Although they are currently effectively controlled by chemicals, sweet potato whiteflies have the potential to once again be a dominant pest in Arizona vegetables. We need to explore alternatives such as biological control so that we are not reliant solely on pesticides. We have been examining dispersal by the whitefly parasitoid Eretmocerus sp. in order to find more effective ways to deploy these agents in the field. We have learned in the laboratory that these wasps are efficient flyers since they are capable of moving into strong winds for more than 30 min. We also now know that most flight takes place within a short distance of the release point. We also have a better understanding of differences between male and female flight. This, along with other information we have obtained, will lead to our ability to effectively release these and parasitoids of other insect pests as well.

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 1999. The final severity of downy mildew in this trial was moderately high. Significant reduction in disease severity compared to nontreated plants was achieved by application of standard compounds such as Aliette, Ridomil Gold+maneb, maneb and Trilogy as well as nonregistered chemistries including Acrobat, Actigard, Curzate, Flint, Quadris, Serenade, Sovran, BAS 500, DPX-KP481 and RH-7281. 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.

In Arizona, Sclerotinia leaf drop of lettuce is caused by two different species of fungi, Sclerotinia minor and S. sclerotiorum. Relatively cool and moist environmental conditions favor this disease. Some new fungicides in development were evaluated for control of leaf drop on lettuce during the winter vegetable growing season of 1998-99. Sclerotia of each pathogen were applied to plots after thinning and just before the first of two applications of test compounds. The final severity of leaf drop in these trials was moderately high. Significant reduction in the final count of dead lettuce plants compared to nontreated plots was usually achieved by application of the standard compounds Ronilan and Rovral as well as an appropriate rate of the experimental compounds Elevate, Medallion or Serenade. Medallion and Elevate provided equivalent disease control to that of the current standard materials with 0.178 and 0.5 lb active ingredient (a.i.) per acre, respectively, compared to the current 1.0 lb a.i. per acre required with the standard compounds. Continued demonstration of efficacy by Serenade may provide the opportunity to utilize a biological control product to reduce the incidence of Sclerotinia leaf drop of lettuce.

No description available.

Pendimethalin (Prowl7) and oxyfluorfen (Goal7) applied preemergence (PREE) caused minimal injury and gave very good weed control (>90%). Goal and sulfentrazone alone applied postemergence (POST) gave very good weed control at 6 WAT. The combination of Prowl followed by Goal or sulfentrazone gave complete control of all weeds. Goal and sulfentrazone applied POST following PREE treatments gave nearly complete weed control with good crop safety. Clomazone (Command7) caused significant crop injury and stand reduction when applied PREE. Metribuzin (Sencor7) applied POST completely reduced the crop stand and gave complete control of all weeds. Metolachlor (Dual7), dimethenamid (Frontier7), Sencor, flumetsulam, and imazamox generally did not provide acceptable control of Chenopodium desiccatum (narrowleaf lambsquarters) and Sonchus oleraceus (sowthistle). Bentazon (Basagran7), acifluorfen (Blazer7), and fomesafen (Reflex7) were not effective against narrowleaf lambsquarters but gave adequate control of the other weeds.

The soil applied herbicides EPTC plus safener (Eradicane7), metolachlor (Dual)7, dimethenamid (Frontier7), pendimethalin (Prowl7), and fluthiamide/metribuzin (Axiom7) applied at planting time all provided very good weed control of pigweeds (Amaranthus spp.), grasses, and puncturevine (Tribulus terrestris). Most of the soil applied followed by POST combination treatments gave very good control (>90%) of lambsquarters (Chenopodium spp.), pigweeds, and groundcherry (Physalis wrightii). POST treatments bentazon (Basagran7), dicamba (Clarity7), and diflufenzopyr plus dicamba (Distinct7) applied alone were not as effective as combinations with soil applied herbicides.

New soil injected and foliar insecticides were evaluated for their efficacy towards potato aphids in green leaf lettuce. The soil injected insecticides, Platinum and V10066, both appear to be viable alternatives to Admire, providing effective aphid control through harvest or ca. 90 days post-planting. Two foliar applications of Acetamiprid or Aphistar timed ca. 14 days apart beginning at the onset of aphid colonization provided superior aphid control over Provado or Fullfill, and control similar to that of the soil injected insecticides.

Proclaim and a normal use rate of 5 oz/ac of Success were highly effective against cabbage looper, Heliothis and beet armyworm. A low rate of 1.5 oz/ac of Success provided sufficient control of Heliothis and beet armyworm, but was weak against cabbage looper. While a low rate of 2.56 oz/ac of Warrior was not especially active against any of the target species. However, when this rate of Warrior was mixed with the low rate of Success, control across all the species was good, and was statistically similar to the higher rate of Success. Although Intrepid appeared slightly more active than its sister compound Confirm, it appears that it too will benefit from the addition of a pyrethroid for control of Heliothis and cabbage loopers on large lettuce plants.

Susceptibility to spinosad (Success®/Tracer®) of beet armyworm (Spodoptera exigua) from the southern U.S.A. and Southeast Asia was determined through exposure of third instar larvae to dipped cotton leaves. LC₅₀ values of field populations ranged from 0.6 to 14 μg spinosad/ml. Field populations were 3.0 to 70-fold less susceptible to spinosad than was a susceptible reference population. The least susceptible population was collected from Thailand. We hypothesized that this population was resistant to spinosad because: (1) it was significantly less susceptible to spinosad than all other populations evaluated and than any other reports in the literature; (2) it regained susceptibility while in culture; (3) it was collected from a region of very intensive insecticide use and severe insect resistance problems; and (4) it exhibited significant survivorship on field-treated cabbage leaves. Piperonyl butoxide (PBO), diethyl maleate (DEM), and S,S,S tributyl-phosphorothiolate (DEF) failed to synergize spinosad in this resistant Thailand population, and PBO failed to do so in the least susceptible domestic population evaluated, the Parker, AZ, field strain. However, the synergist and field residue studies were conducted using a Thailand population that had levels of resistance that declined while in laboratory culture.

During the past 5 years, the efficacy and field performance of several new insecticides for control of Lepidopterous insects on desert lettuce crops has been investigated in small plot trials at the Yuma Agricultural Center and in produce fields with commercial cooperators. The objective has been to determine how these new chemistries will fit into pest management programs in Arizona. Thus, research programs have been focused on studies to define use patterns for these insecticides chemicals that can be integrated into our local management programs in the most cost-effective way possible. This report was created to provide an overview of the new chemistries being developed, their field activity and characteristics, and guidelines for use in head lettuce. In addition, an approach for sustaining the long-term efficacy of these products is discussed.