Līga Astra Kalniņa & Kerik Cox Cornell University Plant Pathology and Plant Microbe Biology
Flyspeck and sooty blotch usually will develop over time during time periods of very high humidity, so they are favored by prolonged cloudy weather, frequent showers, dense tree canopies and clustered fruit. Flyspeck sooty blotch can be a bigger problem in older, high-density orchards. Once these colonies form, secondary infection can happen from conidial infection that causes the fungus to spread during warm, wet humid weather.
In warmer regions where the disease occurs regularly, such as Long Island and Hudson Valley it is common for infections to be initiated during the early cover spray period, stop development during a hot and dry mid-summer, then finish incubating and finally become apparent when conditions become more favorable towards the end of summer.
Because both diseases are so dependent on long periods of extreme humidity around the fruit, annual pruning to open tree canopies and to promote air circulation can minimize the periods favorable for their development. It can be helpful to have supplemental summer pruning in dense-canopied trees as it can provide additional benefits in some years. Most of the inoculum stems from outside the orchard. Good sources for inoculum often come from alternate hosts, such as brambles, vines, shrubs and hedgerows.
The need for and timing of fungicide sprays to control these diseases is variable among orchards and years. In parts of the state where, where it is warmer and humid throughout the summer the infections can occur regularly, so applications should start around first cover and be repeated as necessary according to the prevailing weather conditions and material being used.
Flyspeck sooty blotch disease predictions begin in petal fall. Usually your apple scab/powdery mildew sprays that you make during petal fall and 1st and 2nd cover will cover your flyspeck sooty blotch infections.
Ascospores are released during rain, similar to apple scab, for a 1–2-month period starting petal fall and start causing infection 2-3 weeks after petal fall. So, for most of the state, we are in this time frame currently. Once flyspeck sooty blotch spores land on fruit, they germinate in temperatures between 61-83 F and begin to establish a fungus colony on the fruit surface. A cumulative amount of 270 hr. of wetting hours is required for flyspeck sooty blotch to show up on fruit. The largest risk period is also after 270 wetting hour accumulation, especially in orchards near grooves or woods, where secondary infections can stem from.
Some products that arrest flyspeck sooty blotch development include Sovran, Flint Extra, Merivon, Pristine or Inspire Super. Once the fungicide residue is depleted, the flyspeck sooty blotch population will be able to resume growing. These fungicide applications should be renewed every 14-21 days (or when there is more than 3 in of rainfall and the residue can be washed away) and can be timed with summer cover sprays.
As of right now, you should be protected if you have made your 1st or 2nd cover fungicide application from apple scab, as they will keep your population low. With this prolonged dry hot weather, there is currently no risk of flyspeck sooty blotch infections. Once prolonged wetting periods are predicted, we will be able to provide management and timing recommendations based on disease forecasting.