By Nancy Bolton
Summer time and the living is easy…right? …except for having to maintain your grass in Central Virginia’s hot, humid August weather. The lawn could be totally brown from lack of rain or have brown patches (fungus) if we have wet weather followed by high humidity.
Virginia is located in a transition zone for turfgrasses, with climates that can be harsh in both winter and summer. Cool-season grasses are the most commonly used and include Kentucky bluegrass, rye and tall fescue. They grow strong enough and deep enough to cope with our hot summers and cold winters. Warm season grasses such as Zoysia and Bermuda grass are sun tough, drought and humidity tolerant, but they do go dormant in the winter making for a brown lawn from November until Spring.
Mow High
Is your lawn turning a whiter shade of pale, sick yellow or brown? You may be scalping it. Recommended mowing heights are 3 inches for the cool season grasses and 1.5 to 2 inches for warm season grasses. Letting your grass grow to its maximum height or above slows its growth, conserves moisture and inhibits weeds.
Mowing is a carbohydrate depleting process. What does it actually do to the grass? It decreases the leaf surface area, which is the site of photosynthesis. Each time we cut, we decrease the plant’s ability to produce carbohydrates essential for root, shoot, rhizome and stolon growth. Cutting only 1/3 of the height at any one time and having sharp mower blades decreases this damage. According to Dr. Mike Goatley, VA Tech’s turf grass specialist, cutting grass more than 1/3 of its height will “shock the plant and force it to redirect food resources from roots and stems toward new leaves.” Go to http://pubs.ext.vt.edu/430-532/ – “Spring and Summer Lawn Management Considerations for Cool-Season Turf grasses.”
Wound hormones are produced every time we cut the lawn. These compounds along with some enzymes are involved in wound healing, which decreases food reserves. Cutting with a dull blade creates a severe wound requiring more wound healing compounds and more use of stored food reserves. This may affect survival especially during the stress-filled months of July and August. If the wound cannot heal, it can provide an entry point for fungal diseases which we often see by August here.
Off with the bagger too! Leave the grass clippings on the ground. They decompose and act as mulch and retain moisture and return organic matter decreasing the need for fertilizer. Using a mulching mower is helpful because clippings are small enough to filter through the grass canopy and down into soil.
Water
Earlier in the summer, when rain is more plentiful, 1 to 1.5 inches of water per week, preferably over two different days, should be sufficient. However, by August, this may not be enough to keep the lawn lush and green and your grass may go dormant. Although the grass may turn brown, the roots will still be alive and the lawn will recover in the Fall as rain comes and the temperatures recede.
Identify Fungal Diseases
Healthy turfgrass will be better able to fight off disease when under stress such as heat and humidity than turf in poor condition. Cultural practices include deep, infrequent watering in the early morning, avoiding heavy fertilization in the spring and reducing compaction by core aeration. However, is there still a fungus among us?
Although there are several the most common fungal diseases in Virginia include:
- Brown patch (Rhizoctonia blight)
- Summer patch
- Fusarium blight
Brown patch occurs this time of the year during hot, wet weather. Typical symptoms are a circular area of brownish coloration with a grayish color at the outer edge often referred to as a smoke ring or halo. This happens more when homeowners go overboard in applying fertilizer that is high in nitrogen. So go easy! Brown patch kills the blades of the grass but not the roots. It can be spread on grass clippings, mowing equipment and even your shoes.
Summer patch and Fusarium blight occur more often in compacted soils such as high traffic areas or near paved areas and buildings. Summer patch is characterized by small, scattered, dark green, wilted patches of turf that turn tan in color. The patches are usually elongated in a shape less than 12 inches across, sometimes with a green spot in the center. The grass blades die back from the tip. In addition to compaction and wet, warm weather, summer patch strikes heat stressed grass that is mowed too short.
“A characteristic symptom often associated with Fusarium blight is a “frog-eye” patch containing a healthy ring of turf within a circular shaped area of blighted leaves.” See “Spring and Summer Lawn Management” at http://pubs.ext.vt.edu/430-532/. In this article several fungicides are recommended for the treatment of summer patch and Fusarium blight and include products that include Triadimefon, Myclobutanil and Propiconazole.
Treat grubs
Did you see all the Japanese beetles in July? They were laying their eggs in the soil, primarily in well-watered lawns in full sun. The best time to treat for grubs is mid July to mid August while eggs have hatched and the grubs are very small.
Insecticide use should be carefully considered since beneficial insects may also be eliminated. Pull up disturbed turf and count the number of grubs per square foot. If more than 6-10 grubs are seen, treatment may be indicated. Look for products that contain Imidacloprid or Halofenozide. Biological controls include beneficial nematodes which are applied in late spring and Milky spore, which only works for Japanese Beetle grubs. Milky spore is best applied in late August.
Prepare for Fall seeding
Next month we will discuss in detail how to seed or overseed the lawn . Prior to seeding, have a soil test done if you haven’t had one done within the previous three years. The results may take two weeks to return. See information on how to properly sample your soil, at http://pubs.ext.vt.edu/452-129/ -“Soil Sampling for the Home Gardener .”
In summary, the tasks for August include the following:
- Keep grass height high
- Mow only 1/3 of the turf’s height
- Sharpen mower blades
- Leave grass clippings on the lawn
- Treat for grubs if not done in July
- Test soil prior to reseeding in the Fall