October 2011 saw a continuation of our two-year drought. Even under normal rainfall conditions, October and March are traditionally the driest months in southwest Louisiana. One good thing about a dry month was that you probably mowed grass less often than normal. Another good thing was the low incidence of brown patch disease. Since the fungus that causes brown patch disease develops best under conditions of free moisture and moderate temperatures, its presence was minor.
The dry late summer and fall contributed to another condition, “take all disease.” This fungal disease primarily attacks grass roots in plants that are under environmental stress. “Take all disease” at first glance can be misdiagnosed as brown patch. To put it simply, brown patch disease attacks the leaves of the grass. “Take all disease” will destroy the roots. These diseases are each favored by different environmental conditions. The drought, coupled with low fertility, contributed to more cases of “take all” than we normally experience. Proper irrigation and maintaining soil fertility during the summer months is the most effective method of preventing “take all disease.” Gardeners who have St. Augustine lawns that have experienced “take all disease” should pay specific attention to improving the fertility of their lawns next spring and summer. Multiple applications of complete fertilizer (containing nitrogen, phosphorous and potassium) are often needed to correct the situation. The presence of “take all disease” is just another reason to take a soil sample for fertility from the lawn on a regular basis; about once every three years. If you know which nutrients your lawn lacks, you can make proper applications to prevent the problem.
September ends lawn care for most of the country. Louisiana is the exception. Most years, we mow and irrigate lawns at least until Thanksgiving. Even if you plan to have a dormant lawn this winter, one without perennial ryegrass, there are several chores you may perform to help the vigor of next year’s lawn.
When should you stop mowing for the winter? That depends on when the lawn grass slows growth. Usually in November, growth slows to the point that mowing can cease. Most experts believe that a little height is necessary to properly insulate the crowns and roots of the lawn grass. We don’t normally have a problem with winter-kill, but the dormant leaves can serve to protect your summer grass and act as mulch through the winter. Your winter lawn may look shabby, but your grass will probably be healthier next spring.
Should you fertilize lawns in the fall? That depends on the nutrient content of your soil. If your soil pH is 6.2 or above, you may apply phosphorus and/or potassium fertilizer. If your soil pH is lower than 6.2 (more acid), these nutrients will probably be bound to the soil in such a way that the grass won’t be able to utilize them in the spring. Applying phosphorus and potassium when the lawn breaks dormancy in spring is a more efficient use of the fertilizer. Unless you have planted ryegrass, do not apply nitrogen fertilizer in the fall. The dormant grass cannot utilize this nutrient and it will not store in the soil until next spring. Any winter weeds that you might have can utilize nitrogen fertilizer. You will only be fertilizing the winter weeds.
November is an excellent time to apply Atrazine herbicide to prevent winter weeds. Atrazine is a pre-emergence herbicide. It prevents weeds from coming up. To be effective, you need to apply it before the weeds germinate and emerge. That time is November. Atrazine controls annual bluegrass (winter grass), sticker weeds, clovers, dollarweed, Florida betony and a host of other broadleaf weeds. Follow the label for rate. Do not use Atrazine around trees, shrubs or winter flowers. Do not use Atrazine if you have planted perennial ryegrass or plan to plant it. Atrazine should be used only on St. Augustine, centipede, zoysia or dormant Bermuda grasses. If you have one of these lawn grasses and are free of trees, ryegrass and shrubs, Atrazine will work for you.
Many lawns do not lend themselves well to Atrazine use for weed control. If this is your situation, you will need to control broadleaf weeds with a post-emergence herbicide after the weeds begin to grow. Scout for these weeds and begin control when the weeds are young. This usually is in December. Young weeds are much easier to kill than mature weeds. If you wait until spring, weed control won’t be as complete and, in the case of sticker weeds, stickers will have already formed. Annual bluegrass (winter grass) cannot be effectively controlled after it has emerged and began to grow. If you can see winter grass, you will probably have to live with it until it dies in late spring.
Earlier this fall, I talked about planting ryegrass in the lawn. November is not too late to establish ryegrass for winter lawns. In fact it is the ideal time. Sow 5 to 10 pounds of perennial ryegrass seed per 1000 square feet of lawn. Use the higher seeding rate in St. Augustine lawns. Rake or drag the seeded area to increase the seed to soil contact. After the ryegrass emerges, apply 8 to 12 pounds of 13-13-13 fertilizer per 1000 square feet of area. You should have a green lawn through the winter. Of course, you will also have to continue mowing through the winter.