Summer decline can be a major problem on putting greens during summer months, affecting both bentgrass and bluegrass. It can be attributed to several main factors: high soil and air temperatures during the day and night, excessive or deficient soil moisture, poor soil aeration, and relatively high humidity. Surprising to many, high soil temperatures are more challenging to turf than high air temperatures and promote summer decline. Reduced evapotranspirational cooling (due to poor air movement) and high humidity contribute to high soil temperatures. When soil temperatures reach, on average, above 86 degrees, the basic physiological functions of turfgrass become greatly diminished. An excessive number of days with highs above 90 degrees, nights with lows over 70 degrees, or when the dew point is above 70 or winds are lower than 10 mph are conditions that promote bentgrass decline. Symptoms of summer decline include poor turfgrass vigor, chlorotic turf, reduced turf density, increased disease activity, inhibited root system, and overall worsened turf quality.

When it comes to summer decline, as well as many other turfgrass issues – an ounce of prevention is worth a pound of cure. Reducing the severity of summer decline begins with year-round cultural practices. Root zones with poor water infiltration and low percolation rates will be more susceptible to decline. Wet soils retain heat longer than well-drained soils, and are conducive to plant pathogens such as rhizoctonia solon and pythium sp. Cultural practices such as aerification and topdressing have both short and long-term impact on overall turf health and to help prevent decline. Practices to consider both prestress and during the heat of the summer include:

  • Regularly topdress prior to summer stress periods.
  • Use watering practices that promote deeper roots and precondition turf for summer conditions.
  • Monitor soil temperatures.
  • When possible, raise height of cut to help turf produce more carbohydrates and provide more leaf area for transpiration and cooling in heat. When stress conditions arrive, root loss increases as HOC decreases.
  • Switch to solid rollers – they are less aggressive and reduce overall stress to turf.
  • Alternate rolling greens with mowing if possible. Rolling greens produces a healthier turf, reducing stress and effectively providing an increased HOC without sacrificing green speed.
  • Increase air circulation and light to greens with any means possible. Thinning or removing trees around green complexes can provide tremendous benefit. When available, fans should be used during the day and night when stress is highest.
  • Vent greens every 14 days to improve gas exchange, water infiltration, and stimulate new roots.
  • When cooling greens, syringe with a fine mist. Properly train watering staff the difference between cooling greens and watering greens.
  • Prior to heat, utilize a deep and infrequent irrigation cycle. During hot weather, water in the AM if possible and hand water as needed.
  • Use quality foliar products containing seaweed-based raw ingredients and amino acids to provide nutrient uptake at times when roots aren’t functioning at full speed or at all.
  • Utilize humid acid-based products with wetting agent applications, which can release tied up soil nutrients, buffer bicarbonate and sodium and provide additional water-holding capacity.
  • Utilize a preventative fungicide program. Fungicide applications should begin in late spring / early summer, prior to the onset of heat and humidity, and continued throughout the stress periods. Summer decline fungicide programs should be based on a fosetyl-Al product, typically combined with another contact or systemic fungicide depending on conditions to provide broad spectrum disease control

Preventing summer decline is truly an all-season task. Tree work around greens done in January can pay huge dividends in August. Proper fertility and fungicide planning can reduce the need for more costly rescue applications. Lastly, a well thought out cultural practice program can make all the difference.