For Release September 18, 2001

Grass Sandburs Are A Real Pain

AGRI-VIEWS
by Chuck Otte, Geary County Extension Agent

Hot, dry, droughty weather is not necessarily bad for all plants. Take grass sandburs for example. Judging by the number of sandburs that I have seen, encountered or received calls on, they have done real well this year.

Before we go any further, let’s clarify what sandburs are. There are about three different plants that local residents call sandburs. The sandbur that I’m talking about is the field or grass sandbur. When it first starts growing it looks like another annual grass, but then it develops seeds and look out! The other two are both broadleafed plants with yellow flowers. One grows upright and is very prickly (buffalobur). The other is a spreading vine that grows flat on the ground but can be several feet across (puncturevine).

Sandbur is an annual grass. It has already produced plenty of seeds this year and will die soon with colder weather. The bur itself contains one, two or rarely three seeds. It is a warm season annual grass, like crabgrass, so the weather has to warm up a little in the spring before it will sprout and grow.

Like many other plants that have multiple seeds in the same capsule, one will normally sprout the first season, while the other(s) have an induced dormancy that will keep them from sprouting until later in the season or even another season. In other words, this won’t be a one year battle to get them out of your lawn. It will also require you to use a multi-pronged attack. This is not an easy battle, but it can be won!

The reason we have so many sandburs is because the hot dry weather has thinned out desirable grasses leaving bare spots. When bare spots are left, weeds will move in. So the first step is to try to get the grass stand improved. A strong aggressive turf will keep the soil covered and the sandburs won’t have a chance. Reseed this fall or use an aggressive fertilizer schedule to get that lawn back on track.

Many of the crabgrass preventers will help suppress sandburs. You need to make sure that you get them down at the right time for crabgrass control in early spring. Then read the label and reapply at a later date if the label tells you to. But there will be sandburs that make it through the crabgrass preventer. You will need to deal with those using a postemerge burn down product. This fall, while you can still see where all the sandburs are growing, you need to draw a map or stick some markers in the ground. Do anything so that next year, in June and July, you can find those sandbur areas again.

Crabgrass killers are herbicides that are designed to burn down the seedling sandburs after they emerge. To be most effective, the sandbur plants still need to be small. Since most of these products depend on a chemical burn they also work best when it is warm or hot and sunny. These products need to be applied as a liquid spray. This is not something you will spread with a fertilizer spreader.

In early June, mix up some of the crabgrass killer and on a warm sunny afternoon, spray the area thoroughly. Expect to see some leaf burning on the desirable grasses. This is normal and the established perennial grasses will grow out of it. Then about every three weeks, through late July or early August, treat again. Then go through the same procedure the following year and maybe the year after that. It’ll take a few years to get all the seed germinated and killed. Sandburs are a nasty pest. But with dedicated effort, you can control them!

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