Let’s discuss some of the insects and diseases I’ve been seeing on vegetables here in the county:
Powdery Mildew on Squash:
I have seen quite a few squash fields with powdery mildew so be on the look out. Below are some images to illustrate the symptoms:
A good spray program for powdery mildew in squash would be Torino rotated with Procure or Proline.
Proline is a new product by Bayer that provides effective control of powdery mildew, anthracnose, gummy stem, and fusarium.
To no ones surprise I am seeing a lot of silverleaf as well. Silverleaf is a physiological disorder that occurs as a result of whitefly feeding on the underside of leaves. See pictures below:
Neonicotinoids in general control whiteflies. Venom (dinotefuron) has shown better efficacy than some other neonicotinoids. Rotate Venom with a different mode of action such as Coragen (chlorantraniliprole).
Downy Mildew on Cucumbers:
Downy mildew is going around in cucurbits right now, with some possible resistance concerns with Zampro and Ranman. Here are some pictures I’ve taken in the county:
A tell-tale sign of downy mildew is the shape. Downy mildew tends to be square shaped because it is bound by the veins and will never cross over the vein.
Potyvirus in Cucumbers:
A potyvirus (papaya ringspot, watermelon mosaic, or zucchini yellow mosaic virus) was confirmed in a cucumber field last week. Potyvirus is introduced by aphids. Aphids carry the virus passively on their mouth parts and infect plants when they feed. Even undetectable populations of aphids can infect an entire field with a potyvirus. Below are some images of how the virus appears on cucumber:
There are no effective chemical controls to stop the spread of potyvirus. Insecticides are non-effective in controlling the spread of the virus because they are unable to kill aphids before they have acquired and transmitted the virus. The incidence of these viruses is unpredictable between years and locations.
Flea Beetles on Eggplants:
Eggplants are typically pest free, however, one pest we can count on to arrive are flea beetles.
Historically pyrethroids would take care flea beetles, however, recently we have seen reduced efficacy. Nevertheless, your best option remains a pyrethroid. Apply a high rate of bifenthrin and if needed combine with lannate.
Pepper weevils have been found in the county so be on the look out!
Thomas County Agent, Andrew Sawyer recently posted a great blog about pepper weevils: