Old World Bluestem control in Kansas grasslands

Old World Bluestem (OWB) is a name collectively used to refer to Caucasian bluestem [Bothriochloa bladhii (Retz.) S.T. Blake] and various cultivars of yellow bluestem [Bothriochloa ischaemum (L.) Keng] including Turkestan bluestem and King Ranch bluestem. 

These species were introduced into the U.S. for conservation purposes and as a forage crop for haying and grazing. In recent years OWBs have been used commonly in the southern Great Plains (Oklahoma and Texas) in grassland plantings and on Conservation Reserve Program (CRP) acres, but are not recommended for use in Kansas. Seedings of Old World Bluestems in Kansas probably started during the 1930s and continued to some extent into the 1960s. Although a number of species are called bluestems, OWBs are not closely related to the native grasses little bluestem and big bluestem.

Old world bluestems are aggressive and prolific seed producers. They are adapted to high calcareous and high pH soils, and do well on any well-drained soil. Today, OWBs can be seen along roadsides and are increasing in our native grasslands. The invasive nature and lower palatability of OWBs allows them to increase once established. Left uncontrolled, OWBs have the potential to dominate our grasslands.

The OWBs are just starting to shoot seedheads in late July. During the growing season OWBs are a light green color and easy to recognize (Fig. 1).  In the dormant season OWBs turn to a light straw color (Fig. 2)

Figure 1.  Caucasian bluestem (light green grass) spreading up draw in Riley County. Photo by Walt Fick, K-State Research and Extension.

Figure 2. Old World Bluestems turn to a straw color in the fall. Photo by Walt Fick, K-State Research and Extension.

Previous research

Early screenings of various grass control herbicides applied at the 4- to 5-leaf stage of yellow OWB by Keith Harmoney at the KSU Agricultural Research Center-Hays indicated that glyphosate and imazapyr provided greater than 90% control of OWB 9 weeks after treatment. One year after treatment, the frequency of OWB in imazapyr-treated plots was less than those treated with glyphosate. In a subsequent study, applications of glyphosate and imazapyr were applied at the 4- to 5-leaf stage and again 8 weeks later to Caucasian bluestem. Glyphosate applied at 1 lb/acre at each application reduced the frequency and tiller density of Caucasian bluestem. Imazapyr at 0.25 lb/acre at each application also reduced the frequency of Caucasian bluestem 1 year after treatment. Both herbicides also controlled remnant native vegetation.

I conducted a study in Ellsworth County to determine the efficacy of glyphosate and imazapyr for Caucasian bluestem control and determine the impact on native vegetation. Treatments were applied at the 4- to 5-leaf stage. Glyphosate at 3 lb/acre and imazapyr at 1 lb/acre both provided greater than 90 percent control of Caucasian bluestem one year after treatment. Native warm-season grasses were nearly eliminated by glyphosate, but were more tolerant of imazapyr.

Recent research

In 2014, I initiated studies to determine the rate effect of imazapyr on Caucasian bluestem control and monitor impacts on native vegetation. Herbicide treatments were applied at two locations in mid-June, 2014 and were evaluated one year after treatment. The Chase County site was burned in 2014 and 2015. Compared to the original cover, OWB declined, warm-season grasses increased in cover, and bare ground increased at imazapyr rates ≥ 0.75 lb/acre (Table 1).

The Riley County site was burned in 2014, the year of herbicide application, but was not burned in 2015. A good rate response was measured with imazapyr (Table 2). Warm-season grasses were ≤ 8% of the cover. There was a dramatic increase in forbs, even on the untreated plots. The lack of a prescribed burn in 2015 and a wet spring contributed to an increase in annual broomweed and marestail. Bare ground also increased following application of imazapyr.

Figure 3. Imazapyr applied June 13, 2014 at the rate of 0.35 lb/acre. Photo by Walt Fick, K-State Research and Extension.

Figure 4. Imazapyr treatment 3 months after application. Green grass is predominantly native warm-season species. Photo by Walt Fick, K-State Research and Extension.

Summary

Old World Bluestems are an invasive species in Kansas. It can be controlled, but control becomes progressively more difficult and expensive the longer the grass is allowed to grow and spread. Burn or mow OWB prior to herbicide treatment to remove old growth and increase herbicide uptake. Broadcast applications of glyphosate at 3 lb/acre and imazapyr (Arsenal) at 0.25 to 0.5 lb/acre can provide control of OWB. Spot treatment with 1-1.5% glyphosate or 0.25% imazapyr (Arsenal) is recommended. 

Remember, one application will not solve the problem. Wiping or wicking glyphosate can be done, especially when OWB is taller than associated species. Tillage and planting of Roundup Ready crops is an option on areas previously cropped and dominated by OWB. 

Walt Fick, Rangeland and Pasture Management Specialist
whfick@ksu.edu