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 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.

A new product for homeowners has appeared on the market that is called “Roundup” but it does not contain glyphosate which is the active ingredient that most people associate with “Roundup”.  Although this is not an agricultural issue, it points out the need to always read the label to verify what you are spraying. Commercial names can be misleading. This new product is called “Roundup for Lawns” and it contains MCPA, Quinclorac, Dicamba and Suldentrazone. It does not contain Glyphosate. Marketing this product as “Roundup”(Glyphosate), even though it does not contain “Roundup” (Glyphosate), will confuse many people. Glyphosate is sold under many commercial names, including Roundup, and is typically non-selective and kills both grass and broadleaf plants. It also has no soil activity and is not volatile.  The active ingredients for “Roundup for Lawns” include a couple growth regulators that can be volatile and injure nearby broadleaf vegetation. It also contains a couple ingredients that can have some soil activity. 

“Names can be Misleading”

Area wide Insect Trapping Network   VegIPM Update, Vol. 11, No. 22, October 28, 2020

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

Corn earworm: Moth activity is about average for mid-October, particularly in Dome Valley and south Yuma Valley. 

Beet armyworm: Moths remain active throughout the desert, especially active in Tacna and Dome Valley.

Cabbage looper: Cabbage looper activity remains unusually low for early October, likely a result of unusually hot weather. Larvae are yet to show up in many fields.   

Whitefly: Adult movement has been about average for this time of year. Activity highest in Tacna near fall melons.

Thrips: To date, thrips activity has been seasonably low at all trap locations; activity increased significantly in Roll. 

Aphids: Aphids beginning to show in most traps along the Colorado River (Bard, Gila, Yuma) which is normal for this time of year.  Recent high winds may begin to disperse them throughout the area.

Leafminers: Adult activity below normal for September, but high numbers caught in Wellton in areas where melon harvest has commenced.