Floodwaters bring invaders

Northern Nevada’s winter weather has always been unpredictable, but the winter of 2017 will go down in the record books. We received incredible amounts of snow and rain, enough to make local and national headlines. Snow in the Sierra Mountains closed roads and ski resorts, and residents on the valley floor are still assessing flood damage.

The recent floods not only damaged homes, businesses, driveways and landscapes with rushing water, they also carried debris and what every homeowner dreads– weed seeds.

Weed seeds are not something people commonly think about when they see water rushing down streams, rivers or county ditches. But, because of the water which flowed off the landscape and people who drove through flooded areas, there is the potential for plants to spread onto your landscape from miles away.

Sometimes the cause of plant spread lies closer to home. If your neighbor has plants or weeds that spread by seed and water flowed from their property onto yours, you may see those plants starting to sprout in your landscape. Some weeds or plants are just a nuisance and can easily be controlled or eradicated. Others are deemed noxious by the state and are difficult to control.

First, which plants spread by seed can be deemed a weed? The answer is simple: a weed is any plant that produces viable seed and spreads to areas where you do not want it. Many people love the Virginia creeper vine. Others find it unappealing. It has the ability to spread very easily by seed, and birds deposit seeds throughout the area. But, floodwaters spread much more than just a couple of seeds. When these seeds land and sprout where you do not want them to, those sprouts are weeds.

What is the distinction between nuisance weeds, like tumbleweed or even Virginia creeper, and state-regulated noxious weeds, such as perennial pepperweed? Noxious weeds are regulated by the Nevada Department of Agriculture and defined in the Nevada Revised Statutes, NRS 555.130. They are “any species of plant which is, or likely to be, detrimental or destructive and difficult to control or eradicate.”

How are they determined and regulated?  Again, the answer is found in the Nevada Revised Statutes. “The State Quarantine Officer may declare by regulation the weeds of the state that are noxious weeds, but a weed must not be designated as noxious which is already introduced and established in the State to such an extent as to make its control or eradication impracticable in the judgment of the State Quarantine Officer.”

This statute is technical, but important. It means that one of our high fire-hazard weeds, cheatgrass, is not on the noxious weed list. This is because there is no way to eradicate it from the state. Only destructive weeds we can control are added to the noxious weeds list.

Noxious weeds like purple loosestrife and perennial pepperweed have a high potential to spread to new areas because of flooding. These noxious weeds can not only drop property values, but also cost homeowners and businesses hundreds to thousands of dollars to fight when plants are allowed to multiply. It is important to take steps now to control them.

Floodwaters erode property. Photo by Wendy Hanson Mazet.

Your first step is to assess the damage to your home and landscape. If you have areas where water moved soil from another property to yours, do not assume that soil is weed-free. Hold off on incorporating it into the garden or other desirable growing areas. Set newly deposited soil aside, and see what grows. This is critical to make sure you do not incorporate soil which looks nice on the surface but which is actually filled with weed seeds.

The second step is awareness. Be aware that while removing flood-spread soil and debris from your property, you could further spread weed seeds.

Finally, as your home and landscape comes back into order and spring weather begins, it will be important to continually monitor the landscape, promptly identify seedlings and plants and quickly find appropriate solutions for their control.

If you need help identifying weeds or plants in your landscape, bring photographs and live samples to the Master Gardener Volunteers at Washoe County Cooperative Extension, 4955 Energy Way in Reno. We will identify plants as well as provide information on controlling them.


Noxious weeds spreading by seed

While all weeds are a nuisance, noxious weeds can be devastating. By Nevada state law, every person owning or occupying land in the state shall cut, destroy or eradicate all weeds designated as noxious before they propagate. It can be a daunting task. But, if you keep an eye on your property, noxious weeds can be kept at bay when controlled early.

Noxious weeds which could easily be spread due to recent flooding include medusahead grass, perennial pepperweed (also known as tall whitetop), yellow starthistle, Scotch thistle, tamarisk (also known as saltcedar), purple loosetrife and puncturevine.

Each is different. Some are annuals, like medusahead, yellow starthistle and puncturevine. They will complete their lifecycle in one growing season. These plants can easily be hand-pulled early on, and your control is finished until more seeds in the soil germinate.

Many thistles, like Scotch Thistle, are biennial. These weeds form a rosette the first year and flower and set seed the next. Control is the same: earlier is better and easier.

Perennial pepperweed, tamarisk and purple loosetrife are perennials. They will not only come back from their original root system, but will also spread by seed. The longer perennial weeds have to establish, the more difficult it will be to eradicate them.

As you walk through your gardens and landscapes this spring, look for things you did not plant but which have started to grow. When plants are allowed to grow and set deep root systems, control becomes more difficult and costly. The earlier an unwanted plant is identified, the more chances you will have to control its invasion.

Resources to help you include the Nevada Department of Agriculture’s Quick Reference Guide available online at http://agri.nv.gov/uploadedFiles/agrinvgov/Content/Plant/Noxious_Weeds/Documents/quick_reference_guide_final.pdf, Cooperative Extension’s website at https://www.unce.unr.edu/programs/sites/ipm/ and the Nevada Department of Agriculture’s website at http://agri.nv.gov/Plant/Noxious_Weeds/Noxious_Weeds_Home/.


Wendy Hanson Mazet is a horticulturist and certified arborist with University of Nevada Cooperative Extension. Have questions about your plants? Contact a Master Gardener at 775-336-0265 or mastergardeners@unce.unr.edu, or visit www.growyourownnevada.com.