Turf needs a long wake-up call
There are two types of people: chirpy folks who wake up early and then there are the rest of us. Until we get coffee, we don’t like perky early risers.
Lawns soon will be waking up. In December, low temperatures put turf to sleep. Centipedegrass, St. Augustine, bermudagrass and zoysia, referred to as warm-season turf, appear brown in the winter. In the Lowcountry, warm-season turf goes mostly dormant and greens up slowly. Anything that appears green during the winter is most likely a weed or the result of ryegrass overseedings.
In some parts of the country, fully dormant warm-season turf can be sprayed with Round-up to kill weeds while not affecting the turf. However, our mild winters make that a risky practice that is not recommended. If you pull the turf apart, you’ll see green tissue near the base that can still absorb and translocate herbicide.
Cool-season turf grows in the upper states. It’s a perky early riser. In fact, it prefers to be fertilized early in the spring. Warm-season turf, in contrast, wants to wake up slowly. That means leave it alone until its completely awake.
The transition from dormancy to green-up is a stressful time for warm-season turf. It’s relying on carbohydrates (food supply) that were stored before winter, when it still had green foliage. This limited supply of carbohydrates is used to establish new roots and shoots. Once the new foliage is established, it can begin photosynthesizing. Our job is to not add more stress, like fertilizer.
The first application of nitrogen should not be applied until the end of April or beginning of May. Nitrogen is not food, it’s more like fuel. It increases the consumption of carbohydrates that results in faster growth and greener tissue. However, nitrogen can exhaust the limited carbohydrate supply.
That may not be a problem because turf is growing new tissue and photosynthesizing to produce more, but a late frost will kill the new growth. Now the carbohydrate supply is depleted as well as the new foliage. This severely weakens the turf’s ability to wake up as well as resist disease, especially centipedegrass.
So maybe you’re wondering about all those weed-and-feed products? Mid-February is the ideal time to apply pre-emergent herbicides to control summer annual weeds. Pre-emergent herbicides are not necessarily required. A dense, healthy turf often can outcompete many summer annual weeds.
However, pre-emergent herbicides can get existing annual weed problems under control. The most problematic summer annual weed is crabgrass: It’s an aggressive grassy weed that can take over a large area. Many people may not even realize their lawn is mostly crabgrass because it looks good during the summer but turns purple as autumn temperatures cool and dies at first frost, leaving a big dead spot for winter annual weeds to emerge. This becomes a vicious weed cycle.
If you want to apply pre-emergent herbicides, avoid weed-and-feed products in mid-February. Instead, use Crabgrass Prevent, Dimension or any other pre-emergent product that does not include nitrogen. Some pre-emergents contain potassium (0-0-7), which is good. However, you can use weed-and-feed products with nitrogen during fertilization in May to extend weed control.
If your lawn is already filled with winter weeds, you can kill them with post-emergent herbicides, but you want to apply them before the turf dormancy breaks. Even though post-emergent herbicides don’t kill healthy turf, they can add more stress to turf that’s waking up. And warm-season turf is cranky, so always read the pesticide label. Some herbicides will recommend waiting until May, when the turf is fully emerged.
Henbit has small purple flowers and already has invaded some dormant lawns. In many cases, mowing is a good option. The lawn mower can reduce winter annual weeds without the need for herbicides. The winter annual weeds’ life cycle ends in late spring, but mowing can make them much less noticeable until they die.
Mowing also removes dead foliage from the lawn, allowing new shoots to emerge sooner. Setting fire to dead grass, however, is not necessary. It does not help control thatch.
Tony Bertauski is a horticulture instructor at Trident Technical College. To give feedback, email him at firstname.lastname@example.org.