Summer is in full swing, and the pests are no exception. This past week saw an escalation of many of our common insect pests. For control of any of the pests mentioned below, please consult the Cucurbit chapter of the Midwest Vegetable Production Guide for our most up to date recommendations.
Striped cucumber beetles– The summer generation has emerged and an uptick of beetles can be found on the lower stem and leaves of plants, and particularly in flowers. While the beetles pose no immediate threat to larger plants, keep an eye on the sizing green fruit which can be susceptible to feeding and eventually scarring, potentially affecting marketability.
Wilting plants– For those areas of the state where it has been hot and dry, pumpkin and squash plants may naturally wilt a bit during the day but then recover in the evening when temperatures cool off. If the plant stays wilted and shows any symptoms of leaf yellowing or even necrotic or brown tissue between the veins, it might be bacterial wiltor squash vineborer.
Severely wilted plant…is it bacterial wilt or squash vine borer? Can’t reliably tell just by looking at the plant.
To check for bacterial wilt, cut the plant stem and press the two ends together, then slowly pull them apart. If strings of syrupy liquid can be seen between the pieces (cut ends), it is likely the plant is infected. This test is usually fairly reliable but if no strings are seen, the plant may still be infected. Unfortunately, for plants that are infected, there is no remediation and should be rogued out.
Before you cut the stem and look for bacterial wilt, look closely near the base of the plant for evidence of squash vine borer (SVB) entering the stem. If there hasn’t been a significant rain event recently, look for brownish wet sawdust material (insect frass or excrement) which is strong evidence for this pest. If you decide to sacrifice the plant, slice down the stem and you may find more frass and up to several white grub like insects tunneling through the stem. As the immature SVB chew through the water conducting tissue of the vines (xylem), wilting results. Once the borers are in the vines, there is no treatment. It is possible that plants can have both bacterial wilt and SVB, for a double whammy of wilting.
Squash vine borer frass at the tip of the blade.
Slice the base of the plant open to find squash vine borer larvae (at tip of blade).
To round out the insects increasing on squash and pumpkin crops, keep an eye on Squash Bug populations. Whitle these insects can vector Yellow Vine Decline, it has not been a huge economic concern in Ohio so far. Heavy numbers of bugs feeding on plants can cause them to collapse.
Squash bug eggs.
A squash bug adult.
An emerging disease in the state with several names (Plectosporium, Microdochium, and White speck) can now be readily seen affecting foliage, petioles, and the veins on the backs of leaves. As this disease progresses, it will eventually bleach and kill the vines, ruin the handles and mar the fruit, giving them a white blotchy appearance. Dr. Sally Miller will be writing a more detailed article on this disease and its management in an upcoming veg blog post.
Plectorsporium symptoms on pumpkin leaves.
Plectorsporium on leaf petiole. Note the diamond or spindle shaped lesions on the petiole and major leaf veins.
Be on the look out for powdery mildewin the next week or two, as it has been arriving in Ohio anytime from the middle of July through the first week of August. As of this blog post, no powdery mildew or downy mildew has been reported in the state.
Lastly, mark your calendar for the annual Pumpkin Field Dayto be held at the Western Ag Research Station in South Charleston on August 23 from 6-8 pm. More details will be forth coming.