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Hot , Dry Weather Brings out Southern Chinch Bug

August 12, 2010
by Rick Brandenburg

Chinch bugs, the most injurious pest of St. Augustinegrass, are very active at this time. The southern chinch bug is a pest that loves hot, dry conditions. It thrives this time of year and is starting to cause damage to St. Augustinegrass. Damage usually starts out as small irregularly shaped discolored areas (yellow or tan) that eventually die. Problems often start in areas that receive the most sun and are very dry. Populations are high so unless we see a lot of rain this summer, chinch bugs are going to remain a problem in St. Augustinegrass.

This pest accounts for millions of dollars in damage to turf and control costs each year. The adults and nymphs have piercing-sucking mouth parts, and as they suck plant juices from stems, crowns, and stolons they also inject a toxin that causes the grass to yellow and die. Damage occurs any time from May to November, but is most evident during dry conditions, when populations as low as 25 - 30 insects per 0.1 m2 can cause severe damage. Southern chinch bugs prefer open sunny areas of St. Augustinegrass, especially lawns with abundant thatch. The insect aggregates in scattered patches. Small spots of damaged grass initially become noticeable. However, as the infestation progresses, the damaged areas, if left uncontrolled, coalesce into larger areas of dead turf. Damage shows up first in sunny, drought -stressed, or heat-stressed areas of the lawn.

In southern Florida, a southern chinch bug has 7 - 10 generations per year. Reproduction is continuous throughout the winter. In northern Florida and Louisiana there are 3 - 4 generations per year and probably 2 or 3 in North Carolina. Adults comprise most of the overwintering population. The first large surge of nymphs occur during February in southern Florida, late March to early April in northern Florida, and early May in North Carolina. The greatest damage occurs during hot, dry periods in mid to late summer. The onset of cool weather causes a sharp decline in the population, and damage to turf is reduced. Adults are about 1/6 inch (3.1 - 3.6 mm) long and 0.04 inch (1 mm) wide. The body is oblong and oval shaped, and grayish-black. The wings are shiny white and folded flat over the back so the tips overlap. There's a distinctive triangular-shaped black marking in the middle of the outer edge of each wing. The wings may be long, extending to the tip of the abdomen, or short extending about halfway to the tip. Nymphs are bright reddish-orange with a white band across the abdomen. As the nymphs mature, their coloration gradually darkens and they gain small wing pads. Fifth instar nymphs are gray-black and almost as large as adults with wing pads that extend at least to the second abdominal segment.

Southern chinch bugs are easy to control if detected early. Check for chinch bugs by parting the grass at the interface between healthy and damaged areas and inspect the lower stems and thatch. Another method is flotation. Cut off both ends of a large coffee can or similar container and remove one rim with tin snips to produce a sharp edge. Push the edge down through the thatch in areas to be checked. Flood the can with water to the brim. If chinch bugs are present, they will float to the surface within a few minutes. Infestations of 20 - 25 nymphs per ft2 (4 - 5 per 6 inch diameter can) will cause enough damage to warrant control.

Discourage infestation. Watering lawns during dry periods in summer enable better tolerance of chinch bug injury. Moisture also encourages the growth of Beauveria fungus that greatly reduces chinch bug populations. A well-balanced fertilization program enables lawns to tolerate chinch bug injury. Excessive fertilization seems to encourage buildup of chinch bug populations.

Once chinch bug infestations reach damaging levels, insecticides are the only reliable means of control. Various pyrethroids are registered for use against chinch bugs. Use ample spray volume to wet the surface of the thatch. Be sure to read and follow label instructions regarding application rates and watering in. Natural predators like the earwig and big eye bugs can provide some control of chinch bugs. Resistant cultivars of St. Augustinegrass (Floratam, Floralawn, FX33 and FX10) have been developed as management tools to control chinch bugs.

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