Are you noticing small, white, slightly fuzzy spots on the undersides of your tree's leaves? Chances are, you're dealing with a case of downy leaf spot. The good news is that in terms of fungal diseases that trees can develop, this is a pretty minor one. The bad news is that because downy leaf spot can weaken the tree and leave it susceptible to other, possibly deadly diseases, you do have to take action and treat it. Here's a closer look at this condition and how you can treat your tree.
What causes downy leaf spot?
This disease is caused by a specific species of fungus called Microstroma juglandis. It can affect most any species of tree, though it is most common in hickory, walnut and pecan trees. Like most fungi, the fungi that cause downy leaf spot thrive in moist, warm conditions -- so you're most likely to notice downy leaf spot appear after a bout of moist, rainy weather.
How will downy leaf spot affect your tree?
The white spots that you're noticing now are actually fungal spores. They will soon sprout and develop into adult fungi, which will leach nutrients out of your tree's leaves, causing them to yellow. Some of the yellowed leaves may fall to the ground prematurely in the late summer or early fall. Downy leaf spot often starts off in just a few branches, but if you don't treat it, your entire tree may eventually be affected.
How do you treat downy leaf spot?
If there are only a few branches effected right now, removing them from the tree should mostly solve the problem. Dispose of the branches by burning them so the fungi don't spread to any other nearby trees.
If the spots are found on a large number of branches, you'll want to wait until the end of the season and then take measures to try and prevent the fungi from re-infecting the tree the next year. Clean up all fallen leaves or twigs, and burn them to kill the fungus. Also, have the tree trimmed in late winter. This will allow air to circulate through the branches more readily, keeping them dry and making them less appealing to the fungus. Before the buds emerge in the spring, have your tree professionally sprayed with fungicides to help dissuade the fungus. You may have to repeat these treatments several years in a row before your tree is completely free of leaf spots. Contact a tree service for more information.