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.

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%). Spinach ‘Revere’ was seeded, then sprinkler-irrigated to germinate seed Jan 18, 2024 on beds with 84 in. between bed centers and containing 30 lines of seed per bed.  All irrigation water was supplied by sprinkler irrigation.  Treatments were replicated four times in a randomized complete block design.  Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed.  Treatments were applied with a CO₂backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles. 
 

Month	Max	Min	Average	Rainfall
January	68	42	54	1.14 in
February	73	47	59	0.50 in
March	77	50	63	0.31 in

 
Downy mildew (caused by Peronospora farinosa f. sp. spinaciae) was first observed in plots on Feb 19  and final reading was taken on February 26, 2024. Spray date for each treatments are listed in excel file with the results.   Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft² areas within each of the four replicate plots per treatment.  The number of spinach leaves in a 1-ft² area of bed was approximately 144. 

The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Products that  provided effective control against the disease include Orondis ultra, Thrive 4 M, Fungout, Cevya, Eject and Zampro. No phytotoxicity was observed in any of the treatments in this trial.

Herbicides that have residual soil activity are very useful in the low deserts, where weed seeds continue to germinate with each irrigation year-round. These herbicides can also be hazardous, however, when sensitive crops are planted into soil where they are still active. Determining the potential for crop injury from herbicides used on previous crops can be difficult. Injury potential is related to several interrelated factors such as soil type, irrigation practices, tillage, environmental conditions, organic matter and other conditions. Injury can vary from field to field, year to year and even be variable within the same field. Rotational crop restrictions on product labels must often cover many diverse conditions and geographic regions and are frequently much longer than needed. This link will give you a chart that contains the labeled and likely rotational crop interval for the major crops and herbicides used in the deserts as well as the usual soil persistence for each product. 

Tests can be conducted prior to planting to evaluate the potential for crop injury. Many times soil samples are taken and sent to a lab for analysis, These tests are usually done using a High Performance Liquid Chromatograph (HPLC) or a Gas Chromatograph (GC) and can be costly, time-consuming and difficult to interpret. A simpler and more direct test can be done by using a bioassay or growing sensitive plants in pots containing soil from the questionable field. This technique is less expensive, requires little equipment and can be done by anyone. Bioassays are often conducted by growing species of plants that are known to be sensitive to a specific herbicide or class of herbicides. It is reasonable, however, to use the crop that is to be planted. If, for instance, lettuce will be grown, the seed used in the bioassay should be from the variety and lot number that will be used. Bioassays can be more accurate than more sophisticated lab tests in predicting potential crop injury. These tests are only good, however, if the soil sample collected is representative of what is in the field. Sample collection is very important and small amounts should be taken from several areas of the field. Herbicide concentration often varies within fields and separate samples should be collected and labeled to indicate in which part of the field they came from. Samples are normally taken from the top 2-4 inches from the surface. Soil must also be collected from similar soil types in the same vicinity that have not been treated for comparison. 

We hope to start a pilot bioassay program this season to help growers evaluate potential herbicide injury using the new greenhouses at the Valley Agriculture Center. We would like to determine if such a program is needed and would be effective in identifying potential injury problems. If you have fields that you would like to have bioassayed for potential herbicide injury please contact either Barry Tickes (928-580-9902) or Marco Pena (928-782-5871) for guidelines on how to collect and drop off soil samples.

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 19, Sep 18,2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:           
CEW moth counts low in most traps; below average for this early produce season. 
 
Beet armyworm:         
Trap counts high in Tacna and Wellton, and about average for early September
 
Cabbage looper:           
Cabbage looper trap counts low in all locations, typical for early September.
 
Diamondback moth:    
Adult activity not picked up in traps yet.  Overall, typical of early September with minimal Monsson activity.
 
Whitefly:                      
Adult movement most active in Dome Valley and S. Yuma Valley; overall below average for early September
 
Thrips:                          
hrips adult movement beginning to increase in Tacna and dome; overall activity typical for early September. 
 
Aphids:                         
Aphid movement absent so far; anticipate activity to pick up when winds beginning blowing from N-NW. 
 
Leafminers:                 
Adult activity light in all areas, about average for this time of season.