The first line of defense in avoiding whitefly issues in the fall produce/melon plantings is for PCAs and growers to be vigilant in controlling whiteflies this summer. To a large extent this means effectively avoiding large populations in cotton, a major source of whiteflies on fall produce and melons crops. But before whitefly management begins in cotton, it is important that whitefly populations be prevented from building up to large numbers in the spring melons that have recently finished, or are nearing completion of harvest in the next few weeks. Although whitefly numbers appear to be relatively lighter this spring than normal, adult numbers have increased significantly over the past week in melons coinciding with higher temperatures and area-wide melon harvests. Growers and PCAs should not hesitate to knock these populations down with a timely insecticide application on pre-harvest melons. Not only does this prevent sooty mold contamination, but also reduces the potential numbers of adults that might migrate to adjacent crops and weeds. The high temperatures that are expected in the next week or so may allow whitefly nymph populations to rapidly build-up and cause honeydew/sooty cold contamination on fruit. Once harvest is complete, proper sanitation in spring melons is critical for preventing unnecessary whitefly migration into cotton and alfalfa. It is highly recommended that melon growers quickly destroy crop residue as soon as possible following harvest. A delay in disking under melon fields following harvest can allow adult whiteflies to readily disperse into cotton and alfalfa, especially if they don't need to fly very far. My observation this spring has been that the majority of melon fields have been gown in close proximity to cotton. These spring melons fields are can also potentially extend the host-acquisition period for Cucurbit Yellows Stunting Disorder Virus (CYSDV). Once melons fields have been disked and flat-watered, it is common for volunteer melons to germinate and emerge during July and August. The destruction of volunteer melons before fall crops are established can reduce the source of whiteflies and virus inoculum available to infect newly emerging melon plants. Volunteer plants should be destroyed as soon as practical. This can be done by disking or applying a contact, burn-down herbicide to fields. Recent research has indicated that fall melons grown near spring melons with volunteers (<1.8 miles) are at a high risk of CYSDV infection. Ideally, it is in the Ag communities best interest to use sound cultural management practices, such as sanitation, to eliminate and avoid unnecessary sources of whiteflies before the fall produce and melon seasons begin. For more information on cultural management practices for whiteflies see: Insect Management on Desert Melons: Whiteflies. 

In response to the recent outbreaks of Diamondback moth (DBM) , Plutella xylostella in Yuma, we have established a pheromone trap network designed to monitor the activity and movement of adult populations of DBM. PCAs have had difficulty controlling DBM in cabbage, broccoli and cauliflower since October. Traps have been placed in Roll, Wellton, Dome Valley, Gila Valley and Yuma Valley in locations where cole crops are presently being grown or in areas where infestations were known to occur this fall.

This study was conducted at the JV farms at Gila Valley. Lettuce variety ‘Guapo’ was seeded, then sprinkler-irrigated to germinate seed on September 19, 2023, on double rows 12 in. apart on beds with 42 in. between bed centers.  Rest of the irrigation 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 on October 9, 2023 at the 3-4 leaf stage to a 12-inch spacing. Treatment beds were separated by single nontreated beds. Treatments were applied by incorporating in soil before seeding or 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
September	100	71	86	0.71 in
October	93	61	77	0.00 in
November	80	51	65	0.08 in
December	71	44	57	0.82 in

 
Fusarium wilt (caused by Fusarium oxysporum f. sp. lactucae ) rating was done in the field by observing the typical symptom of lettuce wilt. Confirmation was done by cutting the cross section of roots. Disease scoring/rating was done on December 6, 2023. 
 
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. The disease pressure was extremely high in 2023, and most treatments showed little or no control against the disease. The treatments that showed some activity were Bexfond, Cevya, Rhyme, and Serifel. Plant vigor was normal and phytotoxicity symptoms were not observed in any 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:

Area wide Insect Trapping Network   VegIPM Update, Vol. 12, No. 20, Oct 6, 2021.
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts continue to be active, about average for this time of the season; particularly active in Wellton and Yuma Valley.
 
Beet armyworm:         
Trap counts increased slightly in most locations, but well below average for early October. Most activity in Dome and Yuma Valley.
 
Cabbage looper:           
Cabbage looper trap counts remain steady in most areas. Activity about normal compared to previous years. 
 
Whitefly:                       
Adult movement increasing Dome Valley and Wellton, but down in many other locations; movement is below average for this time of year, but should anticipate increase movement with melon harvest beginning. 
 
Thrips:                         
Thrips adult movement increased slightly in some locations, particularly in Wellton and Tacna, but remains below average for mid-September.
 
Aphids:                        
Aphid movement has been absent since early June typical with high summer temperatures, and the monsoon flow.  Picked a up a few aphids last week with the break in weather and change in wind direction. 
 
Leafminers:                  
Adult activity remains low in most location; below average for this time of season.
 
Diamondback moth:    
Significant increase in moth activity in the last week, particularly in Dome Valley and N. Gila Valley in traps located adjacent to cauliflower and cabbage transplants.