Vegetable Report 2007
ABOUT THE COLLECTION
The Vegetable Report is one of several commodity-based agricultural research reports published by the University of Arizona.
This report was first published in 1965.
The purpose of the report is to provide an annual research update to farmers, researchers, and those in the agricultural industry. The research is conducted by University of Arizona and USDA-ARS scientists.
Both historical and current Vegetable Reports have been made available via the UA Campus Repository, as part of a collaboration between the College of Agriculture and Life Sciences and the University Libraries.
Contents for Vegetable Report 2007Pathogen Management
- Assessment of Fungicides to Manage Sclerotinia Drop of Lettuce in 2007
- Evaluation of Fungicides for Management of Powdery Mildew on Lettuce in 2007
- Examination of Fungicides for Management of Powdery Mildew on Cantaloupe in 2007
- Efficacy of RADIANT (Spinetoram) Against Western Flower Thrips in Romaine Lettuce
- Further evaluation of Soil Solarization as a Management Tool for Fusarium Wilt of Lettuce: 2006 Field Trial
- Effect of Fungicides and Lettuce Cultivar on Severity of Botrytis Gray Mold: 2007 Study
- Biotype Designations and Insecticide Susceptibility of Southwestern Bemisia tabaci
- Have Distances Traveled by the Sweet Potato Whitefly Been Underestimated?
- Insect Crop Losses and Insecticide Usage for Spring Melons in Southwestern Arizona for 2007
- Insect Crop Losses and Insecticide Usage for Spring Melons in Central Arizona for 2007
- Comparative Efficacy of Insecticide Combinations Against Whitefly Adults in Melons
- Insect Crop Losses and Insecticide Usage for Head Lettuce in Arizona: 2006/2007
- Efficacy of RADIANT (Spinetoram) Against Western Flower Thrips in Romaine Lettuce
Crop Phenology for Irrigated Spring Cantaloupes (Cucumis melo L.)Field experiments were conducted in 2007 to evaluate a cantaloupe (Cucumis melo L.) plant development model as a function of heat units accumulated after planting (HUAP). Field experiments were conducted in 2007 in the Yuma Valley, Arizona (32° 42' N, 114° 42' W), about 150 feet (~ 32 m) elevation in four commercial cantaloupe fields managed by a cooperator-grower using four varieties. Plant measurements were made on regular 14-day intervals and the following growth stages were identified in relation to plant measurement data collection: pre-bloom, early fruit set, early netting, and physiological maturity (harvest). The model was evaluated by comparing the observed HUAP versus the predicted HUAP values using a repeated measures design. Mean differences within each sampling stage were separated using the Fishers’ protected least significance difference (LSD) test at P≤ 0.01. In addition, regression models were performed for all in-season data collected and the accuracy of the model was evaluated on the basis of the R² values with a specified level significance (α = 0.01). No statistical differences were found between the observed phenological data and the predicted values from the model throughout the study period. Also, the model presented an overall accuracy of 54 ± 37 HUAP (2 ± 1 day) in predicting cantaloupe-harvesting time. It can be concluded that the model can be used as a useful tool to assist cantaloupe growers in predicting and identifying critical stages of growth for irrigated spring cantaloupe crops in Arizona and the desert Southwest.
A Crop Phenology Model for Irrigated New Mexico Chile (Capsicum annuum L.) Type VarietiesField experiments were conducted with the objective of developing a general New Mexico chile type plant (Capsicum annuum L.) phenological model as a function of heat units accumulated after planting (HUAP). Field experiments were conducted from 2003 through 2005 in the Sulfur Springs Valley of Arizona, near Sunsites in Cochise County, Arizona (31° 56" N, 109° 52" W, about 4,000 feet elevation) on a Borderline fine sandy loam (coarse-loamy, mixed, superactive thermic Typic Calcigypsids) and in the Animas Valley, New Mexico (31° 57" N, 109° 48" W, about 4,400 feet elevation), on a Vekol fine sandy clay loam (fine, mixed, thermic, Typic Haplargids). Plant measurements were collected routinely and important phenological stages that corresponded to first bloom, early bloom, peak bloom, physiological maturity, and red harvest were identified and recorded. Results indicate that within locations, all varieties performed similarly in relation to HU accumulation patterns. A general New Mexico chile type plant phenological model as a function of HUAP for all sites and varieties was obtained. First bloom occurred at 954 ± 254 HUAP, early bloom at 1349 ± 306 HUAP, peak bloom at 1810 ± 261 HUAP, physiological maturity at 2393 ± 215 HUAP, and red chile harvest was identified to occur at 3159 ± 220 HUAP. The purpose of this phenological baseline or model is to provide a crop management tool for growers for predicting and identifying critical stages of growth. Further development and validation of this model is a continued objective of this research program.
