Turf
Frequently Asked Questions

  1. I have large circular areas in my St. Augustine turf that seem to be dying. What should I do?
  2. What is the best kind of fertilizer to use on my St. Augustinegrass?
  3. How do I determine how much fertilizer to put on my lawn at one time?
  4. How often should I fertilize my lawn?
  5. What would you recommend as a routine weed control program in my St. Augustine lawn?
  6. I occasionally see holes in my yard about the size of a quarter with a little pile of dirt beside the hole. I never see anything entering or leaving the hole. Is this some type of insect?

1. I have large circular areas in my St. Augustine turf that seem to be dying. What should I do?

Chinch bugsIt is always difficult to determine the exact cause of developing brown spots in St. Augustine lawns. The problem could be chinch bugs, fungus, drought and/or a large buried item and they all look pretty much the same. The best approach is to eliminate the possible problems one at a time.

Drought should not be a problem if the watering restrictions allow you to water twice per week. If you have once per week watering restrictions, then drought, particularly in April, May and September, could be killing spots in your lawn. It is legal to water these hot spots daily with a hand held hose before 8:00 a.m. and after 5:00 p.m.  Make sure your irrigation system is working correctly - 1/2 to 3/4 inch should be applied at each irrigation event. You will need to check your system periodically for broken parts and calibrate the output with flat sided containers such as coffee cans or tuna fish cans. If the spot is receiving enough water but it is not sinking in, then a mild detergent can be applied to the spot with a watering can.

If the irrigation is working properly, then you next need to check for chinch bugs. These are small insects about 1/8th inch long with silver wings laying flat on their back. The immature chinch bugs are red with a white line across their back. 

There are several methods to find chinch bugs. One is to slowly part the grass in the area between the bad spot and the good grass and look for these insects. Secondly you can drive a coffee can down into the turf and fill it with water; the chinch bugs will float to the surface. Thirdly, pour a soap solution (2 ounces dish soap per 2 gallons water) over a 2 square foot area. Within a few minutes the chinch bugs will come to the surface. Chinch bugs can be controlled with Ortho Lawn Insect killer Granules containing bifenthrin. There are several other registered products for homeowner use on turf such as permethrin, and Sevin, but bifenthrin seems to work best. Chinch bugs seem to be developing resistance to synthetic pyrethroid insecticides such as bifenthrin and permethrin. If you notice that bifenthrin is not working as it has in the past switch back to another class of insecticides such as Sevin.

brown patch disease on St. AugustinegrassIf you don't find chinch bugs, then the problem may be caused by a fungus. There are several fungi that cause leaf spots and large circular problem areas in St. Augustine turf. The two most common fungus diseases which produce a brown patch are take-all root rot and brown patch diseases. Two common diseases that produce leaf spots are gray leaf spot and Cercospera leaf spot. 

There are no products which will give complete control of take-all root rot, only suppression. Bayer Advanced Fungus Control for Lawns (triadimefon), Scotts Lawn fungus Control (thiophanate methyl), Banner Max (propiconizole) and Immunox (myclobutanil) fungicides will control many St. Augustine diseases. Daconil can no longer be used for turf diseases, but can still be used for ornamental disease control. 

root rot on St. AugustinegrassIf you cannot determine the disease, then samples can be taken and sent to the Florida Extension Plant Disease Clinic for analysis and recommendations.  Visit the University of Florida Turf Web Site for more details on turf disease control or call the Extension Office and ask for the circular titled "Disease Control in Turf: Common Turf Diseases". Or check the May 2004 Urban Horticulturer Newsletter and read the article on diagnosing lawn problems.

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2. What is the best kind of fertilizer to use on my St. Augustinegrass?

We first recommend that you conduct a pH and fertility test on several different sites in your lawn. If the pH is below 6.5, then you need to add dolomite, which is calcium and magnesium. The ideal pH for St. Augustinegrass is 6.5. Every 5 pounds of dolomite applied per 100 square feet will raise the pH 1 point; therefore if your pH is 5.5 you will need to add 5 pounds dolomite per 100 square feet to raise the pH to 6.5. The Polk County Master Gardeners conduct soil pH tests every Thursday morning at the Extension Office for a $3.00 fee.

To determine fertility, i.e. the amount of calcium, phosphorous, magnesium and potassium, the sample will have to be sent to the University of Florida soil's lab. They will test for pH and fertility for $7.00. After you determine the pH and fertility, then you can shop for a fertilizer.

