Vegetable Report 2004
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 2004Entomology
- Foliar Activity of Assail®, Fulfill® and Flonicamid® on Aphids in Leafy Vegetables
- Impact of Planting Date on Aphid Infestations and Contamination in Head Lettuce
- Insect Pests in Yuma Winter Vegetables: Review of the 2003-2004 Season
- Seasonal Abundance of Western Flower Thrips Populations in Desert Head Lettuce
- Comparative Efficacy of Oberon® (spiromesifen) Against Bemisia Whiteflies in Spring Cantaloupes
- Is Aphid Management Sustainable in Desert Head Lettuce?
- Whitefly Resistance to Insecticides in Arizona: 2002 and 2003 Results
- Comparative Efficacy of Fungicides for Management of Downy Mildew of Broccoli in 2004
- Comparison of Products for Management of Powdery Mildew on Cantaloupe in 2003
- Evaluation of Products to Manage Sclerotinia Drop of Lettuce in 2004
- Field Evaluations of Lettuce Cultivars for Resistance to Fusarium Wilt: 2-Year Summary
- Fungicide Performance for Management of Powdery Mildew on Lettuce in 2004
- Management of Powdery Mildew on Cantaloupe in 2004
- The Comparison of Aerial and Sprinkler Applied Delayed Applications of Kerb® to Lettuce
- The Effect of UV-Reflective Mulching on Yield and Quality of Cantaloupes
- Yield and Microbial Quality of Head Lettuce as Affected by Field Moisture at Harvest
- Comparison of Preemergence Herbicides in Spinach
- Preemergence and Postemergence Herbicide Combinations for Weed Control in Melons
Arizona Crop Information SiteThe Arizona Crop Information Site (ACIS) http://cals.arizona.edu/crops was launched by the University of Arizona in 2001. This site provides a one-stop resource for those seeking information on Arizona crop protection and production information. The site is the result of input and cooperation across Arizona’s agricultural community. The amount of information on the site continues to grow as does the site’s importance, usefulness and number of visitors.
Preemergence and Postemergence Herbicide Combinations for Weed Control in MelonsSandea at 0.05 lb ai/A tank-mixed with Matrix at 0.02 lb ai/A and applied POST following Prefar applied preemergence on cantaloupes gave very good control of pigweeds, lambsquarters, purple nutsedge, and junglerice. Melon injury was just acceptable at 15%. The tank-mix treatment applied POST was similarly effective on the pigweeds, lambsquarters, and nutsedge but grass weed control decreased slightly and melon injury increased when following preemergence herbicide treatments of Dual Magnum, Outlook, or Chateau. Single or multiple POST applications of Sandea alone were not effective against pigweeds.
Comparison of Preemergence Herbicides in SpinachSpinach exhibited progressively increased injury and crop stand reduction with increasing rates of s-metolachlor and dimethenamid-p. At the lowest rate applied, s-metolachlor at 0.38 lb ai/A caused minimal injury at 10% and slight stand reduction compared to the untreated check. Dimethenamid-p injured spinach 25% at the lowest rate applied and significant stand reduction was observed at 0.5 lb ai/A or greater. At equivalent rates, dimethenamid-p was more injurious to spinach than s-metolachlor.
Yield and Microbial Quality of Head Lettuce as Affected by Field Moisture at HarvestThe effect of moisture conditions on microbial quality (as total aerobic bacteria) and yield of head lettuce was investigated. Head lettuce cv. Honcho II grown at the Yuma Agricultural Center was evaluated for microbial population at harvest and postharvest quality either following different irrigation termination schedules or after a rainfall event. The last irrigation was scheduled 24, 16 and 6 days prior to harvest resulting in soil’s water content of 15.9%, 17.0% and 17.2%, respectively, at harvest. Lettuce receiving the last irrigation 6 days before harvest had 10% more weight, higher total aerobic bacteria and shorter shelf life than plants irrigated 24 days before harvest. The plants with the last irrigation scheduled 16 days before harvest showed similar weight at harvest, lower total aerobic count and longer shelf life than plants with irrigation termination scheduled 6 days prior to harvest. The effect of field’s moisture prior to harvest on quality was further evaluated with lettuce harvested 1 and 7 days after a rainfall event. A day after rain the microbial population in both outer leaves and head leaves increased. The microbial population in head leaves continued increasing during the week after rain. The results from this study suggest that managing moisture conditions at harvest is important to enhance quality of lettuce. Although the potential decrease in weight produced with an early irrigation termination is a great concern of growers, it was shown in this study that excessively late pre-harvest irrigation of lettuce is not necessary to obtain maximum weight at harvest.
