Historically, our Areawide Pheromone and Sticky Trap monitoring for insects was terminated around the first of April as the produce season ended. Beginning 2 years ago however, we continued our Areawide Trapping Network throughout the summer to collect trapping data from all 16 areawide trap locations year-round.  So why is this additional trapping data useful? For several reasons. First, understanding the activity of some of our key pests when produce is not grown during the summer may give us an indication of what to expect as the fall produce season begins. This may be particularly helpful for predicting moth flights and whitefly flights in August-September coinciding with early transplanting and direct seeded crops.  Another example is keeping track of corn earworm which can unexpectedly show up near the beginning of fall harvests. Secondly, trapping for pests during the summer has shown us that 2 of our more important produce pests are not caught in traps during the summer. We presume this is due to the absence of brassica crops and weeds for diamondback moth, and high daytime/nighttime temperatures lethal to aphids. The fact that trap catches resume in the fall supports our conclusion that these pests are absent in the summer, only to reenter the desert via winds and/or transplants in the fall. And finally, it gives me something to do in the summer.  So, visit the Areawide Summer Trap Network if you’re curious what our key pests are up to. We also continue to monitor thrips activity during the summer. This involves plant sampling using a dislodgement sampling method (beat pan) to determine the relative abundance of thrips adults and larvae on alfalfa, cotton, melons, wheat, Sudan grass, and weeds.  This is being conducted to supplement our yellow sticky trap data that only indicates thrips adult flight movement an area. With this plant sampling we should be able to determine the primary host plants thrips are colonizing in the cropping season during the long hot summer. We are also trying to determine whether these crops allow for the reproduction of thrips. So far, all the crops and weeds we have sampled have shown that thrips will reproduce and complete their life cycle on them. This is important, particularly for weeds, as we are trying to determine whether INSV can be survive the summer in the absence of lettuce. It is also important because it allows us to determine potential exposure of thrips to key insecticides like Radiant and Lannate for resistance management purposes. These crops essentially serve as untreated refugia that likely sustains insecticide susceptibility and is the reason these products are still effective against thrips.  We will be conducting this work throughout the summer, as well as through next produce season. We will periodically provide updates of these thrips monitoring results throughout the summer.  As my dad used to say, “to solve the problem, you must first understand the problem”.

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.

A special local need registration has recently been approved for Prefar in Arizona that raises the use rate in lettuce from 4 to 6 quarts to 5 to 9 quarts. These higher rates will help reduce some of the variability in weed control that is characteristic of Prefar and will also increase the possibility of crop injury. Variable weed control of from 0 to 100% with Prefar can be frustrating and is often caused by three factors:1) weed spectrum, 2) water use and 3) timing. Weed spectrum. Prefar is active on a relatively small spectrum of weeds. These include most grasses, purslane, pigweed, goosefoot and lambsquarters. There are more than 50 weed species that are common in lettuce in this region and Prefar has no activity on most of them. It is normally used in combination with other herbicides to broaden this spectrum. Irrigation method and amount are also important variables that affect the performance of Prefar. Prefar is exactly opposite from Kerb in this regard. Prefar adheres strongly to the soil and it works best when large amounts of water are applied by sprinklers to push it down to where the weeds are germinating. It does not work well when incorporated with furrow irrigation or light amounts of water. Kerb does not adhere strongly to the soil and it works best with furrow irrigation or delayed applications applied just before or after weed germination to avoid leaching it below the germinating weeds. Time of application is another important variable affecting the performance of Prefer. Prefar only works on the roots of developing seedlings. It does not move in the plant and only stops cell division at the tip of the roots that it contacts. It must be in the soil before the weeds germinate. It again differs significantly from Kerb in this regard. Kerb does move in the plant and will still work on small seedlings of many weed species. Early postemergence applications can be effective. Partial weed control can be the result of all of these variables and the higher use rates now registered will help overcome some of this. If weed infestations are heavy, however, even 90% control can look like a complete failure without an untreated check . Lettuce has a good tolerance to Prefar at even higher rates than 9 qts. under ideal growing conditions. When any stress occurs ,this tolerance goes down. Stress can be from anything including environmental factors, pests, water, salts and many other variables. Heat and rain caused many problems earlier this season. Unfortunately, growers have a low tolerance for crop injury. This is a major reason why there are few herbicides registered for use on lettuce and this rate increase can be discontinued if many problems are reported. The SLN can be found by clicking the following link: ld142002

 Area wide Insect Trapping Network   VegIPM Update, Vol. 14, No. 1, Jan 11, 2023
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts are down areawide average for this time of year. 
 
Beet armyworm:         
Trap counts increased in most ll 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. About average for this time of the year.
 
Whitefly:                       
Adult movement light and is typical for this time of year. 
 
Thrips:                          
Thrips adult counts beginning to slowly increase in the past 2 weeks. Currently, below average compared with previous years.
 
Aphids:                        
Aphid movement increased significantly in North Yuma and Gila Valleys consistent with winds and storms. About average for early January.
 
Leafminers:                   
Adult activity up in many locations, and above average for January.