Consistent with the warm weather we have been experiencing lately, Lettuce aphids, Nasonovia ribisnigri, (aka., Red aphid) are beginning to show up in desert lettuce again. In the past week, we've positively identified lettuce aphid appearing on both head lettuce and romaine in Dome Valley and Wellton. In addition, we have picked up a couple of alate (winged) lettuce aphids on the Ag Center, but no colonization of apterous (wingless) aphids has been observed yet. However, previous experience has taught us that daytime high temperatures in the high 70's and low 80's are ideal for population growth. Thus, we anticipate that lettuce aphids will begin colonizing rapidly throughout March. A few things to remember about lettuce aphids relative to the other aphids we commonly see. First, the immature nymphs are small and have a red appearance, whereas the apterous adults are typically a large brown colored aphid with dark bands running across the abdomen. Second, among the crops we grow locally, lettuce aphids are only found on the lettuce types (Lactuca spp.). Lettuce aphids prefer to colonize the terminal growth, and can often be found in heads or hearts, whereas green peach aphids are often found on the frame leaves in high numbers before moving into the heads. Sampling should be focused in the terminal growth of young plants, and in the heads and hearts of older plants. Third, they can reproduce prolifically, producing many more winged alates than other species, which can quickly lead to widespread abundance throughout a field or a growing area. Finally, as the saying goes "he who hesitates is lost". If lettuce aphids are found on your lettuce, it is recommended that you respond quickly with an insecticide treatment. The product of choice is Movento at 5 oz/ac. Because of its systemic activity, Movento will reach aphids in the protected terminal growth. Be sure to include a penetrating adjuvant for best results at a rate of at least 0.25% v/v. It normally requires 7-10 days of activity before significant reduction in the infestation is observed. For more information please refer to the bulletin: "Lettuce Aphid on Late Season Produce"
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:
Results of pheromone and sticky trap catches can be viewedhere.
Corn earworm:
CEW moth counts decreased slightly after a above average peak in activity for September; particularly active in Wellton and Roll.
Beet armyworm:
Trap counts decreased slightly in most locations, but well below average for September. Most activity in Wellton and Yuma Valley.
Cabbage looper:
Cabbage looper trap counts down in all locations but remain quite active Wellton. Activity normal compared to previous years.
Whitefly:
Adult movement increasing Dome Valley, but down in most other locations; movement is below average for this time of year.
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. Expect activity to begin with N and NW winds.
Leafminers:
Adult activity remains decreased in mostr location and remains low; below average for this time of season.
Diamondback moth:
Beginning to pick up a few moths in Dome Valley and Gila Valley; below average for September so far.
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
