To say this has been an unusual year for landscapes and gardens is an understatement at best.
Our first snowstorm of winter was on December 23rd, which was quite late, but then I think pretty much everyone still remembers the last couple of snow events that dumped feet of wet snow on us in late March and April. Combined with regular rains and cooler temperatures our spring not only started late but persisted for quite a while.
The lengthy cool spring had several effects that are now being noticed by gardeners throughout our area. Some plants that suffer in hot temperatures look great this year (astilbe, phlox, hostas, quaking aspen). A lot of fungal diseases have showed up. Roots became waterlogged and stressed out some trees and shrubs that had never been stressed before. And for some folks, myself included, the pre-emergent crabgrass preventer either never got applied or was applied early on but became ineffective by the time seeds started germinating because our cool spring lasted so long.
Lawns that miss-timed or never had pre-emergent applied to it are easy to spot now as crabgrass is at it’s peak. Crabgrass has a much lighter green hue and broader, smooth leaves than standard fescues and bluegrass. It can quickly take over a lawn and dominate the desired grasses to the point where if things are left alone too long some re-seeding might be part of the recovery process of the lawn.
Pre-emergent is used in the spring and works best when applied just before the soil temperatures get to the 52-55 degree range for a 2-3 day period. It’s at those temperatures that seeds start germinating. If this window is missed the next step is to start eliminating the growing plant later in the spring or summer. But at this time the plants have already well past the seed stage so instead of a pre-emergent herbicide, another herbicide must be used. The most common chemical is quinclorac, although several others (Tenacity is one of them) are available.
The best product depends on what grass species make up your lawn; for our area that usually means quinclorac. Broadleaf weed killers will not affect crabgrass. A product labelled as non-selective will definitely kill crabgrass, but it will also kill anything else it comes in contact with.
As with any lawn or garden chemical, proper use and application instructions must be followed. Two areas to be especially careful about when using any herbicide spray is wind drift and temperature. Avoiding wind drift is simple: don’t spray when the wind is blowing. If temperatures are about 85 degrees the chemicals can volatilize and disperse in vapor form. This vapor may just rise into an adjacent tree canopy and negatively affect the trees or worse, even the slightest breeze can carry the chemicals quite far away. Spraying any chemical when you cannot control where it’s going to land is simply irresponsible and dangerous.
If your crabgrass infestation is severe, a schedule of fall overseeding of desired grass seeds, aeration, and fertilizations should be built which I’ll address later this year.
Art Smith is a co-owner of East Pierre Landscape and Garden Center, 5400 SD Hwy 34, Pierre