AMHERST, Mass. - Due to a prolonged period of lack of rainfall throughout many areas, turf has gone off color and, where irrigation has not been available on a regular basis, is the color of straw. What happens to the turfgrass plant when these stresses act upon it? What steps can be taken to encourage recuperation?
HEAT STRESS. When stressed by high temperatures, turf reduces its growth in several ways. Shoot growth, root growth, tillering, stand density and leaf size all decrease. Photosynthesis plummets, and carbohydrate production is severely decreased. Because the turf is thus weakened, its recuperative potential is reduced. Those swards that had well-developed, deep root systems and dense canopies have fared better than those that did not. Turf growing on poor, shallow or compacted soils has been especially hard hit.
Heat stress injury is often aggravated by water stress. As transpiration from leaves rises in response to high temperatures, leaf stomata close down. The result is a loss of the cooling effect that transpiration has on a leaf surface. Leaf temperature rises and plant injury at the cellular level increases. When cellular injury is allowed to continue, we begin to actually see the damage. Turf wilts, and leaves begin to die and turn brown. Syringing (very light watering) especially sensitive turf can help to cool down the leaf surface and, therefore, decrease heat damage.
DROUGHT. When a turfgrass plant experiences water stress, it reacts by closing down leaf stomatal openings. This is a positive physiological method that helps to conserve water. As noted above, this stomatal closing increases leaf temperature. Unless water is supplied to the plant in adequate quantity, leaves begin to lose turgidity. Plants wilt. Photosynthesis decreases. The plant is weakened. Carbohydrate reserves within the plant are reduced; the plant is unable to replenish these reserves and may enter into a starvation situation.
SECONDARY PROBLEMS. Turf weakened by heat and water stress is susceptible to additional damage from secondary causes. These should be minimized whenever possible to ensure survival of the turf.
Watch closely for insect infestations. Chinch bugs thrive in hot weather. Their damage may be mistaken for drought injury.
Japanese beetles actively lay eggs in turf that is not too severely damaged, and if soil moisture levels increase or are kept adequate through some irrigation when eggs are ready to hatch, populations will be large. Conversely, if soil is very dry and moisture is not replenished, Japanese beetle egg hatch may be very low.
Large ant populations can cause problems. Tunneling and mound building activities can aggravate an already excessively dry soil situation and cause severe root injury.
Billibugs and sod webworms may cause damage in some lawn locations.
Black turfgrass ataenius can also be troublesome this time of year.
The mid- to late-summer season is a time to closely monitor insect activity and population levels to avoid unnecessary pesticide application, to salvage turf and to manage the budget.
Traffic on heath and drought stressed turf will only increase the damage, not only to leaves and roots, but more importantly, to the crown. If possible, reduce traffic and use on heavily stressed areas. As weather cools, moisture becomes more available and growth resumes; traffic and use may then be gradually increased.
MANAGEMENT STRATEGIES. Turfgrass managers should take steps now to increase the ability of stressed and damaged turf to recover. Any steps that favor turfgrass growth, especially root growth, will tip the scales in favor of the turf.
The recuperative ability of a turfgrass rests in large part in the crown. It is from the crown that tillers, rhizomes, stolons, leaves and roots emerge. While leaves may die, the crown has the ability to withstand high stress, and unless conditions have been severe for a prolonged period, the crown has the ability to resume growth when water is again available. When lower temperatures, especially at night, resume, the potential for crown growth and recovery increase still further. Management practices, which encourage the recovery and activity of the crown, as well as regrowth and development, will hasten the recovery of the turf on the whole.
If possible, replenish soil moisture. This should be done so that the soil is moist to as deep an extent as is practical and possible. This will encourage root growth downward, so that the plant can pump a greater volume from the available soil moisture reservoir.
Fertilization of heat and water stressed turf should focus on encouragement of root growth, and not excessive shoot growth. Though the tendency may be to get something green growing fast, remember that the long-term survival of the plant is most important. High nitrogen fertilization, especially with predominantly water soluble or high salt index fertilizers, should be avoided. High nitrogen fertilization, while encouraging leaf growth, can slow the replenishment of carbohydrate reserves, especially necessary for recovery, production of new plant tissue and winter survival.
Potassium fertilization can increase heat and drought resistance as well as disease and cold resistance. Root development is encouraged by adequate potassium. Research has shown that potassium has a positive influence on recovery of water stressed turf, especially when applied in a balanced combination with nitrogen and phosphorous. Slow release fertilization of damaged turf is preferred. A 1:1 ratio of nitrogen (N) to potassium (K) will encourage root development and stress resistance. For those areas with very sandy and well-drained soils, a ratio of 1:2 (N:K) may be used.
When mowing, allow the turf to grow to the highest cut practical for the specific turfgrass and use intended. Let the clippings lie. Be sure blades are very sharp.
EVALUATE. As conditions, both naturally occurring and manipulated by the turf manager, begin to favor the recovery and regrowth of damaged turf, continue to evaluate the level of damage. If necessary, begin overseeding and renovation procedures after mid-August.
The author, Mary Owen is an extension educator in turf at the University of Massachusetts Extension, Amherst, Mass. For more information about the UMass Extension’s turf program visit www.umassturf.org.
The above article is reprinted from the July/August 2001 Newsline newsletter distributed by the Associated Landscape Contractors of Massachusetts, South Natick, Mass.