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Landscape plant diseases
respond to 2007 drought
By
Aimee Nielson
LEXINGTON, Ky., (Jan. 2, 2008) – 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. |
Contact: John Hartman, 859-257-7445, ext. 80720
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The UK College
of Agriculture, through its land-grant mission, reaches across
the commonwealth with teaching, research and extension
to enhance the lives of Kentuckians. |
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