Summer is finally over. Brassica transplants are in the ground, and direct-seeded broccoli and lettuce plantings are now beginning.  In the past week, I’ve observed or received reports from PCAs of key insect pests beginning to show up (or not) on melon and early produce crops in the desert.   
 
Seedling pests:  Flea beetles (FB) are beginning to show up in transplanted crops like they always do, but pressure has been light so far. We haven’t seen much in our experimental plots at YAC either.  Remember, FB adults lay eggs in the soil of their favored local host plants (i.e., alfalfa, cotton, purslane, pigweed and nightshade) where larvae feed on the roots to later emerge as adults. So, keep in mind, the source of that FB infestations hitting your new stands may not just be freshly cut hay, defoliated cotton, or disked weeds. In some areas (Yuma Valley), crickets seem to be very abundant. Crickets like moisture and are often found under sprinkler pipes but can also be found in cracks in soils around fields or in drainage areas. 
 
Bagrada bug:    We’ve already had reports of bagrada bug adults on two transplanted cauliflower fields in Dome Valley. Not sure whether they arrived with the transplants or are moving from surrounding crops. However, it’s still early and they might surprise you as the season progresses.   Look for those fresh feeding signs on cotyledons and young leaves.  Experience suggests that they are most abundant after the humidity breaks.
 
Lepidopterous Larvae (worms):   Worm pressure seems to be below normal. Trap catches so far show that Cabbage looper moths are almost non-existent, and no reports on melons to date. They should pick-up as we approach October. No reports of Beet armyworm larvae on the earliest transplants yet, and areawide pheromone traps suggest that moth activity is below normal. But they will show up sooner or later, so get ready.  You have numerous insecticide alternatives at your disposal to control them.  Have had a couple of reports of Diamondback moth larvae on newly transplanted brassica crops. However, we’ve yet to capture moths on pheromone traps which suggests that adult immigration on high altitude winds associated with storms has not occurred. Remember, DBM disappear each summer and reestablish on desert crops via transplants or migrate in on monsoon/tropical storms. I strongly stress that you check your Cole crops closely this fall, particularly following storms or on plants originating from coastal CA. 
 
Whiteflies:       Area wide sticky trap captures have been about normal for early September, but whiteflies can migrate long distances on high winds. Adult numbers increased on my melon plants last week and remain high. Reports in area melons range from light to moderate numbers so far, but there is still a lot of cotton out there yet to be picked. The good news is there are several insecticide alternatives to control them in produce. 

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.

Arizona is one of only four states in which no cases of herbicide resistance have been confirmed. All of the surrounding states, including the Imperial Valley of CA, have confirmed cases of herbicide resistance, which is a source of growing concern. Weeds inherit characteristics that determine how they will likely respond to herbicides. When a weed species is treated and is not controlled and never has been we say that it is tolerant to that particular herbicide. On the other hand, when a weed species is controlled by a herbicide we say that it is susceptible to that herbicide. It is when weed species change from susceptible to tolerant that we say that they may have developed resistance to that herbicide.

Resistance of Littleseed Canarygrass to some of the ACCase Inhibitor herbicides, including Poast, Select, Fusilade and generics of these, has been confirmed in the Imperial Valley, CA. Poor control of Canarygrass and Rabbitsfootgrass from Poast have been reported in a few fields in the Yuma area in recent years, although resistance has not been confirmed. We hope to evaluate this further next season.

Weed populations may look uniform but in fact, they are very diverse on a genetic level. Resistance to a particular herbicide occurs when there are naturally occurring variants of the weed species that are tolerant. Two principals that are important to understand are 1) the tolerant variants are not caused by the herbicide but occur naturally and 2) individual weeds do not change to become resistant, rather the weed population changes to become resistant over time. What happens is that if the same herbicide is used continuously for a prolonged period of time, the susceptible biotypes will die out while the resistant biotypes will survive and reproduce, passing on their resistance to the next generation.

More information on the current state of herbicide resistance can be found here:http://www.weedscience.org/In.asp

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.