Vegetable Report 2001
ABOUT THIS 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 2001Birds
- Beet Armyworm Resistance to Cry1Ac
- Eggs of Eretmocerus eremicus, a Whitefly Parasitoid
- Influence of Admire and Platinum on the Population Growth of the Lettuce Aphid Under Field Conditions
- Interactions Between Insecticides, Spray pH, & Adjuvants
- Neonicotinoids and Azadirachtin in Lettuce: Comparison of Application Methods for Control of Lettuce Aphids
- Residual Efficacy and Field Performance of Thiacloprid (Calypso) Against Whiteflies in Melons
- Sustaining Arizona's Fragile Success in Whitefly Resistance Management
- Comparison of New Fungicides for Management of Downy Mildew of Broccoli in 2001
- Evaluation of Fungicide Rotations for Control of Powdery Mildew of Cantaloupe
- Evaluation of Fungicides for Control of Powdery Mildew of Greenhouse Pepper
- Evaluation of Products to Manage Sclerotinia Leaf Drop of Lettuce in 2001
- Examination of New Chemistries to Control Powdery Mildew of Cantaloupe in 2000
- Fungicide Performance for Control of Powdery Mildew on Lettuce in 2001
- Interaction of Pepper Experimental Lines with Phytophthora Crown and Root Rot in 2000
- Reaction of Different Cultivars of Lettuce to Development of Powdery Mildew on Lettuce in 2001
- Field Evaluation of Broccoli Varieties Grown in Southwest Low Desert Soils
- Field Evaluation of Romaine Lettuce Varieties Grown in Southwest Low Desert Soils
- Effect of Prowl and Prefar Herbicides on Onions
- Evaluation of New Preemergence and Postemergence Herbicides for Onion Weed Control
- Grass Weed Control in Melons
- Herbicide Screen for Melons
- New Postemergence Herbicides Evaluation in Cantaloupes
- Preemergence Herbicides for Weed Control in Melons
- Safety of New Preemergence Herbicides on Lettuce and Broccoli
- Timing of Glyphosate Application for Weed Control in Glyphosate Tolerant Lettuce
- Timing Kerb Applications in Lettuce
Timing Kerb Applications in LettuceKerb (Pronamide) is often ineffective when it is leached below germinating weed seeds with sprinkler irrigation. Efficacy can be improved by making delayed aerial applications after the sprinklers have been started and before weeds have become established. Tests were conducted to determine the optimal time of application. Optimal times varied with the season and ranged from two to three days after the sprinklers had started during the early season (Sept.) to five to six days during the late season (January).
Timing of Glyphosate Application for Weed Control in Glyphosate Tolerant LettuceStudies were conducted to determine the optimum time to apply glyphosate to glyphosate-tolerant Lactuca sativa cv. Raider (head lettuce). The study was initiated near Yuma, Arizona in September 2000. Single applications of glyphosate at 1.0 lb AI/A were made to head lettuce at development stages of 2, 4, 6 and 8 leaves. Glyphosate treatments did not injure lettuce. A single application at the 2 or 4 leaf stage was optimal for near complete control of Portulaca oleracea (common purslane), Chenopodium murale (nettleleaf goosefoot), Malva parviflora (cheeseweed), and Leptochloa spp. (sprangletop). Later applications at the 6 or 8 leaf stages allowed weeds, especially, common purslane to compete with the crop. Treatments applied at the 2 or 4 leaf stages required the least amount of time to hand weed and resulted in highest fresh weight yields.
Safety of New Preemergence Herbicides on Lettuce and BroccoliCarfentrazone at 0.0125 and 0.025 lb AI/A was safe on all three lettuce cultivars. No stand reduction was observed. Sulfentrazone confirmed the initial screening test rate range of 0.05 to 0.1 lb AI/A for demonstrating marginal lettuce safety. Flumetsulam and thifensulfuron showed greater selectivity only in head lettuce while severely injuring romaine and red leaf lettuce. Rimsulfuron caused considerable stand reduction of all three lettuce cultivars. Sulfentrazone, fluroxypyr, and thifensulfuron exhibited good tolerance on broccoli as no stunting or stand reduction was observed at maturity.
