Weed control is important no matter what part of your land you’re working on. Spare time for digging up weeds is always limited, so focusing on weeds that are harmful to livestock or impact crop productivity is important. Here are a few weeds to be on the lookout for on your working lands.
Tansy ragwort (Senecio jacobaea) is a noxious weed that poses a serious threat to horses, cattle, and other grazing animals. Every part of the plant contains poisonous alkaloids that cause irreversible liver damage to livestock (and humans) when consumed.
Luckily, tansy ragwort is not difficult to identify once you get to know it. Tansy has bright yellow flowers arranged in flat-topped clusters. Its flowers begin blooming in July and last all the way through the summer.
Tansy ragwort is often confused with another plant also called tansy, common tansy (Tanacetum vulgare). Common tansy is a closely related weed, but it is not dangerous to livestock. Examining their flowers helps differentiate these plants. Common tansy’s flowers are button-like and never open, whereas tansy ragwort’s flowers have individual ray-like petals.
Tansy ragwort is tricky to control because each plant can produce up to 150,000 seeds annually. Most seeds fall within 30 feet of the plant, but some can move far and wide aided by wind, animals, or mowers. If you see tansy in the neighborhood, make sure your neighbors are aware of the problems associated with this weed and stress the importance of control.
Small patches can be hand pulled while wearing gloves. Spring is the best time to manually remove it. Mowing is not recommended since it will stimulate more growth. Don’t leave removed plants in pastures. Wilted tansy and tansy that is dried and baled in hay are equally as dangerous. Once tansy is dried and baled, livestock have a hard time distinguishing what to eat and are unable to avoid eating the tansy. The safest way to dispose of tansy ragwort is to put the dead plants into large trash bags and put them out with your regular trash.
The good news is that there are several biological control insects already in Oregon that help keep large infestation in check. The ragwort flea beetle (Longitarsus jacobaea), ragwort seed fly (Botanophila seneciella), and cinnabar moth (Tyria jacobeae) feed on tansy. Like other biological controls, these insects go through boom-and-bust cycles where their population (and ability to control tansy) will fluctuate greatly from year to year.
Depending on the size of the infestation and your situation, herbicides can offer immediate control. Remember to read and follow the label and wear proper protective equipment when applying herbicides. Its best to consult a weed treatment professional when considering this option.
Effective control of tansy ragwort may take several years, but it is well worth the trouble compared to vet bills or the loss of a family horse or show animal.
Creeping Thistle & Bull Thistle
Thistles are a prickly problem on agricultural lands across all 50 states. They are notorious for draining nutrients from soil, which damages pasture and crop productivity. They also soak up large amounts of water, which makes soil dry and increases the potential for erosion.
Thistles tend to spread quickly too. They attribute their success to the variety of ways their seeds disperse. Using wind, human, and animal traffic, thistle seeds can travel miles from the original source. Once thistle is in the neighborhood, you’ll likely see it on your land.
Two of the peskier thistles in Washington County are creeping thistle (Cirisium arvense) and bull thistle (Cirisium vulgare). Both plants look similar, growing to around five or six feet tall with intimidating, spiked leaves. They produce purple flowers around the middle of summer. Towards the end of summer, these flowers become seed producing machines. Individual plants can produce upwards of 1,000 seeds annually.
Preventing seeds from spreading is key to dealing with thistles. One of the best ways to do this is with routine mowing. While this may not eradicate the plant, it will prevent them from going to seed, preventing further spread.
Ideally, thistles should be fully removed to stop them from regrowing. Digging or hand-pulling plants in the spring before they produce seeds will provide effectively control. Be sure to remove the entire plant and its roots, especially paying attention to creeping thistle’s large taproot.
You may need to apply herbicides to help control an infestation. Its best to consult a weed treatment professional when considering this option.
Field bindweed (Convolulus arvensis) is one of the most common agricultural weeds in the Pacific Northwest and one of the most difficult to control. Sometimes called morning glory or creeping Jenny, it has a deep root system that competes with crops for water and nutrients. Its vines climb on crops and smothers them. Like many other agricultural weeds, field bindweed produces lots of long-lasting seeds – seeds can remain viable in soil for up to 20 years!
Since seeds survive in the soil for decades, total eradication is not a realistic short-term goal. However, with diligence you can control field bindweed by incorporating multiple treatment strategies. Using a combination of cultural (introducing competitive grasses), mechanical (consistent tilling, mowing, and hand-pulling), and chemical (applying herbicides) controls will help manage a field bindweed infestation.
Consult Tualatin SWCD for Help
Weeds on your working lands can be difficult to manage, but there are resources out there to help! Tualatin SWCD has a long history of working with farmers and ranchers to help manage agricultural weeds. Browse our Weed & Pest Directory to see control recommendations and identify other weeds on your property. If you’d like specific help or tips, let us know!