May 26, 2016 – The rain events of the last few days have resulted in infection periods for foliar diseases on apple, cherry and grape. The bacterial disease fire blight is of concern to apple growers with the presence of open flowers, rain/fog/heavy dew, and temperatures in the low to mid 70’s
|Degree day comparison 2013-2016|
|Date 5/25||2013||2014||2015||2016||20 yr avg|
|DD Base 50||191||192||263||231||255|
Disease Pressure – Apple scab infections resulted from the rain events on 5/24 & 5/25. Currently we are about 75% of the way through primary scab season, which typically lasts through mid-to-late June. Continue early season protectant fungicide applications on scab susceptible varieties like McIntosh & Cortland to protect leaf tissue, as scab spores will continue to be released during future rain events. Adding a fungicide like Luna Tranqulity, Inspire Super, and Merivon now through petal fall will help protect susceptible varieties like Cortland and Honeycrisp from powdery mildew. Other fungicides that can be used for powdery mildew include Rally and Indar or the stroblurin materials Sovran and Flint.
Streptomycin applications to protect apple blossoms from fire blight infection should be made every 4-5 days during bloom on susceptible varieties. Temperatures in the low 70’s and higher are conducive to the development of this bacterial disease. Any wetting (even rain, fog or dew) can trigger an infection once blossoms have opened.
Insect Pressure – We continue to see a fair amount of green fruit worm and oblique banded leafroller larva activity on blossom clusters. . European red mites have recently hatched and numbers appear to be lower than in other years. Growers should begin scouting blossom cluster to determine if petal fall miticide applications will be necessary.
Disease Pressure – The first cherry leaf spot infection periods were recorded on 5/24 & 5/25. Unfolding leaves will need to be protected with fungicide applications for cherry leaf spot infection. Products containing chlorothalonil (Bravo, Echo, Equus, etc.) are the fungicides of choice through shuck split for cherry leafspot control. Remember that there is a minimum 10-day application interval on these products.
Insect Pressure – Continue to scout for presence of green fruit worm and oblique banded leafroller larva. We have not seen the heavy pressure in cherries that we have in apple so far this season.
Disease Pressure – Grapes are now susceptible to black rot infection on vegetative growth. It is important with varieties like St Croix, La Crosse and Frontenac that fungicide applications to control this disease are made now through two weeks after bloom. Controlling early leaf infections will help reduce later season infections of the fruit, which is much more of an issue concerning fruit quality. At this time of the season, with high temperatures in the upper 60’s to mid 70’s, only seven or eight hours of wetting is needed for infection to occur.
Insect Pressure – Now is the time to begin scouting for flea beetle and climbing cutworm. Pressure for these two pest has been minimal here so far at the research station.