By Ben Bain
After one of the driest years on record, we experienced one of the wettest winters. What does it mean for vegetation and weeds this summer?
The good news is that there will be a lot of native plants and grasses filling in bare areas created by the drought. The bad news is there will be just as many non-native invasive plants coming in as well.
If you have been paying attention recently, you may have noticed that it was a banger spring for cheatgrass, mustards and other annuals. By now, it’s too late to control many of these plants. Your best bet is to either mow or spray unseeded plants or bag the heads of those already seeded, since they have already reached the end of their life cycle.
However, there is already another wave of weeds coming up that will be a force to reckon with. There have been large amount of kochia and Russian thistle (tumble weed) popping up with ground cover similar to carpet. Also, musk thistle is thriving and will need to be controlled as soon as possible. Although some of these plants may be smaller and blend in with the rest of the vegetation out there, they will be quite noticeable soon. You shouldn’t wait until they are huge and flowering to control these weeds because it will likely be too late by then and the plants will seed out.
Most weeds are much easier to kill with herbicide when they are relatively small. Once the plant gets more than 1 to 2 feet in height, herbicides have a weaker effect and may not kill the plant. If the plant survives, it will seed out and may become resistant to that herbicide in the future. There are many kochia populations that are resistant to glyphosate now.
When spraying, timing is the biggest factor for effective treatment, along with the right product and concentration. I know some people think that if the weeds are bigger they just use more herbicide and ignore the label. There are many field studies that show using more than the recommend amount can be less effective at killing weeds and can damage desirable grasses, along with costing you more money.
Tillage is another activity that some might use for eliminating weeds. If timed right, tillage controls plants that reproduce by seed, but it also depletes soil moisture and leaves soil more vulnerable to wind and water erosion. If a deep-rooted perennial like Canada thistle is tilled, each root segment will grow into a healthy plant and ultimately come back stronger. Mowing can be effective with annuals and biennials only if one repeatedly mows low to the ground because the plant will try to flower after being cut. Or if you have just a few, you can dig up those plants.
Heed my warning! We will see weeds over 6 feet tall sooner than later. Need help? Call or email me.
Ben Bain is the weed control coordinator for La Plata County and is located at the Colorado State University Extension Office at the La Plata County Fairgrounds. Reach him at ben.bain@co.laplata.co.us or 382-6470.
