Three strawberry concerns as of April 27, 2012
Three problems being seen in strawberries in the last few days – angular leaf spot, strawberry clipper, and lack of nitrogen.
In my visits to strawberry growers the last three days, I have seen above average amounts of angular leaf spot disease in many fields, an alarming number of fields that have heavy feeding damage from strawberry clipper, and that all fields need some additional nitrogen. I want to share a bit more detail about these three strawberry problems.
Angular leaf spot has been seen in a good number of plantings in the last few days; in fact, about three-quarters of the fields that I visited have light to moderate amounts of this disease. This bacterial disease causes small, water-soaked angular spots on lower leaf surface, and dark, wet-looking blotches on the calyx of fruit. If the leaf is held up to the sun, the spots on the back of the leaf have a translucent appearance.
Conditions which favor the disease are cool, daytime temperatures; low, nighttime temperatures; and high humidity. We sure have had these conditions over the last few weeks. Frost protection tends to increase the severity of the disease as well, and this season has seen a very intense need for frost protection at most farms. Some strawberry varieties are more resistant to this disease than others. Growers need to do a thorough job of scouting for this disease in the next few days. Also, there are many strange-looking spots on leaves this year. These burned or scorched spots have been caused by our cold, windy season. Please don’t mistake this leaf scorch for angular leaf spot. If present, copper sprays are the only recommended pesticide listed for angular leaf spot in the Michigan Fruit Management Guide (E-154).
Secondly, I have seen very high amounts of damage from strawberry clipper at a few farms this week. Adult clippers first feed on immature pollen by puncturing nearly mature blossom buds with their snouts, causing small holes in the petals when the blossom opens. The adult female also clips the fruit stem so that the bud hangs down or falls to the ground. Here again, growers are encouraged to do scouting for signs of damage from this insect, especially close to woodlots and fence rows. Consult the Michigan Fruit Management Guide (E-154) for control recommendations.
Thirdly, all of the strawberry fields I have looked at this week appear to be in need of some nitrogen to encourage stronger leaf growth. Light, frequent amounts of foliar nitrogen are suggested on a weekly basis over the next two to three weeks. Be careful not to over fertilize, however.