Last week, I talked about noxious weeds in general. This week's topic is a specific noxious weed, tall whitetop. This tall plant with flowers resembling baby's breath grows along rivers and roadsides, and in fields. We even see it invading home landscapes now, as people allow the plants to grow, thinking they are wildflowers. People even use them in fresh or dried flower arrangements. After a year or so, the weed takes over the yard, and people call begging for knowledge on how to kill it.
Tall whitetop is a prolific plant producing more than 6 billion seeds per acre. Most of these seeds are shed in the fall. So, if you have tall whitetop on your property now, go cut all the flowers off and bag them up before the seeds spread.
The weed also spreads by creeping underground roots that grow three feet to over 10 feet long, and send up hundreds of new shoots. Plants can grow from parts of roots as small as one-tenth of an inch in thickness. As a stand increases in density, herbicide application becomes more and more difficult, due to the woody stems that develop each year. The spray gets trapped on the dead overgrowth before it can reach the new leaves sprouting up from the plant base.
Tall whitetop was not evident along the Truckee River in 1971, but by 1992, it occupied about 12,000 acres along the lower river. Today, tens of thousands of acres have been invaded across the state, destroying valuable habitat. It is a difficult weed to control, particularly as a stand ages and covers more area. Control is most effective when initiated during the first year of growth.
If you see a single plant of tall whitetop in your yard, dig it out immediately, bag it up, and put it in the trash. Keep desirable plants in the area healthy, so that they can compete with or crowd out the tall whitetop.
Hand-pulling works only when a few plants are present and if you pull any new growth as it appears for the next four to six years. Goats like to eat tall whitetop, but can wreak havoc on a landscaped yard! Chemicals are the most effective way of reducing tall whitetop stands, but you must also establish competitive vegetation to achieve long-term success. Chemicals must also be applied properly and at the right stage of growth. When using any chemical product, always read and follow all label directions.
For information on chemical controls for tall whitetop, go to the University of Nevada Cooperative Extension publication, "Fighting Invasive Weeds," bulletin 05-02, Page 57, http://www.unce.unr.edu/publications/EBPubs/EB0502.pdf. Or, contact me at 887-2252 or skellyj@unce.unr.edu.
For more information, e-mail skellyj@unce.unr.edu or call me at 887-2252. You can "Ask a Master Gardener" by e-mailing mastergardeners@unce.unr.edu or call your local University of Nevada Cooperative Extension office. Check out many useful horticulture publications at www.unce.unr.edu.
• JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension.