Historically, beet armyworm and cabbage looper are the most important pests of produce during September and October based on our annual Lettuce Insect Losses surveys. Now with produce planting well underway, it is no surprise that worms are everywhere, particularly in Dome Valley where reports of heavy armyworm have been numerous over the past week or so. Corn earworm larvae have also been found in a number of lettuce fields. Here at the Yuma Ag Center, one can easily find newly new egg masses and neonate beet armyworm larvae on 8 day old lettuce and broccoli stands. Similarly, cabbage loopers are beginning to show up and their populations will likely increase. Remember, temperatures drive larval development and adult activity, particularly when night time temps remain high (in the mid-70s or higher). Moths will activily oviposit when evenings are warm and winds are light. Don’t be fooled by this recent break in the weather. As long as the average temperature remains around 80-85°F, worms should be active at damaging levels. Those ideal conditions are consistent with the weather forecast for the next 10 days (highs in the mid-thigh 90’s and lows in the 70’s). Fortunately, there are a number of very effective insecticides that can be applied as stand-alone foliar products that provide effective residual control of both of these lepidopterous species. Radiant, Proclaim, Intrepid, Avaunt and any one of the Diamide products (Coragen, Belt, Voliam Xpress and Vetica) can provide good knockdown and extended residual control of armyworms and loopers. A newly registered diamide, Exirel provides both worm and whitefly activity. Over the past few years, our research trials have demonstrated that these products provide comparable control on lettuce and cole crops. Of course, residual control will often depend on the rate applied. In general, the higher the rate, the longer the residual, but this will also depend on how fast the plant is growing and plant size. Before selecting a product for Lep control, be conscious of products (chemistries) previously used on the crop. Avoid using products with the same mode of action more than twice on any given field. More information on the insecticides available for effective control of beet armyworm and cabbage looper can be found in this document:Lepidopterous Larvae Management in Desert Produce Crops.

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%). Lettuce was seeded, then sprinkler-irrigated to germinate seed on Nov 28, 2023 on double rows 12 in. apart on beds with 42 in. 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, which contained two 25 ft rows of lettuce. Plants were thinned Jan 4, 2024  at the 3-4 leaf stage to a 12-inch spacing. 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.

Month	MaxTemp(°F)	Min Temp (°F)	Average Temp (°F)	Rainfall
November	80	51	65	0.08 in
December	71	44	57	0.82 in
January	68	42	54	1.14 in
February	73	47	59	0.50 in

 
Downy mildew (caused by Bremia lactucae) rating was done on variety Eblin, Bobcat, and 180 (partially funded by AILRC grant). Disease was first seen on 1-30-24. Please see attached excel file for chemicals application date. Disease rating was done on February 29^, 2024. Disease severity was determined  by rating 10 plants within each of the five replicate plots per treatment using the following rating system: 0 = no downy mildew present; 0.5 = one to a few very small downy mildew colonies on bottom leaves; 1 = downy mildew present on bottom leaves of plant; 2 = downy mildew present on bottom leaves and lower wrapper leaves; 3 = downy mildew present on bottom leaves and all wrapper leaves; 4 = downy mildew present on bottom leaves, wrapper leaves, and cap leaf; 5 = downy mildew present on entire plant.
The data in the table illustrate the degree of disease control obtained by application of the various treatments in this trial. Most of the treatments exhibited activity against the disease to some extent. Latitude, Amara, Eject, Previcure flex exhibited good control in the variety Eblin (highly susceptible variety). Whereas Cevya, Stargus, Latitude, Amara, Revus, Thrive 4 M, Actigard, Instigo+Carbose+intereact showed activity against the pathogen in variety Bobcat. Please see excel file for the full list of chemicals and their efficacy. The lettuce variety 180 was resistant to the disease and no downy mildew was observed on the particular variety. No phytotoxicity was observed in this field.

Dacthal was first registered in 1959 but like most older products that are still used, we are constantly adapting it to our changing cultural practices. Dacthal is a mitotic inhibitor and kills germinating weeds by stopping cell division. This is the same mode of action as many other preemergence herbicides such as Trifluralin, Prowl, Balan, Kerb and others but its chemistry and how it moves in the soil and plant are different. Dacthal is absorbed by both shoots and roots of germinating seedlings although most of the activity is from shoot absorption. When absorbed by the shoots, it will move upward into the plant. It is not absorbed by foliage and can be safely applied over the crop. Dacthal has a strong affinity for soil and adsorbs strongly to soil particles. If Dacthal is applied to dry soil, it sometimes will not work because the herbicide it stuck on the soil and not available to kill weeds. Conversely, if the soil is saturated, it may not be adequately incorporated. The best time to apply Dacthal is when the soil is moist but not saturated.

When Dacthal was first being developed it was tested for use on lettuce. If it is sprayed on or chemigated it will cause severe injury to lettuce. If it is mechanically incorporated it is surprisingly safe to lettuce. It is fairly broad-spectrum bur weak on mustards.

Area wide Insect Trapping Network   VegIPM Update, Vol. 15, No. 21, Oct 16, 2024

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

Corn earworm: CEW moth counts increased in most traps; about average for early October.

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

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

Diamondback moth: Adult activity increasing, particularly in the Yuma and Dome Valleys.  Above average for this time of season.

Whitefly: Adult movement increasing Tacna, Dome Valley and Yuma Valley; overall about average for early October.

Thrips: Thrips adult movement picking up in all areas, overall activity above average.

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

Leaf miners: Adult activity light in all areas, about average for this time of season