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Wait for the right time to fertilize or use weed-and-feed on La. lawns

News Release Distributed 02/28/11

With the recent warm weather, homeowners are anxious to fertilize their St. Augustine grass and centipede grass as well as get weed-and-feed out on their weeds.

It’s not time, however, to put either conventional lawn fertilizer or weed-and-feed out on St. Augustine grass or centipede grass right now, says LSU AgCenter horticulturist Ron Strahan.

“Fertilizing this early with high-nitrogen lawn fertilizer or weed-and-feed can contribute to winter kill with a late-season freeze and bring on brown patch disease,” Strahan says. “The best time to apply weed-and-feed in St. Augustine grass and centipede grass is to make them your first application of fertilizer.”

Timing the first fertilizer or weed-and-feed application depends on where you are located in the state. Strahan gives the following times for first fertilizer and weed-and-feed applications on St. Augustine and centipede lawns:

– New Orleans, late March.

– Baton Rouge/Lake Charles/Lafayette, late March or early April.

– Alexandria, early April.

– Monroe/Shreveport, mid-April.

Weed-and-feeds are not always the most effective weed killers, but they are definitely convenient to apply because you can use a fertilizer spreader and cover large lawns quickly, Strahan says.

“Overall, granular weed-and-feed performance has not been as good in my field trials as spraying liquid atrazine – best on winter weeds – or products such as Weed Free Zone, Weed B Gon and Trimec, which are all 2,4-D/dicamba-based products,” Strahan says.

But if homeowners are going to use weed-and-feed products, they might as well apply them properly and time them correctly, he adds.

“No doubt, homeowners like to use weed-and-feed products like Scotts Bonus S, which has atrazine, or some type of granular “trimec” herbicide, such as 2,4-D, dicamba or mecoprop, for their winter-weed problems,” Strahan says.

Most weed-and-feed herbicides have the herbicides impregnated on a very high-nitrogen fertilizer granule, but timing is important.

If it is an atrazine-based weed-and-feed like Scotts Bonus S (the package usually will say for St. Augustine grass and centipede grass), the product must be watered in after application. Atrazine works mainly through root uptake so watering after spreading gets the herbicide into the root zone.

If the weed-and-feed product contains Trimec, it should be applied when there is a heavy dew or after the lawn has been watered, Strahan says. “The granules need to stick to the weeds for the herbicide to work with ‘Trimec’-type weed-and-feeds.”

Finally, Strahan says, both weed-and-feed types must be used away from the drip lines and root zones of trees and shrubs.

Rick Bogren
Last Updated: 3/31/2011 1:18:04 PM

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