The symptoms of flyspeck and sooty blotch have begun to make their appearance. I know this because 1). I’m starting to see spots, and 2). We have accumulated MORE THAN enough hours of post- petal fall leaf wetness needed for infection to occur.
On no-spray or poorly managed orchards, flyspeck and sooty blotch are probably the least of your problems.
First, what is enough hours of post- petal fall leaf wetness needed for infection to occur? Different states have developed different levels and standards, with highs of 270 hours (hours must be greater than 4 hrs to be counted) needed in North Carolina, compared to 175 period identified in Iowa. In Kentucky, John Hartman found 185-251 hours were needed, but did not stipulate that a minimum of 4 hrs was required to accumulate leaf wetness. We have not yet developed a guideline for Indiana. In the interim, using either the Iowa or Kentucky model may reduce your fungicide usage in a normal year. For much of Indiana, ‘normal’ is a state we hear about—a utopia between our extremes of tropical rainforest (2015, 2016) and drought (2012).
Sprays: Topsin-M tanked with captan is an effective combination (Ziram is another option). However, some orchards may be experiencing Topsin-M resistant flyspeck and sooty blotch populations. If you suspect you are one of those orchards with SBFS fungicide resistance, or you were late getting started, use Flint or Pristine to eradicate any infections that may have started. Thereafter, captan alone at appropriate intervals (2 weeks or 2 inches off rain; 10 days or 1.5 inches of rain) should provide fair to good control. If disease pressure is high, and you haven’t exceeded your four applications of strobies, Pristine or Flint all provide the best protection against this disease complex. We do not know if these fungicides are protecting against the disease, or are effective eradicants, but we do know that they work quite well against this complex.