Weed & Feed Damage on Centipede Turf – Spring 2015

It has recently been brought to my attention that there are some folks who are not satisfied with the results of applying certain weed and feed products to their centipede lawns. The specific product that seems to be causing the most issues is Scotts Turf Builder Bonus S Southern Weed & Feed, which is a new / reformulated product for spring 2015. It was the only weed and feed product available for sale at several of the largest chain stores in the area. This product is labeled for the most common southern turf grasses: St. Augustine, Bermuda, zoysia, and centipede. The complaint we have heard is that centipede lawns that had this stuff applied to them several weeks ago now appear to be dying, some in spots, others altogether. Since this is not a product that we carry, I had to familiarize myself with it. After doing so, it is fairly easy to understand why centipede turf has potential to react badly to it.

For those of you who simply want to fix it, we'll discuss that first and follow with an explanation of why there is a problem and how to prevent it in the future.

Unfortunately, there is no quick fix. Per the instructions on the bag, areas treated with Bonus S Southern Weed & Feed should not be reseeded for two months after application. On the plus side, by the time two months goes by, you may start to see some recovery of turf that was not killed outright. So what to do in the meantime? Basically, nothing. The only thing that may help decrease the damage is an application of a fungicide to prevent fungus from taking advantage of the weakened turf and excess nitrogen in the soil. You may also rake lightly to remove some of the dead grass and improve air flow. Other than that, leave it alone. Unless it stops raining and doesn't do so for 10-14 days, do not water, and by all means, DO NOT FERTILIZE! Think of it like this: if a person is having a severe allergic reaction to something and struggling to breathe, you're not going to shove food and water down their throat, right? I'd hope not! The grass needs to recover from what is ailing it before being pushed to grow. After two months has passed, reassess the situation and reseed if needed. Only after giving the new seed time to sprout and grow a bit should you think about fertilizing.

Now for the explanation. First of all, there is no excuse for not knowing the area in square feet of your yard. It doesn't really matter what fertilizer or weed and feed you're using, if you apply enough product for 15,000 sq ft but you really only have 5,000 sq ft, there WILL BE a problem. This is preventable on your part and it is not the fault of the product you're using. That being said, even using Bonus S Southern per the instructions on the bag can cause a problem on centipede and here's why:

The analysis of a fertilizer generally consists of three numbers, for example: 16-4-8, 13-13-13, 46-0-0, etc. The numbers are percentages indicating the amount of nitrogen (N), phosphorus (P), and potassium (K). So a 16-4-8 fertilizer is 16% N – 4% P – 8% K. This means that in 100 pounds of 16-4-8 fertilizer, there are 16 pounds of nitrogen, 4 pounds of phosphorus, and 8 pounds of potassium. St. Augustine and Bermuda grass both like a fairly high amount of nitrogen throughout the growing season, about 1 pound of nitrogen per 1000 sq ft, applied as often as every 4-6 weeks. In order to get 1 pound of nitrogen from a 25-0-12 fertilizer, you would have to use 4 pounds of the fertilizer since it is only 25% nitrogen. The Bonus S Southern has an analysis of 32-0-9 and a 15.65 pound bag covers 5,000 sq ft. In that 15.65 pound bag, there are 5 pounds of nitrogen (15.65 lbs x 32%). This equates to 1 pound of nitrogen per 1000 sq ft, which would be perfect, except that centipede has about half the nitrogen requirements of the other southern grasses. Under no circumstances should more than ½ pound of actual nitrogen be applied to centipede at one time. The Scotts product does not differentiate between applications to centipede versus other turf grasses, unless you count the very, very small print at the bottom of the “Scotts Recommended Feeding Routine" section on the bag, under a heading that says “Florida Application", at which point anyone not in Florida would quit reading.

Now that we know a 15.65 pound bag of Bonus S Southern will actually provide twice the recommended amount of fertilizer to 5,000 sq ft of centipede, let's talk about the herbicide, metsulfuron-methyl. The math gets a bit complicated here, but the bottom line is that in addition to over fertilizing, applying the recommended amount of Bonus S Southern to centipede will also put the maximum recommended amount of metsulfuron-methyl on it. This isn't necessarily a problem in itself, but according to the label of other herbicides containing the same chemical, some chlorosis (yellowing) or stunting may occur after application to centipede. It stands to reason that if any damage will occur, it will most likely occur at the highest rate. The lowest recommended rate for metsulfuron-methyl on centipede is half of the highest rate. What makes all of this so incredibly absurd is that if Scotts had just specified a use rate for centipede that was half of the rate for St. Aug and Bermuda, there might not be so many yards burned up as a result of using their product, provided the product was applied at an appropriate time.

That brings us to why I tend to not be a fan of weed and feed products in general. Weed and feed is marketed as the solution to all of your lawn problems in one bag. The issue is that when people are most likely to want to kill weeds, it usually is not time to fertilize. Grass needs to be very actively growing to effectively utilize fertilizer. Any fertilizer applied prior to spring green-up is money wasted at best, at worst, it is food for lawn diseases. Clover, dandelions, annual bluegrass, etc. are all winter annual weeds. They started growing in November and by February or early March, they appear to be taking over your yard. By all means, kill the weeds! But kill them with a stand alone herbicide (available in granular or liquid) in January rather than using a weed and feed in February or March, because by then, you are fertilizing too early and killing weeds too late. Also, fertilizing your grass early will not make it come out of dormancy any quicker. Again, the unused nitrogen in the fertilizer can create problems with diseases such as brown patch. The grass will green up and grow when the soil temperature is right, not when you decide you want it to. Just like you can't force a pecan tree to sprout leaves in January by fertilizing, some things simply take the time that they take. Grass should be fertilized in April at the soonest, but a good rule of thumb is wait to fertilize until after you have had to cut it (the grass, not the weeds) two or three times.

Finally, in addition to the huge overdose of fertilizer and the high rate of herbicide, we then proceeded to get quite a large amount of rain. The rain moved the herbicide into the root area of the turf where it would be better if it didn't go. It also caused any fertilizer that might have been “slow release" to release pretty darn quickly. Basically, it was a perfect storm of conditions that has your centipede yard looking so pitiful. Have patience and don't add insult to injury by trying to speed the recovery process with more chemicals. The damage may not be as catastrophic as it seems, but only time will tell.

Please feel free to contact me with any questions.

Courtney Duhe
Manager – Old Time Farm Supply, Inc.