Community Agriculture Alliance: Bulbous bluegrass — a newer concern for landowners
July 13, 2017
Every spring presents a unique weather pattern and a corresponding unique set of plants that respond to that weather. Some years will see a particular plant flourish, while others lay low and wait for more favorable conditions to come along. This year has seen a tremendous increase in the spread of bulbous bluegrass in the Yampa Valley, and that should be of concern to anyone who owns pasture or rangeland in the area.
Bulbous bluegrass, or Poa bulbosa, is a short-lived perennial grass that grows quickly in the spring and completes its lifecycle prior to many of our other grass species. It has unusual features that make it distinctive: It has bulbs at the base from which it grows, and it produces seed-like bulblets that enable the plant to reproduce asexually.
The bulblet can germinate without a dormancy period, so if one falls to the ground, it can begin to grow immediately. This means = bulblets left intact in hay or dropped from the mouth of an unsuspecting animal can produce new plants quickly, enabling the plant to spread easily. The plant spreads so easily, in fact, it has recently been designated a List C Colorado Noxious Weed.
According to the United States Department of Agriculture, the grass was originally introduced to the United States as a contaminant of alfalfa and clover seed. Many trials have occurred since the early 1900s to determine how the grass may be used for lawns or other purposes, with results fairly consistently showing it was not a good choice for these situations. The spreading nature of the grass that made it a potential lawn and erosion control grass is also what makes it weedy in pasture situations.
Because the plant matures so early and provides little biomass, it is not a desirable plant for grazing situations. And, because it spreads easily, it can invade alfalfa, crops and pastures, displacing more desirable plants.
Control of bulbous bluegrass is difficult. Grazing the plant early can produce good results, since that is when the plant is palatable, and it keeps the bulblets from being produced. But overgrazing an area can lead to reduced vigor in desirable plants, giving bulbous bluegrass an opportunity to spread.
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Because the bulblets can produce a new plant when dropped on bare soil, mowing of the plant can actually spread its growth. Hand pulling can be effective where practical, but any bulb left in the ground will support a new plant.
Chemical control is also difficult, because herbicides used for control can harm desired grasses, but well-timed applications of certain herbicides have shown success. Sulfuron chemicals have shown some success in getting control of this plant when applied as a pre-emergent, and local anecdotal evidence shows pre-emergent herbicide Kerb® may be an effective tool against bulbous bluegrass. Official tests have not been conducted locally.
Glyphosate has proven useful in controlling actively growing bulbous bluegrass, so it is an option for infestations in Round-Up® Ready alfalfa or in other areas where the bulbous bluegrass is growing and desirable species are dormant.
Recognizing this plant now and taking care of small patches before they spread will help limit the foothold this plant will get in our area. And while we've seen a dramatic increase in it this year, hopefully, next year, we won't have conditions that continue to promote its spread.
Todd Hagenbuch is agriculture extension agent for Colorado State University Extension Office.