Preemergence Herbicides for Weed Control in MelonsAll herbicide treatments, Prefar, Frontier, Dual Magnum, Valor, and Prefar combined with Dual Magnum or Frontier caused less than 10% injury on cantaloupes. Frontier at 0.75 lb AI/A, Dual Magnum at 1.0 lb AI/A, Valor at 0.03 and 0.05 lb AI/A controlled weeds similar to Prefar. Prefar at 4.0 lb AI/A combined with Frontier controlled tumble pigweed (94%), narrowleaf lambsquarters (95%), Wright’s groundcherry (97%), and horse purslane (94%). None of the preemergence herbicide treatments controlled purple nutsedge.
New Postemergence Herbicides Evaluation in CantaloupesHalosulfuron applied POST with an adjuvant and ammonium sulfate was effective against lambsquarters and nutsedge. Rimsulfuron, flumetsulam, and thifensulfuron were effective against the pigweeds and purslane with minimal activity against lambsquarters. Halosulfuron and rimsulfuron were safe on melons and flumetsulam and thifensulfuron were marginally safe on cantaloupes. The combinations of these products may offer broader spectrum weed control.
Herbicide Screen for MelonsIn the preemergence test, azafenidin, flufenacet, thiazopyr, isoxaben, dithiopyr, and thifensulfuron exhibited safety on cantaloupes and watermelon at rates higher than rates required for effective weed control. In the postemergence test, the margin of selectivity for melon safety and weed control was narrow for MKH-6561, flufenacet, and thifensulfuron. MKH-6561 and CGA-362622 applied preemergence did not offer any acceptable crop safety relative to the weed control that was observed. Azafenidin, thiazopyr, isoxaben, and pyrithiobac did not demonstrate adequate melon safety compared to providing good weed control.
Grass Weed Control in MelonsEfficacy of the grass herbicides showed that Select (clethodim) and BAS-620 (BASF Corporation) at rates as low as 0.1 lb AI/A were nearly comparable in controlling 2 leaf stage of growth watergrass or when applied a week later on 3-4 inch tall watergrass. Fusilade DX (fluazifop-p-butyl) was intermediate in controlling grasses and 0.188 lb AI/A was necessary to give equivalent control of larger grasses as compared to the 0.1 lb AI/A rate that gave acceptable control of smaller grasses. Poast (sethoxydim) at 0.188 lb AI/A gave acceptable control of small grasses but lower rates or later timed applications were not as efficacious.
Evaluation of New Preemergence and Postemergence Herbicides for Onion Weed ControlIn the preemergence test, flumioxazin at 0.1 to 0.3 lb AI/A severely reduced the onion crop stand. Flumioxazin applied caused significant onion injury of 23 to 37% at 2 WAT for rates of 0.04 to 0.1 lb AI/A. Fluroxypyr and carfentrazone applied postemergence did not show any onion injury at 5 WAT. Fluroxypyr and carfentrazone did not offer acceptable control of annual yellow sweetclover at any rate. Carfentrazone at 0.063 lb AI/A demonstrated activity on lambsquarters and control nearly approached acceptable levels at 83% after 5 WAT. Fluroxypyr did not provide acceptable control of lambsquarters.
Effect of Prowl and Prefar Herbicides on OnionsSignificant onion height reduction was observed when Prowl (pendimethalin) and Prefar (bensulide) herbicide combinations were applied preemergence (PREE). The onions resumed growth but the height was still slightly reduced later in the growing season compared to the handweeded check and the standard herbicide treatment, Dacthal (DCPA). The onion crop stand emerged initially but later in the season, a significant crop stand reduction was observed for the higher rate of Prowl at 0.5 lb AI/A plus Prefar. A lower rate of Prowl at 0.25 lb AI/A plus Prefar also caused a reduction of the onion stand compared to the handweeded check or Dacthal.
