Recently I have visited with several homeowners related to st. Agustinegrass lawns having problems.
Expanding, irregular patches of dead or stunted grass surrounded by a halo of yellowing, dying grass can have several causes including drought, fungal infections or chinch bugs. The “islands” of dying grass cause by chinch bugs tend to increase in size and merge as insect numbers increase.
Damage can develop rapidly, especially in sunny locations during hot, dry weather. Chinch bug damage can be confused with certain lawn diseases or other physiological disorders. For example, brown patch is a common disease affecting the leaf blades of St. Augustinegrass. Brown patch symptoms, however, usually occur in a circular or semi-circular pattern, as opposed to the irregular-shaped areas of dead and dying grass that result from chinch bug feeding. Chinch numbers of the insects themselves is the best proof of chinch bug damage. Too little or too much water also can cause chinch bug problems. Chinch bugs prefer hot, dry environments. Dry weather enhances survival of chinch bug nymphs and eggs by reducing the incidence of disease within chinch bug populations.
Also, drought-stressed lawns are more susceptible to chinch bug injury. On the other hand, over-watering causes saturated, oxygen-deprived soils that cannot sustain the microbes needed to decompose thatch. St. Augustinegrass lawns should be watched closely during the summer for signs of drought stress. The lawn should be watered immediately when edges of grass blades begin to curl, grass fails to spring back quickly when walked on, or the turf begins to have a dull bluish-gray color.
Due to the various soil types and depths in Texas, the amount of water needed will vary. First determine whether a problem truly exists when considering pesticides for chinch bug control. An easy method to detect chinch bugs is using a soap-water mix (a mixture of dishwashing detergent (one spoon) in water (one gallon) drenched in the affected area of the lawn. Chinch bugs do not like the detergent in the mix and will literally “crawl” away from the drenched area. Be ready to observant and look carefully for them immediately after drenching the area. If your neighborhood is prone to chinch bug problems, inspect your lawn weekly during the spring, summer and fall. Look for off-color areas, especially in direct sun, and along sidewalks and driveways. When there are numerous chinch bugs, they will cause grass to yellow. You can often find them by parting the grass at the edge of affected areas and by examining the soil and base of the turf. You should check areas with suspected infestations several times. When chinch bugs are numerous, you might see them on leaves or scurrying about on adjacent sidewalks during the day.
Insecticides can prevent further injury when chinch bugs are abundant enough to cause visible damage. A variety of liquid and granular insecticides is available for chinch bug control. Granular insecticides can be applied with a standard fertilizer spreader and irrigated lightly (1⁄8- to 1⁄4-inch of water) to activate the insecticide. Drop-type spreaders are good for keeping insecticide granules from scattering into gutters, sidewalks and driveways. There they can be washed into storm drains and streams which is why you should sweep up and properly reapply any granules landing in such sites. Liquid sprays are usually applied using a hose-end sprayer that can apply 15 to 20 gallons of water per 1,000 square feet. To ensure even coverage, spray back and forth across the same area.
Watering the lawn before application can help the pesticide penetrate the turf, but irrigation is not recommended following application of liquid insecticides. Use spot treatments where chinch bugs are restricted to isolated areas of the lawn. Treat the off-color turf and all surrounding infested areas. Inspect the site every 3 to 5 days for at least 2 weeks to determine if the infestation is under control. Spot treatments help prevent environmental contamination. They also minimize the impact of pesticides on beneficial insects. For more information in this or any other agricultural topic please contact the Hopkins County Extension Office at 903-885-3443 or email me at [email protected].