The weather this winter thus far has been favorable for aphid development and colonization. Green peach aphid and foxglove aphid have been found colonizing lettuce and broccoli at the Yuma Ag Center for the past week or so. Winged aphids are also beginning to pick up again on small plants. Our local weather forecast suggests that temperatures will be in the mid to high 60’ this week, climbing to the mid-70’s the week after, and with moderate nighttime lows for the next two weeks. Assuming the weather service is correct, these conditions may be ideal for aphid population growth, particularly foxglove aphids. Research has shown us that green peach aphid population growth tends to be high when temperatures average around 55 °F. Because we’ve seen an increase in winged green peach aphids on our yellow sticky traps, PCAs should be extra vigilant in scouting for aphid colonies. Given our weather to date, I predict that Foxglove aphids may become more abundant in the next several weeks as they tend to be more biologically active under warmer temperatures; that is when avg. temps are around 60 °F. For more information, see Foxglove Aphids on Desert Produce. If the field has been treated with imidacloprid at planting, then chances are you are in pretty good shape. But, continue to monitor as imidacloprid doesn’t generally last all season, particularly in cool, cloudy weather when the plants transpiring at a rapid rate. Regardless of whether you find green peach aphid or foxglove aphid the key to effective aphid management with foliar insecticide is to initiate sprays at the time apterous (wingless) aphids begin to colonize. If you can regularly find aphid colonies on imidacloprid treated lettuce, then it is probably time to treat with a foliar insecticide. Of course, this requires diligent scouting and sampling. On older lettuce, make sure you thoroughly examine developing heads/hearts; this is where foxglove aphids are most abundant. Fortunately, PCAs have alternatives for foliar aphid control. Note: Sequoia (sulfoxaflor) was recently re-registered for use on leafy vegetables. For more information on insecticide alternatives please visit Aphid Management in Desert Produce Crops – 2017. So keep your eyes open for new aphid colonies and plan according. 

In response to the recent outbreaks of Diamondback moth (DBM) , Plutella xylostella in Yuma, we have established a pheromone trap network designed to monitor the activity and movement of adult populations of DBM. PCAs have had difficulty controlling DBM in cabbage, broccoli and cauliflower since October. Traps have been placed in Roll, Wellton, Dome Valley, Gila Valley and Yuma Valley in locations where cole crops are presently being grown or in areas where infestations were known to occur this fall. 

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%). Spinach ‘Revere’ was seeded, then sprinkler-irrigated to germinate seed Jan 18, 2024 on beds with 84 in. between bed centers and containing 30 lines of seed per bed.  All irrigation water was supplied by sprinkler irrigation.  Treatments were replicated four times in a randomized complete block design.  Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed.  Treatments were applied with a CO₂backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles. 
 

Month	Max	Min	Average	Rainfall
January	68	42	54	1.14 in
February	73	47	59	0.50 in
March	77	50	63	0.31 in

 
Downy mildew (caused by Peronospora farinosa f. sp. spinaciae) was first observed in plots on Feb 19  and final reading was taken on February 26, 2024. Spray date for each treatments are listed in excel file with the results.   Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft² areas within each of the four replicate plots per treatment.  The number of spinach leaves in a 1-ft² area of bed was approximately 144. 

The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Products that  provided effective control against the disease include Orondis ultra, Thrive 4 M, Fungout, Cevya, Eject and Zampro. No phytotoxicity was observed in any of the treatments in this trial.

For those of you interested in the latest developments in Vegetable IPM and/or in need of CEU’s, Yuma County Cooperative Extension has created online workshops that offer CEU and CCA credits for both AZ and CA. Current offerings are the recorded workshops from 2021 Southwest Ag Summit. There’s an ag mechanization session entitled “Advances in Weed Control Technologies”, and several others that readers of this newsletter may be particularly interested in including: “Integrated Pest Management Regulatory Update” “Pesticide-Related Updates: The Latest Presented by the Greatest” “Influence of Irrigation on Insect, Weed, and Disease Management” “Advances in Weed Control Technologies” “Integrated Pest Management in Vegetables”. Please recognize Yuma County Cooperative Extension Agricultural Agent Robert Masson who spearheaded this effort. Click on the image, or here to access Veg IPM workshops online.

Weeds that are outside of fields can still be harmful to crop production. This does not include ditch banks or fallow fields. Non-crop weed control includes weeds around buildings, roadways, equipment yards, fence lines etc. It is different than fallow ground or ditch banks weed control and includes places where crops are not grown. Weeds in non-crop areas can be a source of weed seeds that blow or are carried into places where crops are grown. They can also be a refuge for insects,  diseases and rodents. The reason that these herbicides are registered for non-crop areas is that they are broad spectrum and persistent. Some are registered for use in fields but at much lower rates than for non-crop areas. For instance, Diuron can be used on alfalfa at 1 to 1.5 qts/ac. but is used for non-crop areas at 12 qts/ac.

Herbicide	Weeds Controlled	Activity	Soil Residual	Comments
Bromacil	Broadleaves and grasses	Preemergence	1 to 2 years	The nuclear option Should be incorporated with water. Keep away from roots of desirable vegetation.
Hexazinone	Broadleaves and grasses	Preemergence and Postemergence	1 to 2 years	Keep away from roots of desirable vegetation. Incorporate with water.
Diuron	Broadleaves and grasses	Preemergence and Postemergence	2 years	Incorporate with water but do not leach into roots of desirable vegetation
Prometon	Broadleaves and grasses	Preemergence and Postemergence	1 to 2 years	Must be incorporated with water
Tebuthiuron	Broadleaves and grass. Good on hardwood trees	Preemergence and postemergence	2 years	Incorporate with water. Contact with even on feeder root of desirable vegetation can be lethal
Imazapyr	Broadleaves and grasses	Preemergence and post emergence	1 year	Primarily a postemergence herbicide but is readily absorbed by rootsif incorporated with water
sulfometuron	Broadleaves and grasses	Preemergence and post emergence	1 year	Must incorporate with water
Aminopyralid	Broadleaves	Preemergence	1 year	broadleaves only. Shorter soil residual for weeds but crops can not be planted for 1-2 years

Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:            
CEW moth counts decreased considerably y in the past 2 weeks and about average for late summer
 
Beet armyworm:         
Trap counts stay active in some locations (Yuma Dome Valley and Wellton) particularly near alfalfa
 
Cabbage looper:         
Cabbage looper numbers remain low consistent previous years.
 
Diamondback moth:      
DBM moths were not caught in any trap since June; average for this time of the year.
 
Whitefly:                      
Adult movement decreased in past 2 weeks consistent with previous years
 
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 has highest in Wellton and Dome Valley, and slightly above average for early August