Question
I have had a chinese elm removed form my front yard, and the stump was ground, but tere are still sprouts coming up in various places in my yard.  I live in Albuquerque NM and do not water much.  I have two elms in the back yard, and one has sprouts that continually come out of the stump that I cut back and they bkeep returning.  Can I stop them from regrowing?  

I also have a Pyracanta that was removed, but there is one shoot coming back.  How do I get rid of these unwanted sprouts?

Lisa Johnson

Answer
Treat the sprouts with a herbicide called Roundup. This can be either sprayed on the foliage of the sprouts or wiped on the foliage. Roundup will kill and green plant it get on so if there are plants under the sprouts (grass) then instead of spraying the Roundup I would take a sponge and wet it with the Roundup and wipe the foliage. The plant will take the herbicide to the root system and kill the plant. You may have to do this a couple of times to rid the old tree of its root system. I would wear plastic gloves if you use the wiping method. The Roundup does have an odor and can be absorbed into your skin--this will not harm you but is difficult to wash it off. You can just keep mowing over the sprouts and over time the tree root system will run out of energy and die.

Extra environmental "stump talk"

Roundup is not highly toxic.
Many people have the misconception that all compounds whose name end in "cide," such as insecticide, herbicide, rodenticide, or fungicide, can be lumped together as dangerous, highly toxic chemicals, and unsafe at any application level. This is simply not the case for the vast majority of agricultural pesticides and is certainly not true of the herbicides used on right of ways and public lands.

Herbicide means herb--plant cide-- killer. They are formulated to interfere with the cells of a plant in the case or Roundup with the green cells.  For Roundup to be toxic to a 100 lb (45.5 kg) person they would have to ingest about 196,128 mg of the pure active ingredient of Roundup to kill them. Roundup varies from 41% active ingredient down and when it is sprayed on plants diluted to 1%.   

Table 1 provides the acute toxicity of the active ingredient in several herbicides for comparison to some other common chemicals. The table lists the LD50, which is a rating system for chemical toxicity.

A low LD50 indicates that a small amount of chemical is toxic and is a more dangerous substance. Likewise, the larger the LD50 the less toxic the chemical.

Most of the herbicides used on public lands have active ingredients that are less toxic than caffeine. And, the active ingredient is diluted to make the herbicide product sold on the market. All over-the-counter formulations of the products listed in Table 1 have LD50s above 1,700 mg/kg (milligrams of chemical per kilogram of body weight) and so are therefore less toxic than aspirin! Even so, we still limit their use to the minimum necessary to prevent the spread of noxious weeds.



Table 1. The Relative Toxicity of Commonly Used Herbicides Trade Name Active Ingredient
                          LD50*  mg/kg  
Arsenal imazypyr             5,000  
Garlon triclopyr               630
Oust  sulfometuron methyl    5,000  
Roundup glyphosate           4,320  
Tordon picloram              8,200  
Velpar hexazinone            1,690  
Weedone  2,4-D                 375  
For Comparison: >    
Table Salt                 3,750
Aspirin                    1,700  
Malathion (insecticide)        370  
Household bleach             192
Caffeine                     200  



*LD50 is the dose that is lethal to 50 percent of a test animal population, expressed as milligrams (mg) of chemical per kilogram (kg) of body weight.


How can this be so? How can a chemical with such low toxicity be so effective at killing plants? Imazapyr, for example, has an LD50 above 5,000 mg/kg, making it practically non-toxic. Yet this compound is a very effective herbicide and can control many of the largest trees. The secret to understanding this apparent contradiction comes from realizing that herbicides work on biochemical pathways that are specific to plants. For example, only plants photosynthesize (produce food from carbon dioxide and water), so, if a compound inhibits one or several of the steps in the long biochemical pathway that is photosynthesis, that compound is then toxic to plants. At the same time, this compound may have no effect on animal systems because the biochemical pathway for photosynthesis does not exist in animals. As another example, some herbicides work on amino acid pathways that are specific to plants and not found in animals. All of these types of compounds can be very effective herbicides yet are safe for animals because the biochemical basis for toxicity does not exist.