Phytophthora blight of peppers (Capsicum annuum), caused by the oomycete pathogen Phytophthora capsici, occurs in most regions where this crop is grown. The root and crown rot phase of the disease develops on plants in areas of the field where soil remains saturated with water after an irrigation or rainfall. Subsequent periods of soil saturation encourage further disease development. Actigard (acibenzolar-S-methyl), is a chemical activator of plant disease resistance, has no known direct antifungal effects and is thought to mimic salicylic acid in the signal transduction pathway that leads to systemic acquired resistance (SAR). Foliar applications of Actigard were evaluated for suppression of root and crown rot on pepper plants growing in the greenhouse in pots and inoculated with Phytophthora capsici or grown in soil naturally infested with the pathogen. Inhibition of stem cankers on pepper cultivars Bell Tower and AZ9 after two to four treatments with Actigard was significantly greater than on plants receiving a single treatment of the chemical. Inhibition of stem canker elongation on Bell Tower or AZ9 peppers ranged from 93.2 to 97.2% and 87.4 to 92.4% when plants were inoculated with P. capsici at 1 or 5 weeks, respectively, after the fourth application of Actigard. Survival of chile pepper plants in field soil naturally infested with P. capsici was significantly increased by three foliar applications of Actigard compared to nontreated plants in all three trials when pots were watered daily and in two of three trials when pots were flooded for 48 hr every 2 weeks. When soil was flooded every 2 weeks, establishing conditions highly favorable for disease development, plants treated once with Ridomil Gold survived significantly longer than those treated with Actigard. On the other hand, when water was provided daily without periodic flooding, establishing conditions less favorable for disease development, there was no significant difference in plant survival between the two chemicals in two of three trials. Growth of shoots on chile pepper plants treated with Actigard, watered daily and grown in soil containing P. capsici generally was greater than nontreated plants. Pepper plants subjected to periodic saturated soil conditions and receiving three foliar applications of Actigard plus a soil treatment of Ridomil Gold survived significantly longer and produced a greater amount of shoot growth than plants treated with either chemical alone. This work suggests that Actigard could be an important management tool for Phytophthora root and crown rot on pepper plants.

Incidence of Charcoal rot, caused by the soil borne fungus Macrophomina phaseolina, may be increased in some crops by the addition of stress on the host caused by high salinity of soil or irrigation water and infection by plant pathogenic nematodes. Since both of these factors may be problematic in melon production in Arizona, studies were initiated to determine if higher salt concentrations of irrigation water and infection by Root-knot nematode (Meloidogyne incognita) may be involved in recent increased incidences of Charcoal rot of melon. In greenhouse trials, higher concentrations of salts in irrigation water significantly increased the percentage of plants that died due to Charcoal rot. However, no significant difference was found in the percentage of dead plants inoculated with both root-knot nematode and M. phaseolina compared to plants inoculated with M. phaseolina alone. Results of these trials indicate that salinity may be a factor in the increased incidence of Charcoal rot of melon, but that root-knot nematode infection may not play a role.

Messenger is based on naturally occurring proteins called harpins that trigger natural plant defense systems to protect against disease and pest damage as well as activating plant growth pathways for potential improvements in crop yield and quality. An experiment was established in a commercial chile pepper field in Cochise County to evaluate the effect of Messenger on chile pepper production and bacterial spot. Bacterial spot of pepper occurs wherever this crop is exposed to moisture due to rainfall or overhead irrigation. Foliar application of Messenger, Kocide 2000 + Maneb 75DF (a standard bacterial spot treatment) or Messenger + Kocide + Maneb was performed June 5, 19 and 28; July 16; and August 8 and 22. A foliar defoliation (bacterial spot) rating was performed September 5 and yield (weight and number of chile peppers) was determined September 20 and 21. Compared to nontreated plants, the mean weight of chile peppers harvested from plants treated with Messenger, Kocide + Maneb and Messenger + Kocide + Maneb increased 11, 15 and 24%, respectively, whereas the number of peppers increased 14, 15 and 21%, respectively. The severity of bacterial spot symptoms was numerically (but not significantly) lower on plants treated with Messenger, Kocide + Maneb and Messenger + Kocide + Maneb compared to nontreated plants.

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 2002. Powdery mildew appeared in our plots by February 15 and reached moderate levels of severity by plant maturity on March 6 to 8th. Nontreated lettuce plants were moderately infected with powdery mildew at plant maturity, whereas the level of disease was low to virtually nonexistent in plots treated with Microthiol Disperss, Rally, Quinoxyfen, Flint, and Rally alternated with Kaligreen. Furthermore, other tested products provided moderate suppression of powdery mildew. The future availability of one or more of the tested chemistries not currently registered for lettuce could help in efforts to control powdery mildew on this crop and to establish and maintain a fungicide resistance management program for plant disease control products.

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 2001-2002. Sclerotia of each pathogen were applied to plots after thinning and just before the first of two applications of test compounds. Significant reduction of Sclerotinia leaf drop caused by S. minor occurred in plots treated with Endura, whereas other products tested against this pathogen did not significantly reduce the level of disease compared to nontreated control plants. The highest level of disease reduction in plots infested by S. sclerotiorum was achieved by the fungicide Ronilan as well as the biological material Contans. Somewhat lower but still significant disease control was achieved with Endura on plots infested with S. sclerotiorum. In this field trial, Endura provided the best level of disease control in plots infested with S. minor, whereas Contans provided the best level of disease control in plots infested with S. sclerotiorum.