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.

Herbicides that have residual soil activity are very useful in the low deserts, where weed seeds continue to germinate with each irrigation year-round. These herbicides can also be hazardous, however, when sensitive crops are planted into soil where they are still active. Determining the potential for crop injury from herbicides used on previous crops can be difficult. Injury potential is related to several interrelated factors such as soil type, irrigation practices, tillage, environmental conditions, organic matter and other conditions. Injury can vary from field to field, year to year and even be variable within the same field. Rotational crop restrictions on product labels must often cover many diverse conditions and geographic regions and are frequently much longer than needed. This link  

will give you a chart that contains the labeled and likely rotational crop interval for the major crops and herbicides used in the deserts as well as the usual soil persistence for each product.

Tests can be conducted prior to planting to evaluate the potential for crop injury. Many times soil samples are taken and sent to a lab for analysis, These tests are usually done using a High Performance Liquid Chromatograph (HPLC) or a Gas Chromatoaph (GC) and can be costly, time-consuming and difficult to interpret. A simpler and more direct test can be done by using a bioassay or growing sensitive plants in pots containing soil from the questionable field. This technique is less expensive, requires little equipment and can be done by anyone. Bioassays are often conducted by growing species of plants that are known to be sensitive to a specific herbicide or class of herbicides. It is reasonable, however, to use the crop that is to be planted. If, for instance, lettuce will be grown, the seed used in the bioassay should be from the variety and lot number that will be used. Bioassays can be more accurate than more sophisticated lab tests in predicting potential crop injury. These tests are only good, however, if the soil sample collected is representative of what is in the field. Sample collection is very important and small amounts should be taken from several areas of the field. Herbicide concentration often varies within fields and separate samples should be collected and labeled to indicate in which part of the field they came from. Samples are normally taken from the top 2-4 inches from the surface. Soil must also be collected from similar soil types in the same vicinity that have not been treated for comparison.

We hope to start a pilot bioassay program this season to help growers evaluate potential herbicide injury using the new greenhouses at the Valley Agriculture Center. We would like to determine if such a program is needed and would be effective in identifying potential injury problems. If you have fields that you would like to have bioassayed for potential herbicide injury please contact either Barry Tickes (928-580-9902) or Marco Pena (928-782-5871) for guidelines on how to collect and drop off soil samples.

Area wide Insect Trapping Network   VegIPM Update, Vol. 12, No. 13, Jun 30,  2021
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased significantly over the past 2 weeks consistent with last summer’s trend.
 
Beet armyworm:         
Trap counts down after peaking two weeks ago.
 
Cabbage looper:          
Cabbage looper numbers remain low consistent with the lack of activity this summer compared to last season.
 
Whitefly:                      
Adult movement increased significantly, particularly in Bard and Wellton consistent with melon harvest and destruction of plant residue.
 
Thrips:                         
Thrips adult movement declining in most areas; thrips activity significantly higher in Tacna.
 
Aphids:                        
Aphid movement has been absent for the past 6 weeks similar to what we typically observe in the summer. 
 
Leafminers:                  
Adult activity has highest in Dome Valley and Tacna, consistent with melon harvests and land prep.
 
Diamondback moth:   
DBM counts very low and continue to decline. Adults only captured in areas where seed crops were grown.