The defoliation of the asparagus ferns reduces yields in the following year. The loss of photosynthetic area results in insufficient reserves being stored in the roots.
Leaf spot [Stemphylium botryosum]
The symptoms appear starting in June and into October, brown spots on the ferns. When nursery blocks and production blocks are in close proximity to each other, the infected nursery blocks can also infect the production blocks from September on.
Pattern of damage
Red-brown spots on stalk, side shoots and leaves causing the plant above the infected areas to die back. Black spore pustules develop in infected areas.
To prevent the fungus from overwintering on last year's asparagus ferns, the latter must be finely chopped prior to incorporation. A fungicide treatment must be applied as soon as the first ferns become defoliated.