Vegetable Report 1996
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 1996
- Broccoli Variety Trials 1995/96
- Cabbage Variety Trials 1995/96
- Cantaloupe Variety Trials 1996
- Cauliflower Variety Trials 1995/96
- Crisphead Lettuce Variety Trials 1995/96
- Mixed Lettuce and Romaine Variety Trials 1995/96
- Sweet Corn Tolerance and Herbicide Weed Control
- Soil-Applied Herbicide Weed Control in Cantaloupes
- Postemergence Herbicide Weed Control in Broccoli
- Broccoli Preemergence Herbicide Weed Control Studies
- Postemergence Herbicide Weed Control in Onions
- Management of Downy Mildew on Broccoli: Efficacy of Fungicides in 1996 Field Trial
- Management of Powdery Mildew on Cantaloupe: Efficacy of Fungicides in 1995 Field Trial
- Management of Sclerotinia Leaf Drop on Lettuce: Efficacy of Fungicides in 1996 Field Trial
- Management of Downy and Powdery Mildew on Lettuce: Efficacy of Fungicides in 1996 Field Trial
- Whitefly Control in Arizona Vegetables: Development of a Resistance Management Program for Imidacloprid (Admire®)
- Late Season Biological Control of Whiteflies in Fall Cantaloupe Using Formulations of Beauveria Bassiana
- Air-Assisted Electrostatic Application of Pyrethrois and Endosulfan Mixtures for Sweetpotato Whitefly Control and Spray Deposition in Cauliflower
- Optimal Soil Placement and Application Method of Admire® for Sweetpotato Whitefly Control in Head Lettuce
- Insecticides for Whitefly Control in Cantaloupes
- Whitefly Control with Foliar Insecticides Following Imidacloprid in Cantaloupes
- Timing and Frequency of Provado® Applications for Management of Aphid Populations in Head Lettuce
- Admire® Aphid Control in Spring Cabbage
- Evaluation of Insecticides for Aphid Control in Cabbage
- Temporal Activity of New Insecticde Chemistries Against Beet Armyworm in Lettuce
- Residual Activity of New Insecticide Chemistries Against Beet Armyworm in Lettuce
- Lannate Resistance in Beet Armyworm in Yuma
- Evaluation of Insecticides for Lepidopterous Insect Pest Control in Cabbage
- Deposition and Efficacy of Capture and Thiodan Applied to Melons Using Several Application Technologies
- Trends in the Temporal Distribution and Host Plant Relations During 1988-1994, and Virus-vector Characteristics of Two Whitefly Populations in Arizona
- Effect of a Plant Growth Regulator on Green Beans Grown for Processing
- Thermodormancy in Lettuce
- Mulching Cantaloupes with Plastic at Yuma 1996
- Water and Nitrogen Interactions in Subsurface Drip Irrigated Broccoli and Cauliflower Production
- Petiole Sap Nitrate Tests for Determining Nitrogen Status of Broccoli and Cauliflower
Petiole Sap Nitrate Tests for Determining Nitrogen Status of Broccoli and CauliflowerNitrogen (N) status of vegetable crops is often monitored by analysis of dried plant tissues. However, dry tissue analysis often causes a significant delay between sampling and analysis. This study was conducted to examine the accuracy of a portable nitrate meter for determining petiole sap nitrate (NO₃) concentrations in broccoli (Brassica oleracea L. Italica group cv. Claudia) and cauliflower ( Brassica oleracea L. Botrytis group, cv. 'Candid Charm'). The relationship between NO₃-N concentration in fresh petiole sap and in dried petiole tissue was Studied for these crops in southern Arizona during the 1993-94 and 1994-95 winter growing seasons. Experiments were factorial combinations of 3 irrigation rates and 4 N rates, both ranging from deficient to excessive. Petioles were sampled throughout each season, and were split for sap and dry tissue analysis. A linear correlation was obtained between the two measurements in both seasons, with no consistent effect due to irrigation treatment or crop maturity. The regression coefficients did not differ among seasons. Regression equations were derived to convert petiole sap nitrate concentrations to dry tissue nitrate concentrations. These equations can be used to relate sap test measurements to existing guidelines for NO₃-N concentrations in broccoli and caulker petioles. These results suggest that the quick sap test, using the portable nitrate ion meter, is a valuable technique for monitoring N status of broccoli and cauliflower.
