May 4, 2016 – Apples are now at 1/2″ green tip and cherries are at green tip to early tight cluster here at the station. Grape buds have just begun to swell. Fruit crop development has slowed with cooler weather over the last week or so. Forecast temperatures in the low 60’s for the weekend should push plant development along from this point forward. It looks as there may also be a chance for rain early in the weekend and apples will need protectant fungicide applications to protect expanding leaf tissue from scab infections during rainfall events. Lime sulfur and copper applications can still be made on grapes for control of phomopsis, black rot, and powdery mildew.
Currently critical temperatures for 90% flower bud kill remain between 15ºF & 20ºF for cherry and apple at their current stage of development. Grape buds continue to be slightly more tolerant of cold temperatures at this time but will be less so the more buds begin to swell. Click a link below for more information on fruit crop bud cold temperature injury.
Critical Temperatures McIntosh & Cortland
Grape Cold Temperature Injury (article by MSU’s Mark Longstroth )like McIntosh & Cortland
|Degree day comparison 2013-2016|
|Date 5/3||2013||2014||2015||2016||20 yr avg|
|DD Base 32||386||363||550||601||597|
|DD Base 50||39||35||107||90||105|
Disease Pressure – There have been no infection events since 4/24 with only a low chance of rain for the coming weekend. Continue early season protectant fungicide applications on scab susceptible varieties like McIntosh & Cortland to protect leaf tissue, as scab inoculum has matured to the point were spores are ready to be released during future rain events. Apple scab is best managed at this time with 7-10 day protectant applications of Captan or one of the EBDC fungicides. Keep susceptible varieties covered with fungicide treatments through the end of primary scab season; typically mid to end of June in Northeast WI.
With a variety like Honeycrisp that is only mildly susceptible to scab but much more prone to powdery mildew infection, an additional fungicide is necessary. Good choices for this include the newer fungicides Luna Tranqulity, Inspire Super and Merivon. The tight cluster through petal fall time period is the most critical for control of this disease. Other fungicides that are effective on powdery mildew include SI fungicides like Rally and Indar or the stroblurin materials Sovran and Flint.
Insect Pressure – Oil applications targeting overwintering European red mite eggs can still be applied through tight cluster. Oil can have phytotoxic effects on green tissue, buds and blossoms if it is applied in or around below freezing temperatures. Avoid applying oil 48 hours before or after a frost. Also check labels of fungicides being applied with or near oil applications to make sure they are compatible. Captan should be avoided when making early season oil applications.
Green fruit worm have begun to fly but do not yet pose a damage threat. Scout for presence of their hatching larva as well as overwintering oblique banded leafroller larva now through petal fall.
Disease Pressure – Looking ahead to bloom, European brown rot can be an issue on tart cherry trees. The Balaton variety is more susceptible than Montmorency, but Montmorency can be infected when conditions are right (cool and wet) . To prevent infection, an application of Indar at the popcorn stage is suggested; a later Indar application during bloom will also help to prevent infection. Other fungicides options for this disease are available, please see the following article by George Sudin from MSU New-old options for European brown rot control in tart cherries
Insect Pressure – Green fruit worm adults have begun to fly and lay eggs. Once significant leaf tissue begins to develop, scout for presence of their hatching larva as well as overwintering oblique banded leafroller larva.
Disease Pressure – Applications of lime sulfur or copper fungicides before bud burst prior to the development of leaf tissue can still be made on grapes for preventative disease management. For these fungicide applications to be effective on the overwintering stages of phomopsis, black rot and the mildews, they must be applied with sufficient water to achieve complete coverage.
Insect Pressure – Once leaf tissue begins to emerge, scouting for flea beetle and climbing cutworm will need to begin.