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%). Variety: Deluxe (HMX2595) was seeded, then sprinkler-irrigated to germinate seed on March 20, 2024on 84 inches 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. 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. 

Spray treatments were done on 05-21-2024, 05-31-2024, 06-07-2024 and 06-14-24. Powdery mildew was first seen on 06-05-24. Please see excel file for additional details.  

Disease severity of powdery mildew (caused by Sphaerotheca fuliginea and S. fusca) severity was determined 6-17-2024 by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 1 = one to two mildew colonies on leaves  ;2 = powdery mildew present on one quarter of leaves; 3 = powdery mildew present on half of the leaves; 4 = powdery mildew present on more than half of leaf surface area ; 5 = powdery mildew present on entire leaf. These ratings were transformed to percentage of leaves infected values before being statistically analyzed.

The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. Quintec, Merivon, Tesaris, Luna Sensation, and V6M-5-14 V gave the best disease control. Phytotoxicity symptoms were not noted for any treatments in this trial.

ANR Webinar 10/17 click link for details.

Dacthal, Prefar, and GoalTender are the primary herbicides used in the low deserts on broccoli and cauliflower. Other options include Trifluralin (Treflan), Devrinol, Stinger, Poast and Select. All of these herbicides have different characteristics and should be used differently for maximum weed control and crop safety.

Dacthal(DCPA) is effective only when applied prior to weed emergence but does not prevent weed seed germination. It is absorbed at the growing points between the radicle and cotyledon leaves. This is called the coleoptile on grasses and the hypocotyl on broadleaf weeds. Weeds sometimes emerge but stop growing. To be effective, this herbicide has to be concentrated near these growing points. It sticks strongly to the soil and needs a fair amount of water to incorporate it when using sprinklers. Furrow irrigation works as well if the bed tops are thoroughly moistened. Applying Dacthal to dry soil and incorporating it with light amounts of sprinkler or furrow water does not work. It works best when the soil is moist at application. Dacthal is fairly broad spectrum but is weak on mustards, sunflower and the thistle family. 

Prefar(Bensulide) also adheres very strongly to the soil but rather than working on the region between the radicle and cotyledon leaves, it works at the root tips. Both Dacthal and Prefar are not systemic and move very little in plants. They work only where the roots and shoots contact them. Prefar must be incorporated with large amounts of sprinkler water or chemigated. Furrow irrigation, even when it thoroughly moistens the bed, will not incorporate this herbicide on most soils. Prefar is best on grasses, purslane and pigweed and will control lambsquarters and goosefoot in some situations.

GoalTender(Oxyfluorfen) differs greatly from both Dacthal and Prefar. It works primarily on the foliage, even when used as a preemergence herbicide. It is used both preemergence and postemergence and has no activity on roots or shoots. GoalTender inhibits the production of an enzyme in the plant that leads to destruction of cell membranes. It is fast acting, dependent on sunlight and acts like a contact herbicide. Even when used preemergence to the weeds, it is dependent on sunlight and the weeds must emerge from the ground. They absorb the herbicide as they emerge and twice the postemergence rate is normally required. Because a barrier is created on the surface, any disturbance of the soil after application can reduce control.

Area wide Insect Trapping Network   VegIPM Update, Vol. 12, No. 12, Jun 16,  2021
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:          
CEW moth counts increased significantly ober the past 2 weeks reaching their summer peak so far.
 
Beet armyworm:          
Trap counts remain high in some locations (Yuma and dome Valleys, Wellton) comparable to numbers we saw in October.
 
Cabbage looper:          
Cabbage looper numbers remain low consistent with the lack of activity this fall and summer compared to last season.
 
Whitefly:                       
Adult movement continuing to increase slowly, particularly in the Yuma Valley consistent with melon harvest and destruction of plant residue.
 
Thrips:                           
Thrips adult movement highest in Dome Valley, but areawide started to decline to numbers comparable to this time last year.
 
Aphids:                        
Aphid movement has been has been absent for the past month similar to what we typically observe in the summer. 
 
Leafminers:                  
 Adult activity has highest in Dome Valley and Tacna, and about average for mid-summer.
 
Diamondback moth:      
DBM counts continue to slowly decline and adults captured only in areas where seed crops were recently harvested.