Fall melon planting is right around the corner and local fields are being prepared for planting. Growers and PCAs are well aware of cucurbit yellow stunting disorder virus (CYSDV) and the impact it can have on fall melons. This whitefly transmitted crinivirus was first identified on desert melons in the fall 2006 where widespread infections on cantaloupes, honeydews and other melons occurred. CYSDV can cause significant losses in melon fruit yield and quality, and without question, desert melon crops have been seriously affected by this virus. Melon IPM has also been impacted by CYSDV where insecticide usage on fall melons has increased significantly. We have been studying the epidemiology of CYSDV for over 10 years trying to understand the complex relationships between the virus, vector and our local cropping system. Our ultimate goal is to develop practical approaches for reducing CYSDV impact on fall melon production. In addition, we continue to develop new information on chemical control of the whitefly vector (Bemisia whitefly adults). 

Last fall, whitefly populations were lighter than normal, and CYSDV incidence on fall melons was the lowest we’ve recorded on melons since the virus as first reported 11 years ago. Thus far, whitefly numbers this spring and summer have been relatively light compared to previous years and the incidence of CYSDV was generally light on spring melons. How these low numbers translate into virus incidence on the fall melon crop is unknown? Regardless, experience suggests that growers should anticipate CYSDV to be present. Further, given the aggressive management programs that PCAs and growers are now using, it will be interesting to see how CYSDV impacts melon production this fall. We’ll be tracking both whiteflies and CYSDV incidence again in 2017. Our research to date suggests that fall melons produced near cotton or near areas where spring melons were recently produced are at the highest risk of infection. When possible, growers should attempt to isolate fall melon plantings as far away as possible from these sources of whiteflies and CYSDV. Growers forced to plant fall melons near these crops should be vigilant in minimizing adult whitefly infestation levels with insecticides during pre-bloom growth stages. To view a summary of the status of CYSDV in Yuma County and guidelines for management visit  2017 Guidelines for Whitefly and CYSDV Management on Fall Melons.

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 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.

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.