The following are some of the inquiries received at the UW-Extension office and Master Gardener plant helpline this season in regards to vegetable gardens.
Squash vines are wilting; leaves are yellowing then turning brown; frass is visible along the stem.
Culprit: Squash vine borer. Adults lay eggs at the base of the plant in late June. Eggs hatch and larvae emerge and bore through the stem disrupting water transport in the plant. It is difficult to control.
Floating row covers can be used to cover susceptible plants while adults are present, but it needs to be removed after a few weeks to allow pollinators to visit the flowers. Insecticidal treatments may be used on the adult stage, but timely applications are necessary. If squash vine borer is suspected, remove affected plants and destroy.
Tomato fruits are distorted with black lines encircling and indenting them.
Culprit: Environmental conditions or herbicide injury. This disorder is referred to as “catfacing” and usually occurs on heirloom or large fruited tomato varieties. If temperatures drop below 50 degrees F during flowering and fruit set, pollination is affected and can lead to catfacing. Also, fluctuating soil moisture and 2,4-D herbicide injury can cause this affliction. Select resistant varieties to reduce the incidence of catfacing in future plantings.
Radishes are cracked when pulled from the soil.
Culprit: Environmental conditions or time of harvest. Fluctuating moisture can cause radish roots to swell quickly, which leads to cracking. Also, waiting too long to harvest may cause the roots to crack. Split radishes are edible.
White, powdery spots developing then enlarging on the leaves of pumpkin plants.
Culprit: Powdery mildew. Powdery mildew is a fungal disease that favors humid conditions. It affects melons, squash, cucumbers and gourds. Wind-blown spores land on susceptible plants, infecting it and spreading rapidly to cover the entire leaf and other plant parts. Fewer and smaller fruits may be produced by infected plants.
To reduce the incidence of powdery mildew, increase air circulation around plants and select varieties that have shown resistance to it. Fungicides may be applied, but remember they are preventative not curative.
Unique yellow, mottling on the leaves of watermelon.
Culprit: Mosaic virus. It is difficult to identify the exact virus attacking a plant just by the symptoms. Spread by insect vectors, such as aphids or beetles, viruses can affect the growth of the plant which, in turn, results in small, deformed, or discolored fruit.
There is no control for viruses; yet, management of the vectors transmitting the virus may be helpful in alleviating the problem. Plant resistant varieties, and keep weeds under control since some weeds allow viruses to carry over from season to season. Remove and destroy a plant with a viral infection.
To view photos and to learn more about these or other issues that cause garden grief, check out the UW-Extension Learning Store for helpful publications https://learningstore.uwex.edu.