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 JV farms at Gila Valley. Lettuce variety ‘Guapo’ was seeded, then sprinkler-irrigated to germinate seed on September 19, 2023, on double rows 12 in. apart on beds with 42 in. between bed centers.  Rest of the irrigation 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 on October 9, 2023 at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied by incorporating in soil before seeding or with a tractor-mounted boom sprayer that delivered 50 gal/acre at 100 psi to flat-fan nozzles spaced 12 in apart.

Month	Max	Min	Avg	Rain
September	100	71	86	0.71 in
October	93	61	77	0.00 in
November	80	51	65	0.08 in
December	71	44	57	0.82 in

 
Fusarium wilt (caused by Fusarium oxysporum f. sp. lactucae ) rating was done in the field by observing the typical symptom of lettuce wilt. Confirmation was done by cutting the cross section of roots. Disease scoring/rating was done on December 6, 2023. 
 
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. The disease pressure was extremely high in 2023, and most treatments showed little or no control against the disease. The treatments that showed some activity were Bexfond, Cevya, Rhyme, and Serifel. Plant vigor was normal and phytotoxicity symptoms were not observed in any treatments in this trial.

The list of herbicides available for use in melons is very limited. Fortunately, most of the types of melons produced here grow rapidly and nonchemical weed control practices like cultivation and plastic mulch can be effective.

Shallow cultivation and nonselective herbicides with no soil activity can be effective if used after bed formation and before planting. Both contact (Gramoxone, Aim) and systemic (glyphosate) herbicides can be used. Prefar can be applied either before or after planting, but before weeds emerge. Prefar sticks very strongly to the soil and must be incorporated with as much overhead water as possible. It does not work well when drip or furrow irrigation are used.

There are more herbicide options after the crop has emerged and developed three or four leaves. Dacthal and Trifluralin can be used as layby applications before weeds have emerged. Both can cause unacceptable stunting of the crop if applied too early. Prowl is not safe to melons at normal use rates and is not registered. Sandea is registered and can be effective on nutsedge and several broadleaf weeds. It is safe to most melon types after they have four leaves and before blooming. Carryover in the soil is a consideration if sensitive crops are to follow.

The grass herbicides, Select, Select Max, Poast, and generics of these, are registered and effective on most grasses. Poast will not control sprangletop or annual bluegrass, but the highest rates of Select, Select Max, and generics of Clethodim will. Temporary crop injury from Select Max can occur where the sprayer overlaps or slows down at the end of rows. This normally only occurs where a 2x or greater rate is applied.

Area wide Insect Trapping Network   VegIPM Update, Vol. 12, No. 20, Oct 6, 2021.
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts continue to be active, about average for this time of the season; particularly active in Wellton and Yuma Valley.
 
Beet armyworm:         
Trap counts increased slightly in most locations, but well below average for early October. Most activity in Dome and Yuma Valley.
 
Cabbage looper:           
Cabbage looper trap counts remain steady in most areas. Activity about normal compared to previous years. 
 
Whitefly:                       
Adult movement increasing Dome Valley and Wellton, but down in many other locations; movement is below average for this time of year, but should anticipate increase movement with melon harvest beginning. 
 
Thrips:                         
Thrips adult movement increased slightly in some locations, particularly in Wellton and Tacna, but remains below average for mid-September.
 
Aphids:                        
Aphid movement has been absent since early June typical with high summer temperatures, and the monsoon flow.  Picked a up a few aphids last week with the break in weather and change in wind direction. 
 
Leafminers:                  
Adult activity remains low in most location; below average for this time of season.
 
Diamondback moth:    
Significant increase in moth activity in the last week, particularly in Dome Valley and N. Gila Valley in traps located adjacent to cauliflower and cabbage transplants.