Water and Nitrogen Interactions in Subsurface Drip Irrigated Broccoli and Cauliflower ProductionField experiments were conducted during the 1995-96 winter growing season at The University of Arizona's Maricopa Agricultural Center to determine the response of broccoli and cauliflower to a factorial arrangement of water rates and nitrogen (N) fertilizer rates. Both the broccoli and cauliflower experiments were randomized complete block factorial designs with three water levels (deficient, optimum, and excessive), four N fertilizer levels (deficient, suboptimal, supra optimal, excessive), and four replications. Drip tubing was buried at a depth of eight inches along the midline of each planting bed. Irrigation was applied daily as needed to maintain the predetermined target soil water tension levels and N fertilizer (urea ammonium nitrate solution) was applied in 4 or 5 split applications. Broccoli spears and cauliflower curds were harvested weighed and graded according to prevailing commercial practices. The optimum marketable yield of broccoli of 4.6 tons/acre was achieved with a total application of 18.9 inches of water and 267 lbs. N/acre. The optimum marketable yield of cauliflower of 9.5 tons /acre was achieved with a total application of 18.5 inches of water and 178 lbs. N/acre. For both crops a nitrogen deficiency had a greater negative impact on marketable yield than either deficient or excessive water application. Optimum marketable yields, earliness and head quality for both crops were achieved when the average soil water tension level for the entire season was maintained at about 10 cbars (or 13 cbars uncorrected gauge reading).
Mulching Cantaloupes with Plastic at Yuma 1996Six mulches were compared to no mulch on cantaloupes at Yuma in the Spring of 1996. The IRT film and black mulches caused "Mission" cantaloupes to produce significantly higher early yields than white mulch or no mulch. Silver mulch gave good early and total yields. All mulches seemed to favor total production but in this test differences for total yields between mulched and non-mulched plots were not significant.
Thermodormancy in LettuceMost lettuce (Lactuca sativa L) seed fails to germinate at high temperatures. This phenomenon thermodormancy, is common in desert regions where 87% of all lettuce is grown in the U.S.A. A study was conducted using a non-thermodormant plant introduction, PI 251245, and two highly thermodormant Dutch butterhead cultivars, 'Dabora' and 'Severa'. Reciprocal crosses were made and germination trials conducted to observe how maternal and paternal influence and seed color contribute to thermodormancy. At 25 °C, germination was 100% for the three parents and the reciprocal F1 hybrids. Germination differences occurred at both 30° and 35 °C among the parents, with P1251245 with 100% germination and Dabora and Severa with less than 10% germination at both temperatures. Segregating F3 and F4 populations from Dabora x PI 251245 were investigated further. Genetic variation found between families suggests that breeding lettuce for improved thermotolerance may be possible. Seed color did not influence thermodormancy.
Effect of a Plant Growth Regulator on Green Beans Grown for ProcessingThree rates of the plant growth regulator Foliar Triggrr were applied to green beans grown for processing at 5% bloom. The 6 oz rate increased yields of size 1 and 2 beans compared to all other treatments and the untreated check and had the fewest size 3 beans (which would be culls). The 11 oz rate was similar to the untreated check while the 16 oz rate decreased yields. Total bean numbers per plant were similar. Although treatment differences in this experiment were not statistically significant, a yield increase of 10.2% for the 6 oz rate compared with the untreated check may well result in increased economic returns.
Trends in the Temporal Distribution and Host Plant Relations During 1988-1994, and Virus-vector Characteristics of Two Whitefly Populations in ArizonaThe abrupt and widespread introduction and establishment of the B type whitefly B. tabaci (Genn.) (also B. argentifollii) in Arizona in approximately 1987-1990 has given rise to unprecedented losses in vegetable and fiber crops in Arizona, and elsewhere throughout the sunbelt states. This report documents the discovery and the tracking of B type whitefly over time in Arizona crop and weed species, and reports important biological characteristics of the A and B whitefly populations with respect to host range, host preferences, and virus-vector capabilities. Here, from tracking data, we provide direct evidence that the A and B whitefly populations existed simultaneously in the state for a short period of time during 1989-90, and that by 1991, the B type population had become predominant whitefly pest and whitefly vector of plant viruses in Arizona crops. Unique host ranges and host preferences represent the most important distinctions between these two populations of B. tabaci, and are largely responsible for the altered epidemiologies of several whitefly- associated virus diseases, and for new pest problems in previously unaffected crops. From these collective data, it is possible to present an historical documentation of the emerging importance of the B whitefly as a pest and virus vector in Arizona. An unusually broad host range and the ability to induce phytotoxic disorders, set the B population apart from the historically problematic, local A type B. tabaci, and provide insights into the underlying basis of its unprecedented impact on crop production in Arizona. Baseline information about whitefly biology, host range, and virus-vector capabilities is relevant to the design and implementation of management practices aimed at controlling the whitefly as a pest and virus vector in Arizona crops.
