The U.S. Environmental Protection Agency (EPA) recently proposed additional mandatory pesticide label restrictions that would prohibit the application of acutely toxic pesticides during the time crops are in bloom and commercial bees have been placed in or near fields for pollination services. If these proposed label changes are implemented they could have important implications for managing key pests on desert crops which require the use of contracted bees for pollination. Specifically, the proposed labelling reads as follows: “Foliar application of this product is prohibited from onset of flowering until flowering is complete when bees are on-site under contract”. This label would apply to pesticides that have an acute contact toxicity value less than 11 micrograms per bee (LD50<11 μg/bee). Unfortunately for desert producers, the list of acutely toxic insecticides includes all of the pyrethroid, organophosphate, carbamate and neonicotinoid insecticide active ingredients currently used for control of major pests. Also included in this list are Exirel, Radiant, Success, Sequoia, Abamectin, Proclaim, Avaunt and Torac. Even insecticides approved for organic production are not exempt, as azadirachtin (e.g., Aza-Direct), pyethrins (e.g., Pyganic), spinosad (Entrust) and rotenone are also on the restricted list. The full description of the proposed label changes, including the list of acutely toxic pesticides (Appendix A) affected and proposed label language (Appendix B), can be found here: EPA’s Proposal to Mitigate Exposure to Bees from Acutely Toxic Pesticide Products In my view, fall melons would be most directly affected by this proposed label change. Economic production of fall melons requires pollination services, but of course also requires adult whitefly control during the bloom/pollination period to suppress the spread of virus (CYSDV). Based on EPAs proposed label restrictions, application of industry standards like Assail, bifenthrin, fenpropathrin, and Exirel would not be allowed anytime, day or night, on fall melons as long as commercial bee hives are present. This could make whitefly/CYSDV control during bloom very difficult. UA research has clearly shown that the remaining alternatives labeled for whitefly control not on EPAs proposed list (i.e., Knack, Vetica, Oberon, Coragen, Fulfill, Beleaf) have little effect on preventing virus infection. Under this scenario, spread of CYSDV in some fields could essentially go unchecked for several weeks. If you are interested in voicing your opinion on this new proposal, EPA is currently accepting public comments until July 29, 2015. For more information on how to submit comments go to: http://www2.epa.gov/pollinator-protection/proposal-protect-bees-acutely-toxic-pesticides and http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2014-0818. 

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.

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.

We are always adjusting how we use herbicides to fit the unique conditions in this area. The herbicides that are registered for use on lettuce here are limited  and they all require a little different management. Environmental conditions, soil characteristics and  Chemical properties all can greatly affect how well the 3 preemergence  herbicides used in lettuce will work. These include Balan, Prefar and Kerb. Environmental conditions and  soil characteristic vary greatly from year to year and field to field. It is difficult to make general recommendations on how best to use these three herbicides because of this. Chemical characteristics do not vary, however, and we can make some generalizations on how they should be used.

We use a lot of water here during stand establishment and at this time of year.  The water solubility of Balan, Prefar and Kerb vary widely and should be considered when deciding how to use them. Water solubility is the amount of the herbicide that will dissolve in water. This is usually given as PPM or mg/liter. The higher the number the more soluble it is. Solubility will effect leaching into the soil and runoff. The solubility of Balan is 0.1 PPM,Prefar is 5.6 PPM and Kerb is 15 PPM. What this means is that Balan is very insoluble and has to be mechanically incorporated. Prefar is 56 times more soluble than Balan and can be incorporated with overhead water but this is still not a very soluble herbicide and a lot of water is needed. Kerb is 150 times more soluble than Balan and almost 3 times more soluble than Prefar. Kerb will leach and the amount of overhead water applied must be carefully managed.

Results of pheromone and sticky trap catches can be viewed here.
 
Beet armyworm:               
CEW moth increased the Tacna/Roll area last week, but areawide below average for mid-September.
 
Beet armyworm:         
Trap counts about the same in all locations, below average for mid-September.
 
Cabbage looper:         
Cabbage looper numbers remained low consistent with mid-September.
 
Diamondback moth:   
DBM moths beginning to appear in traps in Tacna/Dome Valley.
 
Whitefly:                     
Adult movement increased in the past week, consistent with cotton defoliation and harvest. Above average for mid-September. 
 
Thrips:                           
Thrips adults increased in most locations, and trending above average to previous years.
 
Aphids:                        
Aphid movement is absent and consistent with what we typically see during the summer and September. 
 
Leafminers:                   
Adult activity tending downward in most locations, below average for mid- September.