Many areas of the Midwest and Illinois are under abnormally dry to droughty conditions. These conditions have been going on for most of the summer — really, for the past several years.

Weather patterns appear to be getting more extreme, and can begin to take their toll on trees and their ability to fight off lethal insects and disease problems. This summer we have already seen quite a bit of tip dieback in the tops of trees, and are seeing maples already launching into early fall color.

During hot, dry conditions or even drought, the fine feeder roots that trees depend on for uptake of moisture and nutrients can dry out and die. These roots reside in the top 12 to 18 inches of soil and are vulnerable to high soil temperatures.

For example, during the 2012 drought, soil temperatures at 1 to 2 inches were over 90 degrees F. These high temperatures are not only lethal to fine roots and root hairs, but also can be detrimental to many of the specialized soil microbes that are vital to such soil processes as nitrogen fixation. That can affect larger critters like earthworms and insects that are important in soil conditioning and organic matter decomposition. If the fine feeder roots die, they have to be replaced, and this costs the tree energy. I like to think of the roots as the tree’s infrastructure.

Lack of soil moisture also drastically affects the tree’s ability to make “food” via photosynthesis. Remembering basic biology class in school, carbon dioxide plus water, in the presence of sunlight, is needed for photosynthesis. That results in production of carbohydrates and sugars. If the tree cannot make enough food to supply its energy needs, then it has to begin making some tough choices — just like when we have to make cuts in our personal budgets.

Additionally, many plants undergo physiological changes when they come under stress, which can make them more vulnerable to pests, diseases and non-living problems. For example, in the 1970s and 1980s, oak trees in the Northeast experienced years of defoliation by gypsy moth (now known as spongy moth), and as a result, oak trees started dying from the two-lined chestnut borer and armillaria root rot. Neither of these pests are able to invade and colonize a healthy tree, but repeated defoliations lowered the trees’ ability to fight them off.

Of course, defoliation from an insect is just one example. Other causes of defoliation such as foliar leaf diseases, chemical damage and weather events can have the same effect. Remember, the leaves are a tree’s food factory, and anything that interrupts food making will have long-term consequences.

Obviously, we cannot control the weather, but we can take four steps to alleviate drought stress:

1. Water as needed. A good rule of thumb is to give a tree 1 inch of water per week during hot, dry weather when there has not been any precipitation for a week or so. Weather extremes make this tricky. A 1- to 2-inch rain in 45 minutes to an hour is not going to get the job done. Most of it will run off and not soak in. Also, be alert to soil drainage. Heavy clay soils will be slow to drain, and sandy soils will dry very quickly, so check the soil for wetness before watering.

2. Mulch well. Lay a 3- to 4-inch layer of mulch around the base of the tree, preferably out to the dripline, with organic material like compost or cured wood chips. The mulch will help preserve soil moisture, help mitigate extremes in soil temperatures, keep weeds down, and prevent lawn mower and weed-eater “blight.”

3. Avoid fertilizer during dry spells. Fertilizers are salts and will dry out roots and do more damage than good. Additionally, plant nutrients have to be taken up by roots in the soil solution. If the soil is dry, the roots cannot take them up.

4. Ward off pests. Especially for newly planted trees or trees that are struggling, it’s important to prevent heavy insect defoliation — think Japanese beetles — or foliar leaf diseases by using an appropriate pest management tactic.

Miller is a horticulture professor at Joliet Junior College in Joliet, Ill., and a senior research scientist in entomology at The Morton Arboretum in Lisle, Ill. Email your tree questions to him at [email protected]. The opinions of this writer are not necessarily those of Farm Progress/Informa.