Efficacy of RADIANT (Spinetoram) Against Western Flower Thrips in Romaine LettuceRADIANT, a new 2nd generation spinosyn insecticide has recently been introduced to the vegetable industry that has shown excellent activity against western flower thrips in lettuce. Several studies were conducted over 2 growing seasons at the Yuma Ag Center to evaluate the efficacy of RADIANT against thrips in romaine lettuce. Three trials were conducted in spring lettuce under moderate and heavy population pressure, and two fall trials were conducted under low to moderate thrips pressure. In each study, RADIANT performed statistically comparable to or better than Success for control of thrips, but at lower use rates. It appears to provide better residual activity against larvae than Success and the standard compounds presently used, but does not appear to provide any additional adult efficacy. RADIANT will be an excellent addition to our IPM programs, however because it has the same mode-of-action as Success, it will not provide an additional rotational partner for our resistance management programs.
Insect Crop Losses and Insecticide Usage for Head Lettuce in Arizona: 2006/2007Impact assessment is central to the evolution and evaluation of our local Insect Pest Management (IPM) programs. Quantifiable metrics on insecticide use patterns, costs, targets, and frequency, crop losses due to all stressors of yield and quality, and other real world economic data (e.g., crop value) are our most objective tools for assessing change in our systems. We recently initiated a project to measure the impact of insect losses and insecticide uses in head lettuce grown in Yuma, AZ and the Bard-Winterhaven area of Imperial County, CA. The data generated in this report is useful for responding to pesticide information requests generated by EPA, and can provide a basis for regulatory processes such as Section 18 requests, as well as for evaluating the impact of our extension programs on risk reduction to growers. This information also confirms the value of PCAs to the lettuce industry by showing the importance of cost-effective management of insect pests in desert lettuce production.
Comparative Efficacy of Insecticide Combinations Against Whitefly Adults in MelonsSeveral large plot field studies were conducted in the spring of 2006 and 2007 to evaluate and compare the efficacy of several insecticides (used alone and in combinations) for knockdown and residual control of adult whiteflies in cantaloupes. Treatments were initiated when adult whitefly populations exceeded action threshold of 2 adults/ leaf. Evaluations of adult and immature control were made a various intervals following each application. The results of this study demonstrate that the synergized pyrethroid still provides the most significant knockdown activity on whitefly adults among registered alternatives in melons. In most cases, the addition of endosulfan (Thionex) with bifenthrinin provided 7-14 days of adult suppression below the action threshold. Residual control of adults was less effective following a second sequential application. Other alternative tank-mix partners with Capture were less effective, but might be useful to use in rotation with the Capture+Thionex treatments to provide adult knockdown. As we anticipated, adult and immature whitefly control did not differ among the bifenthrin formulations (Capture vs. generics). Finally, because of the risk of whitefly resistance and the heavy reliance on pyrethoids in all vegetable crops grown in the desert, new alternatives for adult whitefly control are needed.
Insect Crop Losses and Insecticide Usage for Spring Melons in Central Arizona for 2007Impact assessment is central to the evolution and evaluation of our IPM programs. Quantifiable metrics on insecticide use patterns, costs, targets, and frequency, crop losses due to all stressors of yield and quality, and other real world economic data (e.g., crop value) are our most objective tools for assessing change in our systems. We recently initiated a project to measure the impact of insect losses and insecticide uses in cantaloupes and watermelons grown in central Arizona (Maricopa, Pinal and La Paz counties). The data generated in this report is useful for responding to pesticide information requests generated by EPA, and can provide a basis for regulatory processes such as Section 18 or 24c requests, as well as for evaluating the impact of our extension programs on risk reduction to growers. This information also confirms the value of PCAs to the melon industry by showing the importance of cost-effective management of insect pests in desert production.
