April 21, 2009
 
Turfgrass Science Program (http://turf.uark.edu) – Turf Tips

1. Spring dead spot is now appearing for many
2. Sharpen your mower blades
3. Spreading tall fescue?
4. When to fertilize your lawn?
5. Mark your calendar for the Turfgrass Field Day: Wednesday, August 5, 2009

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1. Spring dead spot is now appearing for many

Spring dead spot (SDS) is generally considered to be the most significant disease of bermudagrass. Spring dead spot disease can show up each year on bermudagrass home lawns, however, it tends to be more prevalent on intensively managed bermudagrass. Low cutting height, soil compaction, high pH, overfertilization, and thatch accumulation may contribute to the onset of the disease. This disease becomes evident at spring green-up time during March or April in Arkansas.  Although several root-infecting fungi have been identified as being responsible for the disease in other regions, Ophiosphaerella korrae seems to be the causal fungus in Arkansas.

The diseased area appears in the spring as well defined dead circular patches than can range in size from a few inches to more than 3 feet in diameter (Fig. A). Symptoms may sometimes be confused with winterkill and injury from soil insects such as white grubs. Although spring dead spot symptoms may occur on bermudagrass lawns of all ages, it typically appears 3-4 years after the turf has been established. This disease primarily affects the roots. Death of the plants is believed to occur following normal low winter temperatures. The roots and stolons of diseased plants develop a dark brown to black colored rot (Fig. B).  Leaves become bleached, gray, and straw-colored. The dead, sunken patches can often get larger year after year.  Diseased areas may not fill in with bermudagrass until July or August.  Bermudagrass recolonization is slow, but regrowth may mask disease evidence by the late summer (Fig. C).  Weeds will often colonize the affected areas and slow the recovery of the turfgrass.  Additionally, application of certain preemergence herbicides in the spring may also slow recovery (Fig. D).

Images of Spring Dead Spot

The fungi which cause SDS usually begin to colonize the roots, stolons, and crowns of bermudagrass in the late summer or fall and again in the spring when soil temperatures range from 50-70º F. Even though root and crown infections occur in the fall, foliar symptoms do not show up until green-up in March and April of the following year.  The fungus can over-winter as mycelium in infected roots and crowns of the turf.  Excessive nitrogen fertilization during the late summer months tends to enhance symptom development during the following spring season.

Proper plant nutrition and thatch management can play a pivotal role in disease management.  Homeowners should be sure that there is an adequate potassium level in the soil.  A regular soil test should be done to monitor potash and other elemental levels.  Acidic soils tend to reduce the severity of the disease.  If soil pH is high (> 7.0), ammonium sulfate can be used to lower soil pH in a range of 6.0 to 6.8. Heavy applications of fast release nitrogen fertilizers should not be made in the summer following an outbreak of the disease.  Nitrogen applications should be avoided after August in northern areas of Arkansas and not after September 15 in the southern part of the state if the lawn has a history of SDS.  Nitrogen fertilization after mid-September may predispose the turf to many diseases. Fertilizing and irrigating too much can lead to thatch buildup, which favors disease activity. Management of thatch by verticutting and core aerification and soil compaction through core aeration should be an integral part of the disease control/prevention program. There appears to be a close correlation between cold hardiness of bermudagrass varieties and disease susceptibility.  When establishing a lawn, homeowners should consider growing tolerant varieties (Table 1). Bermudagrass varieties show substantial difference in their tolerance to the disease.  However, the most tolerant varieties still get the disease but not as severely as the least tolerant varieties. 

Table 1.  Relative tolerance of bermudagrass cultivars to spring dead spot.

Relative Tolerance

Cultivars

Most

Midfield, Midiron, Midlawn, Patriot, Riviera, Tifsport, Yukon

Moderate

Cheyenne, Mirage, Sundevil II, Tifway (Tifton 419)

Least

Arizona common, Tifton 10, Numex Sahara, Princess 77, Pyramid, Sunbird, Savannah, Transcontinental, Tifgreen (Tifton 328),

Removal of affected patches followed by re-sodding can be useful if there are only a few small diseased areas within the lawn.  Fungicides which containing fenarimol, propiconazole, azoxystrobin, thiophanate-methyl, or myclobutanil are labeled for disease control, however control by these materials is often incomplete and inconsistent.  Research in the Carolinas found fenarimol to be the most effective of these products.  For effective control, emphasis should be placed on the cultural control aspects of fertility, irrigation, and thatch management rather than relying exclusively on fungicides.  For maximum effectiveness, these materials need to be applied according to label directions at least twice in the fall when the fungus becomes active.  Homeowners should consider using a professional service to apply these materials appropriately.  