The Effect of UV-Reflective Mulching on Yield and Quality of CantaloupesThree trials, one during Fall 2003 season and two during the spring 2004, were conducted at the Yuma Agricultural Center to investigate the influence of UV reflective mulching on yield and quality of cantaloupes. We report here results from the first two trials. The results showed that reflective mulching increased the total number of fruits by over 25%. The silver film allowed early harvesting, it produced fruits with higher content of soluble solids (°Brix), pulp with more intense color, and early-harvested fruits with higher content of vitamin C. This technique seems promising for the production of melons and probably other cucurbits but the grower is ultimately the one who needs to determine whether the economical return, associated with the mulch, compensates the costs of implementing it in their fields.
The Comparison of Aerial and Sprinkler Applied Delayed Applications of Kerb® to LettuceFive tests were conducted to compare delayed applications of Kerb applied by air with applications made through sprinklers. Applications were made commercially to plots ranging in size from 11 to 18 acres. Broadleaf weed control was better in all tests from the sprinkler applied Kerb than from aerial application. The control of volunteer sudangrass was poor in one test from both types of applications and worse from the sprinkler than the aerial application. It was concluded that applying Kerb though sprinklers to lettuce is effective and often superior to aerial applications.
Management of Powdery Mildew on Cantaloupe in 2004Powdery 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.
Fungicide Performance for Management of Powdery Mildew on Lettuce in 2004Powdery 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.
Field Evaluations of Lettuce Cultivars for Resistance to Fusarium Wilt: 2-Year SummaryFusarium 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.
Evaluation of Products to Manage Sclerotinia Drop of Lettuce in 2004Sclerotinia 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.
Comparison of Products for Management of Powdery Mildew on Cantaloupe in 2003Powdery 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.
Comparative Efficacy of Fungicides for Management of Downy Mildew of Broccoli in 2004Downy 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.
Whitefly Resistance to Insecticides in Arizona: 2002 and 2003 Results"Whitefly resistance to insecticides is a constant threat to successful management of sticky cotton resulting from inadequate control of Bemisia whiteflies. A three-stage resistance management program was implemented in Arizona cotton following a severe whitefly resistance crisis in 1995. This program has been highly successful for eight years. Success has been fostered by intensive investments into improved whitefly sampling and treatment decisions, coupled with conservation of natural enemies. This latter component has hinged on limited, strategic use of two insect growth regulators in cotton, use of the neonicotinoid insecticide, imidacloprid, in vegetables and melons, and tactical deployment of non-pyrethroid and pyrethroid chemicals. Statewide monitoring of whitefly resistance to insecticides in cotton, melons and greenhouse crops has permitted annual assessments of the status of whitefly resistance management in Arizona. In this paper we summarize susceptibility of whitefly collecions made in cotton in the 2002 and 2003 seasons and discuss longer term trends in resistance development. No major problems regarding field performance of insecticides against whiteflies were observed or reported in 2002 or 2003. However, monitoring confirmed the early stages of evolution of resistance to pyriproxyfen (Knack®) and showed that whiteflies possessing this resistance could be detected in all cotton-producing 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. However, 50 and 25% of cotton fields sampled in 2002 and 2003, respectively, had resistance levels expected to result in inadequate performance of synergized pyrethroid treatments. Whiteflies from throughout Arizona were highly susceptible to imidacloprid (Admire®/Provado®) and two other neonicotinoid insecticides, acetamiprid (Intruder®) and thiamethoxam (Actara®/Centric®/Platinum®)."
