Oct. 2, 2007

Photos and Graphics Click for larger images

CANYON – New products make controlling prickly pear and cholla cactus a paying venture, as long as planned for on a long-term basis, a Texas Cooperative Extension specialist said.

J.F. Cadenhead, Extension range specialist from Vernon, spoke recently with producers about the second year of cactus control on a demonstration plot of rangeland southwest of Canyon.

"We sprayed this in 2005 in the fall, and we see more work from the chemical as the years go by," Cadenhead said.

The plot is an aerial test of the new Dow chemical called Surmount, which is a mixture of Tordon 22K – the standard herbicide recommended for cactus control – and a product called Vista, which was recently labeled for rangeland use, he said.

The test also looked at a variety of surfactants to see if any of them would provide equal or better effects than the standard diesel oil-in-water carrier traditionally used in cactus spraying, Cadenhead said. Surfactants are soap-like agents used with herbicide applications to assist in spreading the herbicide droplets on the target plant for better coverage, penetration and uptake by the leaf.

Compared to the standard surfactants, a methylated seed oil with an organosilicone additive was also tested. This particular additive has 20 times the spreading power according to research, he said.

The treatments included applications of four-pints per acre versus three-pint per acre rates of Surmount application with: crop oil concentrate – about eight ounces per acre; diesel-in-water emulsion – 1-5 ratio; and non-ionic surfactant – two ounces per acre.

Using the four-pint rate per acre of Surmount, the results were:

– The treatment including diesel showed a 44 percent kill of all prickly pear. Another 50 percent had more than half of the plant pads dead.

– The treatment including the crop oil concentrate had a 60 percent kill, with another 37 percent showing more than half top kill.

– The treatment including the non-ionic surfactant had a 46 percent total kill, with an additional 39 percent more than half top kill.

Also included as a check was a test of the standard recommended rate of Tordon 22K at two pints per acre rate with all three of the surfactants.

A final test included was a rate of three-pints-per-acre rate of Surmount with three-ounces-per-acre rate of the methylated seed oil. It showed 47 percent kill, with another 44 percent having more than half top kill.

The highest degree of root kill on prickly pear was achieved with the crop oil concentrate, rather than the standard diesel-in-water emulsion. In this study, the three-pint-per-acre rate of Surmount looked as good as the four-pint rate when both were used with the crop oil concentrate, Cadenhead said.

Cholla is usually much more difficult to control than prickly pear, he said. When it comes to treating the cholla cactus, the plant should be knee high or shorter for best aerial control, he said. Anything taller usually requires individual plant treatment for adequate control.

"We can see here even though we are not killing the cholla completely, for two years we've kept them from blooming and forming seed," he said.

Herbicide costs for these treatments will be in the range of $25 to $30 per acre for the chemical alone, Cadenhead said. Spreading that out over a 10- to 12-year expected treatment life should make this practice pay for itself.

"That first year, it's hard to show it is economical to treat that rangeland," he said. "But over a period of time, the water previously used by those cactus will go into forage production and you will see an increase in grass production.

"Just remember, in treating cactus, you have to be patient," Cadenhead said. "It generally takes two to three years to achieve the maximum control with those herbicides."