Common spring tree diseases – identification & management


You can’t deny it – warm weather, though not consistent, is on it’s way. And this change in the weather can bring changes to your trees as well, but not always for the better – they can introduce pests, make conditions ideal for bacteria & viruses, and encourage decay. Let’s cover some of the basics, so you know how to spot them and what options are available to you when your local tree starts to show signs:

Leaf spots are one of the most common issues you can find, usually on ornamental trees, no matter where you are. They’re caused by leaf-inhabiting fungi that discolor and kill small, circular areas of tissue between or on a leaf’s veins. Naturally, they’re spurred on by cool, very moist conditions and are actually spread by the wind. Most of the damage done by leaf spots is only cosmetic, so keep this in mind when considering how to help your tree. Fungicides are effective only when the fungi are producing spores – otherwise, the best remedy is to clean up leaf litter, irrigate and avoid overhead watering (watering the foliage) and excessive watering.

Anthracnose is another disease impacting leaves – this time, however, the victims are different shade tree species, including ash, oak, maple and sycamore. The lesions leave a “scorched” appearance along veins and leaf margins, and twigs and branches may die back if the infection is severe enough. Anthracnose is another typically moisture-reliant disease though, so fungicides are not often necessary – just be sure to give the tree proper care. Prune dead branches and remove leaf litter, avoiding overhead watering (watering the foliage) and excessive watering.

Cedar-apple and quince rusts are different in some ways, but both are common among often-planted landscape trees. Both the cedar-apple and quince varieties require multiple species within two or three seasons in order to survive, but only impact a narrow scope of species. Both start by hibernating on eastern red cedar and several other junipers throughout the winter in large glands. Come spring, brightly-colored, gelatinous horns emerge from the cedar-apple’s galls during wet weather (in contrast, quince’s galls give way to small and spindle-shaped spores).

Then the crab-apple’s spores open up to the wind, spreading to apple, crabapple and hawthorn leaves and fruit, and by summer rusty or orange-colored spots appear on infected leaves. These infections can cause premature defoliation, stunted growth, and poor quality fruit. And by late summer, these spores have spread on via the wind back to cedar and juniper species, repeating the cycle heading into winter.

Quince rust’s spores impact apple, crabapple, hawthorn, quince, mountain ash, and cotoneaster species, stunting and killing fruit while swelling and distorting twigs and petioles (often to death). To combat these disease, prune affected branches 6-8 in. below galls during dry weather with sterilized tools. Sometimes, moving alternate hosts outside of a specific range can be helpful, but try to plant disease-resistant cultivars whenever possible.

For more information about basic tree care in the spring, check out our Spring Almanac. For more information about these common diseases and others, download: Rutgers’ Plant Disease Control guide (our source for this article).

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