With the produce season essentially finished, it’s time to begin thinking about insect management in melons. Spring melon crops are rapidly growing, and so are insect pest populations. Cabbage loopers and leafminers are becoming evident in some areas, and PCAs should start ramping up their monitoring and sampling. More importantly, whitely populations are quietly becoming abundant on the spring melons of all sizes. Adults can easily be found on recently planted melons located at the Yuma Ag Center, and reports from local PCAs suggest that adult populations are beginning to show up on older plantings. As temperatures increase and crops/weeds mature, avoidance of excessive feeding from whitefly nymphs should be the primary concern on all melon types. Although CYSDV does occur in later spring melons, it is rarely yield limiting. But honeydew and sooty mold contamination on cantaloupes, mixed melons and watermelons can significantly reduce quality and marketability is whiteflies are not adequately controlled. Our research has shown that to prevent fruit yield and quality losses on spring melons, a foliar insecticide treatment should be applied on threshold; that is, when average adult numbers exceed 2 per leaf when averaged across an entire melon field. At this level of adult abundance, immature populations are beginning to colonize. Timing sprays based on the adult threshold has been shown to significantly reduce the chance of yield / quality losses during spring harvests. This threshold applies for the use of recommended IGRs (Courier, Knack, Cormoran, and Oberon), foliar applied neonicotinoids (Assail, Venom, Scorpion), neonicotinoid-like compounds (Sivanto prime and Transform), diamides, (Exirel and Minecto Pro) and the feeding disruptors (PQZ and Sefina). For more information on whitefly management and available insecticides, go to these documents on Insect Management on Spring Melons: Whiteflies and Whitefly Control Chart-Spring Melons -2024. Also, be aware of honey bees and other pollinators in or around melon fields. If bees are present, be sure to carefully read labels and determine bee safety of a product before making an application in a melon field. If applications are necessary during bloom, only apply a product that is considered bee safe (e.g., PQZ, Sefina, Sivanto, Assail). We also recommend that insecticides only be applied when honeybees are not actively working in the field (e.g. 10:00 pm – 3: 00 am).
Lettuce dieback is a soil-borne disease caused by two closely related viruses from the family TombusviridaeTomato Bushy Stunt Virus (TBSV) and Lettuce Necrotic Stunt Virus (LNSV) that has been reclassified as Moroccan Pepper Virus (MPV). The disease has been observed throughout the main lettuce producing areas of California and Arizona.
This year we have been receiving some samples that looked like lettuce dieback disease. The samples came positive for a new virus named as Lettuce dieback associated virus and negative for tomato bushy stunt virus. In the past we have seen symptoms in resistant cultivars (with Tvr1 gene) which suggests that the new virus is involved in the symptomology.
The virus is soilborne, and has been found to have more correlation with the dieback disease more than Tomato bushy stunt virus. Flooding or poor drainage, high salinity, plant stress, and soil saturation have been associated with high incidence of virus .
If you have plants showing symptoms of Tomato bushy stunt virus, please bring the samples to Yuma Plant Health Clinic for diagnosis.
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.
Managing Water with Preemergence Herbicides in Lettuce
We are always adjusting how we use herbicides to fit the unique conditions in this area. The herbicides that are registered for use on lettuce here are limited and they all require a little different management. Environmental conditions, soil characteristics and Chemical properties all can greatly affect how well the 3 preemergence herbicides used in lettuce will work. These include Balan, Prefar and Kerb. Environmental conditions and soil characteristic vary greatly from year to year and field to field. It is difficult to make general recommendations on how best to use these three herbicides because of this. Chemical characteristics do not vary, however, and we can make some generalizations on how they should be used.
We use a lot of water here during stand establishment and at this time of year. The water solubility of Balan, Prefar and Kerb vary widely and should be considered when deciding how to use them. Water solubility is the amount of the herbicide that will dissolve in water. This is usually given as PPM or mg/liter. The higher the number the more soluble it is. Solubility will effect leaching into the soil and runoff. The solubility of Balan is 0.1 PPM,Prefar is 5.6 PPM and Kerb is 15 PPM. What this means is that Balan is very insoluble and has to be mechanically incorporated. Prefar is 56 times more soluble than Balan and can be incorporated with overhead water but this is still not a very soluble herbicide and a lot of water is needed. Kerb is 150 times more soluble than Balan and almost 3 times more soluble than Prefar. Kerb will leach and the amount of overhead water applied must be carefully managed.