Field Evaluation of Romaine Lettuce Varieties Grown in Southwest Low Desert SoilsRomaine lettuce plays an important role in Yuma’s economy. An estimated 10,000 acres are cropped to large number of varieties each year with planting season that spreads from September to March. The demonstration site was selected to compare new and existing varieties of romaine lettuce on growers’ fields using standard farming practices. Selected growth parameters were evaluated throughout the growing season. Results indicate that varieties tested at Barkley Farms in Yuma are expected to do well if grown under similar growing conditions and planting time. Varieties tested during this planting slot did not experience any incidence of diseases. There was no significant head size and head weight difference among varieties evaluated. Number of heads per bed and number of heads left after harvest were significantly different among varieties tested.
Field Evaluation of Broccoli Varieties Grown in Southwest Low Desert SoilsBased on the acreage, broccoli is the third largest vegetable crop in Yuma County, after head lettuce and romaine. It generates over 36 million dollars to Yuma's economy. Efforts are continuously made by growers, seed industry and the University of Arizona outreach program to produce better crops that respond to consumer’s choice. Selection of newly adapted varieties is made based on agronomic performance as well as commercial value. Stand uniformity disease resistance, vigor, head shape and head size are among characteristics that are evaluated. The objective of this demonstration trial is to evaluate the performance of newly developed varieties grown under standard cultural practices and to provide unbiased observations to growers and the seed industry. Fourteen varieties were tested on growers' fields in Yuma County. No incidence of disease was observed among varieties tested and the overall evaluation rating was greater than 4 indicating that most of varieties tested will grow well under similar growing conditions and planting date. Significant head diameter and plant height was observed among varieties evaluated.
Reaction of Different Cultivars of Lettuce to Development of Powdery Mildew on Lettuce in 2001Seven different cultivars of lettuce were seeded and watered on Dec 1, 2000 at the Yuma Valley Agricultural Center. Cultivars were rated for severity of powdery mildew caused by Erysiphe cichoracearum at plant maturity (Mar 21). The highest levels of powdery mildew were found on the cultivars Winterhaven and Silverado, whereas lower disease severity was observed on Jackel, Cibola, RC-74 and Accolade. All tested cultivars would have required application of fungicides to reduce the amount of powdery mildew to acceptable levels. On the other hand, planting of lettuce cultivars with some disease tolerance may require less fungicide inputs to achieve acceptable disease control compared to planting susceptible cultivars.
Interaction of Pepper Experimental Lines with Phytophthora Crown and Root Rot in 2000This study was conducted in the greenhouse at the Yuma Agricultural Center. Thirty-nine experimental lines of pepper from the Texas A&M pepper breeding collection were seeded and grown in the greenhouse in 8 fl. oz. plastic pots. When plants were 2 months old (Aug 8), the potting mix in each pot was infested with Phytophthora capsici. Plants were placed in 2-in. deep containers filled with water for 48 hr every 2 weeks, which maintained the potting mix in a saturated condition and encouraged disease development. The mean temperature of the potting mix from the time it was infested with Phytophthora capsici to the termination date of the study was 81 °F. Disease progress and the relative susceptibility of each test plant to Phytophthora crown and root rot was assessed by recording the date when each plant displayed necrosis around the lower stem and was permanently wilted. The environmental conditions during this study were very favorable for disease development. The mean duration of plant survival for pepper selections ranged from 9 to 51 days. If no plants had died due to Phytophthora crown and root rot, the duration of plant survival would have been 74 days. Most plant selections were readily attacked and killed by Phytophthora capsici. The experimental lines with the highest survival rating may be somewhat tolerant to disease; however, additional testing in further greenhouse and field trials is required to substantiate these preliminary results.
