Vinca species are frequently used in landscaping as a ground cover or in hanging pots. these plants are typically prized for bright blue flowers that appear in late spring, but breeding programs have resulted in large-flowered cultivars available in a variety of colors. If a vinca begins to suffer from curling leaves, it may be indicative of a serious insect infestation or virus or it may simply be a response to temporary environmental conditions.
Leaf roller insects infest both vinca major and vinca minor. Diagnose leaf rollers as the culprit behind the curl by unfolding a curled leaf; there will either be sawdust-like frass (insect excrement), the webbing-like pupa or a very small caterpillar. This caterpillar feeds on the leaf, creating holes and causing the leaf to turn brown. Leaf rollers can cause major damage to vincas in late summer if the infestation is especially heavy.
Addressing Leaf Rollers
If the leaf roller infestation is minor, a simple option is to remove and destroy infested leaves. Mature, healthy plants can typically recover quickly from a minor infestation. If the leaf rollers pose a serious threat, apply a spray or dusting of Bacillus thuringiensis (BT) to the plant. This deadly bacterium is ingested by the caterpillar. Serious infestations can be controlled with contact insecticides containing active ingredients spinosad or neem. If an area is known for annual problems with leaf rollers, apply a systematic insecticide two or three weeks before the damage usually begins to appear.
Tomato Spotted Wilt Virus
The tomato spotted wilt virus (TSWV) occasionally affects vinca in the landscape. Normal symptoms of TSWV on vinca include yellowing, distortion and stunting of young leaves accompanied by small black rings, spots or patterns. Vinca flowers also become distorted and discolored and the entire plant suffers from stunted growth.
Addressing Tomato Spotted Wilt Virus
Thoroughly inspect vinca for signs of the virus before purchasing the plant. Avoid planting vinca near broadleaf vegetables that are susceptible to tomato spotted wilt. Remove any infected plants as soon as symptoms become visible. Insecticides are ineffective against the thrips that spread the virus.
Hot or Dry Conditions
Vinca may normally curl up during hot, dry summer weather as part of an effort to conserve water. This should not be cause for alarm; the leaves will unfurl in the evening when temperatures drop and humidity increases. Use good cultural practices like mulching and regular, thorough watering to prevent any serious drought damage.