January 2, 2008 | By: Aimee Nielson

The effects of the 2007 drought are widespread and landscape plant diseases are yet another area Kentuckians should pay close attention to as they prepare their gardens for spring. 

Many home gardeners and landscapers may be familiar with leaf scorch symptoms associated with dry weather. During the 2007 drought, leaves of drought-stressed plants, while wilting, closed their stomata which reduced their rate of photosynthesis. 
“Reduced photosynthesis may not kill a tree or shrub,” said John Hartman, University of Kentucky College of Agriculture extension plant pathologist. “But, it does mean the plant makes and stores fewer carbohydrates for future use. Thus, many landscape plants are low on energy reserves, especially seedlings and recently transplanted trees and shrubs, because they lack extensive root systems.”

Because their energy reserves are low, many landscape trees and shrubs are at risk of contracting fungal diseases, and Hartman said some fungal diseases of landscape trees and shrubs often don’t show symptoms until the season following the drought, so the upcoming season is one to closely monitor.

“It’s possible that the stress condition interferes with the plant’s defense against such pathogens, or possibly, the reduced carbohydrate reserves allow the plant little energy to fight invasion by pathogens,” he said.

Hartman said to expect certain fungi such as oak pathogen Hypoxylon and Armillaria, which attack woody plants, to appear this year, due to last year’s drought conditions. Diseases caused by other fungi will also appear including, but not limited to:

• Thyronectria – cause of honey locust canker
• Cytospora or Valsa – causes cankers on prunus, poplar, willow, maple, spruce and other conifers;
• Sphaeropsis – causes pine tip blight;
• Botryosphaeria and Nectria – causes cankers on many woody plants such as rhododendrons, crabapples, dogwoods, maples and others. 

Some woody plants may have sacrificed their surface roots to the drought when trying to search for water, relying on deeper roots to sustain life. 

“With the return of excessive rain, like what Kentucky experienced in December last year, partial flooding could render the deeper roots more prone to diseases,” Hartman said. “That could leave the woody plants with few functional roots. So, we can expect additional woody plant death.”

Hartman did say that the drought could have one possible benefit to landscape plants – reduced instance of foliar diseases. However, that benefit may be short lived if spring weather is wet and rapidly repeating cycles of these diseases occur. 

“Also, cedar rust infections may be reduced in future years due to the drought,” he added. 
Perennial flowers and ground covers, like their woody counterparts, could have reduced energy reserves due to the drought. Hartman said that could make them more vulnerable to cankers and root, corm or bulb rot diseases. 

“Gardeners who watered regularly during the drought will be rewarded with healthier plants this year,” Hartman said.


John Hartman, 859-257-7445, ext. 80720