Disease Update: Scab Infection Period March 27–April 1

Mar 29, 2017

By Kari A. Peter

Growers need to be on alert for apple scab infection period this week.

Due to the presence of green tip on early varieties of apples combined with rain and mild temperatures occurring this week, we are in our first apple scab infection period for 2017.

Protection is needed for vulnerable green tissue; a copper spray will be useful for trees not at green tip.

The Polar Vortex the last couple of weeks gave us a little bit of a reprieve…but now, Mother Nature can no longer be held back. Spring has sprung: many trees are showing green tissue and the scab spores are mature and releasing.

It is official folks: our first major apple scab infection period is occurring this week, March 27 – April 1.

Dates to be most concerned about:

March 27 – 28
March 31 – April 1

There most likely will be a couple of dry times in between to allow for spraying.

The average temps will be on the warmer side, which will lessen the number of leaf wetness hours needed for scab spores to cause infection. Green tip is a vulnerable time for scab and it is important to be vigilant, especially in blocks with known history. Once scab gets established, it is very challenging to get ahead of the disease.

For folks who have green tip:

Your best bet right now would be to use mancozeb at 6 lb/A. Copper use at green tip could run the risk of phytotoxicity.
If you are nearing half inch green, another option is Syllit at 1.5 pints/A tank mixed with 3 lb/A of mancozeb.
If you are not at green tip: another copper application (2 lb metallic copper/A) could be considered.

Source: psu.edu

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