Downy and powdery mildew are caused by the plant pathogenic fungi Bremia lactucae and Erysiphe cichoracearum, respectively. Cool and moist environmental conditions favor development of downy mildew, while warmer and dry weather is conducive for development of powdery mildew. Potential new fungicides were evaluated for management of these diseases in 1997. A very low level of downy mildew occurred during this trial; however, all treatments significantly reduced the number of leaf lesions compared to nontreated lettuce plants. Powdery mildew was quite intense at crop maturity and was significantly lower, compared to nontreated lettuce, on plants treated with Microthiol Special, BAS 490 + Bravo Weather Stik, Quadris, and two additional treatments not usually found to reduce this disease.

Leaf drop of lettuce is caused by the plant pathogenic fungi Sclerotinia minor and S. sclerotiorum. Cool and moist environmental conditions favor disease development. Sixteen diffirent cultivars of head lettuce were evaluated in the field for susceptibility to Sclerotinia leaf drop in plots inoculated with sclerotia of Sclerotinia minor or S. sclerotiorum. Significant differences were detected among the tested cultivars in the amount of lettuce plants killed by Sclerotinia minor. On the other hand, there were no significant differences among tested cultivars in the number of plants destroyed by Sclerotinia sclerotiorum

Proclaim 1.6 was evaluated in head lettuce in side-by-side large plot aerial and ground application demonstrations compared to commercial standard treatments. Proclaim consistently provided excellent control of beet armyworm and cabbage looper larvae. Worm control by Proclaim was equivalent to, or better than the commercial standards.

Confirm was evaluated in head lettuce for control of lepidopterous pests when applied by air, and when applied by ground at 4, 8 and 12 mph. By air Confirm may not provide commercially acceptable control when used alone. Confirm must be ingested to exhibit activity and aerial applications may not provide adequate spray coverage. When used by ground, applicators should avoid exceeding 8 mph, again because good spray coverage may be compromised.

The beet armyworm pheromone dispenser, Yotoh-con-S, was evaluated for its ability to inhibit mate location and subsequent population growth of beet armyworm in head lettuce. Pheromone dispensers were very effective in preventing male beet armyworm moths from locating point pheromone sources. Pheromone dispensers also appeared to result in an approximately 75 % reduction in beet armyworm larvae relative to untreated fields.

A large block experiment was conducted at the Yuma Ag Center to compare the field performance of three lettuce management programs for control of lepidopterous larvae. Conventional, experimental and biorational insecticides were sprayed to control beet armyworm, cabbage looper and Heliothis species throughout the growing season. Differences in populations of total larvae among the four treatments, relative to insecticide treatments and timing of application were observed throughout the season. In general, the standard and experimental treatments provided the most consistent control of lepidopterous larvae following each application. Harvest data showed that the spray regimes had a significant influence of head lettuce yield or quality. Maturity and quality were significantly reduced in the untreated control. An economic analysis shows that net returns varied widely among the management programs at different market prices. In conclusion, this study provides preliminary data to support the need for more development of experimental and biorational insecticide products as alternatives to conventional management programs in desert lettuce production.

Provado 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.

Studies were conducted in small plot field trials to evaluate the efficacy of several experimental and conventional insecticide chemistries against western flower thrips in head lettuce. Results from two trials using new experimental compounds showed that several insecticides have potential for management of thrips populations. All of the products appear to be good candidates for thrips control and had efficacy against adults and nymphs. Success and Fipronil consistently provided comparable control to the standard Lannate/Ammo. In the trial evaluating conventional compounds, Orthene/Mustang and Lannate/Ammo combinations provided the best control of both adult and nymphs. Plant size and temperature may be important factors contributing to the efficacy of these products.

Several new insecticide chemistries were evaluated and compared with standard chemistries for temporal and diagnostic mortality of beet armyworm in lettuce. Field and lab bioassays of small and large armyworm mortality were conducted at pre- thinning thinning postthinning and harvest stages of lettuce. Results from both the field and laboratory indicated similar trends for the temporal activity of the products. The compounds with translaminar activity (Alert, Success, and Proclaim) appear to be have the most rapid "knockdown activity" with 100% mortality consistently occurring by 1-2 DAT. Because of their rapid activity, a large proportion of larvae are found dead on the plants. The products that need to be ingested to cause larval mortality (Larvin, Confirm, Neemix, Crymax, Cryolite, MP 062) generally varied significantly in temporal mortality and in efficacy against larvae. Unlike the translaminar products, a large proportion of larvae on were often found missing from treated plants The results of this study provide basic guidelines concerning the activity and assessment of the performance of these materials in the field PCAs and growers will ultimately be able to develop specific use patterns for these materials within their individual lettuce pest management programs.

Several new insecticide chemistries were evaluated and compared with standard chemistries for temporal and diagnostic mortality of cabbage looper in lettuce. Three field bioassays of small and large larval mortality were conducted at pre-thinning, thinning, and postthinning, stages of lettuce. The compounds with translaminar activity (Alert, Success, and Proclaim) appear to be have the most rapid "knockdown activity" with 100% mortality consistently occurring by 1 -2 DAT. Because of their rapid activity, a large proportion of larvae are found dead on the plants. The products that need to be ingested to cause larval mortality (Larvin Confirm, Neemix, Crymax, Cryolite, MP 062) generally varied significantly in temporal mortality and in efficacy against larvae. Unlike the translaminar products, a large proportion of larvae on were often found missing from treated plants. The results of this study provide basic guidelines concerning the activity and assessment of the performance of these materials in the field PCAs and growers will ultimately be able to develop specific use patterns for these materials within their individual lettuce pest management programs.