Insect Crop Losses and Insecticide Usage for Spring Melons in Southwestern Arizona for 2007Impact assessment is central to the evolution and evaluation of our IPM programs. Quantifiable metrics on insecticide use patterns, costs, targets, and frequency, crop losses due to all stressors of yield and quality, and other real world economic data (e.g., crop value) are our most objective tools for assessing change in our systems. We recently initiated a project to measure the impact of insect losses and insecticide uses in cantaloupes and watermelons grown in Yuma, AZ and the Bard-Winterhaven area of Imperial County, CA. The data generated in this report is useful for responding to pesticide information requests generated by EPA, and can provide a basis for regulatory processes such as Section 18 or 24c requests, as well as for evaluating the impact of our extension programs on risk reduction to growers. This information also confirms the value of PCAs to the melon industry by showing the importance of cost-effective management of insect pests in desert production.
Have Distances Traveled by the Sweet Potato Whitefly Been Underestimated?The importance of the sweet potato whitefly to Arizona vegetable continues to ebb and flow from year to year. Over the last 25 years much of this likely is tied to the invasion by different strains. As we continue to study this insect, an aspect of importance to their management is their ability to disperse. In past studies we have determined how far they are capable of flying in a day’s time, 95% migrate 1.6 miles. We are now investigating their ability to fly multiple days. If they do migrate on more than 1 day, we must readjust our estimates of their influence on surrounding fields.
Biotype Designations and Insecticide Susceptibility of Southwestern Bemisia tabaciWe report biotype identifications and susceptibility to insecticides of whiteflies (Bemisia tabaci) collected from cotton, vegetables, melons and ornamental plans during the 2005 season. No major problems with field performance of insecticides against whiteflies were confirmed in 2005 in Arizona. Whitefly resistance to pyriproxyfen did not increase, relative to levels recorded in 2004. However, we detected pyriproxyfen resistance in all Arizona whitefly samples tested. A single sample collected from cotton in Holtville, CA, had no detectable resistance to pyriproxyfen. Samples from cotton in Buckeye, Coolidge, Scottsdale, and Stanfield, Arizona had the highest levels of resistance, with > 31-45% of eggs surviving diagnostic concentration bioassays of 0.1 ug/ml pyriproxyfen. Whitefly susceptibility to buprofezin (Applaud®/Courier®) has not changed significantly since 1997. Resistance to synergized pyrethroids (e.g., Danitol® + Orthene®) has decreased strikingly on a statewide basis since 1995, though unacceptably high frequencies of resistant whiteflies were detected in some 2005 collections from all commodities sampled. Whiteflies collected from Arizona cotton, melons, and vegetables continued to be highly susceptible to imidacloprid (Admire®/Provado®). One whitefly collection from poinsettias in Phoenix (05-39) was substantially less susceptibile to imidacloprid, and the related neonicotinoid insecticides, acetamiprid, and thiamethoxam. Regression analysis yielded a significant correlation for whitefly susceptibility to acetamiprid and thiamethoxam. Whiteflies from cotton that were least susceptibile to acetamiprid were also significantly less susceptible to thiamethoxam (Actara®/Centric®/Platinum®). The most worrisome of our 2005 findings was that 6 out of 13 samples of whitefly-infested poinsettias collected from retail stores in metropolitan Tucson and Phoenix consisted of only the Q biotype of Bemisia tabaci. The plants were infested with very low whitefly numbers and thus we were unable to establish them in laboratory cultures to evaluate their resistance status. The Q biotype is native to Spain and was first detected in the US by our group in 2004 on a sample taken from poinsettias. The Q biotype strain we detected in 2004 was highly resistant to a broad range of insecticides used to manage whiteflies in Arizona. None of the 26 field collections evaluated in 2005 was the Q biotype.
