Figure 1. Crabgrass cut for hay with seed strips left for volunteer management.

Figure 2. These firstgrazer steers are in a pasture of Red River Crabgrass. This field has been in crabgrass 24 consecutive years without stand or production failure through 1995.

Figure 3. Crabgrass can be managed for perpetual planned volunteer stands as shown by this 18 year old stand that was never planted to this age.

If seed drop is skipped a year, volunteer stands will usually still be good, but after two years without seed drop, only about 12 percent of crabgrass seed in the soil remains viable, which might not be enough for good stands. Crabgrass can be grazed or hayed too severe and have reduced stands caused by inadequate seed drop.

Crabgrass is an indeterminate plant. It makes vegetative growth, seed heads, and ripe seed simultaneously and continually all summer under adequate weather and cultural practices. Crabgrass has a wide range of acceptable darkness-light ratios that cause it to set seed. In Oklahoma, the Red River crabgrass variety, among others, can start making seed in June and continue to October, which makes easy management for extended seed development and high-quality, productive forage for grazing and hay. Except for very early crabgrass grazings, all good summer to fall grazings or hay harvests include vegetative stems, seed heads, and ripening or ripe seed.

The height of good 'Red River' crabgrass at hay cutting usually will be 18 to 24 inches, with some exceptional growth up to 3 feet. Crabgrass is generally a lush (high-moisture) hay, and the weight of the water in the soft stems usually causes it to lodge if it grows beyond 18 inches tall.

To produce good stands and quality hay from volunteer stands, there are several management options, including managing for seed drop for the next season's volunteer stand. The first growth of crabgrass to harvest for hay (June to July in Oklahoma) is usually quite lush and can be without abundant seed heads, especially if the grass is well cultured and fertilized. This first harvest can be very high-quality hay with 15 to 20 percent crude protein and 65 to 75 percent digestibility. Harvesters may not want or need to wait for seed heads but should allow adequate seed drop in regrowths. Regrowths produce many seed heads as the crop matures, because of the stand's variation in plant ages (caused by different seedling emergence dates) and the individual plants' being indeterminate. Choices are to (1) harvest higher-quality hay with limited seed heads, or (2) delay harvest and harvest somewhat lower quality hay. In either event, there must be enough physiologically ripe (dough) and fully ripe seed to shatter during harvesting. One-quarter teaspoonful every 1 or 2 square feet, or about 15 to 30 pounds per acre, is adequate for volunteer stands if tillage is shallow.

Seed color depends on the crabgrass species and ecotype and is not critical for judging seed ripeness, but a brown or light gray-purple seed generally indicates more ripeness. Ripe 'Red River' crabgrass is light green to tan.

Try to harvest when lower leaves are still green or just yellowing, when seed will shatter. If the harvest is delayed too long, the lower leaves die and the hay must be cut higher to ensure survival and regrowth. A 4- to 5-inch height is acceptable, but the last cutting can be very short.

A good approach is to harvest quality hay when it's ready for a particular harvest objective, not necessarily after seed has set, and to leave an uncut strip about 6 inches wide between each or every other swath (figure 1). A combination of methods is useful.

Wind and animals help scatter the seed, as do operators when they harvest hay or make shallow field renovations to perpetuate the stand (figures 2 and 3). Because crabgrass is stoloniferous, if the stand is thin, runners will help cover the soil.

Soil tillage or renovation should be adequate, but not excessive, to encourage upper-level volunteer crabgrass, but top-quality crabgrass pastures can be produced without regular light tillage. Our research shows that about three-fourths of volunteer crabgrass comes from seed on the soil surface and the first one-half inch of the soil profile.

We usually disk, field cultivate, or sweep plow only about 2 to 4 inches deep in order to leave plenty of seed close to the surface.