The Chinch Bug Fertilization Relationship
by Dr. Robert Black, Consumer Horticultural Specialist

The chinch bug is the most damaging insect on St. Augustinegrass lawns and sooner or later most home gardeners have to spray to control this pest. Many people have changed lawngrasses as a solution to the chinch bug problem since the insect only seriously attacks St. Augustine. There is, however, a way to reduce turf injury, and this is by proper summer fertilization.

Research has shown that the rate and source of nitrogen fertilizer has a tremendous effect on the susceptibility of St. Augustinegrass to chinch bug injury. As nitrogen fertilization increases, chinch bug damage increases. There is also difference in damage between nitrogen sources. Lawns receiving fertilizers containing slow-release nitrogen have fewer chinch bugs and less damage than lawns fertilized with highly soluble (fast-release) nitrogen fertilizers. Don't be misled by the term "organic" on a bag of fertilizer. Although nitrogen in slow release fertilizers can be in an organic form such as sewage sludge, there are organic forms of nitrogen such as urea which are very soluble and release nitrogen rapidly.

It is important to remember that the natural color of St. Augustinegrass is light green and not blue green. Maintaining this unnatural blue green color with high levels of nitrogen throughout the summer will greatly increase the susceptibility of St. Augustinegrass to chinch bug injury.

There is another way to maintain the green color of the grass without promoting excessive top growth and increasing susceptibility to chinch bugs. Applications of iron sulfate at the rate of 2 ounces per 3-5 gallons of water per 1000 square feet will provide this greening effect. The effect from supplemental iron application is only temporary (approximately 2-4 weeks), therefore, repeat applications are necessary for summer-long color. Also, because iron will stain, care must be taken not to get iron sulfate solution on concrete walks and driveways.

These recommendations will not eliminate chinch bug damage, but they offer a management tool which can help in reducing the severity of attack caused by the number one pest on St. Augustinegrass.