Weed Control in St. Augustine Grass

1. Q. I agree that grass and lawns contribute much to our environment. Even though grass maintenance requires some natural resource input, the returns are worth the expenditures. How can I remove weeds and weedy grass from my turf areas and purify the St. Augustine I am growing?

A. Except for bermuda and zoysia lawns, postemergence weed control should have been attempted in early spring. High temperatures can cause excessive damage on other grasses even if they are listed on the herbicide label as tolerant.

General home lawn broadleaf weed control can often be accomplished using selective postemergence formulations which contain two or more herbicides. Formulations are available for most southern grasses. Examples are Green Light Wipe-out, K-Mart Broadleaf Weed Killer for Southern Grasses, Spectrum 33 Plus, Trimec, Ferti-lome Weed Out and Ortho Weed-B-Gon II for Southern Grasses.

Most labels will stress use on younger weeds growing in the cooler mid-spring to early summer period. A temporary discoloration of the lawn usually occurs. Repeat application in 2-3 weeks.

Warning: These products contain phenoxy (2,4-D) herbicides. Avoid drift, keep away from gardens and clean sprayers thoroughly with ammonia.

For bermuda or zoysia lawns, weed killer with MSMA or DSMA often provide a wide spectrum of selective control for mostly grassy and some broadleaf weeds in June through August.

A pre-emergence herbicide can be applied to thin lawns to protect them from weeds until they thicken and cover. Mow St. Augustine grass at your lawnmower's highest blade setting to select against bermuda. Mow bermuda lawns lower to select against St. Augustine.

2. Q: I have a resident that has the worst problem with spaghnum moss invading his St. Augustine turf that I have ever seen. The lawn is in full sun but obviously poorly drained. Is there another way to handle it besides a drainage system?

A: Simply apply ferrous sulfate (Copperas) to the area. I have put it down with a fertilizer spreader in an attempt to green up yellowing St. Augustine -- just don't stop to scratch your nose or that fine Copperas will form a pile beneath your spreader. If he wants a rate, Dr. Duble recommends 8 oz. per 1000 square feet and also indicates that adding one-fourth pound of urea per 1000 square feet helps. The iron will remedy the chlorsis problem and the urea will green the grass -- what a simple remedy. We should package a product such as this and name it Moss-Away!!


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