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Rhonda Ferree's ILRiverHort

Rhonda Ferree's Horticulture Blog
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Why Are Some Trees Changing Color Already?

Have you noticed many plants already starting to turn fall colors? According to Rhonda Ferree, Horticulture Educator with University of Illinois Extension, early fall color almost always means that trees are exhibiting symptoms of stress.

Ferree says this is likely due to last summer's severe drought. "The trees probably had enough reserves to make it this far since we had good spring rains, but this recent dry spell has caused many trees to lose enough reserves to go into survival mode."

Last summer's severe drought will impact trees for another three to five years. In addition to early coloring, some trees leafed out later than usual, have sparse tree canopies, or have shoot dieback. Some trees in survival mode produce more seeds than usual, such as maple samaras (helicopters or whirligigs), cones on conifers, and pods on redbud.

Unfortunately, drought also makes trees more susceptible to insect and disease infestations. "Stressed plants just don't have enough energy to fight off most pests," says Ferree. "Stress also prevents the tree from making defensive chemicals it needs to fight."

The University of Illinois Plant Clinic expects an increase many plant diseases over the next several years, especially cankers, wilt, and scorch problems. Examples include pine diplodia, Dutch elm disease, cankers on redbud, oak wilt on the red oak group, bacterial leaf scorch on oaks, and iron chlorosis. There may also be an increase in verticillium wilt problems on maple, elm, boxwood, and sassafras. Spruce problems continue to be high in Illinois.

"Insect borers and some scale insects are likely to be more numerous than normal on trees for the next several years", says Phil Nixon, University of Illinois Extension Entomologist. "During extended dry conditions, trees lose root mass, resulting in a reduction of sap flow and dieback of branches". "The reduced sap flow provides opportunities for borer attack that would not be present otherwise". Nixon expects increasing tree and shrub borer problems until about 2016, then decreasing levels until reaching normal levels around 2018.

Can you do anything to help these struggling trees? Ferree recommends watering plants that are stressed during dry periods to encourage recovery growth and root revival. "Apply enough water to penetrate deeply within the drip line". "Never overwater". To prevent plants from sending out succulent, frost-susceptible growth, avoid fertilizing or pruning until the plants are dormant in late fall. "The added water will not reverse the early coloration, but it will better prepare the plant for winter and possibly less future decline."

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