Deposition and Efficacy of Capture and Thiodan Applied to Melons Using Several Application TechnologiesA study was conducted in 1995 to evaluate five application technologies in the field in terms of deposition efficiency, as well as to assess their abilities to control the sweet potato whitefly and thereby influence crop yield. The FMC and ESS-on treatments provided the greatest deposition on the ventral side of the leaves. The FMC system tended to maintain high ventral deposition efficiencies as the plants grew and the canopy closed, whereas the efficiency of the ESS declined. Differences in ventral deposition efficiency among treatments were not closely associated with differences in whitefly control, although the declining rate of ventral deposition for the ESS-on is also reflected in its declining superiority in adult insect control relative to the CDA and conventional systems. The ESS sprayer provided somewhat better whitefly control than the conventional treatment, and was also associated with a higher yield of #12 melons than the control and Admire treatments, but not better than the conventional treatment. Early control of adults was associated with reduced egg counts later in the season, suggesting that there may be long term control advantages with the ESS system. New application technologies need to be developed to obtain higher ventral deposition and maximum whitefly control, with minimum use of insecticides.
Evaluation of Insecticides for Lepidopterous Insect Pest Control in CabbageExperimental insecticides MK-244 (Merck), Alert (AC 303630, Cyanamid), and Confirm (RH-5992, Rohm and Haas) demonstrated very good efficacy in reducing the lepidopterous pests including plutell4 xylostella (diamondback moth, DBM) and Tricoplusia at (cabbage looper, CL) in cabbage. The total number of small, medium, and large DBM larvae for all treatments was lower than the untreated at most rating dates. The experimental insecticides compared favorably with commercially available products Lannate®, Larvin®, and Kryocide®.
Lannate Resistance in Beet Armyworm in YumaA beet armyworm population was collected from spinach in Yuma, Feb 1996. This population was evaluated for resistance to Lannate. A range of Lannate dosages were prepared by disolving Lannate into acetone. A miroapplicator was used to topically apply the dosages. Dosage-mortality data were obtained from 3rd instar larvae held for 24 hr after treatment. The BAW population tested in 1996 had an LD₅₀ of value of433.34 μg-methomyl/g -worm, compared to a historical susceptible strain which had an LD₅₀ of 17.54 μg/g-worm, a 24.7 fold increase in resistance.
Residual Activity of New Insecticide Chemistries Against Beet Armyworm in LettuceThree new insecticide chemistries (Alert, Success and Confirm) were evaluated and compared with standard chemistries for residual activity to beet armyworm in lettuce. Lettuce was treated in the field with the insecticides and left for 0, 3, 5 and 7 days. Leaves from treated plants were then brought into the laboratory where second instar beet armvworms were reared on them. Mortality was estimated 5 days after the worms were placed on the leaves. Bioassay were conducted at the thinning, heading, and harvest stages of lettuce. Under high temperature and light intensity, only Alert and Confirm provided the best residual control of beet armyworm, exhibiting good activity for about 3 days after application. Success had better residual activity than Lannate, and both were better than Xentari. Under cool temperatures and low light intensity conditions, Alert, Confirm and Larvin exhibited good activity for at least 5 days following an application, (7 days or greater for Alert and Confirm). Lannate and Xentari both had greater residual activity late in the season, but were not as effective as Alert, Confirm or Larvin. Late season activity of Success did not appear to differ much from early season observations, and did not appear to provide more than 3 days residual activity.
