Now that produce planting/transplanting is well underway, one of the first pests you’re likely to encounter is adult whiteflies. Given the high numbers found on spring melons and cotton this summer, one would also expect whiteflies to be heavy on fall produce crops. Surprisingly though, adult numbers have been lighter than expected on fall melons. For instance here at the Yuma Ag Center, whitefly populations in our experimental plots based on vacuum samples taken this week are lower than what we’ve encountered the past few years (see graph below). However, this appears to be site-specific as I’ve observed melon fields in the Wellton/Roll area with very high numbers this past week. This makes sense; whitefly population abundance can be influenced to a large extent by the crop landscape throughout Yuma. Crops planted near or adjacent to cotton and alfalfa are clearly more heavily infested than fields isolated away from these crops. In addition, our monsoon conditions often play a role where humidity and rainfall can influence population abundance. Nonetheless, you can bet heavy whitefly numbers will eventually show up in one of your fields. It is important that PCAs pay particular attention to early whitefly control on their newly planted produce crops. Prolonged feeding by heavy numbers of adults on seedling lettuce/cole crop plants can cause stunted plant growth. If you observe honeydew on leaves in the absence of nymphs then there are way too many adults on the seedling plants. There are likely too many eggs being laid as well. With the loss of endosulfan, growers have few options for effective residual control of adults, but good knockdown can be achieved on lettuce and cole crops with combinations of pyrethroids tank-mixed with Orthene, Lannate, Lorsban, Venom, Scorpion, or Sequoia. In addition, Exirel (the foliar formulations of Cyazypyr) was recently labeled for use on produce crops and can provide excellent adult control. Sometimes it can be difficult to determine whether a product is working 3-4 days following application when adult whiteflies are continuously moving into you field from outside sources. To assess adult control under heavy migrations, try monitoring young leaves for the presence of light-colored eggs (newly laid) using a hand lens. Absence of newly laid eggs can be an indication that adults are not actively feeding on leaves or are dying before they can lay eggs. Furthermore, allowing adults to remain unchecked on small plants generally results in the development of large nymph populations that can cause significant growth/yield reductions in all produce crops. It is strongly recommended that growers apply a soil insecticide on lettuce and cole crops throughout September and early October. Local research has shown that imidacloprid applied at 0.25 lbs AI/ac at planting provides less residual control of nymphs today than it did 10 years ago. However, given the current economics of imidacloprid, cost-effective whitefly control can still be achieved by using higher rates of imidacloprid (0.38 lbs. AI/ac) to extend residual control (e.g., Alias 2F-24 oz; Wrangler 4F-12 oz; Admire Pro- 10.5 oz). Verimark, the soil formulation of Cyazypyr, applied at 13.5 oz/ac can provide excellent control of nymphs when applied at planting similar to the neonicotinoids to lettuce and cole crops. Once plants get larger, products like Movento, Exirel, Venom, Scorpion, Assail, Knack and Courier/Vetica can provide effective control of nymphs. For more information on whitefly biology, management and insecticide alternatives see these reports: Management in Fall Produce- 2014 and Insect Management on Desert Vegetables and Melons: Whitefly.

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.

Earlier this week, we initiated a trial examining the use of band steam for controlling Fusarium wilt of lettuce. The premise behind this research is to use steam heat to raise soil temperatures to levels sufficient to kill soilborne pathogens. For Fusarium oxysporum f. sp. lactucae, the pathogen which causes Fusarium wilt of lettuce, the required temperature for control is generally taken to be > 140°F for 20 minutes. Soil solarization, where clear plastic is placed over the crop bed during the summer, exploits this concept. The technique raises soil surface temperatures to 150-155˚F, effectively killing the pathogen and reducing disease incidence by 45-98% (Matheron and Porchas, 2010).

In our trials, we are using steam heat to raise soil temperatures. Steam is delivered by a 35 BHP steam generator mounted on a custom designed elongated bed shaper (Fig. 1). Preliminary results were encouraging. The device was able to increase the temperature of the top 3” of soil to over 180°F at a travel speed of 0.5 mph as shown in this video of the machine in action (shown below). These temperatures exceed that of those known to control pathogens responsible for causing Fusarium wilt of lettuce (> 140°F for 20 minutes).

Stay tuned for final trial results and reports on the efficacy of using steam heat to control Fusarium wilt of lettuce.

If you are interested in evaluating the technique on your farm, please contact me. We are seeking additional sites with a known history of Fusarium wilt of lettuce disease incidence to test the efficacy and performance of the device.

References
Matheron, M. E., & Porchas, M. 2010. Evaluation of soil solarization and flooding as management tools for Fusarium wilt of lettuce. Plant Dis. 94:1323-1328.

Acknowledgements
This project is sponsored by USDA-NIFA, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council.  We greatly appreciate their support.

A special thank you is extended to Cory Mellon and Mellon Farms for allowing us to conduct this research on their farm.

Weeds are one of the most visible of all agricultural pests. They can’t move or hide and once established often stick up over the crop. Just one weed in a 10 acre field is annoying to look at. With insects and diseases, the damage is often more visible than the pest. That is not the case with weeds. A moderate weed infestation is approximately 10 weeds per square foot. If a herbicide produces 90% control, that leaves 1 weed per square foot or 43 weeds per acre. Without an untreated check, this can look like the herbicide failed!  It is easy to leave an untreated spot in a field and it is well worth doing. Many applicators do so unintentionally because of skips, powerlines and other causes. They help determine crop injury and weed control. Here are some examples of what various levels of control looked like from one of our cole crop trials:

Results of pheromone and sticky trap catches can be viewed here.

Corn earworm: CEW moth counts down in most traps over the last week; about average for early October.

Beet armyworm: Trap counts increased in several areas last week, and about average for early October.

Cabbage looper: Cabbage looper trap counts increased in most locations, but still below average for this time of the season.

Diamondback moth: Adult activity spiked 2 weeks ago, particularly in the Yuma and Dome Valleys, but down over the past week. Average for this time of season.

Whitefly: Adult movement increasing Tacna consistent with melon harvests; overall about average for early October.

Thrips: Thrips adult movement peaked 2 weeks ago but down ovr the past week, overall activity above average.

Aphids: Winged aphids beginning to show up the north Yuma and Gila Valleys; below average for October.

Leafminers: Adult activity increased significantly last week in several locations, above average for this time of season.