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 JV farms at Gila Valley. Lettuce variety ‘Guapo’ was seeded, then sprinkler-irrigated to germinate seed on September 19, 2023, on double rows 12 in. apart on beds with 42 in. between bed centers. Rest of the irrigation 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 on October 9, 2023 at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied by incorporating in soil before seeding or with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.
Month
Max
Min
Avg
Rain
September
100
71
86
0.71 in
October
93
61
77
0.00 in
November
80
51
65
0.08 in
December
71
44
57
0.82 in
Fusarium wilt (caused by Fusarium oxysporum f. sp. lactucae ) rating was done in the field by observing the typical symptom of lettuce wilt. Confirmation was done by cutting the cross section of roots. Disease scoring/rating was done on December 6, 2023.
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. The disease pressure was extremely high in 2023, and most treatments showed little or no control against the disease. The treatments that showed some activity were Bexfond, Cevya, Rhyme, and Serifel. Plant vigor was normal and phytotoxicity symptoms were not observed in any treatments in this trial.
Controlling Disease and Weeds with Band-Steam – Yuma Trials Show Good Promise
In previous articles (Vol. 11 (13), Vol. 11 (20), Vol. 11(24)), I’ve discussed using band-steam to control plant diseases and weeds. Band-steaming is where steam is used to heat narrow strips of soil to temperature levels sufficient to kill soilborne pathogens and weed seed (>140 °F for > 20 minutes). The concept is showing good promise. This past season, three trials were conducted examining the efficacy of using steam for disease and weed control in Yuma, AZ. In the studies, steam was applied in a 4-inch-wide by 2-inch-deep band of soil centered on the seedline using a prototype band-steam applicator (Fig.1). The band-steam applicator is principally comprised of a 35 BHP steam generator mounted on top of an elongated bed shaper. The apparatus applies steam via shank injection and from cone shaped ports on top of the bed shaper.
Trial results were very encouraging as the prototype applicator was able to raise soil temperatures to target levels (140°F for >20 minutes) at viable travels speeds of 0.75 mph. Steam provided better than 80% weed control and significantly lowered hand weeding time by more than 2 hours per acre (Table 1). Results also showed that Fusarium colony forming units (CFU) were reduced from 2,600 in the control to 155 in the 0.75 mph and 53 in the 0.5 mph treatments, respectively (a more than 15-fold reduction). A significant difference in Fusarium wilt of lettuce disease incidence was not found, however disease infection at the field site was low (< 2%) and differences were not expected. At 0.5 mph, fuel costs were calculated to be $238/acre which was considered reasonable and consistent with the values reported by Fennimore et al. (2014).
An unexpected finding was that plants in steam treated plots appeared to be healthier and more vigorous than untreated plots (Fig. 2). This trial is still in progress and it will be interesting to see if this improved early growth translates into increases in crop yield.
In summary, early trial results are showing good promise for use of band-steam as a non-herbicidal method of pest control. We plan on conducting further trials in this multi-year study. If you are interested in evaluating the device on your farm and being part of the study please contact me. We are particularly interested in fields with a known history of Fusarium wilt of lettuce and/or Sclerotinia lettuce drop that will be planted to iceberg or romaine lettuce.
As always, if you are interested in seeing the machine operate or would like more information, please feel free to contact me.
Acknowledgements
This work is supported by Crop Protection and Pest Management grant no. 2017-70006-27273/project accession no. 1014065 from the USDA National Institute of Food and Agriculture, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council. We greatly appreciate their support. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
A special thank you is extended to Mellon Farms for allowing us to conduct this research on their farm.
References
Fennimore, S.A., Martin, F.N., Miller, T.C., Broome, J.C., Dorn, N. and Greene, I. 2014. Evaluation of a mobile steam applicator for soil disinfestation in California strawberry. HortScience 49(12):1542-1549.
Click link below or picture to see the band-steam and co-product applicator in action!
Carryover of Vegetable Herbicides to Wheat Grown in Rotation
Almost all the herbicides used on lettuce, cole crops and melons have restrictions on how soon wheat can be planted in rotation after they have been used. Experience has demonstrated, however, that safe intervals can vary considerably based upon many factors and are almost always much longer than they need to be. The most important factors are rate applied, irrigation practices and tillage. For example, when Kerb used to be banded at 2 to 4 lbs. per acre after planting and incorporated with furrow irrigation, it was common to see treated strips across wheat fields which followed. This is uncommon now that lower rates are Chemigated. We still see some Balan injury at ends of fields or in overlaps especially when sudan is planted. Wheat it not very sensitive to Prefar and carryover injury is uncommon.
Corn earworm:
CEW moth counts are down areawide and average for this time of year.
Beet armyworm:
Trap counts decreased in most locations; about average compared to previous years.
Cabbage looper:
Cabbage looper counts increased in most traps and about average for this time of season.
Diamondback moth:
DBM moths continue to increase in all areas. Below average for this time of the year.
Whitefly:
Adult movement negligible, typical for early January.
Thrips:
Thrips adult counts beginning to decreased in the past 2 weeks, likely in response to rainfall in late December. Currently, numbers are about average compared with previous years.
Aphids:
Aphid movement increased significantly in the past two weeks, particularly in North Yuma and Gila Valleys. Well above average for early January.
Leafminers:
Adults decreased in most locations, but above average for January.
