A Bit Too Green

Tuesday April 29, 2008


Mr Pest Control


What is the best product to control weeds in flower and shrub beds in east central Florida?

Mr Pest Control


Without having a specific kind of weed in mind your question becomes a bit hard to answer without some discussion. In Florida you are blessed with so many different kinds of weeds, including a wide variety of sedges and a year-round growing season, that we may only talk in general terms. Identification of the species of weeds, or at least their family grouping, is important. Once you know what you are dealing with you can better understand their growth characteristics. For example, are these weeds perennials or annuals? Does their growth initiate from underground parts such as rhizomes or roots, or do they start their new growth only from seeds? Are they grasses or broadleaves, or those nasty sedges that look like grasses but biologically are not? Are you going to have to treat over the top of existing desirable plants, or is there bare soil around the bases of the flowers and shrubs you need to protect?

For weeds that grow only from seeds you can apply a pre-emergent such as Surflan or Ronstar, applying the herbicide over the top of the desirable plants and then watering to ensure it is washed down to the soil. In particular you need to wash Ronstar off the desirable foliage or it could cause spotting on the leaves. However, neither of these herbicides causes any post-emergent effect, so they are designed to kill only the sprouting seeds in the soil. There are both granular and spray-on pre-emergent products, and which formulation you choose may depend on the amount of area you need to treat. A very small area may be most convenient with a shaker container of granules, such as Balan or Ronstar G, but for larger areas coverage is easier and more uniform using a sprayed formulation.

If you are facing perennials the use of a strict PRE-emergent is unlikely to take them out, as the developed root system is unaffected by a preemergent herbicide that only affects seeds. So, you need to go to a post-emergent herbicide that can kill the existing weeds. If this is in a flower bed where the soil is pretty well covered by desirable plants, with weeds coming up through them, a non-selective product like Roundup could not be used without killing the desirable plants too. However, if you can carefully treat around the bases of the plants, and for shrubs this may be possible, you could treat the weeds selectively without also spraying the foliage of the plants you want to remain. Combine the spray of Roundup with one of the pre-emergent herbicides mentioned above, and you can kill the weed and prevent new weeds from re-growing from seeds.

There are a few selective herbicides that can be used "over-the-top" of broadleaf plants to kill grass weeds, and two of them are Fusilade and Ornamec. They selectively affect only grasses, including any turf that your overspray may contact, but they can be applied right over plantings of broadleaf plants to kill grass weeds growing up through them. This is a great advantage when you have a weed like bermuda grass infesting an area and growing up through desirable shrubs. The systemic action of these herbicides takes out the entire weed, roots included. Be certain to read the Label of either product first, because it will identify certain kinds of broadleaf flowers or shrubs that could be sensitive to the herbicide.

If you have broadleaf weeds emerging through broadleaf landscape plants you have a bigger problem. Herbicides do not recognize what a "weed" is, but only certain major categories - i.e. broadleaf or grass. There are several herbicides that selectively kill only broadleaf weeds, and we use these commonly on turf, since turf is a grass. These are products like 2,4-D and triclopyr, but if they contact broadleaf flowers or shrubs these plants would be killed too. Thus, your options are limited, and now you may want to hand-pull the weed and apply a pre-emergent such as the Surflan, and over time and with repeated applications the seeds in the soil will eventually be gone. If the weeds are extending well above the desirable plants you could apply a product like Roundup with a "wick" applicator, which wipes the herbicide onto the foliage of the weed without contacting the other plants.

For flower beds a good preparation of the soil will be really helpful too, treating the area prior to planting the flowers in order to kill any weeds there first. While it is still unplanted a product like Roundup would be ideal, killing any and all weeds and leaving only seeds in the soil, which then could be controlled with the pre-emergent product. Roundup should always be applied when wind is minimal or none, so that drift of droplets does not occur to damage nearby desirable plants.

Mr. Pest Control

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Please note, Mr. Pest Control is answering questions supplied by PMP customers across North America. His answers are generated from industry and manufacturer-provided information. The answer may not be specific to the laws and regulations for your State, Province, Territory or Country. In addition, products mentioned may not be registered and or available in all areas. Always check with your local Univar office for specific information to your area. Always read and follow label directions.