Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu
Over the last few weeks, I have been sent pictures of and have seen dark spots on the foliage of strawberry plants (Fig. 1). These spots can look pretty bad at times and are thought to possibly be the start of some disease such as angular leaf spot or anthracnose. The dark spots are usually on the upper or lower surface of the leaf, but at times can be found on both surfaces of a leaf. These damaged areas of strawberry foliage can be very disconcerting when they appear as dark spots on the stems (Fig 2.; these dark markings on petioles are not sunken as they would be if it were anthracnose).
Figure 1. Dark areas on strawberry leaves often mistaken for the start of a foliar disease
No bacteria or fungi have ever been found associated with these dark spots. I have seen this type of discoloration in strawberry foliage many times over the years and have never seen the spots turn into any disease problem or any other type of problem. The best that we can come up with is that the plant has ‘bruised’ foliage, usually appearing within a short time span after high winds occur. It is possible that disease organisms might enter the plant through this damaged tissue, but I have never seen this occur to any extent in the field—even during the wettest spring. Nothing needs to be done about this bruising, growers just need to be aware of the possibility of occurring after wind events.
Figure 2. Strawberry stem with dark spot