What a difference year makes! Last year we prayed for rain that never came. This year is quite the opposite. Abundant winter snows and spring rains have resulted in a profusion of weeds.
But what is a weed you might ask? Well the answer is a simple one. A weed is a plant growing where you don't want it to grow. Those volunteer Siberian elm trees seem to spring up everywhere, especially where they are unwanted. You should expect many. Many elm seedlings this year with the abundance of moisture for germination.
But doesn't that field or highway median filled with purple flowers look absolutely stunning? Well yes and no! As long as these blue mustard weeds (they're purple, why are they called blue mustards?) are on someone else's property, far enough away that their seed won't make their way into my yard, then yes, they are pretty.
The same could be said about those pastures filled with white flowers. When I moved to my newly build house I had a drop dead beautiful slope filled with these white flowering plants. I thought, these are keepers. But my neighbor informed me they were a major weed pest and she would appreciate it if I removed these weeds as a potential seed bank, to spread havoc onto her yard.
If you haven't guessed already, I've been talking about hoary cress, better known as whitetop. This weed, along with field bindweed are perennials, meaning they have a very well developed root system from which new growth springs up each spring. While both of these weeds produce copious amounts of seed, it is their extensive and deep growing root system that causes us problems with control.
So how do you control these two perennial weeds? You want to use a herbicide that is translocated into the below ground root system. This calls for the use of the glysophate herbicide marketed in several formulations by several companies. Roundup is the ubiquitous name given to all glysophate formulations but only refers to one company's trade name product. I would mix this herbicide with 2,4-D and a surfactant (a spreader-sticker) to increase coverage. I often use a teaspoon of dishwashing soap per gallon but you can also purchase a commercial formulation of a surfactant. Don't max out the rates on both chemicals or you will impede the movement of the gysophate into the roots.
The blue mustard is an annual and totally dependent on its seed to perpetuate itself into future years. Just using a 2,4-D herbicide is sufficient if you add a surfactant.
Another troublesome annual is downy brome or cheatgrass. This is the bane of native pastures and rangeland. This weed is easy to control but we'll take a different tact with it. For this weed we'll use a pre-emerge herbicide, one that prevents the emergence of this weed once the seed germinates. But unlike most annuals in which a pre-emerge herbicide would be applied in the early spring, this one germinates in the late summer to fall period. So you'll need to apply this herbicide in late August. This herbicide comes as both a liquid and a granular formulation. Both need to be watered in following application. Trifluralin is available as Preen® but also as Trifluralin. A liquid pre-emerge herbicide formulation, such as oryzalin or Surflan® could be used as well.
With recent rains, annual weeds are easy to pull. But pulling perennial weeds with extensive root systems is a waste of time and in fact makes the situation worse. Oftentimes a pulled perennial weed reacts by sprouting in even more places than the original one. The only caveat that I would give is that removing flowers from perennial weeds at least prevents adding to their seed bank.
Jim Leser retired to Cedaredge in 2007 after a career with Texas A&M University Extension in entomology. He is a member of the Cedaredge Tree Board and a Colorado Master Gardener.