Powdery 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.

Powdery 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.

This 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.

Seven 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.

In 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.

Efficacy 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.

In 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.

Halosulfuron 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.

Studies 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.

Susceptibility of beet armyworm, Spodoptera exigua Hübner, to the Bt toxin, Cry1Ac, expressed in the first generation of transgenic cotton plants was evaluated using a laboratory strain and several foreign and United States field strains. A diet-incorporation assay of neonate larvae was used. Susceptibility was estimated by the degree to which Cry1Ac inhibited larval growth from the first through fifth instar. Regression analyses of larval weights against log concentration of Cry1Ac yielded slope and intercept values that were used to compute I₅₀s, defined as the amount of Cry1Ac that resulted in a fifty percent reduction in larval growth. Three populations exhibiting reduced susceptibility to Cry1Ac were selected on diet containing 1000 micrograms of Cry1Ac per gram of diet. I₅₀s for non-selected populations ranged from 0.0477 micrograms Cry1Ac per gram of diet for the laboratory reference strain to 4.31 micrograms of Cry1Ac per gram of diet for a field strain collected from Yuma, Arizona. Selection of a strain from Belle Glade, Florida, with Cry1Ac yielded the lowest susceptibility to this toxin. Prior to selection, the I₅₀ was 2.43 micrograms of Cry1Ac per gram of diet; after selection the I₅₀ was 17.4 micrograms of Cry1Ac per gram of diet. Thus selection reduced susceptibility of the Belle Glade, Florida strain to Cry1Ac by 7.2-fold and yielded susceptibility that was 360-fold less than the laboratory reference strain. Selection also reduced susceptibility of an Arizona (Dome Valley) population by 3-fold. Our results demonstrate the presence of large (>25-fold) differences in susceptibility of field-collected beet armyworm populations to Cry1Ac. Furthermore, the fact that resistance was elevated three to seven-fold in two selected strains provided evidence of a genetic basis of resistance to Cry1Ac.