Master gardener: Dont worry about leaf spots

The Master Gardener Helpline volunteers often field calls in late summer from homeowners with concerns about leaf spots and browning on deciduous landscape foliage. These are trees and shrubs that lose their leaves each fall.

Similar questions arise from those who see late-season powdery mildew on perennials or non-evergreen shrubs. Is treatment required and what should be used to protect or save their planting?

Conversations about these concerns to these University of Illinois Extension volunteers are first addressed by making certain the master gardener knows what specific planting is being affected. When the homeowner is not certain, questions will be posed to them which can help narrow the field. Digital photos of the tree, shrub or perennial causing concern can be especially helpful when sent to the Helpline email address, listed below.

There is a general rule of thumb that should put most homeowners at ease when it comes to these late-season foliar problems. The planting in question has been photosynthesizing all season long and has produced the majority of the food energy needed for it to make it through the winter. What can be produced in the next few weeks before the leaves fall off is not as important as what was produced up to this point. Treatment of foliar diseases this late in the season is not necessary.

Fall cleanup of diseased leaves becomes extremely important so that the disease spores found on them are removed from your property. This wont always solve the issue, but will certainly help it to not build up for the next growing season. Dispose of the leaves, dont try to compost them. Most home compost piles never heat up to high enough temperatures to kill the disease spores.

Evaluate the area around the planting and see if there are ways to improve air circulation, increase sunlight or in general to help the area dry out more quickly than it might be already. Fungal diseases need moisture to grow, and leaves that stay wet are more susceptible to infection. When selecting new plants in areas where disease has been sited, look for disease-resistant varieties that will help reduce the problem as well.

Email your home garden and lawn questions to uiemg-dupage@illinois.edu or phone the Master Gardener Helpline at 630-955-1123. Visit our website at http://web.extension.illinois.edu/dkk/.

Julie Moore has been a master gardener volunteer with the University of Illinois Extension in DuPage County for 10 years and has a degree in ornamental horticulture from the University of Illinois.

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