Since the bagrada bug became established in the desert in 2010, growers and PCAs quickly found that preventing excessive feeding damage on newly-established crops is critical to economic broccoli production. Local surveys have estimated that the invasive stink bug annually infests more than 80% of the acreage in Arizona and southern California, resulting on average in more than 10% stand losses and plant injury to direct-seeded broccoli crops. The potential for the pest to cause significant crop losses coupled with the lack of biological control alternatives has left little alternative but to control outbreak populations with foliar applied insecticides. Furthermore, because bagrada bug can quickly cause significant feeding damage to seedling plants, effective insecticide treatments applied in the field need to be quick acting. Currently, vegetable growers in Arizona and California rely heavily on frequent applications of pyrethroid insecticides to control adult infestations on seedling cole crops. Given the magnitude of pyrethroid usage historically applied to desert vegetable crops, alternative insecticides will be needed to protect desert cole crops from bagrada bugs and conserve the pyrethroid chemistry. Among the newer classes of chemistry, foliar-applied neonicotinoids such as Venom/Scorpion have been shown to effectively control bagrada bug adults, but at-planting, soil systemic applications of neonicotinoids such as Admire Pro, Belay and Venom do not prevent bagrada bug from damaging seedling broccoli plants. However, in other parts of the world neonicotinoid seed treatments have been shown to provide protection against bagrada bug. For example, in India, field trials showed that planting mustard seeds treated with imidacloprid resulted in significantly lower plant damage due to bagrada bug. Recently, Valent U.S.A. registered clothianidin as a seed treatment on broccoli under the name of Nipsit®. Based on our research, this technology provides another tool for broccoli growers to use in their annual battle against bagrada bugs in the desert. The results of field trials conducted at the Yuma Ag Center from 2012-2014 that evaluated the effectiveness of Nipsit (clothianidin) seed treatments for preventing bagrada bug feeding damage and yield loss in broccoli can be found in Evaluation of Clothianidin Seed Treatments for Bagrada Bug Control in Broccoli.
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.
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:
Area wide Insect Trapping Network VegIPM Update, Vol. 11, No. 21, October 14, 2020
Results of pheromone and sticky trap catches can be viewedhere.
Corn earworm: Moth activity is above normal for early October ad has been steadily increasing since mid-September, particularly in Dome Valley and south Yuma Valley.
Beet armyworm: Moths remain active throughout the desert, especially in Texas Hill and Dome Valley growing areas.
Cabbage looper: Cabbage looper activity remains unusually low for early October, likely a result of unusually hot weather. Larvae just starting to show up in some fields.
Whitefly: Adult movement has been about average for this time of year. Activity highest in Wellton and Roll near fall melons.
Thrips: To date, thrips activity has been seasonably low at all trap locations; most activity found in Bard. Numbers beginning to slowly trend upward
Aphids: Aphids have been caught in only one trap thus far (Bard). Normal for this time of year. Still early, anticipate they will begin to show up in heavier numbers in mid-late October.
Leafminers: Adult activity below normal for September, but moderate numbers caught in Wellton and south Gila Valley in areas where cotton was recently harvested and disked under.