Temperatures are still warm and worm pressure remains steady in most growing areas.   Here at the Ag Center, beet armyworm pressure is about average for early October, and still troublesome on new stands. Cabbage looper eggs are beginning to now show up. Pheromone trap counts for armyworm and loopers remain below average in most areas. However, diamondback moth larvae are present on broccoli and transplants at the Ag Center.  I’ve had several PCA reports of diamondback pressure in transplanted brassica crops in Wellton and Roll, and in the Yuma Valley. Trap catches have begun to increase also. So far, all insecticide products we’ve tested are providing good Lep control and no complaints from the field.  
 
Fortunately for local PCAs, several insecticide alternatives are available that provide excellent residual activity on Lep pests.   Perhaps equally important, many of the products have unique modes of action (MOA) that can be alternated throughout the growing season. This is important because the most fundamental way to reduce the risk of insecticide resistance is to eliminate exposure of multiple generations of Leps to the same MOA.   By using a different MOA on each subsequent spray application, you can minimize the risk of resistance by Lep larvae to these insecticide compounds. In contrast, repeatedly applying insecticide products with the same MOA for Lep control in the same area will significantly increase the risk of resistance.  This is particularly important with the Diamide group of insecticides (IRAC group 28). These products can be applied as both foliar sprays and soil systemic treatments, and currently 7 Diamide products are labeled for use in leafy vegetables - all with the same MOA (Coragen, Durivo, Besiege, Minecto Pro, Verimark, Exirel and Harvanta).  To avoid confusion among the Diamides, the IRAC group number (28) is placed on each label, adjacent to the product name.  Furthermore, applying a Diamide product (i.e., Coragen/Verimark) to the soil at planting or as a tray drench, and then subsequently applying Diamide foliar sprays (i.e., Harvanta/Besiege) on the same field is not a good idea as it can expose multiple generations of Leps to the same MOA.  For example, under ideal weather conditions, one could potentially expose 5-6 generations of BAW or DBM to the same MOA given the residual efficacy of the diamides.  That’s not a good way to use these products if you want them to remain effective.   Since the Diamides, as well as the other key products currently available (e.g., Radiant, Proclaim, Intrepid, Avaunt, Bts), are critical to effective management of Leps in leafy vegetables, PCAs should consciously avoid the overuse of any of these compounds. The most effective way to delay the onset of resistance by Leps in leafy vegetables is to consider the recommendations provided in the guidelines entitled Insecticide Resistance Management for Beet Armyworm, Cabbage Looper and Diamondback Moth 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%). 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.

Postemergence grass herbicides have been available for the past 20 to 25 years. These include fluazifop( Fusilade-1985), sethoxydim(Poast-1986, Segment, Vantage and others), and clethodim(Select-1991, Select Max, Arrow, Envoy, Volunteer, and others). They only control grasses and are registered on numerous broadleaf vegetable and field crops as well as trees and vines.

These herbicides are all classified as lipid biosynthesis inhibitors. They work by inhibiting the production of an enzyme (ACCase) used to produce fatty acids which are needed in the formation of cell walls and other plant membranes. They are slow acting and have no soil activity. There are some herbicides that use this same mode of action but are used safely on wheat and barley. These include Discover(clodinafop), Puma(fenoxaprop), and Achieve(tralkoxydim) which are commonly used to control Canarygrass, wild oat and other grasses. 

These herbicides are all fairly broad spectrum and control most grasses although there are differences between them on some weed species. Clethodim will control sprangletop while sethoxydim and fluazifop will not. The same is true for annual bluegrass which is controlled only by clethodim when it is small. All of these are weak on sandbur.

These herbicides have no soil activity and typically need to be applied 2 or 3 times to achieve season long weed control. They all require the use of a crop oil concentrate to help penetrate the leaf surface except for Select Max which requires either a non-ionic surfactant or crop oil.

These herbicides are normally very safe to the crops that they are registered on. There have been only a few instances over the past 25 years where crop injury has occurred. One was to melons where above labeled rates of Select Max was applied in overlaps or at the ends of fields. This was only from Select Max. Another instance was several years ago on onions where liquid fertilizer (AN20) was previously sprayed over the onions for weed control. The third instance was to some leafy vegetables, especially arugula, where the crop oil concentrate caused leaf burn.

Although these herbicides once seemed fool proof, each year more failures are being reported. Last year, for instance, Poast and Select did not control Rabbitfootgrass in a couple fields and Canarygrass was missed by Poast in others. The only documented case of herbicide resistance in this region has been the resistance of Canarygrass to sethoxydim, fluazifop and clethodim in the Imperial Valley. There are several potential causes for herbicide failures and resistance is only one of them and is rare in this region. Please let us know if you have failures so that we can help determine the cause. A video on this subject can be found on this link.

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts remain  at low levels  in all areas, well below average for this time of year. 
 
Beet armyworm:          
Trap increased areawide; about average compared to previous years.
 
Cabbage looper:          
Cabbage looper counts increased to seasonal highs; slightly below average for this time of season.
 
Diamondback moth:      
DBM moth counts decreased in most areas. About average for this time of the year.
 
Whitefly:                      
Adult movement negligible, average for late winter. 
 
Thrips:                          
Thrips adult counts increased in south Gila Valley, down in all other locations. Below average compared with previous years.
 
Aphids:                        
Aphid movement decreased in all area; below average for mid-March.
 
Leafminers:                  
Adults remain low in most locations, average for March.