Alternaria Leaf Spot

• Only the leaves are affected when plants are stricken with alternaria leaf spot. This disease causes irregular black lesions in concentric rings on the leaves. Wind and rain help to disperse this fungus's spores. Infected seeds also spread the disease.
  
  

Angular Leaf Spot

• Both leaves and fruit are affected by angular leaf spot infections. This pathogen thrives in cool, damp weather. Lesions begin as small, circular black spots with a yellow halo around them. As the disease progresses, the lesions enlarge until they involve an entire leaf lobe; lesions on fruit can become large but are superficial and do not penetrate deeply into the fruit.
  
  

Downy Mildew

• Yellow, mottled spots appear on the leaves of plants infected by downy mildew. Lesions become very dark with a yellow border. Over time, this disease causes leaves to curl inward. This fungus spreads quickly, aided by rain and wind.
  
  

Fourlined Plant Bug

• Damage to plants caused by the fourlined plant bug can resemble fungal infections, so the true source is often not treated until after protocols for fungal infections have been tried. These bugs have black heads, antennae and bodies; yellow-green legs with black marks; and wings with four black stripes running down them. The bug feasts on the leaves with its piercing-sucking mandibles, removing the plant's chlorophyll. A toxin secreted in the bug's saliva causes dark spots to appear on the leaves. Affected leaves turn brown, curl up and fall off.