For the last many months, we have been hearing about health care and health care insurance. A major premise of human health care is prevention: getting regular checkups and attempting to live a lifestyle that promotes good health and prevents illness. Trees are no different — except we’re talking plant health care.

The summer of 2017 was a good summer for plants in general, with good rains and moderate temperatures. However, in some cases, there was too much of a good thing. Heavy and frequent rains led to flooding throughout the spring and summer. Other areas were dry, creating more droughtlike conditions. Many of these heavy rains and thunderstorms resulted in storm damage to many of our trees. With moisture and high humidity come foliar diseases like anthracnose and apple scab.

In addition, we had heavy populations of oak leaf skeletonizer defoliating shingle oaks in southern Illinois forests. Statewide, we saw heavier-than-usual Japanese beetle feeding damage on lindens, crabapples, maples and birches growing in rural and urban landscapes. It was also a busy year for oaks, including oak wilt, oak decline and oak leaf tatters. With the exception of oak wilt, none of the aforementioned pests and diseases alone are lethal to a healthy tree. But as with human health, when a tree comes under stress from one or more of these maladies, more lethal pests like wood-boring insects and canker-causing fungi can invade the tree, potentially leading to its death.

What to do?
So what can you do to keep trees healthy and help them fight off problems? If your tree is well-established and mature, watering during dry periods and mulching around the trunk several feet out — or even better, under a good portion of the tree canopy — helps conserve moisture, moderates soil temperatures, promotes fine root growth, and keeps the lawn mower and weed eaters at bay. Applying fertilizer should be done carefully.

With older, mature trees, maintenance is the goal. Like humans, older trees do not react well to major changes in their environment. Avoid drastic changes in soil drainage, and protect trees from construction activity. Prune out dead wood (called canopy cleaning) or storm-damaged limbs as needed, but do not remove more than 25% of the tree canopy at any one time. Most established trees can tolerate a season or two of defoliation from insect pests and diseases, but multiple years can take a toll.

In some cases, treating the tree with a chemical pesticide may be appropriate to give the tree some stress relief. For younger, newly planted trees that are not established yet, watering and mulching is also important for the reasons mentioned earlier. Make sure the tree is well-suited for the site (i.e., can tolerate wet soils, poor drainage, likes full sun versus shade, proper soil pH, etc.).

If the tree is struggling and/or is newly planted, protect it from diseases and insect pests until it can “get on its feet.” As a rule of thumb, it takes about one year for each inch of tree diameter for a newly planted tree to regrow its root system. During this time, the main goal should be to promote root growth, not top growth. Avoid overfertilizing the tree. With a diminished root system, the young tree will not be able to support the canopy. Remove dead, diseased and damaged limbs, but again, no more than 25% in any give season.

It is important to stay vigilant and provide the proper care for your trees. If you need additional guidance or advice, consult a certified arborist or your local Extension office for assistance.

Miller is a horticulture professor at Joliet Junior College, and a senior research scientist in entomology at The Morton Arboretum in Lisle. Email your tree questions to him at [email protected].