With the produce season finally over and the spring melon in full swing, now is an important time to review the insecticide chemistries that you may have used this winter/spring on produce crops and those that you may consider using on melons. Sustaining long-term insecticide efficacy that annually provides cost-effective crop protection requires a conscious effort on the part of PCAs and growers to prevent insecticide resistance. Since the early 1990’s, the Agrochemical Industry has been actively developing and bringing to the vegetable/melon market an unprecedented number of new chemistries that are highly effective, selective and significantly safer than their chemical predecessors. These include the neonicotinoids, spinosyns, tetramic acid derivatives and diamides to name a few. In the last few years, new chemistries have been added including the sulfoxamines (Sequoia, Transform), butenolides (Sivanto) and a METI inhibitor (Torac). The development of new insecticide chemistries has slowed a bit and older chemistries are continually being phased out of the marketplace. It was just last year that flubendiamide (Belt, Vetica) was removed from the market, and EPA is currently assessing risk of neonicotinoids against pollinators which could impact their use on many important crops. Thus, it is imperative to sustain the efficacy of the newer IPM tools currently available. Consequently, insecticide resistance management (IRM) is now more important than ever. The most fundamental approach to IRM is to minimize the selection of resistance to any one type of insecticide chemistry. Historically, alternating or rotating compounds with different modes of action (MOA) has provided sustainable and effective IRM in our desert cropping systems. The Insecticide Resistance Action Committee (IRAC), a coordinated crop protection industry group, was formed to develop guidelines to delay or prevent resistance. Using their most recent IRAC MOA Classification Brochure http://www.irac-online.org/modes-of-action/ we have updated a brief publication which provides Insecticide Modes of Action on Desert Vegetables. This publication also provides general information on the route of activity and pest spectrum for each chemistry. These classification lists will provide you with an additional set of guidelines for the selection of insecticides that can be used in desert IPM programs. 

In response to the recent outbreaks of Diamondback moth (DBM) , Plutella xylostella in Yuma, we have established a pheromone trap network designed to monitor the activity and movement of adult populations of DBM. PCAs have had difficulty controlling DBM in cabbage, broccoli and cauliflower since October. Traps have been placed in Roll, Wellton, Dome Valley, Gila Valley and Yuma Valley in locations where cole crops are presently being grown or in areas where infestations were known to occur this fall.

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%). Variety: Deluxe (HMX2595) was seeded, then sprinkler-irrigated to germinate seed on March 20, 2024on 84 inches 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. 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. 

Spray treatments were done on 05-21-2024, 05-31-2024, 06-07-2024 and 06-14-24. Powdery mildew was first seen on 06-05-24. Please see excel file for additional details.  

Disease severity of powdery mildew (caused by Sphaerotheca fuliginea and S. fusca) severity was determined 6-17-2024 by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 1 = one to two mildew colonies on leaves  ;2 = powdery mildew present on one quarter of leaves; 3 = powdery mildew present on half of the leaves; 4 = powdery mildew present on more than half of leaf surface area ; 5 = powdery mildew present on entire leaf. These ratings were transformed to percentage of leaves infected values before being statistically analyzed.

The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. Quintec, Merivon, Tesaris, Luna Sensation, and V6M-5-14 V gave the best disease control. Phytotoxicity symptoms were not noted for any treatments in this trial.

ANR Webinar 10/17 click link for details.

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:

Results of pheromone and sticky trap catches can be viewed HERE.

Diamondback moth:                

• Adult activity increased in all trapping locations over the past 2 weeks, except in the south Yuma Valley.
• Compared with previous seasons, DBM populations about average for this time of the year.
• DBM captures were highest in Bard, north Yuma Valley and Gila Valley in the past 2 weeks and averaged about 4 moths / trap / night.
• Average moth captures across all traps last week averaged slightly more than 3 moths / trap/ night

Results of pheromone and sticky trap catches can be viewed HERE.

Corn earworm: CEW moth activity increased a bit in the past 2 weeks but remains well below average for late spring.

Beet armyworm: Moth counts increased slightly, but remain very low consistent with seasonal temperatures, and below average for this point in the season.

Cabbage looper: Significant increase in activity in Dome Valley, Gila Valley and Tacna, but moth counts remain unusually low for this time of year, as they have all season.

Whitefly:  No adult movement recorded across all locations and overall low numbers consistent with temperatures.

Thrips: Thrips adult movement beginning to pick up considerably, particularly in Yuma and Dome Valleys. Movement is below average for late March.

Aphids: Seasonal aphid counts down considerably compared with the Feb and Jan.  Counts highest in Bard and Gila Valley.  Below average movement for this time of year. Majority of species found on traps were green peach aphid.

Leafminers: Adult activity up slightly in some locations, but well below average for late season.