Important Insect Pests at Stand Establishment in Fall Melons 2011
Growers will begin planting fall melon crops within the next week or so and PCAs are likely to encounter a number of insects that have the potential to cause serious economic losses to seedling crops during stand establishment. These include flea beetles, crickets (sometimes grasshoppers), darkling and rove beetles, and saltmarsh caterpillars. Seedling crops at the cotyledon stage are most susceptible to these pests, where feeding by large numbers can devour much of the cotyledons or outright kill the small plants. If left uncontrolled, larger seedling plants (2-4 leaf stage) can sustain significant feeding damage on the newly emerged leaves. Not only can this feeding stunt plant growth, but can result in lack of uniformity and maturity at harvest. Host sources of flea beetle, cricket and "wooly worm" infestations include numerous weeds (e.g., purslane, sudangrass, cotton and alfalfa). Experience suggests that melon fields planted adjacent to these crops are at risk from these seedling pest, and particularly flea beetles. As these summer host plants are harvested or terminated during the next several weeks, these seedling pests typically move to the next available host crop - lettuce, cole crops and melons. Fortunately, there are many registered insecticide alternatives available that can be applied via chemigation (i.e., pyrethroids) or foliar sprays (i.e., Lannate, neonicotinoids) that can cost-effectively minimize their abundance and damage to emerging melons crops. For more information on insect pests of leafy vegetables and melons at stand establishment go to: Insect Management on Desert Melons.
Bacterial Fruit Blotch (BFB) in melon seedlings (2024)
Bacterial fruit blotch (BFB) of melon is caused by the bacterium Acidovorax avenae subsp. Citrulli. The bacteria produces large olive green to brown water-soaked lesions on fruit, making them unmarketable. Symptoms of BFB on seedlings begin with water-soaked areas on the lower surface of the cotyledons and inconspicuous lesions on leaves. BFB lesions will become necrotic often with yellow halos. Lesions are frequently delimited by veins. Infected seedlings collapse and die. Greenhouse conditions are usually favorable for dispersal and establishment of pathogen. Thus, good greenhouse practices and sanitation is extremely important. Clean transplant trays must be used (disinfect trays if they will be reused) and new soil. Destroy any volunteer seedlings and keep the area in and around the greenhouse weed free. Avoid overhead watering if at all possible, or water in the middle of the day so that the plants dry thoroughly before evening. The bacterium can spread on mist and aerosols. Relative humidity should be kept low through proper watering and good air circulation in the greenhouse. Separate different seedlots, to reduce lot-to-lot spread. Monitor these isolated seedlings daily and destroy trays where symptoms develop. The remaining trays should be sprayed with a labeled bactericide and the applications continued until the plants are transplanted to the field. The pathogen can be seedborne, so growers should only use seed that has been tested for the presence of the pathogen by a reputable testing facility. Management of BFB includes a combination of preventing the introduction of the pathogen, sanitation to eliminate any inoculum present, and the use of bactericides if the disease appears. There are no commercially available watermelon cultivars that are resistant to bacterial fruit blotch, but there is some variation in susceptibility among cultivars.
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 continued to decline 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, but well below average for late-October. Most activity in Yuma, dome and Gila Valleys.
Cabbage looper:
Cabbage looper trap counts declined in most areas but increased in the Bard and Yuma Valley. Activity below average for early November.
Diamondback moth:
Adults peaked in Gila and Yuma Valleys and above average in all locations for this time of year. Traps located adjacent to cauliflower and broccoli transplants had the highest trap captures
Whitefly:
Adults remains active in Dome Valley, Wellton, and Roll consistent with melon crops completing harvest, but below average movement for this time of season.
Thrips:
Thrips adult movement increased in most locations last week, particularly in Dome Valley, Wellton, and Tacna. Activity about average for early November.
Aphids:
Aphid movement increased sharply in 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 Gila Valley, Roll and Wellton; about average for this time of season.