Tomatoes and peppers are both warm season edible crops that are related to one another by belonging to the nightshade genus of plants. Their leaves have similar texture and colour and unfortunately share some tendency toward leaf roll or leaf curl when exposed to unfavourable conditions. Leaf curl can be caused by cultural conditions, weather or pathogens endemic to the planting soil. The condition can also be brought on by using infected plant stock or even be carried onto the plants by insects. While unsightly, not all instances of leaf curl warrant treatment as the flowers and fruit are commonly not affected. When leaf curl impinges on the health and performance of the plant, then careful inspection of ambient conditions is needed and treatment measures should be deployed.
Refrain from using pesticides not designed for use near or on tomatoes and peppers, especially those containing the active ingredient 2,4-D. Prevent accidental over-spray or wind drift of fumes, and never use pesticide-treated mulch or compost. All of these plus build-up of pesticide compounds in the soil can cause leaf curling, cupping or failure of the leaves to fully develop and unfurl. Cease pesticide applications in the wider area and water the plants deeply and often to dissipate the pesticide.
Control the Begomovirus pathogen that infect tomatoes and peppers and other nightshade plants by curling and mottling or speckling the plant leaves. Remove and destroy any infected plants you see. Carefully observe and manage insect populations that can carry the virus, particularly whiteflies. Introduce ladybug populations to feed on whiteflies, biologically suppressing them. Treat soil and plants with a food-safe insecticide for whiteflies that uses an insect growth regulator to curb their population.
Prevent Begomovirus with good ongoing cultural practices. Remove and discard all weeds in the planting beds and surrounding areas. Plant virus-resistant tomato and pepper cultivars. Refrain from planting ill-looking seedlings or poor quality seeds. Keep other plants that whiteflies commonly infect, such as cotton, away from your tomato and pepper beds. Allow the planting beds to go fallow for a season or more between plantings, or seasonally rotate crops in different locations to drive down whitefly infestations.