OUTDOORS: Are all weeds undesirable?

Weeds can either be annuals or perennials. A few are even biennials such as common mullein. Because of our abundant winter snows and rains, we are seeing the emergence of overwhelming numbers of weeds. I am not going to go into great detail on the weeds that are making their presence known right now. That’s because I already published an article in my column covering my “Ten Most Unwanted Weeds'' in the Delta County Independent a few years back.

But I thought a few comments might be in order on seven weeds making their presence known now. These include the annuals: blue mustard, flixweed, cheatgrass, dandelions, and redstem fileree; and the perennials: whitetop and field bindweed.

My first weed, blue mustard, has been putting on a spectacular floral display this year. I have seen pastures with acres upon acres of this flowering forb blanketing the ground. Their lavender (blue/purple) flowers are quite attractive. And their leaves are quite edible. This weed was introduced from Eurasia and can grow in rather poor soils. Their seeds germinate in late fall to early winter but are so inconspicuous that most folks never know they are there until they begin to grow again and flower in the early spring.

I might keep this weed in more natural areas of my landscape as long as it didn’t get out of bounds or into areas that were more highly managed. This is an easy weed to control with either a post emergent spray of 2,4-D or a pre-emerge in the fall such as Preen® or another commercial trifluralin herbicide.

Flixweed is another mustard making a strong appearance this year. It is taller than blue mustard and has yellow flowers. It too was introduced from Eurasia and is somewhat toxic to cattle. The same control strategy as given for blue mustard would work here but a pre-emerge herbicide would need to be applied in the very early spring.

Cheatgrass is almost considered a dirty word or at least it will elicit words I cannot print here. Again it too was introduced primarily from Eurasia but unlike the forbs I have discussed, it has no redeeming qualities. It is also known as downy brome and as a winter annual its seed germinates in late August into September.

A pre-emerge herbicide application is the best control available short of doing a lot of weed pulling in the spring. But this must be done in the fall. Cheatgrass matures and dries out in the late spring and early summer and becomes a major threat concern as fuel for wildfires. It outcompetes native range grasses, replacing them with a less desirable grass. It is a noxious weed in the intermountain west and Colorado classifies it as a category C noxious weed. 

Redstem filaree is in the geranium family of plants growing as a relatively flat rosette with finely divided leaves like a fern. Flowers are a pretty lavender color. It was introduced from Eurasia and is classified in Colorado as a noxious, invasive weed in category C. It does provide a valuable source of nectar and pollen for bees. So it isn’t all that bad in limited numbers.

Dandelions are one of my favorite weeds. Their flowers add early color to an otherwise green landscape. It too is from Eurasia. Dandelions provide an important early source of nectar for bees before fruit trees begin to bloom in our orchards. I allow dandelions to flower in my yard in the early spring but then use a pre-emerge herbicide to prevent secondary colonization from their seed. Its leaves can provide a nutritious addition to a salad.

Two perennials that I wish I didn’t have are whitetop and field bindweed, both with extensive root systems. Whitetop, also known as hoary cress, is just beginning to bloom while field bindweed is still a few weeks away from its first flowering. These two were introduced from Eurasia and are hard to eliminate. Field bindweed is rated as a category C noxious weed in Colorado while Whitetop is a category B.

Hand pulling is never going to eliminate these two perennials and even herbicides require multiple applications. Glysophate and 2,4-D are herbicides that are often used against these weeds. I usually mix the two, each at below maximum labeled rates in the mixture to prevent burndown. Both weeds can arise from their prolific seed or from their roots, even root fragments. Hand pulling is necessary in flower beds. Soil solarization is a possibility in some cases.

I guess you might have noticed that these weeds were all introduced from Eurasia. Folks coming from over there didn’t do us any favors! These plants are generally invasive and some are very hard to control, much less eliminate. But others are providing attractive floral displays and can be an early source of food for pollinators. So not all weeds are completely bad.

Jim Leser retired to Cedaredge in 2007 after a career with Texas A&M University Extension in entomology. He is a current member of the Cedaredge Tree Board and has been a Certified Colorado Gardener since 2008.