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OVER THE COLES: Watering during drought can reduce stress in trees

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Don’t fret, but some trees may be showing damage from the late frost we received in May for several months to come. Some additional watering during the hot dry months of summer and these trees will be well on their way to a beautiful specimen.

Large dark black sections are showing up on oak leaves in the backyards of Central Illinois. The frost hit them at a vulnerable time when the leaves were just beginning to emerge, rupturing the cells in the leaves. Although not the appealing spring green we are used to with our oak trees, they will suffer little in the long term.

Maples, redbuds, crabapple, flowering cherry, ginkgo, and magnolia may also have experienced some damage. Leaves may shrivel, turn brown, or exhibit black spots with yellowing foliage or leaves that may have already dropped off the plants. These frost-damaged trees will produce new leaves if damaged leaves fall off.

Even some branches may have been killed or slow to leaf out. You may remove dead branches from your trees, but first, be sure they are dead by doing a bark scratch test. A live tree will be green underneath the bark.

Other leaf symptoms may start to appear as the season progresses. These symptoms are due to diseases that thrive from the rainy cool weather of spring. Disease symptoms can be hard to distinguish and may need to be sent to the University of Illinois Plant Clinic to get proper identification. Many instances of anthracnose (on oak, maple and sycamore), and cedar apple rust are two diseases already being reported at the McLean County Master Gardeners help desk. When these disease symptoms show up there is not much homeowners can do but address a stressful growing environment.

It is important to know diseases cannot be cured but instead need to be prevented. Diane Plewa, University of Illinois Plant Clinic Diagnostician, says “Diseases are more prolific in stressed trees, and most of the stress comes from nutritional deficiencies, drought, improperly planted trees, improperly mulched plants. “ If homeowners don’t address issues causing tree stress, reduction of disease symptoms may be impossible.

Watering stressed-out trees during drought:

  • Check and track the rain accumulation in you area on the Illinois State Climatologists site at
  • Most established trees need 1 inch of water a week and 2 inches during hot, dry periods.
  • Newly planted trees or shrubs require more frequent watering than established trees. They should be watered daily the first few weeks after planting and at least weekly for the first season of establishment.
  • Wait until mid-summer or fall to fertilize established trees that experienced a stressful event in order to build up their reserves.

Illinois Extension leads public outreach for University of Illinois by translating research into action plans that allow Illinois families, businesses, and community leaders to solve problems, make informed decisions, and adapt to changes and opportunities.


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