Summer Stress Arrives Early on Cool Season Lawns Figure 1. A fall installed tall fescue sod showing the first signs of summer stress following the arrival of record setting heat in central Virginia in mid June 2015. Today s topic is generated by numerous questions from homeowners, sales reps, and observations by @VaTurf for the late June 2015 period. After much of Virginia suffered warm season turfgrass damage from the winter of 2014 15, Mother Nature has decided to hit our state with a double whammy on its cool season grasses with a major heat wave beginning in mid June. This heat wave has had a very tropical like weather pattern for much of the state with record setting temperatures being accompanied by afternoon thunderstorms. Warm season lawns have generally responded favorably to this pattern, and in many cases, the heat and moisture has led to fairly rapid recovery from the winter damage. However, this pattern has caused a serious decline in the performance and quality of our cool season turfgrasses that looked awfully good during a spring period that was running 2 3 weeks behind in temperature average for quite some time that is no longer the case. Visible stress such as that in Figure 1 is very common on tall fescue, Kentucky bluegrass, and perennial ryegrass with the arrival of the heat, especially in our warmer climates. Observations and comments: In almost every case that @VaTurf or @VTTurfPath has received for analysis, the primary culprit has been soil related rather than the s Page 1
anticipated disease we were asked to check. Any limitations in a soil due to inappropriate nutrition or ph, low soil water holding capacity, and/or physical compaction are going to be exaggerated under these temperature extremes, and even with the rainfall events that much of the state has received, the soil will dry out very quickly where the rootzone is very shallow. There are no quick fixes for these areas but if they have been identified, it will certainly help over time to remediate by way of conducting soil tests and to improve both the physical and chemical properties of the soil with an application of ¼ inch of a quality compost material 1 2 times annually to build up soil organic matter in these low quality soils. Many of our significant diseases of coolseason turf will display some form of a characteristic symptom (visible turfgrass response to the disease) or sign (the physical presence of the fungus itself) that will aid in the diagnosis of whether the problem in the lawn is being incited by an abiotic (non living) or biotic (living) Figure 2. These patches of distressed tall fescue are caused by Rhizoctonia blight, aka Brown Patch. Figure 3. The characteristic necrotic tissue patterns of Rhizoctonia blight on tall fescue leaves. entity. By far the most prevalent lawn disease during the summer in Virginia is Rhizoctonia blight (aka Brown Patch) on tall fescue. This disease is noted for its symptomology rather than actually seeing the fungus (usually by way of a cottony thread like material called mycelia that we see with other diseases). Diseased turf will have random patches of blighted turfgrass leaves that may or may not have a circular pattern (no s Page 2
particular pattern is really evident in Figure 2). However, with a little practice and patience, one can quickly become quite accurate in identifying Rhizoctonia blight by carefully inspecting the characteristic symptoms and shapes of the necrotic tissues of the blighted leaves (Figure 3). You can have your local county extension agent assist in the diagnosis of the disease, and if it truly is a disease, they can also help provide a chemical control strategy if it is desired. Use your smart phone to snap shots of your lawn and any symptoms or signs of the disease, and consult with the agent or turf professional on just how to collect and submit an appropriate sample for disease analysis. Should you decide to spray a curative treatment before confirming what disease it is, then use a broad spectrum fungicide that controls a lot of diseases (typical active ingredients for this type of treatment would be chlorothalonil or myclobutanil). However, it is always best to get the disease properly identified so that you can make the best choice in a pesticide possible. Be aware that not just any fungicide will control brown patch. Consult the Virginia Tech Pest Management Guide for the active ingredients and application levels and strategies of the best products (https://pubs.ext.vt.edu/456/456 018/456 018.html). The best thing about something as seemingly unsightly as brown patch is that it typically does not completely kill the turfgrass plant and the grass recovers when cooler temperatures arrive. The challenge for homeowners is that lawns already are under stress from this disease in 2015 and the calendar has not yet turned to July. s Page 3
