Biological insecticides or “Biopesticides” are becoming more important in desert produce production, particularly for insect management in organic leafy vegetables. The EPA define biopesticides as certain types of pesticides derived from natural materials such as animals, plants, bacteria and certain minerals. Currently, organic growers rely heavily on a select few chemical biopesticides, and to a lesser extent, non-chemical tactics to control insect pests in organic leafy vegetables. Recent statistics from the UA-AMPC 1080 Pesticide Use Database show that the biopesticides used in desert produce for insect control are primarily microbial insecticides that consist of a microorganism (e.g., bacteria and fungi) as the active ingredient, or botanical insecticides where the active ingredient is derived from plants. Based on conversations with growers and PCAs, some of these biopesticides are often marginally effective and require intensive usage to meet produce quality standards. Furthermore, among the numerous pests PCAs encounter, aphids, bagrada bugs and flea beetles are very difficult to control with currently available biopesticides. Other major pests such as beet armyworm and western flower thrips can be effectively controlled with microbial insecticides (e.g., spinosad, Bt), but additional alternatives to be used in rotational programs for resistance management are lacking. Although numerous organically-allowed (USDA and OMRI approved) biopesticides are registered for insect control in Arizona, there is much uncertainty among growers and PCAs whether the products will actually control insects as advertised. Given the demands for high-quality organic vegetables from Arizona, applied research providing information on biopesticide efficacy is needed. Thus in 2016, a project was initiated to develop a research knowledge base for biopesticides specifically for Arizona’s unique desert growing conditions, leafy vegetable crops and pest spectrum. The overall goal of this project was to enhance pest management programs for the organic industry by developing new educational information on biopesticides for controlling insect in organically-certified leafy vegetable crops in Arizona. Results from numerous efficacy trials with biopesticides conducted on leaf vegetables grown in the desert southwest can be found in the following report Biopesticide Efficacy in Desert Produce Crops. An additional goal was to develop a Relative Efficacy Index (REI) for biopesticides based on these efficacy trials that provide growers and PCAs with information on the relative efficacy of organic active ingredients used against the key insect pests. This index can be found in the following: Relative Efficacy Index (REI) for Biopesticides on Desert Produce.
This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Lettuce was seeded, then sprinkler-irrigated to germinate seed on Nov 28, 2023 on double rows 12 in. apart on beds with 42 in. between bed centers. All other water was supplied by furrow irrigation or rainfall. Treatments were replicated five times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed, which contained two 25 ft rows of lettuce. Plants were thinned Jan 4, 2024 at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.
Month
MaxTemp(°F)
Min Temp (°F)
Average Temp (°F)
Rainfall
November
80
51
65
0.08 in
December
71
44
57
0.82 in
January
68
42
54
1.14 in
February
73
47
59
0.50 in
Downy mildew (caused by Bremia lactucae) rating was done on variety Eblin, Bobcat, and 180 (partially funded by AILRC grant). Disease was first seen on 1-30-24. Please see attached excel file for chemicals application date. Disease rating was done on February 29, 2024. Disease severity was determined by rating 10 plants within each of the five replicate plots per treatment using the following rating system: 0 = no downy mildew present; 0.5 = one to a few very small downy mildew colonies on bottom leaves; 1 = downy mildew present on bottom leaves of plant; 2 = downy mildew present on bottom leaves and lower wrapper leaves; 3 = downy mildew present on bottom leaves and all wrapper leaves; 4 = downy mildew present on bottom leaves, wrapper leaves, and cap leaf; 5 = downy mildew present on entire plant.
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most of the treatments exhibited activity against the disease to some extent. Latitude, Amara, Eject, Previcure flex exhibited good control in the variety Eblin (highly susceptible variety). Whereas Cevya, Stargus, Latitude, Amara, Revus, Thrive 4 M, Actigard, Instigo+Carbose+intereact showed activity against the pathogen in variety Bobcat. Please see excel file for the full list of chemicals and their efficacy. The lettuce variety 180 was resistant to the disease and no downy mildew was observed on the particular variety. No phytotoxicity was observed in this field.
Controlling Fusarium Wilt of Lettuce Using Steam Heat – Trial Initiated
Earlier this week, we initiated a trial examining the use of band steam for controlling Fusarium wilt of lettuce. The premise behind this research is to use steam heat to raise soil temperatures to levels sufficient to kill soilborne pathogens. For Fusarium oxysporum f. sp. lactucae, the pathogen which causes Fusarium wilt of lettuce, the required temperature for control is generally taken to be > 140°F for 20 minutes. Soil solarization, where clear plastic is placed over the crop bed during the summer, exploits this concept. The technique raises soil surface temperatures to 150-155˚F, effectively killing the pathogen and reducing disease incidence by 45-98% (Matheron and Porchas, 2010).
In our trials, we are using steam heat to raise soil temperatures. Steam is delivered by a 35 BHP steam generator mounted on a custom designed elongated bed shaper (Fig. 1). Preliminary results were encouraging. The device was able to increase the temperature of the top 3” of soil to over 180°F at a travel speed of 0.5 mph as shown in this video of the machine in action (shown below). These temperatures exceed that of those known to control pathogens responsible for causing Fusarium wilt of lettuce (> 140°F for 20 minutes).
Stay tuned for final trial results and reports on the efficacy of using steam heat to control Fusarium wilt of lettuce.
If you are interested in evaluating the technique on your farm, please contact me. We are seeking additional sites with a known history of Fusarium wilt of lettuce disease incidence to test the efficacy and performance of the device.
References
Matheron, M. E., & Porchas, M. 2010. Evaluation of soil solarization and flooding as management tools for Fusarium wilt of lettuce. Plant Dis. 94:1323-1328.
Acknowledgements
This project is sponsored by USDA-NIFA, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council. We greatly appreciate their support.
A special thank you is extended to Cory Mellon and Mellon Farms for allowing us to conduct this research on their farm.
Weeds are one of the most visible of all agricultural pests. They can’t move or hide and once established often stick up over the crop. Just one weed in a 10 acre field is annoying to look at. With insects and diseases, the damage is often more visible than the pest. That is not the case with weeds. A moderate weed infestation is approximately 10 weeds per square foot. If a herbicide produces 90% control, that leaves 1 weed per square foot or 43 weeds per acre. Without an untreated check, this can look like the herbicide failed! It is easy to leave an untreated spot in a field and it is well worth doing. Many applicators do so unintentionally because of skips, powerlines and other causes. They help determine crop injury and weed control. Here are some examples of what various levels of control looked like from one of our cole crop trials:
Area wide Insect Trapping Network VegIPM Update, Vol. 11, No. 21, October 14, 2020
Results of pheromone and sticky trap catches can be viewedhere.
Corn earworm: Moth activity is above normal for early October ad has been steadily increasing since mid-September, particularly in Dome Valley and south Yuma Valley.
Beet armyworm: Moths remain active throughout the desert, especially in Texas Hill and Dome Valley growing areas.
Cabbage looper: Cabbage looper activity remains unusually low for early October, likely a result of unusually hot weather. Larvae just starting to show up in some fields.
Whitefly: Adult movement has been about average for this time of year. Activity highest in Wellton and Roll near fall melons.
Thrips: To date, thrips activity has been seasonably low at all trap locations; most activity found in Bard. Numbers beginning to slowly trend upward
Aphids: Aphids have been caught in only one trap thus far (Bard). Normal for this time of year. Still early, anticipate they will begin to show up in heavier numbers in mid-late October.
Leafminers: Adult activity below normal for September, but moderate numbers caught in Wellton and south Gila Valley in areas where cotton was recently harvested and disked under.
