It’s been eight years since the bagrada bug first invaded desert cole crops. In the first few years the small stink bug was quite disruptive, but I think most would agree that bagrada bug population pressure has been relatively light the past few years. In fact, last fall had the lightest infestations we’ve seen since the widespread outbreaks in 2010 when the bagrada bug first occurred on desert cole crops at damaging levels. In an attempt to document changes in the severity of bagrada bug infestations on direct-seeded and transplanted cole crops and the intensity of chemical management, we have annually surveyed growers and PCAs from Yuma, Maricopa and Imperial counties since 2010. We recently conducted our annual survey two weeks ago. Results of the survey show that since 2010 the cole crop industry has experienced widespread bagrada bug infestations throughout the desert from September into November, although some years have been less intense than others. Last fall (2017) was the lightest year we’ve seen to date. Based on seasonal population abundance studies of adults infesting non-treated broccoli plants at the Yuma Ag Center (see graphs below), bagrada bug infestations in the fall 2016 and 2017 were lower than what we had observed since the pest first showed up in the desert. Bagrada bug population abundance on non-treated broccoli plots have also been consistently declining since 2012. Estimates of stand losses from bagrada bug infestations at stand establishment in both direct-seeded and transplanted crops have decreased significantly the past 5 years and were particularly low in 2017. The lower losses reported in 2017 are due to the lighter bagrada pressure experienced last season. Plant injury, defined as plants with multiple heads, forked terminals, and/or blind terminals resulting from Bagrada feeding, was also lower in 2017 compared to previous years. These data suggest that PCAs have adopted effective management programs to protect seedling crops during stand establishment. Insecticide usage to control this pest was at its lowest in 2017, and the percentage of acreage was treated in 2017 was lower than previous years. Pyrethroids remain the primary product used for controlling bagrada bug adults either via chemigation or with foliar spray applications. Based on survey results, products that have contact activity appeared to provide the most effective control against bagrada adults on both direct-seeded and transplanted cole crops. Results from the survey also showed that over half of direct seeded broccoli was treated with clothianidin (Nipsit) in 2017 and performed well in controlling adults and protecting stands. Overall, the results of the PCA survey are consistent with results obtained in research trials conducted at the Yuma Agricultural Center over the past four years. A summary of the 2010-2017 survey results can be found in the following report: Impact of Bagrada Bug on Desert Cole Crops: An Eight Year Summary.
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:
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