Figure 4. The weight of the lawn tractor tires has killed the turf in the trafficked areas of a grub infested tall fescue lawn. One other point that turfgrass specialists are always preaching: Mother Nature does not kill in defined lines or patterns. If you see either straight lines (as evidenced in Figure 4) or perfectly manicured curves etc., then suspect that some form of human interaction with a sprayer, spreader, tiller, or the like is likely responsible for the problem. Again, more times than not the problem is an underlying soil condition. Most definitely conduct a soil test if one has not been done over the past 3 4 years to determine if nutrient or ph limitations are contributing to the problem. What can be done during the heat? Very often the best answer is nothing, and that is not intended to be a sarcastic answer! It is meant to convey don t do anything to cool season turf when it is under extreme heat and/or moisture stress. However, nothing has some limitations when folks are searching for answers, so in no particular order of importance (because they are all important) here are the most important tips in surviving the summer stress. 1) Remove all traffic and raise the cutting height to its highest setting and/or refrain from mowing until temperatures moderate and the turf has produced distinct new growth. This should have been done already for cool season grasses, but if it has not, then it should still be done now. Don t expect to have cool season lawns to look every bit as good in a Virginia summer as they do in a Virginia spring. These grasses thrive in temperature ranges of 60 75 degrees F, not 90 degrees plus. The easiest tip to remember about mowing is this: grass doesn t need mowing if it isn t growing. Resist that compulsion to mow a turf that has shut down its s Page 4
growth due to heat and moisture stress. Trafficking a turf under extreme stress can actually kill the turf as seen in Figure 4, where a grub infested fescue turf was damaged by the weight of the tires from a small tractor pulling a clipper over the turf area. 2) Choose an appropriate irrigation strategy: apply no water at all or irrigate deeply and infrequently. Grasses naturally enter a dormant state during periods of environmental extremes outside their optimums. Warm season grasses have a very defined winter dormancy period, and while it is not as well defined because our summer temperatures and moisture patterns are so variable, cool season grasses can have a dormancy phase as well. Let your lawn enter its dormancy phase and stay off the lawn during these periods with either foot or equipment traffic. If you do have an irrigation system, then practice deep and infrequent irrigation, thoroughly soaking the soil with as much water as it will hold in one event rather than providing frequent, light watering. When possible, run the irrigation during the early morning hours to reduce the effects of any wind and limit the leaf wetness period that can promote disease. 3) If you suspect a disease, then be sure to get samples to a turfgrass professional or your local extension agent for an accurate diagnosis. Specific fungi often require specific fungicides in order to control the disease. However, one advantage of dry conditions is that disease pressure is likely to be quite low. It s the persistently hot, moist conditions that typically cause our largest disease outbreaks. 4) If you have had a history of white grubs or are seeing an inordinate number of beetles in and around your lawn and landscape this year you might have a grub problem later this summer. Your cool season lawn is going to inherently have a very limited root system due to the environmental stress, and the lack of roots is s Page 5
only going to be confounded by significant grub pressure. The turf as seen in Figure 4 with the distinct wheel tracks from the mower turned out to have very heavy white grub pressure in the rootzone (Figure 5). The weight of the mower, combined with the feeding pressure on the fescue roots, was enough to kill the turf in those areas. Figure 5. Large numbers of white grubs feeding on the roots, combined with the stress from the weight of the wheels of a mower, have killed turf in very distinct lines on this fescue lawn. You might have to do some scouting in your lawn with a flat edged shovel to determine how many grubs are present at the top 1 of the soil in your lawn. The typical threshold range that can cause appreciable damage in cool season lawns (especially cool season lawns under temperature and moisture stress) is 6 10 grubs per square foot. There are several insecticides available for white grub control and they are detailed in the Pest Management Guide. Typical application times to optimize the effectiveness of most of the readily available grubicides is usually early July to mid August in Virginia. 5) Refrain from using nitrogen fertilizers in an attempt to rejuvenate your lawn. Periods of extreme heat are simply not going to be times when you get a desired response from N based fertilizers on cool season grasses (plus there is more potential for causing water quality problems at this time of year since the plant is not going to efficiently utilize the nutrient). Save your N sources for the end of summer/first of fall after the arrival of persistent fall temperatures and take s Page 6
advantage of periods when both roots and shoots are actively growing to apply your nitrogen. Summary. The challenges associated with lawns in the transition zone will almost always be with us because when you live in a region that truly offers four distinct seasons; winters and summers will present extremes from time to time, it is just that they usually don t follow each other so closely. Do keep in mind that sometimes doing nothing is the most appropriate response at getting your coolseason grasses through some of these most difficult periods. s Page 7