Pest Pressure on Desert Produce and Melon Crops in 2012
At a recent meeting, I made the statement that the insect pest pressure on produce and melons crops in the Yuma area this fall was as heavy as I’ve seen it in many years. That comment was based largely on my observations, both on and off the Yuma Ag Center, as well as from anecdotal reports from PCAs and growers. This claim is further supported by a quick analysis of both recent and historic data on pest abundance recorded from our research plots here in the Yuma area. First, whitefly adult numbers on fall melons and produce were extremely high. In fact, my untreated melons plots on the Ag Center wilted and died rapidly as a direct result of heavy whitefly feeding. Furthermore, captures of whiteflies on yellow sticky traps placed near cantaloupe fields in the Wellton, Tacna Texas Hill area, were twice as high as they have been in the past 5 years, and CYSDV incidence in cantaloupe fields in this area was also higher in 2012. Similarly, worm pressure - particularly beet armyworm and cabbage looper- was higher than I’ve seen it in the past 6-7 years. Populations began infesting plots in early September, and egg deposition and larval development remained steady through October. In fact, worm numbers were 3-fold higher in 2012 than we what observed last fall. Additionally, corn earworm was present in higher numbers than what I’ve observed in past years. Finally, Bagrada bug infestations were the highest I’ve seen on the Ag Center since the invasive stinkbug first showed up in Yuma in 2009. The low-moderate population appeared in early September, but reached very high levels by mid-September and peaking in early October. The numbers I observed were much higher than the populations that occurred last season, and actually slightly higher than we saw in 2010. The infestation levels in our untreated broccoli plots this year remained at damaging levels throughout October. In contrast, thrips population numbers have been low, relative to what we normally see this time of the year, and I have not picked up any winged aphids or colonies on lettuce thus far. However, I’m not sure how that translates to potential population pressure in January and February, and you should anticipate them showing up as usual. I’ve been asked why the pest pressure was so relatively heavy this year. I really don’t know. Could the heavy monsoon moisture we had in July and August have been an influence? It may have, but it may not have. Insect abundance is dictated by many abiotic and biotic factors in our cropping system, and it’s nearly impossible to consider all the factors necessary to draw a reliable conclusion. Nonetheless, graphics showing these recent trends in Whitefly, CYSDV, Lep Larvae and Bagrada abundance can be found at Pest Abundance on Desert Produce and Melon Cops in 2012.
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: