Seedling Pests on Fall Crops at Stand Establishment 2018
Now that desert growers have started planting fall melons and will be planting fall produce crops soon, PCAs will be faced with a number of important insect management decisions. As crops begin to emerge, they can expect to encounter a number of insect pests that have the potential to cause serious economic losses to crop stands. These seedling pests include flea beetles, crickets, grasshoppers, darkling and rove beetles, earwigs, and saltmarsh caterpillars (‘woolly worms’). These insects all have chewing mouthparts and most are capable of consuming large amounts of leaf tissue in a short period of time. Seedling crops at the cotyledon stage are most susceptible; these pests can devour entire cotyledons or outright kill small seedlings. If left unprotected, transplants and larger seedling plants can sustain significant feeding damage on the terminal growing points or newly emerged leaves. Not only can this feeding stunt plant growth, but can result in lack of stand uniformity and ultimately, maturity at harvest. Host crop sources for flea beetle, cricket and "woolly worm" infestations include numerous summer crops (e.g., sudan grass, cotton and alfalfa), volunteer melons, and weeds (e.g., purslane). Crickets have been especially numerous this summer, so keep a sharp eye out for these guys. At the Yuma Ag Center, we are also currently noticing flea beetles and crickets on surrounding Sudan grass and weeds. Salt marsh caterpillars have been reported on alfalfa in the Dome Valley area, and are known to disperse from alfalfa and cotton, particularly Pima cotton. Experience suggests that melon fields planted adjacent to these crops/weedy areas are at a high risk from these seedling pests, particularly flea beetles. As summer crops 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 sprinkler chemigation (i.e., pyrethroids) or foliar sprays (i.e., methomyl, neonicotinoids) that can cost-effectively minimize their abundance and damage to emerging produce and melon crops. Additionally, insecticide seed treatments are available for lettuce and broccoli that will protect stands from flea beetles (i.e., NipsIt). For more information on insect pests of leafy vegetables and melons at stand establishment please see Insect Management on Desert Produce and Melons: Pests at Stand Establishment.
Alfalfa is a major crop grown in Yuma area as a cover crop before vegetable season. Generally expected to be a hardy and easy crop to grow, alfalfa production still can be affected by many pests and diseases. Root and crown rot in alfalfa is a common problem. The pathogen Phytopthora megasperma thrives on standing water, overwatered, and/or in soil that lacks good drainage.
The above ground symptoms typically consists of plant wilting, usually occurring quite suddenly, often followed by plant death. The roots turn tan-to-brown, sometimes turning black. Sometimes orange-to-reddish streaks can be observed in rotted roots. Occasionally, the symptoms can be seen in crowns too. Infected plants succumb to death, or grow at reduced rate thus being susceptible to other pests and diseases.
The causal organism survives in soil as mycelia in infected plant tissue or as thick-walled oospores. It also produces thin-walled sporangia that release motile zoospores in the presence of free water. So it is important to grow alfalfa in well drained soils. Adjust irrigation water in a way that there is no standing water for too long. If possible, install tailwater ditch to remove excess water. Plant resistant cultivars like Agate, Apollo if the problem persists in the field. Till the soil deeply to reduce wet soil pockets, level the land before planting.
If diagnosis is confusing, bring the samples to the Yuma Plant Health Clinic for proper diagnosis. Make sure to bring healthy looking plants, sick plant, plants in between etc. Remember, there is no such thing as too much plant tissue when it comes to submitting samples to the clinic!
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: