Express-News Weekly Column
Saturday, August 23, 2003
Submitted by Calvin Finch, Ph.D., Conservation Director, San Antonio Water System, and Horticulturist

SAND BURS

            It is sand bur time again. Most of the pesky burs are still green, but some have dried out enough to start adhering to pant legs and puppy feet.

            Sand burs are grassy weeds that grow in full sun on well-drained sites. They are not usually a problem in lawns where the soil is enriched with organic material and the sod is thick but, in sandy vacant lots or even sloped caliche soils, they can make life in the late summer miserable. The prickly bur is the seed of the plant. It is spread by adhering to pets, wildlife, or people that travel through the plants.

            The best way to prevent sand burs is to apply a pre-emergent herbicide like Amaze or XL in March and then again in early June. The herbicide prevents the burs from germinating. It often takes two years of treatment to achieve control. I know that does not help you now, but write the dates down on your calendar so that you do not miss it next year.

            There are several other strategies that help deal with the problem if you have let the burs get this far. Mow them immediately and mow them low. If you can get the burs off of the stalks and under the grass and weeds they are less of a problem than when standing up on the stalks. After mowing them down go through and kill the plants if it is possible. In a Bermuda grass lawn a MSMA product will kill the plant. The label of Image and Manage also lists sand burs as a plant that they will kill. In weedy fields a spot treatment with a backpack sprayer works well because the grassy sand burs stand out from the broadleaf weeds. Round-up or Finale also work for the spot treatment. They are herbicides that are especially effective in a wick applicator. Estes Chemical (210-590-1092) carries the wick applicator.

            The reason you are killing the plants after the burs are mowed off is because, if the weather stays hot through the fall, the plants may be able to bloom and produce more burs. Sand burs are also adaptive to mowing. They are probably standing straight up in your vacant lot now but, if you mow frequently, they will grow horizontally along the ground.

            The plant-killing works especially well when you catch them in June or July before the seed heads even form. That is another thing to mark on your calendar.

            For those of you that do not take action now and are blessed with a full crop of sharp mature sand burs in several weeks there is another tactic that is fairly effective. Obtain a piece of carpet remnant that you can drag through the sand bur plants. Thick pile and especially shag carpet works well. A piece 4 ft by 6 ft or several smaller pieces can be dragged behind a riding lawn mower. Your teenagers probably think they are enslaved anyway, make them drag the pieces by rope attached at the corners of the leading edge. It will give them a great story to relate to their sympathetic friends or to their grandmother.

            Bury the sand bur-laden rug or send it off in the garbage.

            Some people do not use the pre-emergent herbicide because the same vacant lot that is full of sand burs in late summer is beautiful with wildflowers in the spring. The same chemical that prevents sand burs from germinating can prevent bluebonnets, coreopsis, and other wildflowers from germinating. If you time the applications right it does not have to happen that way, however. The best pre-emergent herbicides only work their magic for three months in South Texas. The Amaze applied on March 1 will work until about June 1. If the second application is made on June 1 it will be effective until about September 1. That means that the wildflower seeds can germinate in September and October as is normal. In the unlikely event that the herbicide does work for a longer period than expected, wildflower seed is inexpensive and you can reseed later in the autumn or for the next season.

            Once the burs are eliminated you can even go back to seeding cosmos, sunflowers, and other summer germinating wildflowers. On ideal sand bur sites, expect them to reappear within a few years. Keep your wick applicator and Round-up handy for several trips through the area a few times every June and July.