Effect of Fungicides and Lettuce Cultivar on Severity of Botrytis Gray Mold: 2007 StudyGray mold, caused by the fungus Botrytis cinerea, usually has been considered a minor disease in field-grown lettuce. However, for the past two lettuce production seasons, the incidence of this disease has increased significantly in Southwestern Arizona lettuce fields. Most of the infected fields were planted to romaine lettuce; however, some iceberg lettuce plantings were involved as well. The occurrence of gray mold was most prevalent during February and March. The primary symptoms of the disease include plant wilting accompanied by a fuzzy gray growth at the plant base, which contains masses of airborne spores. Sclerotia may also be present on infected tissue. Infected plants that show these symptoms usually wilt and die. Botrytis cinerea can survive on crop debris, as a pathogen on numerous crops and weed hosts, and as sclerotia in soil. Airborne spores that land on senescent or damaged lettuce stems and leaves germinate and rapidly colonize this tissue. Once established, the pathogen grows into adjacent healthy stems and leaves. A field trial was established to 1) evaluate the effectiveness of some fungicides to reduce the incidence of Botrytis gray mold and 2) compare the susceptibility of some lettuce cultivars to this disease. Botrytis gray mold did not develop in plots of the crisphead cultivar 'Winterhaven'; however, the disease was present in all plots planted with cultivars of romaine lettuce. Among the tested romaine cultivars, Botrytis gray mold incidence was lowest in 'A 35585-1', 'Fresh Heart' and 'Rome 59' in untreated plots as well as in plots treated four times with the fungicides Rovral, Endura, or Switch. On the other hand, disease incidence was highest on the cultivar 'Green Towers' in untreated plots as well as those treated with one of the three tested fungicides. To compare the ability of tested fungicides to control Botrytis gray mold, the disease incidence values for each of the five romaine cultivars treated with each specific fungicide were pooled together and compared to disease levels recorded on untreated plants. Foliar applications of treatments were made Jan 24, Feb 1, Feb 16 and Feb 28, 2007. A 31% reduction in disease was recorded on romaine lettuce plants treated with Switch, whereas a 17% reduction in Botrytis gray mold was observed on plants treated with Endura. Rovral did not significantly reduce Botrytis gray mold in this trial. Additional field trials are planned to verify these initial findings.
Further evaluation of Soil Solarization as a Management Tool for Fusarium Wilt of Lettuce: 2006 Field TrialFusarium wilt of lettuce was first recognized in Arizona in 2001. Since this initial discovery, the pathogen, Fusarium oxysporum f.sp. lactucae (Fol), has been recovered from infected lettuce plants from over 40 different fields. This fungus is a soil-borne pathogen that can remain viable in soil for many years. Soil solarization has shown promise in managing Fusarium wilt in other cropping systems as well as in lettuce field trials conducted during 2004 and 2005. In an effort to maximize the solarization effect on subsequent disease development, the following factors were evaluated in a 2006 field trial: 1) solarization of unshaped versus preshaped beds, 2) the effect of soil moisture on solarization efficiency of preshaped beds, and 3) effect of lettuce type on Fusarium wilt incidence after solarization. The entire field was flood irrigated on Jun 21. Plots were solarized during Jul and/or Aug by covering beds with 1-mil thick clear plastic. During the solarization treatment from Jul 3 to Sep 10, the mean soil temperature in preshaped solarized beds at a depth of 2 and 9 inches was 116 and 95°F, respectively, and 102 and 97°F, respectively, in beds not covered with plastic. When solarization was initiated 15 days after soil irrigation, a 20% reduction in Fusarium wilt was recorded for a crisphead lettuce cultivar grown on solarized unshaped beds compared to a 56% reduction in disease when the same crisphead cultivar was grown on preshaped solarized beds. There was no significant difference between a one and two month solarization period in the subsequent number of diseased lettuce plants. Solarization of preshaped beds 15 days after irrigation for one month reduced Fusarium wilt on crisphead lettuce by 56%, whereas the same solarization period initiated seven days after irrigation resulted in a 96% reduction of disease. The same one-month solarization period started one week after soil irrigation reduced the incidence of Fusarium wilt on green leaf (Two Star) and romaine (Green Towers) by 97 and 88%, respectively, compared to plants grown on unsolarized beds. The data show that summer solarization of moist soil can 1) destroy propagules of Fusarium oxysporum f. sp. lactucae in infested fields and 2) be a useful cultural management tool to significantly reduce the incidence of Fusarium wilt in a subsequent crop of lettuce.
Efficacy of New Fungicides as Potential Management Tools for Phytophthora Crown and Root Rot on Pepper PlantsPhytophthora 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. Fungicides are an important component of a Phytophthora disease management system, when used in combination with other management practices such as crop rotation, raised beds, and water management. 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 these additional chemistries for efficacy in suppressing development of root and crown rot on pepper plants grown in soil naturally infested with Phytophthora capsici in a greenhouse environment. The mean duration of survival for Aristotle bell pepper plants in untreated soil infested with P. capsici was 29 days. On the other hand, a significant increase in pepper plant survival was achieved when soil was treated with Reason (fenamidone) + Previcur Flex (propamocarb), SA-110201, Ranman (cyazofamid), Omega (fluazinam), Ridomil Gold (mefenoxam), V-10161(fluopicolide), Forum (dimethomorph), NOA-446510 (mandipropamid), IR-6141 (kiralaxyl), and Maestro (captan). The data from this study suggest that several fungicides currently not registered for use on peppers may be effective components of a management program for Phytophthora crown and root rot. The data is promising; however, additional studies in field soil naturally infested with P. capsici are needed to confirm these preliminary findings as well as to determine the optimal application rate and timing for each new chemistry.
