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.

Two closely related but different species of several summer annual grasses are common in the low deserts. In general, these are all easy to distinguish from each other in the field and they respond similarly to herbicides. Some of these and their distinguishing characteristics are: 

• Watergrass (Echinochloa colonum) and Barnyardgrass (Echinochloa crusgalli) 

These are very similar but watergrass has purple bands or chevrons on the leaves and barnyardgrass often has awns or bristles at the end of the spikelets. Both respond the same to herbicides. 

• Red Sprangletop (Leptochloa filiformis) and Mexican Sprangletop (Leptochloa uninervia) 

Red sprangletop is, in general, a lighter green color and has a finer seed head than does Mexican sprangletop which is darker green or gray and has a visibly coarser seedhead. Both form clumps or crowns that often survive through the winter months. Both are fairly tolerant to Poast (sethoxydim) and Fusilade (fluaziflop) but are controlled with high rates of Select (clethodim). 

• Field Sandbur (Cenchrus pauciflorus) and Southern Sandbur (Cenchrus echinatus) 

Both of these equally miserable weeds are only found in sandy soils and fairly easy to distinguish. Field sandbur has thinner, gray colored leaves and yellowish burs that are longer than broad. Southern sandbur has darker and broader leaves and fatter red colored burs. Southern sandbur has a more compact seed head with distinctly more burs than does southern sandbur. Both of these are fairly tolerant to Poast (sethoxydim), Select (clethodim) and Fusilade (fluaziflop). 

• Southwestern Cupgrass (Eriochloa gracilis) and Prairie Cupgrass (Eriochloa contracta) 

These similar grasses are fairly easy to distinguish in the field. Southwestern Cupgrass is one of the wider leafed grasses in the deserts. Prairie Cupgrass leaves are not as wide and are hairy. Southwestern is more branched than prairie and the ligule is shorter and less prominent. The branches are longer and fewer on prairie than on southwestern Cupgrass. Both respond the same to most herbicides. 

• Green Foxtail (Setaria viridis) and Yellow Foxtail (Setaria glauca) 

Both green and yellow foxtail typically form clumps, produce lots of seed and stand more upright than many other summer annual grasses. They are not difficult to distinguish in the field. Green has a darker greenish or brown seedhead compared to the yellow. The leaves of yellow are generally longer and have more bristles (5-20) per spikelet than green, which typically has 3 or less darker colored bristles. Both respond the same to most herbicides. 

• Purple Nutgrass (Cyperus rotundus) and Yellow Nutgrass (Cyperus esculentus) 

Right! These are not grasses. They are sedges which are much different. Sedges all have solid triangular stems. They are perennial and reproduce primarily by below ground tubers. Purple has bigger( 1/8” to 3/4” ) irregular shaped tubers that are connected by rhizomes and have an almond -like odor. Yellow are smaller pea size and round. They are not connected and don’t smell. Yellow is often taller and has pointed leaves while purple has blunt shaped leaves. 

Area wide Insect Trapping Network   VegIPM Update, Vol. 13, No. 18, Sep 7, 2022
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased in the past 2 weeks, below average for the beginning of the produce season.
 
Beet armyworm:        
Trap counts dropped in all locations, well below average for early September.
 
Cabbage looper:          
Cabbage looper numbers remained low consistent with early September.
 
Diamondback moth:      
DBM moths not active in any trap since June; average for this time of the year.
 
Whitefly:                       
Adult movement increased in the past week, about average for early September. 
 
Thrips:                          
Thrips adults decreasing in most locations, and trending comparable to previous years.
 
Aphids:                        
Aphid movement is absent and consistent with what we typically see during the summer.
 
Leafminers:                  
Adult activity tending downward in most locations, below average for early September.