Aspen are great native trees. They fill many niches in the landscape, including moist areas, small spots and places where you need quick growth for screening. Unfortunately, they are also prone to a number of diseases and insects. So if your aspens aren’t looking quite right, here is what might be wrong.

Curling Leaves can be caused by one of three insects.

Leaf Rollers will turn under both edges of the leaf about ¼” – ½”.  You will usually find tiny eggs or a small worm inside this roll. They won’t kill the tress, just slow its growth and make it unsightly. Spray with a systemic pesticide to rid of Leaf Rollers.

            Tent Caterpillars will create white “tents” around the end of a branch, rolling a number of leaves within it. Prune off in the evening and put in plastic bags in the trash.

            Aphids attack the new shoots on aspens and suck out the juices, the leaves will look misshapen and curled, and there will be a sticky residue. Often ants will be crawling up the tree to feed on the residue. Spray the tree with a strong blast of water; you can also use insecticidal soap or Permethrin, if the infestation is severe.

Leaf Spots can be caused by an insect or a disease.

            Leaf Miners will eat the middle layer of the leaf leaving intricate tunnels between the tan epidermal layers.

            Black Spots look just like its name and is just unsightly, though it can cause early defoliation.

            Tan Spots are cause by Marsonnina, a disease which can also cause small leaves and early defoliation.

The best defense for all of the above is to rake up and dispose of all leaves every fall. Do not put them in the compost pile or use as mulch elsewhere in the yard.

Blackened or Curling New Shoots can be caused by one of two things. The first is frost damage and the other is Shepherd’s Crook, or Shoot Blight. This is a disease that causes blackened new shoots that curl into a crook. They can be pruned off if you can reach them and make sure you rake these up each fall also.

There are 3 things that cause problems with the trunks of trees.

            Lawn-mower-itis, also called weed-wacker-itis; never plant grass right up to the trunk of an aspen, but instead put a ring of mulch around it.

            Borers, these infestations will manifest with a deposit of sawdust at the boring site or at the base of the tree. Treat with Permethrin and spray with Dormant Oil each Fall and Spring.

            Cytospora, this will look like an orange stained area that is soft and sometimes “bleeding”. Advanced cases are black. These trees should be removed immediately, as it is highly contagious.

With all of these conditions, they mostly attack stressed trees. So the best way to insure the health of your Aspen trees is with proper prevention. Keep the trees properly watered. Fertilize each Spring with Nitrogen and Iron (don’t use Nitrogen after Labor Day). Keep grass away from the trunks. Do not use weed killers on their sprouts. Take up the leaves each Fall. Spray with Dormant Oil each Fall at leaf Drop, and each Spring at bud swell before leaf emergence. Enjoy your beautiful quakers and their harvest of gold!