Helping Turf Recover from Summer Stress - Drought and Heat
There is no secret that this summer has been hot and exceptionally dry here in New England. The U.S. Drought Monitor (http://droughtmonitor.unl.edu/) shows Massachusetts to be seriously affected. Ten of the state’s 13 counties are experiencing a ‘Severe’ or ‘Extreme’ level of drought that extends northeast through southern New Hampshire and up into southern Maine.
The stress of drought coupled with repeated periods of high heat and windy conditions has left many lawns, parks and sports fields in trouble. Many unirrigated sites have been dormant for several weeks. The longer the drought dormancy, the higher the heat, and the more the turf is used (walked on, played on, etc), the more likely that the turf is suffering and will need specialized care in order to recover. In some locations recent rains have provided a modicum of relief while lower temperatures, particularly at night, have returned to levels conducive to rooting and turfgrass growth.
While many lawns will survive and the grasses will regrow, some hard hit areas are exhibiting thinned, damaged turf that is easily invaded by weeds and pests. Steps taken now and over the next few weeks will help turf to recover well, go into the winter in good shape, and be ready for whatever challenges that next year’s growing season may bring. Recovery strategies should be focused on protecting the turf from further damage, encouraging rooting and taking steps to ensure a dense canopy of desirable grasses. A deeply rooted, dense turf is the first line of defense against pests and stress.
First, take stock of the situation: What is the condition of the turf?
Is the grass is still dormant (brown or straw colored with no green growth)? Then protect it from further damage. Strictly limit foot and vehicle traffic, or risk damaging the turfgrass crowns from which new growth will arise. Do not mow unless turf growth warrants it. Do not fertilize dormant turf. Instead, wait until the weather cools and moisture returns, when signs of regrowth – new green sprouts - begin to appear before considering a fertilizer application.
Has the grass begun to show any signs of recovery… new green shoots coming from the crown at the base of the plant? Great!
Has the turf been kept out of dormancy through regular irrigation? Adjust the irrigation schedule so as not to overwater, especially as temperatures moderate and the sun’s intensity decreases through the earth’s natural rhythm. Overwatering will actually make turf less tolerant to drought, and can decrease rooting while increasing the potential for disease, as well as wasting a precious natural resource. For a current list of Massachusetts communities with water restrictions, see http://www.mass.gov/eea/agencies/massdep/water/watersheds/municipal-water-use-restrictions.html
If the soil has not been tested in the last few years, this is a good time to do so. For directions on how to take a sample and submit it, visit the UMass Soil and Plant Nutrient Testing Lab at UMass Amherst: http://soiltest.umass.edu/. Results will indicate if liming is needed, and specify if additional nutrients are needed. Providing for adequate soil nutrition is a foundation stone in growing a healthy turf.
Pests can take advantage of the weakened condition of stressed turfgrasses, and the damage of some insects, particularly chinch bugs, can mimic drought symptoms. Scout for insect infestation and plan to manage damaging populations if needed.
Adults of turfgrass damaging white grubs will be more likely to lay their eggs and continue their life cycles on schedule in turf that has not experienced moisture stress. Eggs have already begun hatching and first instar grubs are busy feeding in some irrigated lawns. Adult beetle egg-laying may be delayed on non-irrigated sites that have been heavily stressed or that have gone into dormancy. See Dr. Pat Vittum's recent Management Update for considerations for managing insect pests given the current drought situation.
Many weeds will out-compete stressed turfgrasses. Determine if unacceptable weed infestation has occurred, and plan to manage the situation. Crabgrass in particular will move into summer stressed turf and thrive under hot and dry conditions. If crabgrass is present and going to seed then you can be assured that there will be an infestation next season in the absence of corrective action.
If the weedy grasses are flowering and seeding, then bag the clippings when mowing and dispose of them properly. Use a pre-emergence herbicide next spring.
Crabgrass will begin to lose vigor as temperatures cool, and will die out after a frost or two. However, if the lawn has deteriorated to the point at which a renovation should be done before waiting for frost, then use of a post-emergence herbicide that will not interfere with subsequent seeding may be a part of a pre-plant weed control strategy.
Once growth has resumed, mow at highest height of cut appropriate for the situation and mow frequently enough to maintain that height. Mowing actively growing grasses frequently at the proper height of cut will encourage shoot and canopy density. Again, bag and remove clippings if crabgrass or other weeds are going to seed. Otherwise, drop the clippings as long as they do not clump.
Avoid fertilizing turf that is dormant. The plants do not have the ability to take up the materials and respond until growth resumes. Moisture is the key to pulling turfgrasses out of dormancy, and fertilizer will not be effective until new growth starts. Once that happens, proper fertility provided during the late summer – early fall period is critical to both the short-term and the long-term vigor of the turf and its ability to withstand pests and stress.
Fertilization of stressed turf should focus on encouraging root growth balanced with increasing shoot density. The particulars of a fertilization plan will depend on several factors including turfgrasses present, management level, turf use, and site factors, such as shade, that may impact growth. Opt for fertilizer materials with the highest percent of slow release nitrogen for the particular turf whenever possible. See Table 7 in UMass Extension’s Best Management Practices for Soil & Nutrient Management in Turf Systems for suggestions about fertilizing during this late summer – early fall period.
Plan to overseed thin or damaged areas.
Late summer-early fall is the best time of year to make improvements. Temperatures cool and moisture is usually more available, typically for several weeks, providing the conditions in which our cool season grasses thrive.
Thinned turf and bare spots invite weeds, and the loss of cushioning from turf cover can lead to compacted soil. It is important to get desirable turfgrasses growing before weeds can move in and compaction can occur.
‘Establishment, Renovation and Repair’, section 5 in UMass Extension’s Best Management Practices for Lawn and Landscape Turf, contains guidelines for improving turf from simple spot repairs to major renovations.
Use drought tolerant cultivars of grass species appropriate for the site and use. Adjust pH if needed and follow soil test recommendations for phosphorus and potassium fertilization prior to seeding. For more information on selecting drought tolerant turfgrasses check out the Turfgrass Water Conservation Alliance at http://www.tgwca.org/ and the National Turfgrass Evaluation Program at http://www.ntep.org.
If the physical condition of the soil is poor, then core aerate in conjunction with seeding and apply an organic topdressing such as a finished compost.
Alternatively, use a slice seeder to overseed the area.
Watering is critical when new grass is being started. If water use for irrigation is restricted, wait until mid-September to overseed to take advantage of potential precipitation increases heading into the fall. While there is no guarantee that precipitation will increase (recall that in 2015 we experienced an extended period without significant or widespread rainfall in late summer through early fall), seeding a little later provides a better chance of favorable conditions.
If you have no water available at all for making repairs, mulch seeded areas to conserve any naturally occurring moisture. Another option is to try a dormant seeding very late in the fall, after there is no chance of germination happening this year, and in hope of new growth taking hold very early next spring as the turf emerges from winter.
Evaluating the condition of the turf now and taking steps to aid in turf recovery will ensure that the lawn or park or playing field recovers and thrives, both keys to creating a drought and pest tolerant turf.
Report by Mary Owen, Turf Specialist and Program Coordinator, UMass Extension Turf Program