Fungicide Performance for Control of Powdery Mildew on Lettuce in 2001Powdery mildew on lettuce is caused by the fungus Erysiphe cichoracearum. This disease is favored by moderate to warm temperatures and dry weather conditions. Several potential new fungicides were evaluated for control of powdery mildew on lettuce in 2001. Powdery mildew appeared in our plots by Jan 16 and reached high levels by plant maturity on Mar 13. Nontreated lettuce plants were heavily infected with powdery mildew at plant maturity, whereas the level of disease was low to virtually nonexistent in plots treated with BAS 500, Flint, Rally, Rally alternated with Microthiol, Microthiol and Quinoxyfen. The future availability of one or more of these chemistries under development could help in efforts to control powdery mildew of lettuce and to establish and maintain a fungicide resistance management program for plant disease control products of importance for this crop.
Examination of New Chemistries to Control Powdery Mildew of Cantaloupe in 2000Powdery mildew can occur on melons annually in Arizona. Sphaerotheca fuliginea is the plant pathogenic fungus that causes powdery mildew of 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. Potential new fungicides were evaluated and compared to existing chemicals for control of powdery mildew of cantaloupe in a field trial conducted during the spring of 2000 at the Yuma Agricultural Center A moderately high level of disease had developed by crop maturity (June 22) on nontreated plants. All treatments significantly reduced the level of powdery mildew on both sides of leaves, compared to nontreated plants. The best treatments among those tested with respect to disease control on the underside of leaves, where disease is more difficult to control than on the tops of leaves, included Actigard, Armicarb+Quadris, BAS 500, Benlate+Microthiol, Flint, Flint+Trilogy, Microthiol, Quadris+Actigard, Quadris+Benlate, Quinoxyfen, Nova, Nova+KHHUBF, Topsin, Topsin+Trilogy, Benlate, Benlate+Trilogy, Folicur, Quadris and Topsin+Microthiol. The potential availability of new chemistries for management of powdery mildew of cantaloupe and other cucurbits could help improve overall control of powdery mildew as well as facilitate the development of fungicide resistance management strategies, which strive to minimize the risk of resistance development by the pathogen to these compounds.
Evaluation of Products to Manage Sclerotinia Leaf Drop of Lettuce in 2001Sclerotinia leaf drop in Arizona is caused by two soil-borne fungi, Sclerotinia minor and S. sclerotiorum. Moist soil and moderate temperature favor this disease. Some new products in development were evaluated for control of leaf drop on lettuce during the winter vegetable growing season of 2000-2001. Sclerotia of each pathogen were applied to plots after thinning and just before the first of two applications of test compounds. A high level of disease control in the S. minor plots occurred with an appropriate concentration of Plantpro 45, Fluazinam, Contans, BAS 510, BAS 510+BAS 500, Medallion and Serenade. The same products (except Serenade) at an appropriate rate significantly reduced the amount of leaf drop caused by S. sclerotiorum. Elevate did not significantly reduce disease caused by either pathogen. Two of the products tested, Serenade and Contans, are biological control materials. Continued demonstration of efficacy by one or both of these products may provide the opportunity to utilize biological control agents to manage Sclerotinia leaf drop.
Evaluation of Fungicides for Control of Powdery Mildew of Greenhouse PepperA fungicide trial was established in a commercial style greenhouse at The University of Arizona Campus Agricultural Center in November 2000 to evaluate efficacy of several fungicides for control of powdery mildew on bell pepper. Treatments included five registered fungicides: Microthiol Special (micronized sulfur), Trilogy (neem extract), Flint (trifloxystrobin), Serenade (Bacillus subtilis QST713) and AQ10 (Ampelomyces quisqualis) applied as single treatments every 10-14 days to each of four replicates. In samples to determine the percentage of leaf area affected by powdery mildew lesions and the number of leaves infected within different treatments, Microthiol Special and Serenade were significantly different from non-treated controls, while Flint and AQ10 had fewer lesions and number of leaves infected but were not significantly different from the control. Although Trilogy was not different from the control, this treatment had more lesions and number of leaves infected than all treatments.
