Post-rain could bring Khaki weeds

Green Side Up

A couple of weeks ago the emergence of fire ants after a bit of rain was noted. Another pest that shows up after a little rain while the weather is hot is khaki weed. One of the reasons this pest pops back up in conversation is because it is very difficult to get rid of. Its resilience is due to its being incredibly drought resistant because of its long carrot-like tap root, its ability to produce many seeds that are readily spread, its rhizomes that run under the ground and periodically send up new stems and the fact that it tends to send out roots from stems left touching the ground. Khaki weed (Alternanthera pungens) is a low-growing perennial that originated in Central and South America. It has dime to quarter sized leaves and light tan burrs originating where the leaves attach to the stem. It has invaded much of the southern United States, Spain and parts of Africa. It has become epidemic in Australia and is becoming so in Hawaii. It has become so pervasive in Australia that many people are unaware that it is not a native. The burrs stick to shoes, tires and pet fur and make walking barefoot uncomfortable.

Strangely, there has not been a great deal of research on khaki weed and its control. Studies have been done in Arizona and at Texas Tech. Research has borne out the claim that this is not your average weed.

It seems that the most effective herbicides are those containing a combination of ingredients. The folks at H & H Garden Center recommend Ferti-lome Weed-Free-Zone which is a combination of four chemicals: 2, 4-D, mercoprop-p (MCPP), dicamba and carfentrazone-ethyl. Other chemicals found in combinations that are effective are 2-methyl-4-chlorophenoxyacetic acid (MCPA), metsulfuron, thrichlopyr and fluroxypyr. Round-Up (glyphosate) is not recommended for khaki weed. It is reported to kill the tops of the plant but not the root which will resprout. Spray in the coolest part of the day when chemical uptake by the plant is most likely. When using a spray herbicide, it is often useful to add a teaspoon of liquid detergent (not soap) such as the original blue Dawn into a gallon of the spray mix.

This helps to break down any waxy coating on the plant’s leaves and reduce the surface tension on the leaf allowing the herbicide to better penetrate making it more effective. Most herbicides will require repeated applications at approximately three week intervals. Some products, although effective, may only be available through professional services. Professional services should be verified to be effective against khaki weed. This type of treatment can be both expensive and time-consuming. Keep in mind also that pesticide product labels should be followed meticulously.

Organic methods of control involve consistent attention and removing the plants by hand. Some

organic advocates suggest vinegar, boiling water and burning with a propane burner. At best these

methods are only marginally effective killing the above-ground portion of the plant but not the root. At

worst a large grass fire could result. When removing by hand it is necessary to dig deep enough to

remove the tap root. The plants should be disposed of in a plastic bag. Any small pieces of stems that

are left in contact with the soil have the potential to regenerate and make new plants.

According to the Horizon Pest Control of Carlsbad, New Mexico, the most important steps to

killing/controlling khaki weed are:

1. Diligent persistence. You can’t simply spray once or dig it once and expect it to go away. It

readily grows back from any roots left alive.

2. Don’t let it go to seed. The little burrs are seed heads. Although not verified it is thought that

the seeds are only viable for a couple of years. With existing weeds killed and no new seeds, the

problem should be under control in a few years.