I want to share several vegetable alerts that was brought to my attention by Dr. David Langston.
1. Serious epidemic of Downy Mildew located and confirmed in Cook County. We need to be aware of this discovery because Downy Mildew can spread rapidly and produce devastating effects. You can identify this disease by locating very dark angular lesions on the leaves. The lesions may be present with or without chlorosis surrounding the lesions. Also, the leaves may be curled resulting in a “fiddlehead-shaped” leaf. Please see the attached pictures provided by Tucker Price. Dr. Langston suggests that Ranman and Zampro can be the primary products used to reduce the severity and spread of Downy Mildew. To increase the efficacy and disease control spectrum these products need to be tank-mixed with Mancozeb or Chlorothalonil.
2. Southern Armyworm in Tomato fields. The finding of Southern Armyworm is not unusual. But this season’s discovery has been of Southern Armyworms that are not easily killed. The worms have survived applications of several products, including Pyrethroids. The infested fields have been cleaned up with Lannate.
3. Spider Mites discovered in multiple crops. Injury has been documented in a variety of cucurbits but mostly found in watermelon. Spider mite infestations generally begin at the edge of the fields. But spider mites thrive in hot and dry weather so anywhere there is settling of dust on the crop is a probable early spot of infestation. To scout and verify the presence of mites, look for the actual mite, usually on the bottoms of leaves.
To check for spider mites in watermelons – Generally, the infestations will begin in the crown of a watermelon and spread from that point. Early infestations of spider mites will produce a speckling of the leaf. This symptom is often misdiagnosed as a disease.
To check for spider mites in cantaloupes – The mites are typically found evenly distributed across the foliage. There will be yellow spotting found on the leaves that was produced by the mites.
Control options for spider mites in watermelon and cantaloupe: Agri-mek (and generics) has an advantage in control because it can move through the leaf. This product translocation assists in control of the mites on the bottom of the leaves. Adding a penetrating surfactant will improve the movement of product.
Other spider mite control chemistry can provide control. But, they are contact products and require careful application for acceptable control.
If spider mite infestations are located early you can use Zeal (growth regulator) or Oberon. Because Zeal is a growth regulator, it cannot control adult mites. But, Zeal provides excellent activity on immatures. Oberon will provide good control, that is evident within 5-7 days after treatment. Depending on the rate at which Oberon is applied, more than one application may be needed for control. Oberon applied at a low rate will most likely require a second application. But one application of Oberon is sufficient when applied at a higher rate (8.5 oz.) and at a slow rate of speed.
For rescue treatments, there are 4 options: Agri-mek, Acramite, Portal, Kanemite