Wednesday, October 21, 2009

Reducing overwintering apple scab inoculum using fall-applied urea and leaf shredding

I was (October 20-21) at an annual meeting of tree fruit entomologists and pathologist in Burlington, VT. After what was a high-pressure apple scab year, it's likely there is some (or a lot) of scab out there in the orchard which will be the source of infection for 2010. All things being equal, the more overwintering scab inoculum the higher the scab pressure will be for next year. So, if you can take some steps to reduce the inoculum now -- like right now -- you can help yourself out for next year when it comes to managing scab. There was pretty much agreement on taking these two steps this fall to significantly reduce (up to 90-95%) the amount of overwintering scab inoculum:
  • First, spray your apple trees right now with 50 lbs. of urea (spray urea, 44 lbs. is the actual recommended rate, but hey, 50 won't hurt and that is the bag size) per acre in 100 gallons of water while the leaves are still on the trees. Contrary to popular belief, this will not impact winter hardiness. Just keep in mind you are adding app. 23 lbs. of actual nitrogen per acre to the orchard, so adjust your fertilizer program accordingly.
  • Second, flail mow/chop the orchard as late as you can and when the majority of leaves have fallen from the trees. Sweep or blow leaves into the orchard middle from within the row is helpful so that the majority of leaves can be chopped/shredded.
Doing these two integrated apple scab management practices this fall will help to reduce the number and intensity of fungicide applications and go a long way towards making your overall scab management program in 2010 a success.

Thanks to Bill MacHardy for doing the research on these practices.