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.

Tolerance and resistance are two concepts that are often misunderstood when describing herbicides and weeds.

Weeds inherit characteristics that determine how they will respond to herbicides. When we conduct herbicide trials we often list this response for individual weed species as control, partial control or no control or as a percent control. When there is no control we say that a species is tolerant to that particular herbicide in the area and under the conditions that our tests were conducted. On the other hand, when weeds are controlled, we say they are susceptible to the herbicide. It is when weeds change from sus¬ceptible to tolerant that we say that they have developed resistance to that particular herbicide.

The use of selective herbicides began on a large scale in the U.S. in the late 1950’s and early 1960’s. The first case of weed resistance was documented in 1968 in Washington State and involved the resistance of common groundsel to atrazine and simazine. Over the next 25 years, 110 weed species were reported to be resistant to 15 different classes of herbicides. By 2008, the International Survey of Herbicide Resistant Weeds reported 185 weed spe¬cies resistant to 19 classes of herbicides. Arizona is one of only 4 states in the U.S. in which no cases of herbicide resistance has been reported. The states bordering Arizona have all documented at least one weed species with her¬bicide resistance although in Utah, only kochia, which is not a significant weed in the low desert of Arizona, has been reported as resistant. Twenty-two resistant weed biotypes were documented in California, 3 in Colorado, and 2 in New Mexico. The closest incidence of resistance to the Arizona low deserts has been the resistance of littleseed Canarygrass (phalaris minor) to the ACCase inhibitors, Poast, Fusilade and Select in the Imperial Valley, California. This was first documented in 2001, but has not yet occurred in Arizona.

For more information go to the International Survey of Herbicide Resistant Weeds.

Area wide Insect Trapping Network   VegIPM Update, Vol. 13, No. 14, Jul 13, 2022
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts increased slightly in the past 2 weeks and remains higher than the previous 2 summers.
 
Beet armyworm:         
Trap counts stay active in some locations (Yuma Dome Valley and Tacna) but lower than last summer
 
Cabbage looper:          
Cabbage looper numbers remain low consistent with the lack of activity this fall compared to last season.
 
Diamondback moth:      
DBM moths were not caught in any trap in the past 2 weeks; average for this time of the year.
 
Whitefly:                     
Adult movement continuing to increase, particularly in Gila, Yuma and Dome Valleys consistent with melon harvest.
 
Thrips:                         
Thrips adults decreasing in most locations, and trending comparable to previous years.
 
Aphids:                       
Aphid movement is absent consistent with what we typically see in the summer. 
 
Leafminers:                  
Adult activity has highest in Wellton and Dome Valley, and above average for early July.