Over the past two weeks, the sticky traps in our Areawide Insect Trapping Network placed near recently disked up produce fields have been literally covered with flies. Many of the flies identified on these traps were adult seedcorn maggot (SCM). This is not surprising since it is this time of the year that SCM can cause significant stand reductions in spring melons and other large seeded crops due to larvae feeding on germinating seed, roots and even stems. If SCM populations are high, replanting parts or all of an infested field is often necessary. Not only is this an inconvenience to the grower, but replanting is expensive and can disrupt harvest schedules. Unfortunately, once maggots have been found infesting the soil during stand establishment, there is usually nothing one can do. Thus, avoidance of the problem is the most effective way of preventing stand reductions. First, weather plays a major role in determining the damage potential for SCM to be a problem. Melon stands are more susceptible to SCM during wet, cool spring weather in which seed germination is slowed or delayed. These conditions give SCM a chance to develop in the soil and attack the seeds before they can emerge. So far this spring, our weather conditions have been just the opposite, warm and dry. Secondly, our cropping system plays a key role. Melon crops following produce are the most often attacked because SCM are attracted to fields with high levels of decomposing organic matter. This includes heavy plant residue remaining after harvest of the previous lettuce or cole crop, as well as applications of manure prior to planting. Growers would be encouraged not to plant melons into fields under these conditions. Unfortunately, given the demands on local acreage, this is sometimes not practical. However if growers decide to plant in these conditions, then it would be wise to use a preventative insecticide applied at planting to minimize the impact from SCM and give seedling stands a fighting chance. Guidelines for SCM management can be found in Seedcorn maggot 2014, and alternatives that have shown activity against SCM and may be practical for SCM management in spring melons can be found in SCM Control on Cantaloupes.
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 remained low over the past 2 weeks across all locations and about average for this time of the season.
Beet armyworm:
Trap counts decreased in most locations, and well below average for late-November. Most activity in Yuma Valley.
Cabbage looper:
Cabbage looper trap counts remained low in most areas but increased in the Yuma Valley. Activity below average for late November.
Diamondback moth:
Adults peaked in Bard, Gila and Yuma Valleys and slightly above average for this time of year. Traps located adjacent to cauliflower seed crops had the highest trap captures
Whitefly:
Adults remains active in Dome Valley and Roll consistent with melon crops completing harvest, but below average movement for this time of season.
Thrips:
Thrips adult movement decreased in most locations last week, and most active in Dome Valley, Wellton, and Tacna. Activity about average for mid-November.
Aphids:
Aphid movement peaked so far this season with highest activity in Dome Valley, Bard, N. Yuma Valley and N. Gila Valleys over the past 2 weeks. Activity average for this time of year.
Leafminers:
Adult activity increased sharply in the Dome, Yuma, and Gila Valleys, about average for this time of season.