Select a product which has the same percentage of nitrogen and potassium and with low or no phosphorous such as a 15-5-15 (15% nitrogen, 5% phosphorous and 15% potassium) or a 15-0-15. If your soil fertility test indicates high phosphorous, then use the 15-0-15. Products with analyses like 16-4-8 have been recommended for years, with twice as much nitrogen as potassium. The current thinking now is to use equal amounts of nitrogen and potassium, because of the root building qualities of potassium.

Select a product with 30-50% slow release or water insoluble nitrogen. To determine the percent of slow release N, look on the label under nitrogen and you will see one or more of the following categories including nitrate nitrogen, ammoniacal nitrogen, urea nitrogen, which are all water soluble, and usually last is water insoluble nitrogen or slow release nitrogen.  In many cases, the water insoluble nitrogen is urea, which is an organic form of soluble nitrogen, covered with sulfur. The sulfur slows the release of the urea nitrogen. Sometimes the urea is covered with a poly coating such as with Osmocote products. If the total nitrogen content is 15%, the water insoluble part should be at least 5%.

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3. How do I determine how much fertilizer to put on my lawn at one time?

The general recommendation is to apply 1 pound actual nitrogen per 1000 square feet of lawn if the fertilizer has 30-50% water insoluble nitrogen. If the fertilizer does not have slow release nitrogen, then only apply 1/2 pound. To determine how many pounds of your fertilizer contains 1 pound of nitrogen divide 100 by the percent nitrogen in the fertilizer you are using. In other words, if you are using a 15-0-15 divide 100 by 15 which equals 6.7 pounds. If the fertilizer has 30-50% slow release nitrogen you would apply about 7 pounds of fertilizer in 1000 square feet,  and about 3.5 pounds of fertilizer if it contained no slow release nitrogen at all.

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4. How often should I fertilize my lawn?

This depends upon the level of fertility that you want to maintain. For a moderate fertility program in a central Florida St. Augustinegrass lawn, you should apply a complete fertilizer in March like 15-5-15 or 15-0-15. Make a second application of just slow release nitrogen like Milorganite in May and August with an application of iron in July. Finish the year with an application of a complete fertilizer in October. A minimum fertility program would skip the two slow release nitrogen treatments, but otherwise would be the same.

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5. What would you recommend as a routine weed control program in my St. Augustine lawn?

dollar weedIf a lawn is maintained correctly, it should be thick and vigorous and crowd out most weeds. However, there are times when weeds just get out of control and require treatment. Many broadleaf weeds are controlled by applications of Atrazine - one in February and a second before April 15th. Dollarweed can become a problem in St. Augustine turf and usually can be controlled with an application of Atrazine in the fall. 

basket grassGrassy weeds like crabgrass, goosegrass, Alexandergrass and basketgrass have become a real problem in St. Augustinegrass since Asulox was taken off the market. About the only option is to treat with a pre-emergence herbicide such as Halts (pendimethalin) or a combination pre-emergence product like trifluralin and benefin (Team) 2-3 times per year. These herbicides do not kill the plant itself, but kill the germinating seed, so timing is critical. These products will also kill a few broadleaf weeds such as wood sorrel and spurge.

globe sedgeAnother group of troublesome weeds are sedges including the nutsedges and Kyllinga. These plants are easy to identify because the stems are triangular - "sedges have edges". Basagran will control a few nutsedges as will Image. Image probably does a better job than Basagran. A more expansive product called Manage from Lesco will control most of the sedges and is the product of choice. 

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6. I occasionally see holes in my yard about the size of a quarter with a little pile of dirt beside the hole. I never see anything entering or leaving the hole. Is this some type of insect?

Strategus antaeusI think what you are seeing is an emergence hole of an adult white grub grub probably Strategus antaeus. This is one species of scarab beetle which lives in the ground as a very large white grub (perfect food for armadillos). It is not well known what these particular grubs feed on. They are not known to feed heavily on grass roots - maybe decaying organic matter. They eventually pupate and  become adults. The adults dig their way out of the ground and leave a round hole (about the size of a quarter) and a small pile of dirt behind. 

Certain species of white grubs like the masked chafer can be extremely damaging to home lawns and appear to be most damaging to St. Augustine lawns. They can be successfully treated chemically with Dylox which is short term, but highly effective or Bayer Advanced Grub Control For Lawns which is less effective for larger grubs, but has long residual activity.

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