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.

Dodder has been a difficult to control weed in this area for a long time but it seems to be getting worse in recent years. It is listed as one of the 10 most problematic weeds in the U.S. by the Department of Agriculture. There are more than 150 species of dodder. Fifteen of these can be found in Arizona, 3 are common and one, field dodder (Cuscuta campestris), is a problem in the lower Colorado River region. It can be a problem on almost any broadleaf crop grown here during the summer months but is generally not a problem in grasses Dodder is one of the most unusual weeds we have to deal with. It is a parasitic annual that has no leaves or roots after it is attached to a host. It obtains all of its energy from the plants it attaches to. Dodder germinates near the soil surface and lives off of food reserves in the seed. It must attach to a host within 5 to 10 days or it will die. After it has found a suitable host, it produces adventitious roots called haustoria that grow into the vascular system of the host plant. After it is attached, the lower portion of the dodder seedling dies and all contact with the soil ends. Dodder seed is small, about 1/16 inch in diameter, and germinates in the spring or summer once the soil temperature reaches about 60 degrees. Each plant can produce several thousand seeds. The seed is hard and less than a third of it will often germinate during the first season The remainder can remain dormant but viable for 20 years or more. The seed is small and light enough to float in water and blow in the wind. Most of the movement is probably from contaminated crops, seed and equipment. Controlling this weed starts by reducing seed movement into an area. Most states and countries have laws that prohibit the import of dodder seed. Only certified seed should be planted. A major cause for the spread of dodder in Arizona has been in non- certified alfalfa seed. Once it is present in a field, annual crops that are poor hosts can reduce the spread of this weed. Poor host crops include grasses, grains, and other monocots. Broadleaf weeds can serve as hosts and should be eliminated. Preemergent herbicides can be effective in keeping this weed from becoming established. Postemergence herbicides need to at least temporarily destroy the host. Perennial crops, like alfalfa, can be temporarily burned to the ground with contact herbicides like Gramoxone, Chateau or Scythe plus an adjuvant. Dodder can be selectively killed with glyphosate in Roundup Ready Alfalfa. The most effective control is with preemergent herbicides. These include trifluralin, pendimethalin, benefin, Dacthal and others. When the level of these herbicides has dropped to sub-lethal amounts, dodder seed will germinate and survive. Repeated applications are normally required. 

The last Vegetable IPM Update contained a chart listing “Herbicides for Ditch Bank Weed Control”. A recent registration was mistakenly left out. This is Venue(Pyraflufen). It is labeled by Nichino and is the same active ingredient as ET. It is a contact, non-selective herbicide that can be used on ditch banks and dry ditches. 

Summer Insect Trapping Network   
 

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 14, July 10, 2024
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased to seasonal lows comparable to previous years.
 
Beet armyworm:         
BAW moth counts decreased to seasonal lows comparable to previous years.
 
Cabbage looper:          
Cabbage looper numbers are low consistent with previous years and higher temperatures.
 
Diamondback moth:       
DBM moths were not caught in any trap; average for this time of the year.
 
Whitefly:                      
Adult movement continues to increase consistent with melons harvests and field disking.
 
Thrips:                          
Thrips adult activity declined significantly, comparable to previous summers.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                   
Adult activity slightly above average for early July.