Campbell Vaughn: Now is the time to use preemergence herbicide unless you want a weedy summer

The calls have started, and I have tried to delay everyone, but forget what I told you. It is time to get that preemergence herbicide out soon.

The soil temperature at 2 inches is nearing 50 degrees with some warmer days on the 10-day forecast. I am expecting for the soil temperature to reach the magic 55 degrees, which means our pesky warm season annual weeds are going to start germinating soon.

Let’s get them before they get us.

I want to note what pre-emergence herbicides are, how they work and why I recommend them so often.

Annual weeds complete their life cycle in less than a year and reproduce by seed. Annuals may be further divided into winter (cool season) and summer (warm season) weeds.

Winter annuals germinate in the late summer and early fall months, live during the winter, and die in the late spring or early summer with higher heat. Good examples include annual bluegrass (Poa annua), common chickweed, henbit, and swinecress.

Summer annuals germinate in the spring months, live during the summer, and mature in the fall months and are usually killed with frost. These warm annuals include crabgrass, goosegrass, lespedeza, and knotweed.

The germination of these annual weed seeds is mostly dependent on soil and air temperatures. A soil temperature of 55 degrees is about where we see the switch between cool season weeds and warm season weeds. Currently, we are about to have a transition period with both warm and cool season annual weeds at the same time.

Since annual weeds are only produced by seed, the best way to control them is to get the seed early. This is where pre-emergence herbicide comes into play. Pre-emergence herbicides are applied to lawns prior to weed seed germination. Our standard recommendations are Sept. 1-15 for cool season weeds and mid-February to March 1 for warm season weeds. This can vary based on the weather, like an early spring.

Contrary to popular belief, pre-emergence does not kill seeds. They cause abnormal cell development or prevent cell division when the seed germinates. They stop the plant from growing by inhibiting cell division in the shoot and root tips while permitting other cell duplication processes to continue.

Allowing this product to disturb the natural germination process is why getting the herbicide out in a timely manner is important. Some of the common turfgrass pre-emergences have the active ingredients dithiopyr (Dimension) and prodiamine (Barricade). The easiest way to broadcast these products is with a rotary spreader, so get a granulated formula. I also like to get one with 0-0-7 fertilizer to add a little potassium to the lawn. Different pre-emergences have varying lengths of effectiveness, but three months is a fairly good standard.

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Some things to be conscious of concerning pre-emergence herbicides:

• Apply only according to the written label on the packaging.

• They do not affect a weed that is already present, just the seed.

• Make sure the product doesn’t have high nitrogen levels in it. Weed and feed products are famous for high nitrogen. Most of our plants don’t need nitrogen until May.

• Do not apply to an area that is to be a lawn or newly sodded lawn. They will adversely affect the root growth and can kill the sod.

• Do not apply where seeding may take place. This includes overseeding with rye grass seed, new lawn Bermuda and centipede seeds, wildflower seed or vegetable garden areas.

• Make sure that this herbicide gets watered in with about one-quarter inch within one to seven days.

Preemergence herbicides form the backbone of weed control programs. They do not control all weed seeds that may be present in a landscape, but they are effective for many of the most common weeds.

Get it out soon or it will be a long weedy summer.

This article originally appeared on Augusta Chronicle: Campbell Vaughn: Now is the time to use preemergence herbicide