Temporal Activity of New Insecticde Chemistries Against Beet Armyworm in LettuceThree new insecticide chemistries (Alert, Spinosad and Confirm) were evaluated and compared with standard chemistries for temporal mortality of beet armyworm in lettuce. Field assessment and lab bioassay were conducted at the thinning, heading, and harvest stage of lettuce. Results from both the field and laboratory indicated similar trends for the temporal activity of the products. Alert appears to be have the most rapid "knockdown activity" with 100% mortality consistently occurring by 2 DAT. Spiniest, a naturalyte insecticide, has activity similar to Larvin. Both require 2-3 days to achieve complete larval mortality. Confirm, a new IGR selective for lepidoptera, requires significantly more time to achieve complete mortality (4-5 DAT). It can be compared with Bt (Xentari) activity in that it has initially slow activity. However, unlike Bt, it can effectively cause complete beet armyworm mortality. The results of this study are consistent with similar studies we conducted in 1994 and 1995 and provide basic guidelines concerning the activity and assessment of the performance of these materials in the field. However, PCAs and growers will ultimately be able to develop specific use patterns for these materials within their individual lettuce pest management programs.
Evaluation of Insecticides for Aphid Control in CabbageExperimental insecticides CGA-215944 (Ciba), pyriproxyfen (S-71639, Valent), and RH-7988 (Rohm and Haas) demonstrated very good efficacy in reducing the aphid population in cabbage. Fipronil (Rhone-Poulenc) was not as effective in controlling the aphids relative to the other treatments. Acephate (Orthene®), chlorpyrifos (Lorsban™), and naled (Dibrom®) were highly effective relative to the untreated check.
Admire® Aphid Control in Spring CabbageImidacloprid (Admire®) was applied at planting time in anticipation of providing aphid control in cabbage for spring harvest. In three commercially treated cabbage fields, Admire reduced the number of cabbage (Brevicoryne brassicae) and green peach aphids (Myzus persicae). Two rates of Admire, 10 and 20 oz/A appeared to be similar in performance for efficacy against aphids. Depth of placement of Admire in the soil below the seed appears to have some influence on the efficacy and consistency of performance. Much fewer aphids and greater consistency was observed when Admire was placed at 1-inch depth below the seed compared to 3- to 4-inches below the seed.
Timing and Frequency of Provado® Applications for Management of Aphid Populations in Head LettuceProvado insecticide (imidacloprid) was compared to Admire and other standard insecticides for management of aphids in head lettuce in Yuma 1995 and 1996. Foliar applications of Provado appear to provide an alternative method of controlling aphids on lettuce comparable to prophylactic applications of Admire. The prevention of aphid colonization in lettuce heads with Provado may depend greatly on the timing and frequency of applications before harvest occurs. These studies and other studies on spinach suggest that more than one application of Provado will be necessary to adequately suppress aphid contamination in heads. The label suggests that applications be timed 5-7 apart. Our data tends to support this recommendation. Furthermore, timing applications should be based on days to harvest, level of aphid colonization and duration of aphid migration.
Whitefly Control with Foliar Insecticides Following Imidacloprid in CantaloupesFoliar insecticides for whiteflies (Bemisia sp., WF) were applied as a supplementary control measure at 6 weeks after treatment with imidacloprid (Admire®) at planting time of melons. Beauveria bassiana fungus spores (Mycotrol®), pyriproxyfen (S-71639, Valent), and azadirachtin (Align®) are non-conventional insecticides that could be safer on beneficial parasites and predators. The number of eggs and nymphs counted at all rating dates for all treatments were not significantly different from the foliarly untreated check. Mycotrol treated melons showed higher number of nymphs following the second application. The Align treatment tended to exhibit higher number of nymphs after two applications. The addition of an adjuvant did not appear to enhance pyriproxyfen efficacy.
Insecticides for Whitefly Control in CantaloupesSeveral experimental insecticide treatment combinations were evaluated and demonstrated very good efficacy against Bemisia argentifolii [silverleaf whitefly (WF) also known as sweetpotato WF, B. tabaci]. Adults and immatures were most effectively reduced compared to the untreated check by pyriproxyfen (S-71639, Valent) treatments and fenpropathrin (Danitol®) plus acephate (Orthene®). CGA-215944 (Ciba) plus fenoxycarb (Ciba) treatments compared favorably with many of the pyrethroid combination treatments. Registered products esfenvalerate (Asana®), endosulfan (Thiodan®), cypermethrin (Ammo®), naled (Dibrom®), and oxydemeton-methyl (Metasystox-R®) complemented many of the combination treatments to reduce WF relative to the untreated check
Optimal Soil Placement and Application Method of Admire® for Sweetpotato Whitefly Control in Head LettuceThe effects of Admire formulation and soil placement on colonization by sweetpotato whitefly, Bemisia tabaci (Gennadius), at three plant growth stages of lettuce, Lactuca sativa L., were evaluated in experimental and commercial lettuce plots in 1993-1994. We also evaluated the effects of Admire treatments on yield response and incidence of chlorosis associated with whitefly control. Admire placement had a significant affect on whitefly colonization in lettuce throughout the experimental period. Whitefly densities on lettuce varied at each plant stage relative to depth of placement within the lettuce seed bed. Applications made to the soil surface and at 1.5 inch sub-seed furrow followed by irrigation, provided the most consistent control of whitefly nymphs in both small plot and on -farm lettuce plots. These Admire soil treatments also prevented reductions in head size and incidence of leaf chlorosis associated with whitefly colonization in lettuce. Our data suggest that incorporation of Admire into the upper 1.5 - 2 inches of soil below the seed furrow is optimal for absorption and translocation by lettuce roots. Admire soil treatments may provide a more environmentally suitable and effective alternative to control of whiteflies in lettuce than is currently possible with foliar insecticide reatments.