Is Aphid Management Sustainable in Desert Head Lettuce?New restrictions on insecticides for aphid control presents new challenges for lettuce growers. Dimethoate is soon to be unavailable and the future status of other conventional aphicides is uncertain. However, a number of new active ingredients will soon be available that offer lettuce growers valuable alternatives for aphid management in lettuce. The present dilemma and potential for implementing new chemistries into lettuce IPM programs is discussed in this report.
Comparative Efficacy of Oberon® (spiromesifen) Against Bemisia Whiteflies in Spring CantaloupesSeveral studies were conducted on spring cantaloupes from 2002-2004 to evaluate a new insecticide, Oberon (spiromesifen) for whitefly control in spring melons. These studies demonstrate that this IGR-like insecticide offers melon growers management alternatives for effectively controlling whiteflies. The results strongly suggest that Oberon has good potential for controlling whiteflies in spring melon crops similar to what can be expected from Courier. Oberon provided 21-28 days of residual control of whiteflies under spring growing conditions when applied early in whitefly population growth. Our studies also indicate that spray timing is important for cost-effective control with both Oberon and Courier. They also suggest that action thresholds based on adult abundance and nymph densities differ for these two compounds depending on whether Admire has been applied at planting.
Seasonal Abundance of Western Flower Thrips Populations in Desert Head LettuceStudies were conducted from 2001-2004 to examine thrips abundance in multiple lettuce plantings throughout the growing season. Head lettuce was sampled periodically on untreated, 0.25 acre plots at various intervals from early September through March. Results clearly showed that thrips reproduction and development on desert lettuce is largely influenced by temperature. Thrips adults and larvae populations within each planting were consistently most abundant on lettuce planted in November and December where temperatures averaged 60-65 degrees F during the spring. Population development was at its lowest level in the October plantings, particularly during the cooler winter periods. This study demonstrates that western flower thrips populations are capable of reproducing and developing large densities on head lettuce under winter and spring growing conditions in the desert.
Insect Pests in Yuma Winter Vegetables: Review of the 2003-2004 SeasonInsect pest populations seemed to be exceptionally abundant on our desert vegetable crops this past growing season. It is difficult to explain why some insect populations occurred in larger numbers this year, but the weather we experienced may have had a significant role. Hot, dry weather in the early fall and spring, coupled with moderate winter temperatures provided ideal conditions for some insect pests.
Impact of Planting Date on Aphid Infestations and Contamination in Head LettuceThe influence of planting dates on aphid population growth in head lettuce was measured over a 5 year period to identify planting windows during the season when lettuce is at risk from aphid infestations. Small, untreated 0.2 acre plantings of head lettuce were established beginning in October with final harvest occurring in April. Plant samples were conducted weekly to estimate the numbers of aphid per plant. Based on these studies, planting date and temperature likely has a strong influence on seasonal abundance and damage caused by aphids. Green peach aphid was the least abundant aphid during the 5 year period, and foxglove aphids appear to be increasing in abundance over the past 3 years. All aphid species have the potential to economically contaminate lettuce, particularly in the November and December planting windows.
Foliar Activity of Assail®, Fulfill® and Flonicamid® on Aphids in Leafy VegetablesSeveral small-plot studies were conducted in the spring of 2004 to compare the residual efficacy of several new reduced risk insecticides against aphids infesting desert head lettuce. In 4 head lettuce trials and one broccoli trial, economic aphid control was consistently achieved following foliar applications with flonicamid and Assail. These compounds provided good knockdown of aphids when applied relatively early in lettuce plant development and aphid population growth. Fulfill was less consistent and performance was reliant on correct spray timing. Collectively, the chemical attributes and biological activities of Fulfill, Assail and flonicamid make them extremely attractive for implementation into an aphid management program.