Downy 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.

A 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.

Sclerotinia 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.

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.

A 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.

In the 2001-2002 production season, Fusarium wilt was observed for the first time in six different lettuce fields in the Gila and Dome Valley production areas of Yuma County, Arizona. The disease was found in 11 additional sites during 2002-2003. Fusarium wilt presents a serious threat to the health of the lettuce industry in Arizona. The only effective means of controlling Fusarium wilt of lettuce at this time is to avoid infested fields. On the other hand, Fusarium wilt in other crops, such as tomatoes and melons, is controlled effectively by planting cultivars resistant to the pathogen. The relative resistance of lettuce cultivars grown in the Arizona desert production region is unknown; therefore, a cultivar evaluation trial was established in a field known to contain the wilt pathogen, Fusarium oxysporum f.sp. lactucae. Tested cultivars were grouped into three different planting dates: Sep 7, Oct 17 and Dec 6, 2002. A majority of the cultivars within each planting date were those that would be planted in the desert at that time. Fusarium wilt was severe in the early planting of lettuce (Sep 7), moderate in the second planting (Oct 17) and very mild in the third planting (Dec 6). Disease severity was low in some lettuce cultivars in the second planting and most cultivars in the third planting. Among the types of lettuce tested, head lettuce was usually least resistant whereas romaine was most resistant. The data presented in this report are preliminary findings, subject to confirmation in another study planned for the next lettuce production season.

Downy 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 potential new fungicides were evaluated for control of this disease on broccoli in 2003. A moderate level of disease had developed by crop maturity. Actigard, Actigard alternated with Quadris, Acrobat+Maneb and DPX-KP481 were among the best treatments in this trial. Actigard is not a fungicide, but is classified as a plant activator. When applied to plants, this compound stimulates a defense response in plants to some diseases. Actigard also has performed well in previous trials. Several other new products and some chemistries that are currently available provided significant levels of disease control as well.