In our last update we discussed whitefly management, but now that daytime temperatures are forecasted to be in the 90’s for the next 10 days, I thought that it would be good to review your insecticide options for whitefly management. Several factors play a role in determining which insecticide(s) you may want to apply. If the grower applied a neonicotinoid at planting (e.g., imidacloprid) the soil residual is likely long gone and it is likely no longer providing control of nymphs and newly-emerging adults. Thus, if whitefly population abundance is sufficiently high enough to justify control, a foliar insecticide is recommended. When nymphs can easily be found on the crown and mid-vine leaves, an IGR or IGR-like product is recommended. This would include: Vetica, Courier, Oberon, and Knack. None of these products will provide good adult knockdown, but if applied correctly, will eventually suppress adult populations by preventing the development of the nymphs within the field. Experience has shown that these products can provide 14-21 days of residual control of nymphs. Control of adults infesting plants from outside sources will require a different approach. A Vydate or Lannate combined with a bifenthrin or Danitol tank-mixture is an option, but will likely only provide adult knockdown, with limited residual control (3-5 d). Among the neonicotinoids, Assail and Venom/Scorpion have shown the most consistent residual adult control (7-10 d) in experimental trials and will also provide decent control of nymphs on treated leaves. Because neonicotinoids are used on many crops grown throughout the year be sure to consider resistance management statements on the label as well as the UA Cross-commodity Guidelines before you apply them. A newer mode of action, Exirel (anthrillic diamide) can provide knockdown and residual control (14 d) of both adults and nymphs following foliar application. Because Exirel works via translmaniar movement in treated leaf tissue, good spray deposition on all melon foliage is important for maximizing control of both adults and nymphs. This brings up another factor that is important to consider – presence of pollinators in or near the field. Be sure to check the label carefully for the Environmental Hazards statement, specifically for language and restrictions on honey bee safety. In some cases, products can be used effectively and safely through application timing and rates, whereas in other cases, some products should not be used when plants are flowering and pollinators are actively working fields. You must read the label carefully. The proximity to harvest may limit your choices as well. The PHIs for whitefly products vary anywhere from 0-7 days. Also, the presence of worms near harvest may influence your choice of products. If you’re using a whitefly specific product (e.g., Courier, Oberon, Knack, Assail, Venom/Scorpion) you might consider adding a pyrethroid for cabbage looper control, or a Lep material (e.g., Radiant, Intrepid, Coragen, Belt) for control of both looper and beet armyworm. Products such as Vetica and Exirel are efficacious against both whiteflies and Lep species. Visit these publications for information on products available for Whitefly Control on Desert melons and Lepidopterous Larvae Control on Desert Melons. 

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:

Area wide Insect Trapping Network   VegIPM Update, Vol. 13, No. 2, Jan 26, 2022
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts remain low across all locations; average for this time of the season. 
 
Beet armyworm:         
Trap counts decreased in all locations, and a little below average for late-January.
 
Cabbage looper:          
Cabbage looper trap counts remained low in all locations; below average for January.
 
Diamondback moth:    
Adult activity decreased across all locations, except the North Gila Valley where trap is adjacent to with nearby brassica seed crops. Overall, activity is a little below for this time of year. 
 
Whitefly:                     
Adult movement remained low in all locations consistent with previous seasons.
 
Thrips:                          
Thrips adult movement beginning to increase slightly in most locations last week but increased sharply in Roll. Activity about average for January.
 
Aphids:                        
Aphid movement low in most locations, increased slightly in N. Yuma and E. Gila Valleys. Trap captures slightly below average for this time of season. 
 
Leafminers:                  
Adult activity increased in many areas, particularly in the Yuma Valley; above average for this time of season.