This fungal disease has been observed affecting leaves on Long Island from mid-May to early June. Yield can be reduced directly because the pathogen can also infect fruit under warm conditions and indirectly next year because loss of leaves to this disease can weaken plants. The tiny black structures in the brown tissue in the last photograph below are the fruiting structures (pycnidia) produced by this pathogen. Pycnidiospores produced in these structures are dispersed by splashing water. Fruit rot can also occur.
Management practices include planting certified disease-free plants of less susceptible varieties, removing old infected leaves which is where the pathogen survives over winter, planting where there is good soil drainage and air circulation to minimize leaf wetness, controlling weeds, and applying fungicides. Apply Rally (same active ingredient is in Agristar Sonoma) or Mettle (these are all FRAC code 3) in alternation with Rendition and Topsin-M. Apply these (except Rendition) with copper fungicides for resistance management. To achieve effective control applications need to be started well before symptoms are seen because there is a long period between infection and visible symptoms. Infection can occur early in the growing season and symptoms not appear until during or after harvest.
Please Note: The specific directions on pesticide labels must be adhered to — they supersede these recommendations, if there is a conflict. Any reference to commercial products, trade or brand names is for information only; no endorsement is intended.