Red Oak Leaves Curling up and Falling off in July

(Question)

I planted a Red Oak tree in our front yard 13 years ago.  Up until last summer it always did well.  Last summer, and now this summer, it’s leaves turned brown, curled up and are now falling off (in July).  I had someone come out last year and they diagnosed “anthracnose”.  It was situated between two very large Norway Maples and had received lots of rain.  We thought it should do better this year as one of the Maples was cut down.  This year it started out well but by June the leaves were turning brown and curling.  I am not sure what to do with the tree, as I don’t want this happening every year.

Is this a fungus that is going to appear every year?

Does it damage the tree?

Could it be “Oak Wilt”?

Is there something that can be sprayed or injected on the tree, or should I give up and take it down and start over?

(Answer)

Anthracnose is a fungal disease which needs leaf moisture in order to infect, grow and spread.  It is not fatal to oak trees but two wet springs in a row has caused your tree to have a recurrence.  Even though one Norway Maple is now gone and there is more air circulation, the rainy weather has kept the oak leaves from drying completely which creates ideal conditions for fungal growth.

Oaks can recover from anthracnose.  As temperatures rise in the summer, the incidence of the infection should be reduced.  Let’s hope for the persistent rain to cease.

You can discourage a repetition next year by gathering up all diseased leaf & tree debris during this summer.  In Autumn, make sure you rake up and destroy all leaves and prune out any dead twigs.  This is very important as the fungi can survive in leaves and twigs and then re-infect  new growth next year.  It is best to put this garden waste out for your municipal collection or in the garbage rather than in your home composter.

Also, you can take a number of steps to reduce the stress on your oak, which will better equip it to survive future infections.  These include:

  • mulching around, but not against, the base of the tree out to the trip line with an organic mulch.
  • watering your tree in any periods of drought but let it dry out between watering.
  • avoid injuring your tree by taking care when weeding around the base of the tree.
  • remove any grass from around the base of the tree in order to cut down on competition, leave more nutrients available and reduce the risk of injury from lawnmowers.
  • avoid the use of heavy equipment underneath the tree as it can compact the soil and injure the root system.

If we have another cool wet spring next year, consider applying a fungicide, or get professional help in applying one, as some are still permitted under Ontario’s pesticide laws.

Note:  If your red oak is in fact afflicted with wilt and not anthracnose, it will die eventually.  However, as you have had a professional diagnosis of anthracnose I would not give up on your red oak yet, they are magnificent trees.