Answer: Control of black knot requires a combination of cultural and chemical methods. Cultural practices should include removing wild plum and cherry seedlings from fence rows, woodlots, and along orchard perimeters; inspect orchards and surrounding areas each winter for black knots and prune out infected shoots and limbs; remove pruned knots from the orchard and bury or burn them before budbreak in the spring. When pruning infected material in the dormant season, always make the cut 3 to 4 inches below the margin of each knot, since the fungus grows in the tissue beyond the visible swellings. Consult your local Extension Service for fungicide recommendations since there appears to be some variation in effectiveness from one area to the next. Sprays should be applied from white bud through shuck split (green tip through second cover in problem orchards). Spraying by itself, without implementing the recommended cultural practices, may not provide adequate control of the disease. There is considerable variation in cultivar susceptibility to black knot so you may never completely rid your trees of this disease.
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