Aaron Patton and Steve Vann

2. Sharpen your mower blades

Rotary mowers are by far the most popular type for homeowners, although self powered reel mowers are gaining popularity. Rotary mowers work by cutting the grass blades in an impact, machete type cut. This cut is less precise and often more damaging to the leaf blade. The potential to scalp a lawn is higher when using a rotary mower, but the height of cut is easy to change and blades are easy to sharpen.

Sharply cut leaf blades increase turf health by improving recovery, decreasing water loss, and increasing photosynthesis (Figure 2). Lawns mown with a dull mower blade have poor aesthetics, heal more slowly and have greater water loss (Figure 3). Sharpen mower blades at least twice a year or more often for larger lawns. For commercial uses, mower blades should be sharpened at least every 40 hours.

Mowing quality is poor and the mower blade is dull in images A and B as evidenced by the shredded leaf blades. Some species are more difficult to cut such as zoysiagrass. Additionally, seedheads (Image C) are typically more difficult to cut than leaf blades. Image D illustrates the symptoms of varying levels of mower sharpness. Leaf blade D1 demonstrates what a leaf blade should look like after mowing. Leaf blade D2 demonstrates a leaf blade that was injured by a dull mower blade. Leaf blade D3 was cut by the mower but indicates that the mower blade is not sharp enough. The white tissue sticking out of the leaf blades (D3 and D4) is the vascular tissue of the plant. Leaf blade D4 was mown for quite some time with a dull mower blade.

Imags of shredded leaf tips indicating a dull mower blade

For more information on how to sharpen your mower blade, search http://www.youtube.com  for “How to Sharpen a Lawn Mower Blade” for helpful videos and demonstrations.

For more information about mowing your lawn, see FSA6023 “Mowing Your Lawn

For more information about lawn mower safety, see FSA1005 “Lawn Mower Safety

Aaron Patton

3. Spreading tall fescue?

Tall fescue is a cool-season grass used for lawns primarily in northern Arkansas with some use in shaded areas in central Arkansas. Tall fescue is typically classified as a bunch-type grass, meaning that it has limited ability to spread. Lack of spread is beneficial from the standpoint of reduced edging around landscape beds. However, spreading is desired to help recover from damage and when establishing a new lawn. As such, Kentucky bluegrass – a spreading grass – is typically added to tall fescue seed mixes to help thin areas in these lawns recovery from damage.

Some new types of tall fescue have short rhizomes, which is a specialized stem in some grass species that allows the plant to spread from one area to another. Of the grasses grown in Arkansas, zoysiagrass, bermudagrass, and Kentucky bluegrass have rhizomes. These new “rhizomatous types” of tall fescue are reported to spread more quickly than traditional tall fescue varieties, but this had not been researched until recently.

A study was conducted at Kansas State University in Olathe with the following finds:

For a complete look at this research see St. John, R. J. Fry, D. Bremer, and S. Keeley. 2009. Establishment rate and lateral spread of tall fescue cultivars. Golf Course Management 77(2):-113118

For a list of recommended tall fescue cultivars see FSA2113, “Seeding a Lawn in Arkansas” or FSA7558, Brown Patch of Tall Fescue Lawns”.

Aaron Patton

4. When to fertilize your lawn?

The timing of N fertilizer applications depends on the lawn species. Warm-season turfgrasses such as bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass should be fertilized in the summer months when they are actively growing. Cool-season turfgrass species such as tall fescue should be fertilized mainly in the autumn. A fertilization in September, November, and an application in the spring after the flush of growth (April or May) will result in a healthy turf. Avoid fertilizing tall fescue in the summer months because of increased risk of the disease brown patch. Lawns damaged during summer months and newly seeded lawns may need an additional N fertilizer application in October to help with recovery and establishment.

For more information on fertilizing, see “Fertilizing Your Lawn

For month by month lawn maintenance instructions see one of the following:

FSA6121

Lawn Care Calendar: Bermudagrass

FSA6120

Lawn Care Calendar: Centipedegrass

FSA6119

Lawn Care Calendar: St. Augustinegrass

FSA6118

Lawn Care Calendar: Tall Fescue

FSA6122

Lawn Care Calendar: Zoysiagrass

5. Mark your calendar for the Turfgrass Field Day: Wednesday, August 5, 2009
The University of Arkansas turf field day will be on Wednesday, August 5, 2009. The field day is located in Fayetteville at the Agricultural Research Center. Field day provides individuals the opportunity to hear the latest up-to-date information about new products and research studies as well as providing an opportunity to network with others in the turf industry and visit with vendors at the trade show. Lunch, a hat and an information packet are provided. More information including registration forms will be available in the near future.

Read more about previous field days in our news section

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