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%). Lettuce was seeded, then sprinkler-irrigated to germinate seed on Nov 28, 2023 on double rows 12 in. apart on beds with 42 in. 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, which contained two 25 ft rows of lettuce. Plants were thinned Jan 4, 2024  at the 3-4 leaf stage to a 12-inch spacing. 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.

Month	MaxTemp(°F)	Min Temp (°F)	Average Temp (°F)	Rainfall
November	80	51	65	0.08 in
December	71	44	57	0.82 in
January	68	42	54	1.14 in
February	73	47	59	0.50 in

 
Downy mildew (caused by Bremia lactucae) rating was done on variety Eblin, Bobcat, and 180 (partially funded by AILRC grant). Disease was first seen on 1-30-24. Please see attached excel file for chemicals application date. Disease rating was done on February 29^, 2024. Disease severity was determined  by rating 10 plants within each of the five replicate plots per treatment using the following rating system: 0 = no downy mildew present; 0.5 = one to a few very small downy mildew colonies on bottom leaves; 1 = downy mildew present on bottom leaves of plant; 2 = downy mildew present on bottom leaves and lower wrapper leaves; 3 = downy mildew present on bottom leaves and all wrapper leaves; 4 = downy mildew present on bottom leaves, wrapper leaves, and cap leaf; 5 = downy mildew present on entire plant.
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most of the treatments exhibited activity against the disease to some extent. Latitude, Amara, Eject, Previcure flex exhibited good control in the variety Eblin (highly susceptible variety). Whereas Cevya, Stargus, Latitude, Amara, Revus, Thrive 4 M, Actigard, Instigo+Carbose+intereact showed activity against the pathogen in variety Bobcat. Please see excel file for the full list of chemicals and their efficacy. The lettuce variety 180 was resistant to the disease and no downy mildew was observed on the particular variety. No phytotoxicity was observed in this field.

Any long term weed management strategy has to focus on reducing the reservoir of weed seed in the soil. This can be very difficult because of characteristics that weed seeds possess that allow them to survive. These include seed numbers, seed dormancy, longevity, ability to disperse and rapid establishment.  Seed Numbers: one of the most important characteristics that allows weeds to survive is their sheer numbers. Most are extremely prolific. The number of seeds produced per plant and by species is extremely variable. Representative examples are: canary grass produces 10,000 to 30,000 seeds per plant, sowthistle - 15,000 to 20,000, purslane - 50,000 to 75,000, goosefoot - 70,000 to 100,000 and pigweed - 115,000 to 200,000 per plant. When weeds are allowed to produce mature seeds, they are deposited back into the soil and build up year after year.  Longevity: If all weed seeds germinated at the same time they would be much easier to control. They don’t. Some germinate today, some next week, on and on for up to 40 years for some species. Some of the characteristics that facilitate this are physical, like hard seed coating and some are biochemical. Ability to Disperse: Many weed seeds have characteristics that allow them to fly, float and attach. Sandbur, burclover, puncturevine and others are notorious for their ability to attach to just about anything. Cocklebur was the inspiration for the development of Velcro. Some weed seeds fly with structures that resemble parachutes (sowthistle, groundsel and other composites), gliders(some clovers and trees such as ash, maple and box elder). Other species have structures that allow them to float on water. Curley dock for instance, has a bladder that helps it stay afloat in irrigation and drainage water.  Rapid Establishment: Many weed seeds germinate rapidly before, during or after the crop seed has germinated. Rapid establishment allows some species to be well established before the crop emerges.

Area wide Insect Trapping Network   VegIPM Update, Vol. 12, No. 18, Sep 8, 2021.
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts increased in the past two weeks particularly in Wellton and Roll.  
 
Beet armyworm:         
Trap counts beginning to increase in most locations especially in dome Valley and the south Yuma Valley.
 
Cabbage looper:          
Cabbage looper increased in all locations particularly in Wellton, Dome and N. Yuma Valleys consistent with reports of eggs in the in the field.
 
Whitefly:                      
Adult movement increasing in all locations and particularly in Dome/Wellton; about average for this time of year. 
 
Thrips:                         
Thrips adult movement remains about average for early September.
 
Aphids:                         
Aphid movement has been absent since early June typical with high summer temperatures, and the monsoon flow.  
 
Leafminers:                  
Adult activity remains similarly low, above average for this time of season.
 
Diamondback moth:   
First record of DBM adults since early June. Are appearing sooner than last season, likely from high altitude winds associated with Tropical Storm Nora experienced last week.