September 24, 2007

1. Pest Guys – Diagnosing your lawn pest problems

Every day, Arkansas’ homes, lawns and gardens are under siege by destructive insects, diseases and weeds. How do you cope with them? How do you get rid of them? How do you prevent these problems in the first place? Click here to find out more.


2. Fall fertilization

The timing of N fertilizer applications depends on the lawn species. Warm-season turfgrasses such as bermudagrass (Cynodon spp.), centipedegrass (Eremochloa ophiuroides), St. Augustinegrass (Stenotaphrum secundatum), and zoysiagrass (Zoysia spp.) should be fertilized in the summer months when they are actively growing.

Recent research on bermudagrass found that late-season N applications prior to frost promote fall color retention and do not have a negative effect on bermudagrass winter hardiness. Late-season fertilization is highly recommended for athletic fields and some newly established lawns. The only downside to this practice is that it will increase winter annual weed pressure and may predispose bermudagrass to more injury from spring dead spot (read more about spring dead spot by clicking here) and zoysiagrass to more large patch (read more about large patch by clicking here).

Potassium is thought to also improve winter hardiness of warm-season grasses in some situations. As a result, it is commonly recommended that a “winterizer” fertilizer containing a higher ratio of K be applied in autumn prior to winter dormancy. However, research shows that additional autumn K fertilization will not reduce winter injury if a soil test indicates that your lawn soil has optimum levels of K. Based on data from the University of Arkansas Soil Test Laboratory, approximately 77% of lawn soils in Arkansas have enough potassium to sustain optimum turf growth. Therefore, this additional potassium is usually not needed.

Cool-season turfgrass species such as tall fescue (Festuca arundinacea) 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. Lawns damaged during summer months and newly seeded lawns may need an additional N fertilizer application in October to help with recovery and establishment.

There are many fertilizer choices available to the homeowner. Organic, inorganic, and synthetic organic products are all available. As with all plants, turfgrasses cannot tell the difference between the sources of nutrients. Some products contain high amounts of slow-release N while others contain none. Our recommendation is to use a mixture of quick and slow-release nitrogen sources in most situations. Although there are exceptions to the rule, it is good practice to use products with a greater percentage of slow-release nitrogen sources during warmer months and a greater percentage of quick-release nitrogen sources during cooler times of the year.

More questions
What nutrients does my lawn need?
How do I apply the fertilizer?
How do I calculate how much I need?
How do I calibrate my spreader?
These questions and more can be found in the revised publication “Fertilizing your lawn” FSA 2114.

Aaron Patton, Arkansas Turfgrass Extension Specialist


3. Fall armyworm – Reports of activity in Oklahoma

There are reports of fall armyworm buildups in northeastern Oklahoma in some residential lawns.  In addition, fall armyworm infestations were numerous in sorghum fields in Oklahoma during the latter part of August.  All signs point to the strong possibility that we will see another generation in early to mid September as heavy rains are in the forecast.  Since survival of fall armyworm eggs is highest following rainfall or supplemental irrigation, some serious problems could develop for sod farms, golf courses, and residential lawns.

Fall armyworms are caterpillars that cause direct damage to green turf.  Female fall armyworm moths lay up to 1,000 eggs over several nights on grasses or other plants.  Within a few days, the eggs hatch and the caterpillars begin feeding in groups.  Caterpillars molt six times before maturing, increasing in size after each molt. They can complete a generation in 18-28 days depending on temperature.  Newly hatched fall armyworms are white, yellow, or light green and darken as they mature.  Mature fall armyworms measure 1½ inches long with a body color that ranges from green to brown or black.  They can be distinguished by the presence of a prominent inverted white "y" on their head.  Small larvae do not eat through the leaf tissue, but instead scrape off all of the green tissue and leave a clear membrane that gives the leaf a "window pane" appearance.  Large larvae can quickly denude a turf canopy.

Preventive insecticide treatments are not warranted because outbreaks are sporadic and mortality due to natural enemies is usually high.  Insecticide applications can eliminate these natural enemies from the landscape, causing a worse armyworm problem following treatment.  The key to controlling fall armyworm is early detection because Infestations of fully mature larvae feed voraciously and can completely consume a lawn overnight.  We will not be out of the woods for a fall armyworm outbreak until we get a good killing frost, so don’t let your guard down.

To scout for fall armyworm, examine turf from eight locations measuring 1 square foot each.  Examine turf along the field margin as well as in the interior.  Look for “window paned” leaves and count all sizes of larvae.  Total the number of larvae in each size class and divide each number by 8 to calculate the average number per square foot. Thresholds are not well developed for fall armyworm in turfgrass, but we suggest treatment when average counts reach two or three ½-inch larvae per square foot.

It is crucial that you target smaller caterpillars (1/2 inch or less) for control for two reasons.  First, the caterpillars don’t cause really severe damage until they reach a size of one inch long, and secondly, smaller caterpillars are much more susceptible to insecticide control than larger caterpillars.  Any product labeled for caterpillar control in turf should be effective for fall armyworm control.  Be sure to apply insecticides only when periods of dry weather are expected since insecticide can wash off target with moderate to heavy rain.  This is especially important in the next couple of weeks as the aftermath of recent hurricane activity moves into Oklahoma.  Light irrigation following application of granular formulations may be prescribed on the label, but don’t overdo it.  Be sure to follow all label directions carefully to enhance safety and minimize harmful environmental effects.

Authored by Dr. Eric Rebek, OSU Extension Entomologist:

More information on armyworm control can be found in MP 144 – Insecticide Recommendations for Arkansas


4. New extension publication – Establishing a lawn from sod

Step-by-step instructions for sodding a lawn: Site preparation, selecting a turfgrass species and cultivar, planting instructions, and post planting care. Click here to read the new publication.


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