Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu
Over the years I have seen dark spots on the foliage of strawberry plants like the ones in Figure 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, which can indicate a biotic source for the problem. These damaged areas of strawberry foliage can be very disconcerting when they appear as dark spots on the stems (Fig. 2).
Figure 1.(1) Dark spots on strawberry leaves often mistaken for the start of a foliar disease
Figure 1.(2) Dark spots 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 early in the season 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. And as you look at the spots this is exactly what the damage looks like (kudos to Karen Rane for coming up with this description of the damage). This damage usually appears within a short time span after high winds occur.
Figure 2. Strawberry stem with dark spot
Figure 3 shows a good example of this as you can see the bruised areas of the leaves that appeared a few days after a very windy period. Also notice the tattered appearance of the leaf edges demonstrating that these leaves were knocked around a great deal. 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 occurring after wind events.
Figure 3. Strawberry leaf with bruises and tattered margins