Air-Assisted Electrostatic Application of Pyrethrois and Endosulfan Mixtures for Sweetpotato Whitefly Control and Spray Deposition in CauliflowerPyrethroid and endosulfan mixtures applied at full and reduced rates with three application methods (air-assisted electrostatic, air-assisted hydraulic, and standard hydraulic sprayers) were evaluated in field studies in 1992 and 1993 for control of sweetpotato whitefly, Bemisia tabaci-strain B (Genn.), also known as silverleaf whitefly, Bemisia argentifolii Bellows and Perring, and spray deposition on caulker, Brassica oleracea L. Based on adult suppression, improved control of whiteflies was achieved with full and reduced rates of the air-assisted electrostatic sprayer following two applications in 1992, but percent reduction of adults did not differ significantly among the application methods when full rates of insecticide were applied in 1993. Control based on immature colonization indicated that the air-assisted electrostatic sprayer was the only spray method to significantly reduce nymph densities when compared with the control in 1992, but differences in numbers of eggs, nymphs and eclosed pupal cases varied among application methods and rates of active ingredient in 1993. Comparisons of cauliflower harvest dates indicated that the air -assisted electrostatic sprayer did not provide significantly better control than the other application methods when used at similar rates. Spray deposition with the air-assisted electrostatic application technique was variable throughout these studies with no clear trends being observed. Our results suggest the air-assisted electrostatic sprayer may offer a means to control sweetpotato whitefly with a 50% reduction in insecticide usage.
Late Season Biological Control of Whiteflies in Fall Cantaloupe Using Formulations of Beauveria BassianaBeauveria bassiana is a naturally occurring fungal disease of insects that has been shown to be an effective biological control against whiteflies in cotton and vegetable crops. Six treatments were initiated in drip irrigated fall cantaloupe on October 2, and repeated on October 9 and 23. The six treatments consisted of 1) a check or unsprayed plot; 2) 0.5 lb. Mycotrol WP/acre; 3) 1 Ib. Mycotrol WP /acre; 4) 1 pt. Mycotrol ES/acre; 5) 0.5 lb. Mycotrol WP /acre + pyrethroid tank mix; and 6) 12 oz. Naturalis-L/acre. Under moderate to light sweetpotato whitefly pressure, the Mycotrol formulations provided significant control (68-79%) compared to unsprayed check plots, and were superior to Naturalis-L formulation whose effects were relatively short lived. Mycotrol WP applied in three applications at the labeled rate of 1 lb. product/acre had the cumulative effect of maintaining adult whitefly leaf counts below the currently recommended economic threshold of 3 per leaf at 28 days after treatment initiation, under the conditions of this study.
Whitefly Control in Arizona Vegetables: Development of a Resistance Management Program for Imidacloprid (Admire®)In 1995 we initiated a resistance management program aimed at sustaining the efficacy of Admire®. This paper delineates the groundwork for the program, and describes methodological and conceptual advances toward our goal. Bioassay methods developed for adult whitefly consisted of a 1 day hydroponic uptake procedure using cotton seedlings. A reliable mortality criterion was also established. Results from a statewide survey suggested slight geographic variation in whitefly susceptibility to Admire®. Future studies will 1) continue to monitor susceptibility throughout Arizona, 2) evaluate the risk of resistance to whitefly populations in commercial greenhouses, and relate this to field populations, and 3) characterize the development of resistance in relation to cropping systems and spatial dynamics of whitefly. The overall objective of these investigations is to determine if a sustainable use strategy can be identified for Admire®.