With shorter days, cooler temperatures and winds consistently blowing out of the north and west, PCAs should begin to see an increase in winged aphids and colonies showing up on desert produce crops. We’ve already had reports of green peach aphid colonizing broccoli plants in the Gila and Dome Valleys. Experience tells us that this is an annual occurrence. The key aphid pests found on winter produce do not over-summer here, rather they migrate into our cropping system from mountainous regions of southern California via wind currents during the late fall. Once the aphids reach our desert valleys, they typically move from crop to crop until they find a suitable host to feed and colonize on. No need to panic if you suddenly find a few winged aphids on a lettuce plant. But it is important that you correctly identify the aphid species found on your crops. It is not uncommon to find winged aphids on lettuce or broccoli that do not colonize on the crop. An example of these would be cabbage aphid which will colonize and infest cole crops but not lettuce, spinach or celery. Other examples would include aphids that colonize small grains (i.e., oat bird-cherry aphid) or alfalfa (i.e., blue alfalfa aphid). Because these aphid species will not colonize produce crops, it is important to be able to distinguish them from the aphids that do colonize and require management to prevent problems at harvest (i.e., green peach aphid, foxglove aphid, lettuce aphid, cabbage aphid). Proper aphid ID can also influence your choice of insecticide, but more on that in a later update. Don’t be surprised if you start finding small colonies of cowpea aphids showing up on frame leaves in lettuce. That is a common occurrence every fall. Not to worry, experience has shown us that although small cowpea aphid colonies may be found on lettuce, the populations generally stay low on the plant on the frame leaves and rarely increase to levels causing contamination issues. But you never know. So keep a close watch out for these aphids found in your crops, as our weird weather this year may be more conducive to their development than normal. Bottom Line: proper aphid identification is important; it can save a PCA time and money, and prevent unnecessary insecticide applications. If you find an unusual aphid in your produce, don’t hesitate to drop it by the Ag Center and we’ll get it identified for you. If you want to make fast and accurate IDs, you might use the attached publication Aphid Identification in Desert Produce Crops that can assist you in identifying winged and wingless (apterous) aphids important in leafy vegetables and cole 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%). 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.
Controlling Fusarium Wilt of Lettuce Using Steam Heat – Trial Initiated
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:
Corn earworm:
CEW moth counts increased in the past two weeks particularly in Wellton and Roll.
Beet armyworm:
Trap counts beginning to increase in most locations especially in dome Valley and the south Yuma Valley.
Cabbage looper:
Cabbage looper increased in all locations particularly in Wellton, Dome and N. Yuma Valleys consistent with reports of eggs in the in the field.
Whitefly:
Adult movement increasing in all locations and particularly in Dome/Wellton; about average for this time of year.
Thrips:
Thrips adult movement remains about average for early September.
Aphids:
Aphid movement has been absent since early June typical with high summer temperatures, and the monsoon flow.
Leafminers:
Adult activity remains similarly low, above average for this time of season.
Diamondback moth:
First record of DBM adults since early June. Are appearing sooner than last season, likely from high altitude winds associated with Tropical Storm Nora experienced last week.
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
