Late-Summer Struggles for Cool-Season Lawn Renovation in Virginia

Mike Goatley, Professor and Turfgrass Extension Specialist

The following scenario comes from the VT Plant Disease Clinic and a VCE agent working with a homeowner near Culpeper who is dealing with a cool-season lawn that has struggled all summer.

VCE Extension Agent and VT Plant Disease Clinic: A tall-fescue lawn sample was been received by the Virginia Tech Plant Diagnostic Lab. The accompanying pictures (above and below) show patches of dead grass and overall thinning of the turf. We think it is tall fescue - can you please confirm? The client says the patches have been dead since a drought in the previous year and were overseeded that fall, but never really grew back this year. The lawn itself was fairly shady until recently, as several large trees that were partially shading the lawn have now been removed. At this point in time, the lab has not recovered any root pathogens from our culturing yet. A soil-test report has also been provided.

Matted turf in cool-season lawn

Dr. Goatley’s response: The challenges of summer in Virginia will always produce challenges in maintaining a high-quality cool-season lawn.  The best news is that FALL presents one the opportunity of repairing / renovating the lawn to restore it to the desired quality!

Since it was not mentioned, I'm assuming that there have been no fungicides or insecticides applied to the lawn, either by the homeowner or a lawn care operator.  If those services have been provided, please share that information about what has been done.

The potted-sample (photo below) suggests this sample is pretty much 100% tall fescue, but it is common in much of Virginia for there to be some KY Bluegrass mixed in as well. However, I don’t see any bluegrass in this image.

As always, the problems pictured could be an infinite number of possibilities, primarily leading back to our transition-zone location, and then being exacerbated by Mother Nature, and the varying levels of environmental stressors she provides every year. The lawn showing general thinning of the turf (top photo) is almost to be expected for lawns that are not under intensive management programs of irrigation and pest control in Virginia by late summer. In the other image (phot above) a bit more problematic/worrisome because of how matted down the turf appears. That suggests there could have been an outbreak of Pythium blight earlier in the year, and given the heat and persistently-wet conditions we typically have in a Virginia summer, this type of pest activity from a fungus that is always present in our soils is not unheard of (note: there is nothing to be done about it now, but this type of disease is something to familiarize oneself with for the future).  If the lab finds anything of importance as the fungal cultures develop, please let us know.

I also suggest the homeowner do the "tug test" on the most damaged sod to confirm it is not damage from grub pressure feeding on the roots; if the sod lifts like a throw rug on a hardwood floor, then that's a pretty clear indication of grub feeding. There still would be time to treat with an insecticide if desired to prevent further damage before the grubs go deeper into the soil. There are a variety of Virginia Cooperative Extension publications available to review regarding pesticide selections, and grub management in general, that can be found at: https://www.pubs.ext.vt.edu/.

Matted Tall Fescue Turf Sample

Thanks for providing a copy of the soil test (below).  What strikes me as most critical to address before attempting anything else in a renovation is the pH and nutrition limitations of this soil. A pH of 4.9 is extremely problematic and Low to Low- levels of Phosphorus (P) and Calcium (Ca) are going to further compound any pest activity that might occur. It is already challenging to grow cool-season grasses in Virginia as it is.  Address the pH issue as soon as possible, following the test-report guidelines of applying no more than 50 lbs. lime per 1,000 sq ft, per application. Make the first application as soon as possible in August and time it before a rain event of at least 0.25 in to help move the lime into the soil. Then, apply 50 lbs. lime per 1,000 sq ft on monthly intervals in Sept and Oct, and make the final 30 lbs. per thousand sq ft application in early- to mid-November. 

Follow the soil test recommendations for fertility as well and see if you can locate a specific 1:2:1 ratio product (for example, something like 5-10-5). Specialty stores are more likely to carry these types of fertilizer than big-box retailers. However, even the complete fertilizers at the big box stores will work as you should be able to find 10-10-10 or 13-13-13 at most retailers. If you can locate the 5-10-5 product, apply it at 14 lbs. of product per 1000 sq ft in mid-September and again in mid-October - that should give the plant the Phosphorus the soil test says it needs, and meet the plant's nitrogen requirement as well. You also can use the 10-10-10 or 13-13-13 on the same schedule and apply it at 7 lbs. of product per 1,000 sq ft, or 5.4 lbs. product per 1,000 sq ft, respectively.

Soil Test Report

Once the first lime application has been made in August, some level of soil preparation should be conducted to improve soil to seed contact in the damaged areas – rake it, scratch it, drag it … etc., something to disturb the surface and loosen it up a bit prior to seeding.  Another option is to core aerate/plug the lawn prior to seeding in mid September.  When the cores dry, they can serve as a great way to improve soil to seed contact. Aerate the lawn in a couple of directions, and make that second application of lime, the first application of fertilizer, and apply the seed. Turf-type tall fescue remains our most popular lawn grass, and it makes sense that given the current lawn composition that one would apply more improved varieties of tall fescue in this situation. Try to find seed sources that are 50-67% by weight of varieties listed on the VCE Virginia Turfgrass Variety Recommendation List to optimize your chances for success. Use 6-7 lbs. of tall fescue seed per 1,000 sq ft in the barren areas, cutting the rate in half on the better areas of the lawn; no need to apply seed in the thickest areas of existing turf in the lawn. Then drag/rake everything across the lawn and back into the aeration holes (a piece of carpet or chain link fence drug behind the back of a riding lawn mower is a simple and effective strategy for distributing seed, soil, lime, and fertilizer). 

Decide whether you will or will not apply supplemental irrigation. If you choose to do so in order to accelerate germination, irrigate lightly and frequently on a regular basis for the first 2-3 weeks; keeping the site moist but not saturated. A light over-the-top application of small-grain straw can be applied over the surface as a mulch to conserve moisture. If you are not going to commit to irrigation, just leave it in Mother Nature’s hands rather than applying a little bit of water and then not following up on a consistent basis.

Mow the turf after germination is completed and keep the 1/3rd rule of mowing in play (do not remove more than 1/3rd of the leaf blade at any mowing event). As a rule-of-thumb, a mowing regimen would be letting the grass get 3-in. tall and cutting it to 2 in. during these initial mowing events. Anticipate there to be some weed pressure, especially from winter annual broadleaf weeds and annual bluegrass. It is very difficult to manage annual bluegrass in a newly-seeded tall fescue lawn, so we typically have to rely upon the density of our new turfgrass stand to out-compete the Poa. Be sure to mow the grass at least 3-4 times before applying any labeled broadleaf herbicides for the winter-annual broadleaf weeds that are likely to emerge (an extensive discussion on all of these types of strategies can be found in a VCE publication called Cool Season Lawn Renovation at https://www.pubs.ext.vt.edu/content/pubs_ext_vt_edu/en/SPES/SPES-353/SPES-353.html).

One bit of information that is missing from the soil test report that the client might consider addressing – IF it is a limiting factor – what are the soil organic matter levels? It is possible that since the site was previously wooded that the soil % OM levels are already in the desired 3-5% range (unfortunately, the only way to know this is to conduct another soil test, but that is not a huge cost). In general, we remain very staunch supporters of the use of a quality compost to improve soil health by making periodic applications of around 0.5 cubic yards per 1,000 sq ft. The biggest challenge is getting the product spread, and most often this has to be done by hand.  But pairing this additional treatment with the dragging-in of seed, fertilizer, and lime works well, following a core aeration event.