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. 

Bindu Poudel-Ward, Martin Porchas, and Jason Furr
Yuma Agricultural Center, University of Arizona, Yuma, AZ
 
Bindu Poudel, Martin Porchas, and Jason Furr
Yuma Agricultural Center, University of Arizona, Yuma, AZ
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 ‘Magosa’ was seeded, then sprinkler-irrigated to germinate seed on Nov 16, 2020 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 four times in a randomized complete block design. Each replicate plot consisted of 25 ft of bed, which contained two 25 ft rows of lettuce. 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	Max	Min	Avg	Rain
November	80	49	64	0.00
December	69	41	55	0.01
January	70	42	56	1.31
February	75	44	60	0.00
March	77	46	63	0.00

 
Powdery mildew (caused by Golovinomyces cichoracearum) efficacy trial treatments were made on February 3^rd, February 17, and March 2dn 2021. Disease rating was done on March 8, 2021.   Disease severity was determined  by rating 10 plants within each of the four replicate plots per treatment using the following rating system: 0 = no powdery mildew present; 0.5 = one to a few very small powdery mildew colonies on bottom leaves; 1 = powdery mildew present on bottom leaves of plant; 2 = powdery mildew present on bottom leaves and lower wrapper leaves; 3 = powdery mildew present on bottom leaves and all wrapper leaves; 4 = powdery mildew present on bottom leaves, wrapper leaves, and cap leaf; 5 = powdery mildew present on entire plant. These ratings were transformed to percentage of leaves infected values before being statistically analyzed. Yield loss due to rejected lettuce heads would likely begin to occur on plants with a powdery mildew rating above 2.0 (percentage of leaves infected value of 40).         
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. All treatments significantly reduced the final severity of powdery mildew compared to nontreated plants. The most effective fungicides, that held the percentage of leaves that were infected to 20% or less, included UA Experimental-1, Luna sensation, Quintec, and Torino. Phytotoxicity symptoms were not noted for any treatments in this trial.

It’s October already and soon crews will be thinning and weeding vegetable crops in the Yuma area. Automated machines for performing these tasks are commercially available and being used more and more. Due to significant research and development efforts being made in this area, the technology used for these machines is advancing rapidly. In the next series of articles, I will be discussing the developments made over the summer by automated machine manufactures and what growers in the Yuma area can expect for the upcoming season.

The first technology I’d like to discuss is the autonomous weeding robot “Dino” manufactured by Naïo Technologies[1] (Fig. 1). Briefly, the robot is an 84” wide, self-piloted, mobile power unit equipped with camera guided cultivating tools.

Last season, Naïo demoed the robot for growers in the Yuma area. It was the first year the French based company had operations in the U.S. One goal of the demonstrations was to evaluate the machine in U.S. conditions and get feedback from growers about how the machine might best fit Arizona production systems. The company learned that Arizona vegetable production is very intense and fast paced. Machine productivity and durability were important issues for viability and domestic acceptance.

The company took heed of these observations. Over the summer, the battery that powers the fully electric robot was upgraded to provide 10 hours of operation before needing to be recharged. This improved work capacity from 8 acres/day to about 10 acres/day (work rate = ~ 1 acre/hour). To further address the capacity issue, the company imported three additional machines so that multiple machines could be operated simultaneously in the same field. The new machines are more robust, being equipped with higher torque drive wheel motors and a sturdier frame. The company is also in the process of switching to an improved camera guidance system that should enhance crop tracking ability and close cultivation performance. Some may be aware that the company has developed an award winning active in-row weeding tool that cycles cultivating blades in and out of the crop row (Link). The device is undergoing further testing and is planned for commercial release in mid-2021.

Machines will be available this fall in the Yuma area for demos or for hire as a weeding service. It will be interesting to see how these advanced robots perform and benefit weed management. If you would like assistance evaluating these machines or conducting performance trials, please feel free to contact me.

People often get worried when they see weed seedlings emerge after applying a preemergent herbicide.  However, not all preemergent herbicides kill weeds before they emerge. None of them kill seeds. Some are absorbed only by roots, some only by shoots, and some by both roots and shoots, but in all cases, the weed seed must first germinate. Those herbicides that are absorbed only by roots ordinarily kill weed seedlings before they emerge from the soil. These include trifluralin (Treflan), pendimethalin (Prowl) and benefin (Balan). Those that are absorbed only by shoots often kill weed seedlings soon after they emerge from the soil. These include DCPA (Dacthal) and EPTC (Eptam). Pronamide (Kerb) is absorbed by both roots and leaves and occasionally will not kill some weed species until very early after they have emerged. When used preemergent, some contact herbicides such as oxyfluorfen (Goal) and flumioxyzin (Chateau) are absorbed by seedling weeds only after they germinate and are emerging through the soil where they pick up the herbicide.

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased considerably y in the past 2 weeks and about average for late summer
 
Beet armyworm:         
Trap counts stay active in some locations (Yuma Dome Valley and Wellton) particularly near alfalfa
 
Cabbage looper:         
Cabbage looper numbers remain low consistent previous years.
 
Diamondback moth:      
DBM moths were not caught in any trap since June; average for this time of the year.
 
Whitefly:                      
Adult movement decreased in past 2 weeks consistent with previous years
 
Thrips:                         
Thrips adults decreasing in most locations, and trending comparable to previous years.
 
Aphids:                       
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity has highest in Wellton and Dome Valley, and slightly above average for early August