Summer Decline Overview

Overview

The problem

The decline in turf quality and growth of Creeping Bentgrass and Annual Winter Grass is a major problem on putting greens during the summer months. Both biotic (diseases) and abiotic stresses (high temperature, high relative humidity, excessive soil moisture, poor air movement) may be contributing factors to the severity of Summer Decline. Pathogens such as Colletotrichum Cereale (anthracnose), Rhizoctonia spp. and Pythium spp. can play a role in Summer Decline by attacking stressed turf. Due to the complexity of summer decline, specific causes are not well understood. Previous research by Dr Bingru Huang at Rutgers University found that heat stress is a primary factor contributing to weakened turf during the summer (Golf Course Management 69(7):61–64).

What to look for

Optimum air temperature for shoot growth for cool season grasses is 16–24ºC and optimum soil temperature for root growth is 10–18ºC. Shoot growth ceases when air temperature is above 32ºC and root growth ceases when soil temperature is above 25ºC. These temperatures are often exceeded on Creeping Bentgrass and Winter Grass putting greens during the summer. The high temperatures cause the roots of cool season grasses to decline and the growth of new roots to be inhibited. The declining roots are more susceptible to root rotting fungi and other stresses, while the new roots do not grow to replace the old roots. Summer Decline symptoms can include poor turfgrass vigour, chlorotic turf, reduced density, diminished root system, disease activity and overall inferior turf quality.

The solution

Implementing proper cultural practices is crucial to alleviating turf stress during the summer. Management tactics that encourage root growth will help to reduce the damage, including: aerifying throughout the summer with needle tines or spikers, syringing to lower canopy temperature, improving air movement by removing trees or using fans around the greens, spoon feeding with water soluble nutrients, and raising mowing heights to increase photosynthetic activity.

A preventative fungicide program has been shown to be very helpful in managing summer decline. Fungicide applications should be initiated in late spring/early summer prior to the onset of summer stress and continued throughout the summer months. Signature^® Extra Stressgard^® provides plant health effects and should be tank mixed with other fungicides to control both biotic and abiotic factors that contribute to summer decline.

Symptoms of summer decline on a creeping Bentgrass Green; Chipco® Signature treated (L) and non-treated (R). Photo: Dr Bruce Martin, Clemson University. *Chipco® has been discontinued.	Summer decline on an Annual Winter Grass/Creeping Bentgrass green. Photo: Dr Derek Settle, Bayer CropScience. As of 4th Oct 2022, the Environmental Science division of Bayer was divested and transferred to Envu. Note that this content was produced prior to separation.

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