Taking Another Stab at Prickly Pear Removal

In late summer, the fields were still lush and green

Thanks to an extension of our 2014 LIP (Landowner Incentive Program) grant from Texas Parks and Wildlife Dept., we were able to wrap up some of the brush management work begun in the fall of 2014, and move on to another area that was heavily covered in prickly pear.

Building on what we had learned from other attempts to remove cactus from our rugged rangeland, we decided to divide the project area into roughly three zones, each of which would receive a different treatment method: hand-clearing, mechanical removal by tractor, and herbicide.  We would then compare each zone for cost, re-growth, and overall recovery rates. 

Project Objectives

As always, the objectives for our projects are to encourage more diversity of plant species, reduce areas of bare ground, protect hardwood trees, and to promote resiliency.  We learned from TPWD wildlife biologist Dale Schmidt that prickly pear clumps provide both food and cover for many animals, including our favorites like the Rio Grande turkey. A “clean field” that is free of all cactus and other scattered brush species is not necessarily good habitat.  However, past land use practices in the project area resulted in wall-to-wall cactus typically 2 feet or less apart. 

Over-grazing, bulldozing to “clear brush”, and gritty granite soils created cactus fields dominated by spring forbs, including Hooker plantain (Plantago hookeriana), Redseed plantain (R. rhodosperma), tallow-weed plantain (P. wrightiana), San Saba pinweed (Lechea san-sabeana), wooly croton (Croton capitatus), and slender snake-cotton (Froelichia gracilis). Grass species here are few, and limited to early successional species such as purple three-awn (Aristida purpurea), hairy grama (Bouteloua hirsuta), and Texas grama (Bouteloua regidiseta).  By summer, this area is mostly brown and bare.  In the fall, small stands of California cottontop (Digitaria californica), Southwestern bristlegrass (Setaria scheelei), and windmill grass (Chloris spp.) appear near tree canopies. 

Although we have had no grazing on our property for six years, this area has seen little increase of grass cover or diversity.  We decided that thinning the sprawl of prickly pear would be a good way to make space for both natural recruitment of more grasses, and also to introduce more seed to the seed bank that might hasten the spread of native grasses. 

As always, the question is: “What is the best way to go about this?  How much effort is involved? How long does it take and what does it cost?”  We recognize that methods we might use on our 60 acres would be absurd to try on a larger scale, but on the other hand if trying different things gives us greater understanding of the natural processes of recovery, then we should be able to both use what we’ve learned elsewhere on our property, and also our experience could point to techniques that could be magnified and applied to a larger scale.

Different Methods

As we’ve discussed before on these pages, we know that hand-clearing and using the tractor bucket to haul the material to brush piles is a meticulous and time-consuming method which is very difficult and expensive.  On the other hand, if the crew is good, it’s the best way to incrementally remove prickly pear with the least disturbance and the quickest recovery.  Building brush platforms in many separate areas to minimize the distance to carry the pear is the first step.  Later, burning these piles provides an opportunity to add native grass seed in discrete “seed islands” that could hasten recovery and also add diversity of species that seem slow to appear, even after the land has rested.  The challenge is finding a good crew to help with this chore (which should be tackled during cooler seasons when there is some moisture in the soil).  We used this method in the area that had the most trees and where maneuvering a tractor would have been more difficult.

The second method was straight out mechanical removal with a larger John Deere tractor outfitted with a special attachment of large tines or forks clamped onto the bucket.  We hadn’t had much luck with this method in the past, but we wanted to try again with more supervision and assistance on the ground to see if the results would be different. However, after only two passes of the tractor in the softened ground this spring, it quickly became apparent that despite the careful efforts of my neighbor, the bucket made long scars on the ground, built up wads of dirt, scattered pads and left roots in the ground. The result was that the cactus was essentially re-distributed, not eliminated and more time would be needed to repair the scar and gather scattered pads and roots, resulting in little gain over simply hand clearing in the first place.

The final method was to try spraying clumps of cactus with appropriate herbicide.  In the past, we had been reluctant to use chemicals to treat prickly pear because most contained picloram, which is very active in the soil and could pose a risk to woody plants as well as create larger kill zones around the pear.   But we had heard of a new, unrestricted herbicide that did not include picloram called PastureGuard, and after some research we decided to give it a try. PastureGuard, and another herbicide called Vista are part of a suite of new non-restricted chemicals that can be used without an applicator’s license. Some studies have shown that when used properly, they can kill prickly pear with fewer unintended consequences such as drifting in the soil and harming non-target species.  We mixed a 1% solution in a three-gallon back pack sprayer. The solution consisted of 4 oz. of PastureGuard, 1-2 ounces of surfactant (we use “CideKick” , a non-ionic methylated seed oil as an adjuvant or surfactant because we prefer not to use diesel), plus 1 -2 oz. of tracer dye so you can track where you have sprayed.

 With abundant rains this springs, we were able to spray large areas under optimum conditions. PastureGuard needs sufficient soil moisture in order to deliver the chemical to the roots of the plant.  It can “fix” on the pads fairly quickly, but it needs moisture in the soil to uptake the chemical throughout the plant.  We sprayed at the end of April, and within three weeks we saw the plants begin to yellow and decline.  Lush rains in May did not cause the plant to revive, and best of all, we did not see an empty “dead zone” around each sprayed plant.  Grasses recovered and were growing vigorously until summer drought began.   In this area, we left big clumps of prickly pear and sprayed the smaller plants in between.  Instead of adding seed to burn piles, we will rely on natural recovery to fill in the bare areas once the pear is completely dead, which could take several seasons.

Lessons Learned

Testing these methods side by side essentially confirmed what previous efforts suggested, but it also added the extra tool of herbicide.  Going forward, spot-spraying cactus in large areas will be an easy way to reduce the amount of pear, while hand-grubbing near trees or in discrete areas where we are building trails will be the best way to go for the results we want.  We will reduce the amount of seeding we do each season, but we will always look for opportunities to add diversity, whether from seed or grass plugs.  It will take another season or two to verify how well the area recovered from the digging and sowing and spraying, so meanwhile we wait eagerly for the return of fall rains.

posted on 8/6/2015