As your vegetable garden swells with growth and activity each year, a few pests and diseases inevitably appear. Many of these will not make a big impact on the quality of the harvest. Others may devastate the crops and can either be battled or allowed to take their natural course. Every pest or disease that appears is an opportunity for discovery -- and perhaps a lesson in science -- for children. When it comes to diagnosing the cause of curled leaves on bell pepper plants (Capsicum annuum), there are numerous possible culprits.
The first things to look for if pepper leaves start to curl are any possible insect pests. Potato leaf hoppers are tiny green bugs, less than 1/4 long, that suck sap from the undersides of pepper leaves, causing them to turn yellow and curl. They do not fly, but hop long distances. Aphids are sap-sucking insects that are usually found on tender new growth and can deplete the fluids of pepper plants so much the leaves begin to pucker and curl. Thrips also cause pepper leaves to curl, but are so small they are difficult to see with the naked eye. Bronze or black discoloration of the affected leaves is the characteristic sign of an infestation of thrips.
Two distinct viruses can cause pepper leaves to curl. Curly top disease is transmitted by leaf hopper bugs and also causes a yellow discoloration with the leaf veins remaining green. Aphids are the vector for pepper mottle virus, which causes a mottled discoloration and puckering of the leaves, possibly with deformed fruit, as well. Unfortunately, there is no cure for either disease, though they typically affect only a few individual plants, rarely destroying the entire crop.
Severe cases of powdery mildew cause pepper leaves to curl and may weaken the plants to the point where the fruit is unable to ripen properly. The first signs of this fungal disease are white or gray spots on the undersides of the pepper leaves, usually appearing lower down on the plant. The leaves may then develop a pimply texture, become yellow and begin to curl up.
Physiological Leaf Roll
There is a form of leaf curl in peppers that is caused by environmental factors, rather than any pest or disease. Physiological leaf roll usually does not have a significant impact on the crop and is often a temporary reaction to some from of stress. In this condition, the leaves roll downward and there is no other type of deformation. Excessive heat, drought or moisture can cause this -- taking good care of your pepper plants is the key to preventing this condition.