The black spot on the artichoke leaves may be due to lygus bug (Lygus hesperus) or proba bug (Proba californica). The nymphs and adults feed on leaves by sucking sap. While sucking sap insect injects toxin which results in death of the leaf tissue (necrotic spots).
And the drying of leaves may be due to ramularia Leaf Spot caused by Ramularia cynarae. The symptoms are appearance of circular, brown lesions on both upper and lower surfaces of leaves. This lesions may coalesce and the entire leaf will turn brown and dry up.
Management of lygus or proba bug:
1. You can use white sticky traps (10-inch squares of white material coated with Tanglefoot or petroleum jelly) to monitor and control the bugs.
2. Also you can use botanical insecticide like sabadilla to control the bugs.
Management of ramularia leaf spot:
Remove and destroy the infected leaves.
Avoid stressing of plants
Also avoid wetting of leaf surface
Posted by: Dr. Ravishankar Narayana
Posted: April 8, 2016