Attention turns towards Sooty Blotch and Flyspeck
These two fungal diseases blemish the fruit. If we continue to have a wet, humid growing season and if orchards continue to have very high grass, we can expect to see sooty blotch and flyspeck on fruit if they are not protected. Cultural practices such as summer pruning and mowing can significantly reduce disease incidence by allowing better air movement in the trees. However, in a wet year, fungicide protection becomes more important. Table 15 (page 87) of the 2000-2001 New England Apple Pest Guide outlines fungicide options and timing of sprays. Note that sooty blotch is more easily managed with fungicides than is flyspeck.
Based on the assumption that most of the inoculum for flyspeck infections comes from conidia produced on wild hosts surrounding the orchard, summer fungicides for controlling flyspeck are not needed until 270 hours of wetting have accumulated from 10 days after petal fall. At that point, presumably, flyspeck conidia will become available in the orchard perimeter and will begin blowing into the orchard. [This assumes that infection by flyspeck ascospores within the orchard was prevented by fungicides applied for apple scab through peak flyspeck ascospore release, which occurs approximately 10 days past petal fall.]
Note that captan and ziram do not have any eradicant activity against flyspeck and therefore must be applied before the conidial infections, i.e., before 270 hours of wetting have accumulated. The benzimidazole fungicides (Benlate and Topsin M) provide about 100 wetting hours of eradicant activity against flyspeck. As a result, development of flyspeck on fruit can be arrested if Benlate or Topsin M is applied sometime between 270 and 370 hours of accumulated wetting counting from 10 days after petal fall.
As a measure for comparison, as of June 19th, 184 hours of wetting had occurred at the UVM Hort.Res.Center in South Burlington.