Warm-weather disease control
1 May, 2008 By: Hank Wilkinson Landscape ManagementIt's May, and those of you managing warm-season grasses know that the 2008 season is already two or three months old. One of the "benefits" of being a southern turf manager is that you get three or four summer months when turf disease is a challenge. (Your compatriots up north feel bad for you; then again, they were freezing all winter.)
 1 Brown patch generally appears on warm-season turf in early spring or late fall. |
Speaking of your northern neighbors, we realize that many of you, in addition to caring for Bermudagrass, centipede, zoysia and St. Augustinegrass, also deal with tall fescue, Kentucky bluegrass, perennial ryegrass and a bit of creeping bentgrass. These cool-season grasses are an even greater challenge for you to sustain in the summer than for your northern lawn care counterparts.
Let's take a look at why warm-season grasses grow in a much more varied environment than cool-season grasses. From east to west across the United States, the amount of rainfall can vary from feet per year to inches per year. Likewise, the humidity can range from nine months of high humidity in the Southeast and costal areas to nine months of very low humidity in the Southwest.
The biggest weather challenge that warm-season managers face is the heat, with its swings and duration. In general, warm-season grasses grow from late March to December. Compare that to the growing season in the North: mid-April to mid-October. In the South, the daily mean temperature can reach 90 F or higher for four months; compared to one to two months of comparatively hot temperatures in the North. Why is this important? Disease-causing fungi need heat and water (humidity) to attack your turf. The longer that turf is subjected to heat and wetness, the more severe the disease and its symptoms.
 2 Take-all patch is a big problem for Bermudagrass. |
In the South, disease is more severe, takes longer to manage and you use more control materials, which means more expense. Hopefully, you've explained this to clients. If you can sustain a beautiful lawn through the summer, you are both good and worth the money.
What to know
To be a successful and confident lawn manager, especially when dealing with turf pathogens, you need to understand:
- turf growth, what and when;
- identification and nature of the diseases most likely to attack turfgrass under your care; and
- how to use weather conditions to predict when disease will start and end, and when the turf will recover.
Although the most common warm-season turfgrasses are Bermudagrass, centipedegrass, zoysiagrass and St. Augustinegrass, some of you also will encounter tall fescue, bluegrass, ryegrass and bentgrass. Hopefully, you do not manage lawns of all these grasses. But if you do, then you're faced with the challenge of understanding how each of them grows in your area.
Bermudagrass, centipedegrass, zoysiagrass and St. Augustinegrass rely on rhizomes and/or stolons to spread. This is an advantage over ryegrass and tall fescue. In general, no matter how severe the disease that attacks these warm-season grasses, they can recover, although the time that takes will vary. These grasses also grow in two other ways: plantlets and leaf number. There are two rules for managing turf diseases: 1) Encourage the turfgrass to grow new tissue to replace diseased plants; and 2) Stop fungi from attacking the turf.
The best way to sustain a lawn is to keep the grass growing. Warm-season turf management has a definite advantage over cool-season turfgrasses here. If you understand this, you will be successful at dealing with diseases. Warm-season grass grows mainly from May through October. As long as grass is growing, the impact from disease can be managed. Why? Because the only way to get rid of ugly, diseased leaf tissue is to mow it off. Leaf diseases are most active when the turfgrass is growing most vigorously.
 3 Summer patch, caused by a soil-borne fungus, targets Kentucky bluegrass. |
Does this mean you should push turfgrass growth during mid-summer? No. But make sure it has enough fertilizer and irrigation to remain healthy and growing. If disease develops in your turf faster than you are mowing the damaged leaves off, consider other short-term ways to stop the fungi.
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