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%). 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.

Earlier this week, we initiated a trial examining the use of band steam for controlling Fusarium wilt of lettuce. The premise behind this research is to use steam heat to raise soil temperatures to levels sufficient to kill soilborne pathogens. For Fusarium oxysporum f. sp. lactucae, the pathogen which causes Fusarium wilt of lettuce, the required temperature for control is generally taken to be > 140°F for 20 minutes. Soil solarization, where clear plastic is placed over the crop bed during the summer, exploits this concept. The technique raises soil surface temperatures to 150-155˚F, effectively killing the pathogen and reducing disease incidence by 45-98% (Matheron and Porchas, 2010).

In our trials, we are using steam heat to raise soil temperatures. Steam is delivered by a 35 BHP steam generator mounted on a custom designed elongated bed shaper (Fig. 1). Preliminary results were encouraging. The device was able to increase the temperature of the top 3” of soil to over 180°F at a travel speed of 0.5 mph as shown in this video of the machine in action (shown below). These temperatures exceed that of those known to control pathogens responsible for causing Fusarium wilt of lettuce (> 140°F for 20 minutes).

Stay tuned for final trial results and reports on the efficacy of using steam heat to control Fusarium wilt of lettuce.

If you are interested in evaluating the technique on your farm, please contact me. We are seeking additional sites with a known history of Fusarium wilt of lettuce disease incidence to test the efficacy and performance of the device.

References
Matheron, M. E., & Porchas, M. 2010. Evaluation of soil solarization and flooding as management tools for Fusarium wilt of lettuce. Plant Dis. 94:1323-1328.

Acknowledgements
This project is sponsored by USDA-NIFA, the Arizona Specialty Crop Block Grant Program and the Arizona Iceberg Lettuce Research Council.  We greatly appreciate their support.

A special thank you is extended to Cory Mellon and Mellon Farms for allowing us to conduct this research on their farm.

Weeds are one of the most visible of all agricultural pests. They can’t move or hide and once established often stick up over the crop. Just one weed in a 10 acre field is annoying to look at. With insects and diseases, the damage is often more visible than the pest. That is not the case with weeds. A moderate weed infestation is approximately 10 weeds per square foot. If a herbicide produces 90% control, that leaves 1 weed per square foot or 43 weeds per acre. Without an untreated check, this can look like the herbicide failed!  It is easy to leave an untreated spot in a field and it is well worth doing. Many applicators do so unintentionally because of skips, powerlines and other causes. They help determine crop injury and weed control. Here are some examples of what various levels of control looked like from one of our cole crop trials:

Area wide Insect Trapping Network   VegIPM Update, Vol. 12, No. 20, Oct 6, 2021.
 
Results of pheromone and sticky trap catches can be viewed here.
 
Corn earworm:             
CEW moth counts continue to be active, about average for this time of the season; particularly active in Wellton and Yuma Valley.
 
Beet armyworm:         
Trap counts increased slightly in most locations, but well below average for early October. Most activity in Dome and Yuma Valley.
 
Cabbage looper:           
Cabbage looper trap counts remain steady in most areas. Activity about normal compared to previous years. 
 
Whitefly:                       
Adult movement increasing Dome Valley and Wellton, but down in many other locations; movement is below average for this time of year, but should anticipate increase movement with melon harvest beginning. 
 
Thrips:                         
Thrips adult movement increased slightly in some locations, particularly in Wellton and Tacna, but remains below average for mid-September.
 
Aphids:                        
Aphid movement has been absent since early June typical with high summer temperatures, and the monsoon flow.  Picked a up a few aphids last week with the break in weather and change in wind direction. 
 
Leafminers:                  
Adult activity remains low in most location; below average for this time of season.
 
Diamondback moth:    
Significant increase in moth activity in the last week, particularly in Dome Valley and N. Gila Valley in traps located adjacent to cauliflower and cabbage transplants.