As nitrogen fertilization increases, chinch bug damage increases.
Chinch bugs are the most common and most damaging insect pest of St. Augustinegrass in Florida. But you can make your lawn less attractive to this pest by fertilizing correctly.
Adult chinch bugs are about 1/5 inch long, black with white wings folded flat on their backs. Immature (nymph) chinch bugs range in size from 1/20 inch at hatching to nearly adult size. The small nymphs are reddish in color with a white band across the back but become black in color as they approach adult size. They’re active spring through fall and prefer open sunny areas in which to feed. If you have St. Augustinegrass, you should learn to identify this pest. They can kill large areas within a lawn before you know they’re present.
Inspect your lawn weekly during spring through early fall. The way that I check for chinch bug activity is to get on my hands and knees in an open sunny area where the grass has suddenly turned yellow. I part the grass in a transition area between the yellow grass and the green grass. As I do this, I watch for chinch bugs quickly moving along the grass blades, thatch and soil surface. Remember that they are tiny, about the size of a pinhead when young.
Research has shown a direct relationship with the rate and source of nitrogen fertilizer and the susceptibility of St. Augustinegrass to chinch bugs. Lawns receiving fertilizers containing slow-release nitrogen have fewer chinch bugs and less damage than lawns fertilized with highly soluble (fast-release) nitrogen fertilizers.
Maintaining an unnatural dark blue green color with high levels of nitrogen throughout summer greatly increases susceptibility of St. Augustinegrass to chinch bugs. The excessive tender top growth produced by too much nitrogen fertilizer is appealing to the hungry chinch bugs.
There’s a better way to keep the green color of the grass without promoting excessive top growth. Applications of iron sulfate at the rate of two ounces per three to five gallons of water per 1000 square feet will provide this greening effect. The effect from supplemental iron applications only lasts about two to four weeks. So, repeat applications may be necessary for summer-long color. Iron sulfate solutions can stain walks, driveways and exterior walls.
These recommendations will not eliminate chinch bug damage but they offer a management tool that can help reduce the severity of attack.
More information is available online at http://edis.ifas.ufl.edu/lh010 and at http://edis.ifas.ufl.edu/topic_southern_chinch_bug or from the UF/IFAS Extension Office in your county.
Larry Williams, UF/IFAS Extension Agent, Okaloosa County, June 20, 2014