Q: What’s up with cucumber plants dying so early in the season? We started with gorgeous Diva seedlings, which initially produced tons of tiny or miniature cukes – most of which never grew into actual cukes. After harvesting about 15 cukes from three plants, the leaves started turning yellow or brown. There were lots of small dark specks on the plants. I asked around and almost everyone I chatted with said that their cuke plants also died. I think I had aphids, but not as many whiteflies. When we pulled the plants, it didn’t appear to be nematodes. We rotate our planting every other year.
A: According to UC master gardener Rachel Tooker, cucumbers are a member of a plant family (Cucurbitaceae) that also includes muskmelons, watermelons, pumpkins, squash and gourds. These are warm-weather plants that grow quickly, produce fruit, and then die within one growing season.
Depending on the variety, harvest time for cucumbers usually occurs from 50 to 75 days after planting, and plants start to die back soon after production ceases.
It is important to harvest the cucumbers regularly. If they are allowed to grow too large, this signals to the plant that its work is done and it will begin to die back even more quickly.
After the last cucumbers are picked, the plant’s leaves will turn yellow and die back. Pull up the dying plant immediately to reduce the potential for attracting insect pests or fostering diseases.
The small mite-like bugs that you mention are possibly aphids or thrips. Aphids are small, soft-bodied insects that feed on plant fluids. Large populations can cause curling, yellowing and distortion of leaves and stunting of shoots. They also exude a sticky substance known as honeydew, which often turns black with the growth of a sooty mold fungus.
High levels of nitrogen fertilizer can stimulate plant growth. This rapid production of tender shoots favors aphid reproduction. Use less-soluble forms of nitrogen, or apply a urea-based, time-release formulation.
As soon as you do see aphid growth, usually a strong blast of water will be enough to knock them off your plants and kill them. Do this early in the day to allow the plants to dry off. If absolutely necessary, you can apply an insecticidal soap or neem oil to the undersides of the leaves.
Thrips are tiny, slender insects with fringed wings. Most thrips range in color from translucent white or yellowish to dark brown or blackish, depending on the species and life stage. Thrips have several generations a year. The life cycle from egg to adult may be completed in as short a time as two weeks when the weather is warm.
Thrips like to feed in rapidly growing tissue. Feeding by thrips typically causes tiny scars on leaves and fruit, called stippling, and can stunt growth. Healthy woody plants usually tolerate thrips damage; however, high infestations on certain herbaceous ornamentals and developing fruits or vegetables may justify control.
If control is necessary, use an integrated program of control strategies that combines the use of good cultural practices and conservation of natural enemies with the use of least-toxic insecticides such as narrow range oils.
Also take care that you are not overwatering your cucumbers. Ensure good drainage.
Additional information on aphids and thrips is available online at http://ipm.ucdavis.edu.
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