Evaluation of Fungicide Rotations for Control of Powdery Mildew of CantaloupeA fungicide trial was established at The University of Arizona Marana Agricultural Center in April 2000 to evaluate rotation and timing of application for several fungicides used for control of powdery mildew on cantaloupe. Treatments included seven registered fungicides: azoxystrobin, micronized sulfur, neem extract, potassium bicarbonate, benomyl, thiophanate methyl and trifloxystrobin. Different rotations and timing of application of these fungicides were applied either before or immediately after initial signs of powdery mildew infection and up to three times thereafter depending on rotation scheme. By the second application, disease severity was mild but increased rapidly, and it was severe by the time of the last application. Powdery mildew was controlled to some degree on the upper leaf surface by all treatments. However, efficacy was more variable on the lower leaf surface and was reduced when applications were made only at dates 1 and 2. Results show the increased efficacy of fungicides with systemic or trans-laminar activity and the possibilities of rotations with contact fungicides for resistance management.
Comparison of New Fungicides for Management of Downy Mildew of Broccoli in 2001Downy mildew of broccoli, cauliflower and cabbage is caused by the fungus Peronospora parasitica. 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 2001. The final severity of downy mildew in this trial was moderate. Significant reduction in disease severity compared to nontreated plants was achieved by application of available compounds such as Aliette, Bravo, Maneb, Serenade and Trilogy. The nonregistered chemistries Acrobat, Actigard, Curzate, Flint, BAS 500, DPX-KP481 and Quadris also were active against broccoli downy mildew. Actigard was the superior treatment in this trial, as plants treated with this compound were almost free of disease. The future registration and subsequent availability of one or more of these new chemistries for broccoli and related crops could enhance the overall level of disease control as well as help minimize the risk of development of resistance to fungicides used to manage downy mildew.
Sustaining Arizona's Fragile Success in Whitefly Resistance ManagementArizona cotton experienced a severe crisis in 1995 stemming from resistance of whiteflies to synergized pyrethroid insecticides. The insect growth regulators (IGRs), Knack® (pyriproxyfen) and Applaud® (buprofezin), served a pivotal role in resolving this problem. Similarly, Admire® (imidacloprid), the first neonicotinoid insecticide to obtain registration in Arizona, has been the foundation of whitefly control in vegetables and melons. In this paper we provide an update regarding the susceptibility to key insecticides of whiteflies from Arizona cotton, melons, and greenhouses. Overall, whitefly control in Arizona cotton remained excellent in the 2000 season and there were no reported field failures. However, there was a significant decrease in susceptibility to Applaud of whiteflies collected from cotton. One collection from Eloy, Arizona, in 2000 had susceptibility to Applaud that was reduced 129-fold relative to a reference strain. Whiteflies resistant to Knack, detected for the first time in Arizona in 1999, were again detected in 2000 but at lower frequencies than in 1999. Though whiteflies resistant to Admire/Provado® continued to be found at specific locations, overall susceptibility to Admire/Provado in 2000 remained high in whitefly collections from cotton. The new neonicotinoid insecticides, thiamethoxam and acetamiprid, were similar in toxicity to Arizona whiteflies in laboratory bioassays and we confirmed the significant but relatively low-order cross-resistance we previously reported between these neonicotinoids and Admire/Provado. Arizona whiteflies continued to be relatively susceptible to mixtures of Danitol® (fenpropathrin) and Orthene® (acephate). Factors that could undermine the current success of whitefly resistance management in Arizona are discussed. These include: 1) more severe resistance to IGRs in whiteflies from cotton, stemming from increased IGR use within and outside of cotton; 2) resistance of vegetable, melon and greenhouse whiteflies to the various formulations of imidacloprid (Admire, Provado, Merit®, Marathon®); 3) the imminent registration of new neonicotinoid active ingredients in cotton, greenhouses and other Arizona crops.