Learn to identify, handle invasive weeds

by Laurel Baldwin

At this time of year our gardens are growing gangbusters – and so are those weeds. But if you’re watching out for them and you do a little homework first, you can intervene early and spare yourself some expense and a sore back.

It’s important to remember that weeds don’t move themselves from place to place. Wind, water, animals, birds, equipment, vehicles, contaminants of crops or landscape materials and even your boots will spread invasive weeds. We’ve used weeds for culinary or medicinal uses and even plant them on purpose because they are attractive, only to find that once they acclimate they can jump the fence.

Identify your weeds first. You must know your target so that you can understand how to wrangle it. Your local Noxious Weed Control Board staff or the local Washington State University Cooperative Extension office can help identify weeds. There are weed identification books and of course there is the internet. Looking at multiple resources will help you make sure to avoid cases of mistaken identity.

Hedge bindweed. PHOTO BY LAUREL BALDWIN

Life cycle: Annual, biennial, and perennial

Not all weeds grow alike. Knowing the life cycle of a weed makes all the difference between effective weed control and wasted time on mistaken efforts. There are three life cycle types: Annual, Biennial and Perennial. Annual weeds germinate, flower, make seed and die within one season. Some annuals can have multiple generations per year. Annuals might be the easiest of the three to manage because their root systems are not as robust as biennials or perennials. They pull up easily and might not grow back from the roots if the stems and leaves are removed. But they make up for this weakness in their seed production. An example is Bittercress (aka Shot weed). One plant can produce 1,000 seeds or more and those seeds can germinate that same year or wait in the soil germinating over several years.

Biennial weeds complete their life in two years. The first year they send up leaves, sometimes called a rosette. The second year they “bolt” or send up the flowering stems which eventually produce seeds. Since biennials are not producing seed in their first year, you can reduce your workload and maximize your effort by working on removing only those seed-producing second year plants. Poison hemlock is a toxic biennial weed which can produce anywhere from 1,500 to 39,000 seeds which can stay viable in the soil for six years.

Perennial weeds, like hedge bindweed, are usually the most difficult. Like biennials, the first year is all about the leaves and after that they produce seed year after year after year. They can also have very tough root systems, sometimes creeping roots, which store loads of energy to keep coming back after they’ve been repeatedly mowed. Or they may grow new plants just from stem pieces. So it would make sense to get at a perennial weed in that first young year if you can, and not wait for it to bolt and seed.

Poison hemlock with inset and Bittercress (below). PHOTOS BY LAUREL BALDWIN

Tools and strategies

What tools to use?  Knowing your target well will go a long way to help you decide your best strategy. You can use many things to remove the above-ground parts of a plant – mowing, cutting, fire, contact herbicides (like vinegar). But don’t forget about those roots. If you are dealing with a biennial or perennial weed, these tools are not likely to get to the roots and kill those plants completely. But these tools might manage them, weaken them or prevent them from making seed. Mulching plants can help, both organic (bark, compost, straw) and inorganic (plastic, barrier fabrics). There are cultural and biological strategies too. Digging and pulling might be a good bet plus the physical work can be a great stress reliever.

Herbicide requires the most consideration and homework and is often the last resort. As all weeds are not alike, all herbicides are not alike either. Different herbicides will work on different pathways and functions within different types of plants. If you decide to use herbicides it is important that you know both your target weed and the chemical well so that you minimize the herbicide use. It’s always important to READ THE LABEL before you purchase the product (most labels are online). Be certain that the product is suitable for your weed and your site and follow the rates set on the label. More is NOT better. Making the solution stronger can actually make it less effective and uses too much product. Consider the label as a legal document – it’s the law to follow those directions. Please don’t forget to protect yourself: long sleeves/pants, waterproof gloves and boots and eye protection at least. Herbicides advertised as “natural” can be dangerous too, sometimes even more hazardous to you than conventional products, so do protect yourself. 

Different needs with different weeds. Consider your personal threshold for this weed. Is it overtaking your garden or making problems for neighboring property? Could it poison your animals? Is it that you just don’t like it? Most of the time a more realistic goal will be reducing weeds to a more acceptable level over a longer term rather than eradicating them in one pass. If it’s a really large and daunting patch, think about smaller patches where you will not tolerate the weed at all and then clip back other areas to keep them from spreading until you can get them under your full attention. The exception to this could be in the case of certain state or county-listed Noxious Weeds, where control or eradication is mandated by Washington State Noxious Weed Law, Chapter 17.10 RCW.

Consider also what you want to put in place of the weeds removed. Nature is not fond of a vacuum. If you don’t pick out a plant to take the place of the weedy ones you just managed, Mother Nature will pick one out for you.

Follow up. One round hardly ever does the complete job, whether you’re hand-pulling, cutting or using herbicide. This is a longer term project. Keep an eye open for new plants and dig in!

Weed Wrench Loan Program

Have Scotch Broom? The Whatcom County Noxious Weed Board has a loan program for specialized tools called the Weed Wrench™, the Extractigator™ and the Uprooter™. Landowners in Whatcom County may borrow these tools for a week at a time at no cost. The tools are especially useful in removing scotch broom plants, but can also be used on small trees or other woody plants such as Himalayan blackberry and spurge laurel.

If you would like to try out a Weed Wrench or Extractigator, please call the Weed Board office at 360-778-6232 or 360-778-6234 to reserve one for pick up.

Online resources

See Whatcom County’s Noxious Weed information at www.whatcomcounty.us/914/Weeds. Information includes:

• What Are Noxious Weeds?

• Current Weed List

• Noxious Weed Class Definitions & Criteria, and Fact Sheets

• Noxious Weed Education & Resources

• Publications and Public Service Announcements

• Whatcom County Weed Map (PDF)

• Boat Inspections

• Report Noxious Weeds and more

Skagit County information is online at www.skagitcounty.net/Departments/NoxiousWeeds/main.htm.

Laurel Baldwin is a lifelong botanist and gardener specializing in invasive plants. She has been Program Coordinator for the Whatcom County Noxious Weed Board since 1989. She welcomes your questions, so please contact her by email at: LBaldwin@co.whatcom.wa.us or by phone at 360-778-6234.