Garden Talk

with Rebecca Jordi

Q: You often talk about not overusing Nitrogen fertilizers but isn’t it needed to keep the grass growing?

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fertilizer1A:  I am going to take a recent study and use parts of it to answer your question.  Nitrogen is important for growth but we generally are using too much.  A little fertilizer can perk up a St. Augustinegrass lawn as spring arrives, but homeowners who overdo it may find they’re growing more than grass. A University of Florida study suggests repeatedly using large amounts of nitrogen fertilizer can ignite a population explosion of Southern chinch bugs – the No. 1 insect pest of St. Augustinegrass, the state’s most popular turfgrass.  “Everything in moderation,” said Eileen Buss, an associate professor of entomology with UF’s Institute of Food and Agricultural Sciences. “When we try to overly manage a natural system we get the balance out of whack.” UF turfgrass experts advise homeowners to use no more than 1 pound of slow-release nitrogen fertilizer per 1,000 square feet of lawn, a recommendation found in the document “St. Augustinegrass for Florida Lawns,” available at http://edis.ifas.ufl.edu/LH010. In the study, Southern chinch bugs produced the most eggs on St. Augustinegrass fed the equivalent of 2 pounds nitrogen per 1,000 square feet per month. That rate is a worst-case scenario, Buss said, but not unrealistic because people sometimes deliberately overfertilize in their zest to have the greenest lawn in the neighborhood. Resistant chinch bugs may be able to survive exposure to bifenthrin, a pyrethroid which is the top choice for Southern chinch bug control in Florida. However, pyrethroids should still perform well against nonresistant populations of Southern chinch bugs. Future research may examine the role of the nutrients phosphorus and potassium in chinch bug population growth, and the possibility of overfertilization may reduce turfgrass resistance to chinch bugs. Use 15-0-15 starting in April and use is in small increments until September so the plant can absorb it and grow slowly.

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