pest guide 7

Leaf symptoms of fungal diseases, such as downy mildew (A) and powdery mildew (B), can look similar to damage from piercing-sucking insects. Downy mildew is restricted by leaf veins, giving it a blocky appearance with white fungal growth on the underside of the leaf. Powdery mildew has small circular discolorations across the whole leaf surface, often forming white spores on either surface of the leaf. Either of these can be confused with damage from piercing-sucking insects (C, lace bug damage on jack bean with lace bug photo inset), which cause pin-point discoloration where they have fed on the underside of the leaf. This can lead to brown necrotic spots that look similar to downy mildew.