When it comes to weed management, what’s below the surface is often more important than what is above it.
There are two main types of roots: taproots and fibrous roots.
Controlling a taprooted plant is fairly straightforward — just yank it out of the ground. As long as the root crown is removed, or the first 4 inches of the root, it won’t grow back.
Examples of noxious weeds with a taproot are: musk thistle, common mullein, common burdock and salt cedar. Field bindweed also has a taproot and the above-ground portions of the plant are connected to rhizomes, or underground stems. When pulling a 3-foot section of field bindweed root from your garden you may feel the thrill of victory, but the main root is still lurking deep below the surface.
Fibrous roots may be very simple or complex. Some fibrous roots are shallow and easy to pull, like in the case of cheatgrass. Other fibrous (also called adventitious) roots may be attached to rhizomes, which complicates the issue. Plants like leafy spurge, Russian knapweed, Canada thistle, yellow toadflax and oxeye daisy form a colony of aboveground shoots connected underground via rhizomes — much like an aspen grove. The rhizomes are lined with buds, and any disturbance to the root system will actually trigger more above-ground growth. Any mechanical control must be done with diligence over many years to finally sap the energy from the root reserves and starve the plant.
When controlling plants with herbicides, it’s important to know the flow of nutrients. Nutrients move from source to sink. Sugar created in the photosynthesizing leaves is transported to either new growth, flowers or the root system depending on the time of year.
For annuals and biennials, the root system is built up after germination and then all of the energy goes to creating mass and flowering before the plant dies after seed production. Once an annual has produced a bloom and is near seed set it is best to pull it. Biennials have a slight intermission, and only form vegetative mass the first year and then go dormant during the winter. During the second year, energy is flowing up the root into the newly grown tissue. Biennials will enter a vegetative phase before flowering. After producing seed, they will die naturally.
Perennials may live and flower for many years. Short-lived perennials may live for as little as five years, while longer-lived perennials can live for decades. Russian knapweed colonies can survive for upward of 75 years. New seedlings can be hand-pulled, but in the case of Canada thistle, a seedling is considered perennial after 2.5 weeks, meaning it has enough root mass that anything left behind will generate a new plant.
Creeping perennials can often survive a spring treatment as nutrients are flowing upward from the root and the herbicide will not be translocated outside of the foliar tissue. Depending on the species and chemical used, creeping perennials can be treated between full vegetative growth, bloom or a fall treatment. In the fall, the plants are moving nutrients into the roots in order to overwinter and a greater rate of success can be achieved.
Archuleta County Weed and Pest is your local resource for managing noxious weed populations and controlling other pests.
CPR and first aid classes
CPR and first aid certification classes are offered every other month at the CSU Extension office, generally on the second Monday and Wednesday from 6 to 10 p.m. The cost for the classes is $80 for combined CPR/first aid and $55 for CPR, first aid or recertification. Call the Extension office at (970) 246-5931 to register.
Check out the online option on our website, https://archuleta.extension.colostate.edu/.
