With the desert produce season almost completed and the spring melon season beginning, now is a good time to review the insecticide chemistries commonly used in your insect management programs. This is an important consideration as you make the transition from winter produce to alfalfa, spring melons and summer cotton where many of the same insecticide products are available in all these commodities. Sustaining long-term insecticide efficacy that provides cost-effective crop protection requires a conscious effort on the part of PCAs and growers to use insecticides responsibly. Over the past 30 years, Agrochemical Manufacturers have developed and brought to market over 20 new classes of chemistry that are highly effective, selective, and significantly safer than their chemical predecessors. These include the neonicotinoids, spinosyns, tetramic acid derivatives and anthranilic diamides to name a few. Most recently, we have seen new feeding disruptor products, PQZ (pyrifluquinazon) and Versys/Sefina (afidopyropen) being applied to fall melons for virus management and in winter vegetables for aphid management. Although, the development of new insecticide chemistries has been a bit slow over the past few years, we’re now seeing industry beginning to develop several new experimental insecticides for desert crops. You’ll be pleased to know that several compounds are being targeted for western flower thrips. Of course, at best many of these products are a few years away from registration. But this is great news as many of the older products are slowly being phased out of the marketplace. It was just a couple of years ago that flubendiamide (Belt, Vetica) was removed from the market, chlorpyrifos (Lorsban) is now gone, and EPA is currently proposing label changes to the neonicotinoids which could impact their use on many important crops. Thus, it is imperative to sustain the efficacy of the newer insecticide tools currently available and Insecticide Resistance Management (IRM) is now more important than ever. The most fundamental approach to IRM is to minimize the selection of resistance by a pest to any one type of insecticide chemistry. The key to sustaining insecticide susceptibility is to avoid exposure of successive generations of an insect pest population to the same MOA. Historically, alternating, or rotating compounds with different modes of action (MOA) each time you spray has provided sustainable and effective IRM in our desert cropping systems. When it is comes to IRM; “rotation, rotation, rotation”. In other words, never expose a generation of insects to the same MOA more than twice. 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 information we have produced a brief publication which provides the latest local information on the modes of actions, routes of activity and pest spectrum for important insecticide chemistries used in desert produce and melon crops - see the attached Insecticide Modes of Action on Desert Produce Crops. This classification list will provide you with an additional set of guidelines for the selection of insecticides that can be used in desert IPM programs.
With the end of lettuce season, it does feel like a relief from the recent INSV (Imaptiens necrotic spot virus) breakout we had. However, we have to keep in mind that INSV has a very wide host range. It is a common virus in ornamentals. Below is just a small list of ornamental plants that could be a host of INSV. If you have these plants and see any concerning symptoms, please bring them to the plant clinic to test for INSV.
INSV is the first virus to be recorded from a fern (the glasshouse ornamental Asplenium nidus-avis).
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.
Managing Water with Preemergence Herbicides in Lettuce
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.
