Summer Stress – Turfgrass Science at Purdue University

Summer Stress

Summer Stress

With a warm and wet summer, we are experiencing decline in some of our turf around the state due to temperatures, disease, insects, and weeds. In response, we are publishing a four part series on this topic to help turfgrass managers respond. Look forward to the following topics over the next two weeks.

Part I: Too hot: Why some turfgrass species look poor in summer.
Part II: Summer diseases in residential turf.
Part III: Summer weeds: Common summer weeds and their control.
Part IV: Summer insects: Monitoring for summer pests and preparing for fall.

Part II: Summer diseases in Residential Turf

June, July, and August are accompanied by a variety of infectious diseases (see the turf disease calendar posted in May) that can contribute to significant damage– especially in year when summer temperatures remain unseasonably high.  The narrative below outlines the lawn disease concerns and identifies sources of further information regarding disease diagnosis and control.

Root Diseases—Sumer Patch and Necrotic Ring Spot
These two diseases are caused by closely related fungal pathogens that infect turf roots.  Their symptoms are identical, so most folks (including professionals) really do not know which is which.  Fortunately, practices to avoid or mitigate damage also are the same.  Susceptibility to Sumer Patch and Necrotic Ring Spot is the Achilles Heel of Kentucky bluegrass (especially in sodded turf).  Tall fescue and perennial ryegrass are resistant.  When roots are compromised by infection, their function is diminished.  Under conditions of high heat and/or drought stress, infected roots often are unable to keep plants alive.  Infectious diseases of turf have characteristic circular patterns associated with the damage.  Recognizing such patterns are important in distinguishing Sumer Patch and Necrotic Ring Spot from insect damage or general cultural damage.  Check Turf Disease Profiles (BP-115W and BP-116W) for detailed information.

Foliar Blights—Brown Patch, and Pythium Blight
Brown Patch, and Pythium Blight occur during hot, humid, rainy weather.  Kentucky bluegrass is largely resistant to these diseases—perennial ryegrass and tall fescue are quite susceptible.  They produce white-gray cottony mycelium after prolonged periods of wet turf.  The fungal pathogens are very common in Midwestern soils. Brown patch is mostly a foliar disease whereas Pythium blight will kill crowns as well as leaves—so it is important to be able to distinguish one from the other.  Also, different remedial treatments are recommended for these two.  Check Turf Disease Profiles (BP-106W and BP-108W) for detailed information on identification and control.

Rust Diseases
Several different types of rust will infect Kentucky bluegrass and perennial ryegrass in the Midwest.  Diagnostics and control are similar, so it is not really important to sort out the different pathogen species.  Rust outbreaks occur when turf is growing slowly–whether due to drought, low N or both.  Symptoms usually first appear during August and will remain well into the fall.  Rust damage is largely cosmetic, but the orange-brown dust that becomes attached to children and pets can be a serious nuisance (but NOT a health risk).  Rust on recently planted Kentucky bluegrass and perennial ryegrass can kill turf and may require remedial treatment. Check the Turf Disease Profile (BP-110W) for detailed information on identification and control.

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