Extension Plant Pathology Header

Kansas State University | College of Agriculture | Department of Plant Pathology | Site Map | Home


In this Issue:  August 16, 2006
     Plants Get the Summer Blues Too
     Disease Highlights

 

Plants Get the Summer Blues Too

The hot, dry weather is causing problems in many of our plants, from tiny turf plants to mature trees.  In some cases the drought alone causes trouble, and in other situations the drought stress allows certain pathogens to infect the weakened plants.  There have been many examples lately.  I will mention a few here.

For example, in the past couple of weeks I have found a fungal pathogen called Curvularia in several turf samples.  Curvularia (and a similar group of fungi called Bipolaris) are weak pathogens that can only infect turf that is already stressed from factors such as heat or drought.  This type of pathogen is sometimes called a secondary pathogen, stress pathogen, or opportunistic pathogen.  As soon as I see these spores, I know that something else is going on.  In one case, the turf also had a very thick thatch layer.  Thick thatch + drought  = highly stressed turf, ripe for infection by these stress pathogens.  In another case I received photos of the site and called the submitter.  The turf was on a southern facing slope, near the street.  That’s a prime site for drought stress.  Fungicides will not affect these diseases—the key is to relieve the stress.  Once the turf stand is healthy the stress pathogens will go away.



Another recent example of a drought-related problem was a huge cracked, bleeding canker on a mature London plane tree.  When I heard the description from the client, my first thought was a fungal disease called canker stain.  However, after I got the sample and did some observations it became clear that the pathogen was not present.  The tree had multiple longitudinal cracks with dead tissue right under the bark (not extending deeper into the wood).   In the photo you can see where I pulled the bark back around the cracks, showing dead tissue underneath.  Severe drought stress can cause cracking in thin-barked trees such as London plane, young honeylocust, crabapple, mountain ash, and others, especially those with smooth bark.  These same trees are prone to cracking due to frost damage in cold weather.  Our sample was a mature tree planted in spring in a site that was definitely prone to heat and drought.

 
   

The London plane tree simply succumbed to drought.  Like in the turf, certain tree diseases that are caused by pathogens can be exacerbated by drought such as canker diseases (ex: perennial peach canker and white rot canker on apple) and wilt diseases (ex: Verticillium). 

Try to take care of those plants with adequate irrigation.  In some places water use restrictions might be in place, so it could be a challenge.  It’s rainy and cooler today in Manhattan as I write this… it gives me a little bit of hope that the hot, dry pattern might end sometime soon. [Kennelly]

 

Disease Highlights

Bentgrass - Pythium root rot
Cleome - Iron chlorosis + spider mite damage
Fescue - Brown Patch
Giant Hyssop - Pythium root rot
Ornamental pear - Cedar-hawthorne rust
Pumpkin - Phytophthora root rot
Spruce - Environmental stress/scorch, Phytophthora root rot
Soybean - Bacterial blight, bean pod mottle virus, soybean mosaic virus, charcoal rot, drought stress
Tomato - Physiological leaf roll, spider mite damage
Environmental stress/Scorch - Honeylocust, magnolia, maple, spruce, squash, tuliptree, yew

 

Contributing Authors:

Megan Kennelly           kennelly@ksu.edu
Judy O’Mara                jomara@ksu.edu

 

 

Web updated 9/01/06
Web comments to jpierz@ksu.edu