Zoysiagrass Recovery from Weather Woes and Spring Disease

Concerns about the Easter freeze weekend have now subsided as zoysiagrass recovered nicely following initial leaf lost due to the cold temperatures. The warmer than normal temperatures (20 degrees above normal and third warmest period on record for 118 years) during the last two weeks of March had zoysiagrass coming out of winter dormancy in a speedy fashion. Then after three mornings of 20 degree weather (coldest period on record for 118 years), zoysiagrass quickly returned to a dormant appearance. Normal temperature ranges have once again caused zoysiagrass to leaf out for a second time this spring with most lawns back to normal.

In recent weeks, a number of calls have been coming in about large dead patches (eight to 10 feet in diameter) in the center of or on the outer edges of zoysiagrass lawns. Most are concerned this is the result of the Easter freeze, unfortunately it is not. Large brown patch or zoysia patch is a cool to warm weather disease of zoysiagrass. Large circular patches of zoysia fail to green up in the spring with noticeable thinning followed by weed invasion. Homeowners and lawn managers will notice off-yellow to orange coloring of the entire patch with very distinct orange margins surrounding the patch. Although the onset of zoysia patch is related to exact weather conditions, heavy thatch buildup is also a contributor to this disease. Thatch management/control in zoysia will help reduce your potential for this disease. Presently there are no truly effective fungicides available to homeowners that are sold over the counter. Some effective control has been seen with Heritage and Prostar fungicides; however they need to be applied by a professional lawn care operator.

Beyond the winter woes and spring disease problems, standard zoysiagrass maintenance can be very simple. Follow the procedures listed below for fertilization, mowing, watering and thatch control.

Fertilizing
Established zoysiagrass requires less fertilizer than many other species for healthy, attractive turf. A seasonal total of two pounds of nitrogen per 1,000 square feet is ample. Excessive or untimely fertilizer applications can lead to problems such as fewer roots, more thatch, diseases and more top growth that requiring increased mowing.

For best results, soil testing is recommended before fertilizing. A soil test will indicate major nutrient deficiencies and the acidity or alkalinity (pH) of the soil.

Slightly acidic soil pH (6.0-6.5) is best. Lime should be applied only if the pH is less than 6.0.

Established zoysiagrass should be fertilized from May through August. Early spring (March/April) fertilization benefits weeds and promotes premature top growth before roots begin to grow. Late fertilization (September) may interfere with the natural hardening process before winter.

For routine maintenance where soil tests indicate no major deficiencies, use a lawn fertilizer with approximate nitrogen (N):phosphorus (P):potassium (K) ratio of 3:1:1 or 4:1:1 or 4:1:2. A 16-4-8 fertilizer has a 4:1:2 N:P:K ratio.

Where soil test indicates low phosphorus or potassium levels or where basic fertility levels are not known, use a fertilizer with a ratio that more closely approximates 1:1:1 or 2:1:1.

Mowing
Zoysiagrass is mowed at a shorter cutting height (1-2 inches) than Kentucky bluegrass or fescue. In the spring of the year, zoysiagrass lawns may be mowed at the lowest setting on your mower to remove dead leaf tissue. This increases the greenup rate and allows easier and more uniform mowing during the growing season. The mowing height should be raised in September by 1/2 to one inch in preparation for fall.

When mowing, never remove more than one-third of the leaf blade at any one time. Clippings need not be collected if they do not remain as clumps on the lawn surface.

Watering
Zoysiagrass is a drought-tolerant lawn grass that requires less water than Kentucky bluegrass to remain green and actively growing during the summer months. Watering usually is not necessary except during prolonged dry periods.

Cultural practices, such as proper fertilizing, mowing and thatch control can go a long way toward building a drought-tolerant lawn.

When watering, follow these simple rules:

• Water in early morning to reduce disease incidence
• Water deeply, wetting the soil to a depth of four to six inches.

Thatch
Thatch is a layer of decomposed and partially decomposed roots, stems, stolons and rhizomes. Thatch appears as a distinct horizontal layer of brown spongy or felt-like material just above the soil surface. Zoysiagrass is prone to thatch accumulation because of its thick network of rhizomes and stolons and coarse, tough stem tissue. When managed properly, clippings returned to a zoysiagrass lawn contribute little, if any, to the thatch layer.

Lawns should be dethatched when thatch exceeds 1/2 inch in thickness. A spring-tine power rake or vertical mower will accomplish this task.

If thatch is greater than one inch, do not attempt complete removal in one year. Instead, remove the thatch over a period of two or three years. Intensive coring should also be considered since this causes much less damage to the turf than does power raking or vertical mowing.

Thatch buildup can be minimized through good cultural practices, including the following:

• Fertilize moderately to maintain turf density without excessive growth
• Cut grass regularly at the recommended height to maintain vigor and to avoid shock. Clippings may be left to decompose if mowing occurs at regular intervals. No more than one-third of the leaf tissue should be removed with each mowing. Remove excessive clippings that accumulate in clumps on the surface
• Water deeply and only as needed
• Power rake or vertical mow with dethatching equipment as needed to keep thatch less than 1/2 inch thick. For zoysiagrass, early summer after the lawn has greened up is the best time to dethatch
• Where lawns are subjected to traffic, core aerify to improve penetration of water and fertilizer. Leave soil cores on the surface to dry and crumble before mowing .

Brad Fresenburg
FresenburgB@missouri.edu