Using Insecticides to Control Whiteflies in Spring Melons 2015
In our last update we discussed whitefly management, but now that daytime temperatures are forecasted to be in the 90’s for the next 10 days, I thought that it would be good to review your insecticide options for whitefly management. Several factors play a role in determining which insecticide(s) you may want to apply. If the grower applied a neonicotinoid at planting (e.g., imidacloprid) the soil residual is likely long gone and it is likely no longer providing control of nymphs and newly-emerging adults. Thus, if whitefly population abundance is sufficiently high enough to justify control, a foliar insecticide is recommended. When nymphs can easily be found on the crown and mid-vine leaves, an IGR or IGR-like product is recommended. This would include: Vetica, Courier, Oberon, and Knack. None of these products will provide good adult knockdown, but if applied correctly, will eventually suppress adult populations by preventing the development of the nymphs within the field. Experience has shown that these products can provide 14-21 days of residual control of nymphs. Control of adults infesting plants from outside sources will require a different approach. A Vydate or Lannate combined with a bifenthrin or Danitol tank-mixture is an option, but will likely only provide adult knockdown, with limited residual control (3-5 d). Among the neonicotinoids, Assail and Venom/Scorpion have shown the most consistent residual adult control (7-10 d) in experimental trials and will also provide decent control of nymphs on treated leaves. Because neonicotinoids are used on many crops grown throughout the year be sure to consider resistance management statements on the label as well as the UA Cross-commodity Guidelines before you apply them. A newer mode of action, Exirel (anthrillic diamide) can provide knockdown and residual control (14 d) of both adults and nymphs following foliar application. Because Exirel works via translmaniar movement in treated leaf tissue, good spray deposition on all melon foliage is important for maximizing control of both adults and nymphs. This brings up another factor that is important to consider – presence of pollinators in or near the field. Be sure to check the label carefully for the Environmental Hazards statement, specifically for language and restrictions on honey bee safety. In some cases, products can be used effectively and safely through application timing and rates, whereas in other cases, some products should not be used when plants are flowering and pollinators are actively working fields. You must read the label carefully. The proximity to harvest may limit your choices as well. The PHIs for whitefly products vary anywhere from 0-7 days. Also, the presence of worms near harvest may influence your choice of products. If you’re using a whitefly specific product (e.g., Courier, Oberon, Knack, Assail, Venom/Scorpion) you might consider adding a pyrethroid for cabbage looper control, or a Lep material (e.g., Radiant, Intrepid, Coragen, Belt) for control of both looper and beet armyworm. Products such as Vetica and Exirel are efficacious against both whiteflies and Lep species. Visit these publications for information on products available for Whitefly Control on Desert melons and Lepidopterous Larvae Control on Desert Melons.
In our last update we discussed whitefly management, but now that daytime temperatures are forecasted to be in the 90’s for the next 10 days, I thought that it would be good to review your insecticide options for whitefly management. Several factors play a role in determining which insecticide(s) you may want to apply. If the grower applied a neonicotinoid at planting (e.g., imidacloprid) the soil residual is likely long gone and it is likely no longer providing control of nymphs and newly-emerging adults. Thus, if whitefly population abundance is sufficiently high enough to justify control, a foliar insecticide is recommended. When nymphs can easily be found on the crown and mid-vine leaves, an IGR or IGR-like product is recommended. This would include: Vetica, Courier, Oberon, and Knack. None of these products will provide good adult knockdown, but if applied correctly, will eventually suppress adult populations by preventing the development of the nymphs within the field. Experience has shown that these products can provide 14-21 days of residual control of nymphs. Control of adults infesting plants from outside sources will require a different approach. A Vydate or Lannate combined with a bifenthrin or Danitol tank-mixture is an option, but will likely only provide adult knockdown, with limited residual control (3-5 d). Among the neonicotinoids, Assail and
Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum, is one of the oldest described Fusarium wilt diseases and the most economically important disease of watermelon worldwide. It occurs on every continent except Antarctica and new races of the pathogen continue to impact production in many areas around the world. Long-term survival of the pathogen in the soil and the evolution of new races make management of Fusarium wilt difficult.
In 2022, we had a lot of watermelon fields infected with Fusarium from Winterhaven to Yuma, Wellton, and Mohawk Valley. Rain, and overwatering of fields when plants set fruits might have contributed to the disease development. It is always a good idea to look out for any potential diseases that might occur this year!
Symptoms of Fusarium can sometimes be confused with water deficiency, even though there is plenty of water in the field. In Yuma valley we have seen fusarium problem in some overwatered fields.
Initial symptoms often include a dull, gray green appearance of leaves that precedes a loss of turgor pressure and wilting. Wilting is followed by a yellowing of the leaves and finally necrosis. The wilting generally starts with the older leaves and progresses to the younger foliage. Under conditions of high inoculum density or a very susceptible host, the entire plant may wilt and die within a short time. Affected plants that do not die are often stunted and have considerably reduced yields. Under high inoculum pressure, seedlings may damp off as they emerge from the soil.
Initial infection of seedlings usually occurs from chlamydospores (resting structure) that have overwintered in the soil. Chlamydospores germinate and produce infection hyphae that penetrate the root cortex, often where the lateral roots emerge. Infection may be enhanced by wounds or damage to the roots. The fungus colonizes the root cortex and soon invades the xylem tissue, where it produces more mycelia and microconidia. Consequently, the fungus becomes systemic and often can be isolated from tissue well away from the roots. The vascular damage we see in the roots is the defense mechanism of the plant to impede the movement of pathogen.
Disease management include planting clean seeds/transplants, use of resistant cultivars, crop rotation, soil fumigation, soil solarization, grafting, biological control. An integrated approach utilizing two or more methods is required for successful disease management.
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:First significant CEW moth activity since mid-November; particularly active in Dome/Wellton/Tacna areas.
Beet armyworm: Moth counts remain very low consistent with seasonal temperatures, but below average for this point in the season.
Cabbage looper: Slight increase in activity, but moth counts remain unusually low for this time of season.
Whitefly: Adult movement is at seasonal low consistent with temperatures and lack of melons or cotton.
Thrips: Thrips activity beginning to pick up, particularly in Tacna and Yuma Valley. Movement is still below average for February.
Aphids: Seasonal aphid counts peaked in early February and tending down last week. Counts remain high in Gila Valley and Wellton. Above average for this time of year.
Leafminers: Adult activity remains light in most trap locations. Trap counts increasing slightly in the South Gila Valley.