Examination of Fungicides for Management of Powdery Mildew on Cantaloupe in 2007Powdery 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 2007 at the University of Arizona, Yuma Valley Agricultural Center. A moderately-high level of disease had developed when disease severity data was recorded at crop maturity in mid-June. Among treatments, the degree of powdery mildew control ranged from essentially 0 to 100%. Materials that reduced the severity of disease on both the top and bottom of leaves by an average amount of at least 90% included Microthiol Disperss, Procure, Quintec, V-10118, Inspire Super, Endura, Cabrio, and Pristine, when applied on a 7-day spray interval. Other treatments that reduced powdery mildew by at least 80% compared to untreated plants included alternation between the conventional fungicide Procure and the biopesticides, Serenade Max, Sonata, or Actinovate as well as alternation among the two biopesticides Actinovate and Kaligreen. Alternating applications of products with different modes of action is imperative to minimize the development of insensitivity in the pathogen population to one or more of these active ingredients. Among the products evaluated this year, several are registered for use in Arizona for control of powdery mildew on melons.
Evaluation of Fungicides for Management of Powdery Mildew on Lettuce in 2007Powdery mildew, caused by the fungus Golovinomyces cichoracearum (formerly known as Erysiphe cichoracearum), can develop rapidly in spring lettuce during March and April in western Arizona, as the crop nears maturity, when moderate to warm temperatures and dry environmental conditions prevail. The first signs of disease can occur as early as December or January. Successful chemical control of powdery mildew requires the presence of an effective fungicide on plants before disease onset, followed by successive applications of materials to maintain disease control until harvest. A field trial was conducted in 2007 to test and compare the efficacy of some registered as well as new fungicides, applied alone or in a rotational treatment program, for management of powdery mildew. Foliar applications of treatments were made Jan 24, Feb 1, Feb 16 and Feb 28, 2007. Among treatments, the degree of powdery mildew control ranged from virtually complete to minimal; however, all treatments significantly reduced disease severity compared to untreated plants. Treatments that reduced the severity of powdery mildew more than 90% compared to untreated plants included Procure alternated with Quintec, Quintec, Microthiol Disperss, and Procure alternated with Microthiol Disperss. Yield loss due to rejected lettuce heads usually would begin to occur when the powdery mildew disease rating exceeds 2.0. Fungicide treatments that kept disease severity below this level (in addition to the treatments already listed) include V-10118, Procure alternated with Quadris, Procure, Switch, Forum + Cabrio, Endorse, Maneb + Reason, and Endura. 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; however, some of these downy mildew fungicides, such as Forum, Maneb, and Reason, significantly suppressed powdery mildew. Phytotoxicity symptoms were not noted on lettuce for any of the materials tested.
Assessment of Fungicides to Manage Sclerotinia Drop of Lettuce in 2007Sclerotinia drop on lettuce is caused by two soil-borne fungi, Sclerotinia minor and S. sclerotiorum. This disease is favored by moist soil and moderate temperatures. 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 2006-2007. 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, Sclerotinia drop was reduced most effectively by some of the treatments containing boscalid, (Endura), fluazinam (Omega), Coniothyrium minitans (Contans), potassium silicate (Silmatrix), and polyoxin D (Endorse), where disease reduction compared to untreated plants ranged from 34 to 53%.. In plots infested with S. sclerotiorum, disease was reduced most effectively by application of iprodione (Rovral) and Omega followed by cyprodinil+fludioxonil (Switch), where Sclerotinia drop reduction compared to untreated plants ranged from 40 to 52%. Several other treatments provided significant but lessor degrees of disease control in the presence of S. minor and S. sclerotiorum. Two applications of the biopesticide Contans significantly reduced disease in plots infested with either S. minor or S. sclerotiorum. There was no statistical difference in disease control for either pathogen between application of Endura at 50 or 100 gal/acre. Two applications of Endura resulted in significantly higher disease control compared to one application of this product for plots infested with S. sclerotiorum; however, there was no difference in plots containing S. minor. 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.