefly biotype. However, our findings point to the need to formulate contingency plans for management of resistance, in order to insure that Arizona agriculture does not revisit the severe whitefly control problems experienced in the past.
    • Yield and Postharvest Quality of Cantaloupe Melons as Affected by Calcium Foliar Applications

      Fonseca, Jorge; Byrne, David N.; Baciewicz, Patti; The University of Arizona - Yuma Agricultural Center (College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005-12)
      The effect of pre-harvest foliar application of calcium on yield and postharvest quality of whole and fresh-cut cantaloupe melons was investigated. The calcium product (Nutrical®) was applied five times before harvest to a melon field at 2 quarts/acre with a volume of 50 gallons/acre. The supplemented calcium increased by over 10% the weight of melons and increased external firmness at harvest but soluble solids was lower in treated melons than in the control. After 21 days of storage at 40 - 45 °F however, there was not difference in quality factors. Melons were processed in cubes and packaged in plastic lidded containers. The overall quality of calcium treated cubes was better after 5 and 10 days of storage. Juice leakage was also higher in the control than in the treated fruits after 5 days. After 10 days the L* values were lower in the control than in the treated fruits indicating that the tissue was darker in the control, which was an indicative of more water soaked tissue. In further trials conducted the following Spring the results obtained at harvest showed differences only in weight of melons that underwent water stress. The overall results in different experiments in the Yuma area indicate that application of foliar calcium can increase yield of melon crops, notably, when the plants undergo environmental stress.