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Committing Premeditated Herbicide   Linda Rae Nelson

About every year during our winter months, we seem to be faced with the same problems; turf weeds. Some are round, some have flowers, and all are a nuisance. We kill them off and sure enough like clockwork; they show up in the same places we had them last year. It is not uncommon for a homeowner to return to his winter home here in Southwest Florida and see a fresh crop of weeds in the same place he had them the year before. Turf weeds can be divided into three major categories, broadleaf weeds, woody stem weeds and grassy weeds.

Nearly half of the turf weeds we see in our St. Augustine turf are the broadleaf. The most common are Dollar Weed, Chickweed and Dayflower. All will grow in almost any condition but they prefer wet and shady areas. You will most likely find them growing in northern exposures or in between houses and areas of poor drainage. While some broadleaf weeds like Chickweed are easy to control, I Jokingly say that a harsh word will kill most Chickweeds, others are a little more difficult to eradicate. In their best efforts to keep our environment safe, the EPA has eliminated many of the selective herbicides used in controlling these weeds. The products that are still available tend to be less effective than what was used in the “good old days” and therefore, it usually takes several applications of herbicide throughout the winter season. Most herbicide applications can only be done in cooler temperatures when the St. Augustine grass is dormant. The reasoning behind this is that St. Augustine grass tends to absorb less nutrients in cooler temperatures (generally below 80 degrees) and will be less likely to absorb any applied herbicides, while turf weeds like Dollar Weed tends to grow more aggressively, thus absorbing more of the herbicide. Herbicide applications are only one way to rid our lawns of unsightly weeds.

Other method that is effective in helping to solve this dilemma is reducing the amount of irrigation water used. This is most effective in shady areas or areas of poor drainage and will also force the turf to sink their roots deeper into the soil. Reducing the amount of water will also create a healthier turf that will have more access to nutrients that are beyond the reach of shallow roots. A deeper root system will also help the turf to resist fungus and disease and become more drought tolerant while reducing your water bill. We encourage most communities that we work with to accept a watering schedule of two days per week for turf areas during the winter months. Broadleaf weeds will still be able to grow in these conditions but will be much less aggressive. Another way to reduce the amount of Dollar Weed is to increase the amount of direct sunlight, this can be done with proper and regular tree trimming in some areas and reducing large hedges and plantings that cast shadows causing shaded areas.

Woody Stem Weeds are less common in St. Augustine grass. Usually they will be found where the grass is already thin. The most common Woody Stem Weeds are Spurge and Mimosa. Unlike most broadleaf weeds, woody stem weeds are best kept from our lawns by keeping the lawns lush and thick. This is clearly a case where “The best defense is a strong offense”, as a thick lawn will choke out most of the Woody Stem Weeds.

They can also be controlled by using high nitrogen fertilizers that are best applied in the winter months so as not to burn the grass. An application of high nitrogen fertilizer such as 33-0-0 will burn out the weeds while giving the turf an extra boost of energy. This is especially effective in the cooler months when the St. Augustine grass tends to spread its runners horizontally and not have as much vertical growth. It is very important when using this method, to follow the correct application rates to obtain the desired results.

There are many grassy weeds that affect our turf; however, the most noticeable and regrettably the least curable is Carpet Grass. Seeds from Carpet Grass are often picked up by the wind from fields or areas of construction and dropped into our pristine landscapes. To the untrained eye it often goes unnoticed during the summer month; however, in the cooler weather, it will turn brown and the Carpet Grass becomes very unsightly. At this time there is no selective herbicide that will effectively kill Carpet Grass without doing severe damage to St. Augustine. It has been my experience that the only real cure for Carpet Grass is Roundup and a sod cutter. Other Common Grassy weeds include Sedge, Goose Grass and Crab Grass. Although selective herbicides are available for these grassy weeds, if it is possible, the first course of action should always be to reduce the amount of water. The less herbicide, the better, both for the environment and less risk of damaging your lawn. With that in mind, there are times when herbicides are the only way to see our way clear of a weedy situation. Goose Grass and Crab Grass and a host of others not mentioned here, can be eliminated with several applications of herbicides. Be sure to contact a lawn maintenance professional to help select the proper herbicide for your landscape needs.

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