Prune in dry weather. Improving air circulation by properly thinning plants also will help prevent disease problems. Copper based fungicides such as Bordeaux mixture or Phyton 27 can be applied when the disease first appears. Follow label directions. Near-freezing temperatures in the spring can cause browning or blackening of leaf tissue, especially at the margin.
Leaves eventually appear torn around the edges and along the veins.
Puckering of leaves also may occur. Prepared by Paula Flynn , Department of Plant Pathology Iowa State University , Ames, Iowa. This information subject to a usage policy .