Potassium fertilizer materials appropriate for fall application include potassium chloride and potassium sulfate. Researchers report warm-season turfgrass with high levels of potassium are better able to tolerate cold temperatures and extended freezes. Potassium helps plants to produce biochemical compounds similar to anti-freeze, thus lowering the freezing point of the plant cells.
Applying nitrogen to warm-season lawns at this time of year will cause lush growth, actually making lawns less tolerant to cold temperature and freezes. Additionally, adding nitrogen during the fall has been linked to increased incidences of brown patch disease in St. Augustine grass and centipede grass. This is the disease that causes circular dead areas in the lawn. There is no benefit to applying phosphorus in the fall unless a soil test indicates that soil levels are low or very low.
Cool season weeds like annual bluegrass, chickweed and henbit can become a problem during winter months. These weeds can be controlled with various herbicides found commonly at local agriculture retailers and home stores. In the months of September and early October, homeowners can apply pre-emergent herbicides to control these winter weeds before they germinate and become a pest. Another option is waiting for the winter weeds to emerge and then applying a post emergence herbicide. Atrazine is very effective on winter weeds growing in centipede grass, St. Augustine grass and zoysia. Best times to apply atrazine are in November and March.
Granular herbicides are popular because they are easily applied with push type broadcast spreaders. However, many of these products are weed and feeds types that often include nitrogen fertilizer, which as discussed earlier can harm warm-season turfgrasses when applied at the wrong time. Avoid using weed and feed type products until late March.
The LSU AgCenter and the LSU College of Agriculture