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Ask Dr. Hort: Three herbicides will get rid of torpedo grass

Swamp lily, Crinum americanum

JIM DAMASKE | Times (2003)

Swamp lily, Crinum americanum

Three herbicides will work on torpedo grass

Q: You may remember me from my years as a gardening correspondent for the St. Petersburg Times. Well, for the first time in my many years of gardening, I'm faced with a butterfly garden inundated with torpedo grass. I never even heard of it until I moved to my new home. Any suggestions? Bette Smith, Seminole

A: It's great to hear from you, Bette, and I'm sure readers will agree. You've got one nasty weed to control.

There are three herbicides that I am aware of that do a pretty good job of controlling torpedo grass — Arsenal, Fusilade II and Drive. Fusilade II, I think, is the best in terms of its selectivity in what it attacks. It can be used over the top of many ornamentals, but I would still be careful in and around your various butterfly plants. You will most likely need three applications, spaced three weeks apart. Do it while it is actively growing, because it needs to migrate into roots, shoots, rhizomes and stolons, thus killing the entire plant.

Found seed grows into delightful swamp lily

Q: My husband grew the attached plant from a seed he found. It is a great plant and quick to grow, even after a cold season. Can you identify it for us? Maxine Belcher, Tampa

A: You have Crinum americanum, string lily or swamp lily. It grows as a native in swampy areas. As you described in your letter, your placement by the lake was perfect. Its flowers are very fragrant and it can be grown on upland sites as well.

Thrips responsible for ficus trees' leaf loss

Q: I have two large outdoor ficus trees that suddenly shed all their leaves. This is the first time that has ever happened. I also noticed other bare ficus trees in the area. What is causing this? Molly Sanger

A: There seems to be a nudity problem with ficus trees. In my Nov. 20 column, I answered a reader with the same problem. Numerous possibilities existed for that reader's ficus leaf drop, including thrips, but at this point the culprit can be none other than fig whitefly, a new pest to the bay area.

Rake up leaves and remove. Apply a soil drench systemic insecticide such as Orthene (acephate), Safari (dinotefuran) or imidacloprid, sold under the names Bayer Advanced Tree & Shrub Insect Control, Merit and others. You need to apply according to the label under the entire drip line of the tree. You could also call a certified arborist and have the trees injected with an insecticide or call a pest control company that specializes in trees.

Florida grasses could benefit from thatching

Q: We are from Long Island, N.Y., where every couple of years we thatched our lawn by renting a machine from Home Depot. We never see people down here doing that. When should it be done in Florida? Mary Telford

A: Bermuda, Zoysia and St. Augustine are warm-weather grasses that could use some thatching, every two to three years, to allow water to penetrate faster and deeper and reduce disease. It also reduces the height from the lawn to the curb, or other areas where you edge.

The machine used for this task is a verticutter, available through rental outlets. The best time is when the grass is at its peak of growth, the summer rainy season. There's a shorter recovery time and damage is minimized.

Thatch is an accumulation of dead blades of grass between the green stuff and the soil surface that gives you that spongy feeling when walked upon, especially St. Augustine. The faster you grow your grass — generally a result of too much irrigation and fertilizer — the faster and thicker the thatch gets, which creates an ideal environment for diseases and the scourge of St. Augustine grass: the chinch bug.

I wouldn't suggest tackling the job yourself. For example, a 5,000-square-foot lawn, thatched up 2 to 3 inches, will likely reward you with three pickup truckloads of grass debris. If you'd like to learn more, go to and search "verticutting St. Augustine grass" (but don't use quote marks).

Need help? Dr. Hort (Greg Charles) answers questions about garden problems. E-mail him at [email protected] or mail questions to HomeLink, Features Department, St. Petersburg Times, P.O. Box 1121, St. Petersburg, FL 33731. Describe problem in full, and include your name, city of residence and contact information. If possible, include a good-quality photo. Fuzzy ones won't do. Photos cannot be returned.

Ask Dr. Hort: Three herbicides will get rid of torpedo grass 12/03/10 [Last modified: Tuesday, December 7, 2010 1:17pm]
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