Edith on Whitetop -- that is not a flower

by Edith Isidoro-Mills -- Some plants can be pretty but not good in your landscape.  This is especially true if the plant has been designated a noxious weed by the state.  Tall whitetop or perennial pepperweed is one such plant and it is blooming right now. Tall Whitetop, Lepidium latifolium, is on the noxious weeds list for Nevada as well as many other western states.  A plant gets on a state's noxious weed list because authorities have determined it is detrimental to agriculture, natural ecosystems, or human or animal health. If someone reports an infestation of noxious weeds, authorities may come out to check the report and talk to the property owner about controlling the noxious weeds. If you want to know more about what weeds are noxious in Nevada, check Nevada Noxious Weeds.  Note that this list refers to tall whitetop as perennial pepperweed. Perennial pepperweed is a category C weed.  This means it is found in many Nevada counties. If the property owner does not do something to control the weed, the state may come in and use measures such as spraying to control that weed if they determine it could spread to adjacent properties.  They will then charge the property owner for costs of controlling noxious weeds in their yard. In the case of tall whitetop, it is invasive and crowds out crop plants, native plants in the wild, and if it gets in your yard, eventually it will crowd out everything in your yard.   Once it reaches the stage of a thick stand, it is impossible to dig out or between plants. Tall whitetop is a perennial that is difficult weed to control.  It readily spreads by both seed and rhizomes.  Once one plant establishes in your yard, it eventually becomes a solid mass of plants over a period of a couple of years. Digging it up is impossible because it gets a very deep extensive root system sending up more plants wherever this system spreads.  At the same time that established plants multiply by roots, those plants are also setting viable, seed that germinates easily.  The seed is spread by wind, animal fur and feces, and flowing water from a ditch or stream. Equipment used in an infested field or yard may also spread tall whitetop if not thoroughly cleaned after use in the infested location. The best control of tall whitetop is prevention.  Homeowners should check out the source of any soil moved onto their property as fill.  When incorporating manure into your garden make sure it is only composted manure.  Manure scraped out of a corral or animal pen and immediately applied to your garden can be a source of tall whitetop seed if the animals had access to feed contaminated with seed.  To prevent an infestation of tall whitetop, only use composted manure.  Composting creates heat in the pile of manure and other organic matter that will kill seeds. If you do start to see tall whitetop, immediately take action to get rid of it.  If you catch it before it can establish an extensive root system, pulling out the plant will kill it. Once it is tall and producing flowers is too late.  This isn't always possible to determine since young tall whitetop plants can look a lot like other plants that are not weeds. The only way to control well-established stands of tall whitetop is with herbicide.  Even then, it will take multiple treatments and multiple years to control it.  In my own observations, Roundup (glyphosate) is not very effective in killing tall whitetop.  A patch of tall whitetop I observed for the last four or five years has been sprayed every year with Roundup (glyphosate). This patch continues to expand in size and produces a large crop of seed.  Some herbicides may require you to seek a licensed professional to apply them.  For more information on how to control tall whitetop, you can check this Extension publication.     Sign up to receive updates and the Friday File email notices. Support local, independent news – contribute to The Fallon Post, your non-profit (501c3) online news source for all things Fallon.