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Get weeds under control in the flower bed

Q. I find a lot of information on controlling weeds in a lawn, but what about controlling weeds in a flower bed? Can you safely put downpre-emergent weed killers in February and March to control weeds in a perennial bed?

I have a bed that has black eyed susans, daylilies, iris, coneflowers and salvia. It is now over-run with crabgrass, and I'm wondering if I can get a head start next year by putting down pre-emergent weed killers like we do for the lawn.

Also, will post-emergent weed killers work in a flower garden as well? Thanks in advance for some advice on this challenging problem. - Patrice

A. What you need is a pre-emergence herbicide for flower beds. A pre-emergence herbicide prevents weeds from emerging from seed. The most commonly available product, Preen Garden Weed Preventer, prevents summer and winter annual weeds from growing in flower and vegetable beds and around trees and shrubs for up to three months. Without weeds competing for sunlight, nutrients and space, your plants will grow larger and stronger.

Preen Garden Weed Preventer prevents new weeds from growing; it does not kill existing weeds. It works by creating a chemical barrier in the top 1-2 inches of the soil that prevents cell division in developing weed seeds.

Remember, any plants you might have that are self-seeders, or plants that come back every year from seed, will be prevented as well. Apply Preen after planting summer annuals and perennials. It will not prevent perennials that regenerate from underground structures, such as bulbs.

You can find a copy of the chemical's label at this Web site: www.lebsea.com/newlebsea/pdfs/L-PRN63670.PDF.

Q. Is it safe to use Roundup on perennial weeds in my hybrid bermuda lawn while the bermuda is dormant? I was told I could do this, but it makes me nervous. I have what appears to be mondo grass that is invading very aggressively on my grass and have found no answers as yet. Any information you could provide would be welcome. - Jim

A. No, no, no! It isn't safe to spray Roundup over "dormant" bermudagrass. Roundup sprayed over "dormant" bermudagrass will severely damage, if not kill, your turf. Due to our relatively mild winters, warm season grasses such as bermudagrass never really go dormant. The leaves may look dead, but the stolons and rhizomes (the above-ground and below-ground stems) often stay active and green. I have even seen tiny green leaves emerge near the soil in January. You were absolutely correct to be suspicious of this advice.

Q. I need to know if my 9-year-old Arbor Vitae have a disease or some other problem. They develop a brown area that enlarges every year. I cannot find any insects. Please offer any suggestions. - K.T. in Gwinnett

A. Do you have an irrigation system that sprays the plants or that causes the foliage to remain damp? This is a common problem with conifers in the landscape. According to the digital picture you sent me, the problem definitely seems to be related to some environmental factor on the side facing away from the house. There are fungi that can cause similar damage in wet foliage situations. If you want to send in a sample, I will look at it under a microscope for you.

To send a sample, cut a branch with live and dead leaves on it and mail it to: Stephen D. Pettis, Agricultural and Natural Resources Agent, Gwinnett County Cooperative Extension Service, 750 South Perry St., Suite 400, Lawrenceville, Ga. 30045.

Wrap the sample in newspaper and put in an envelope.

Stephen D. Pettis is an agriculture and natural resources agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010 or Steve.Pettis@gwinnettcounty.com.