Research Findings on Chemical Control of Cottonwood

Cottonwoods
Figure 1. Cottonwood infestation in sub-irrigated meadow. This photo was taken during the period of high water table in early spring. (Photo by Stevan Knezevic)

Research Findings on Chemical Control of Cottonwood May 22, 2018

Cottonwood (Populus tremula) is a common tree species across the Midwest. Near rivers, streams and lakes it provides many benefits such as stabilizing river banks and providing wildlife habitat; however, cottonwood also can be considered an invasive species (i.e., weed), as it is characterized by vigorous colonization of areas. Sub-irrigated meadows are one of those areas where cottonwood acts as a weed and reduces the quality of grassland (Figure 1).

Due to a lack of information on the effectiveness of herbicides for cottonwood control, a study was conducted in 2016 and 2017 to test eight herbicides:

  • 2,4-D amine (64 oz/acre),
  • Ally XP® (metsulfuron methyl [2 oz/acre]),
  • Grazon P+D® (picloram + 2,4-D amine [4 pts/acre]),
  • Clarity® (dicamba [32 oz/acre]),
  • Telar®/Glean® (chlorsulfuron [2 oz/acre]),
  • Cimmaron Max® (metsulfuron methyl + dicamba + 2,4-D amine [4 pts/acre]),
  • Picloram 22k® (picloram [3 pts/acre]), and
  • Stinger® (clopyralid [1 pt/acre]).

Trees were sprayed at full foliage (early June). Tree size ranged from 1 to 5 feet.

Results

Cimmaron Max®, Grazon P+D®, and Picloram 22k® provided excellent (100%) control that lasted for more than one year (Table 1). Ally XP® and 2,4-D amine provided fair control (70-76%), while Clarity®, Telar®/Glean® and Stinger® provided very poor (20-33%) control of cottonwood throughout the observation period.

Effective control of cottonwood by picloram-based products (Picloram, Tordon, and Grazon P+D) is not surprising, as picloram is generally known to be effective on woody plants. Despite its effectiveness on cottonwood, we do not recommend using picloram in sub-irrigated meadows as picloram tends to leach through the soil profile and potentially could contaminate high water tables. In fact, the labels for picloram-based products clearly indicate that use should be avoided on soils that are very permeable (textures of sandy loam to sand) throughout the entire profile and which also have an underlying shallow aquifer such as a sub-irrigated meadow.  

Table 1: Herbicide efficacy for control of cottonwood
HerbicideRate / acre% Control
51 DATa
% Control
111 DAT
% Control
463 DAT
2,4-D amine 64 oz 73 70 76
Ally XP 2 oz 80 60 70
Grazon P+DB 4 pts 100 100 100
Clarity 32 oz 33 20 33
Telar/Glean 2 oz 43 27 36
Cimmaron Max 4 pts + 1 oz  100 100 100
Picloram 22kb 3 pts 100 100 100
Stinger 1 pt 27 20 30
a Days after treatment
B Note: Do not use Picloram 22K or Grazon P+D on pastures with a high water table.

It’s important to know the depth of the water table beneath your pasture before using any picloram-based product. In pastures with a higher water table, Cimmaron Max should be used instead.

Metsulfuron-methyl (Ally XP) applied alone provided fair control of cottonwood, however, excellent control was achieved when it was mixed with 2,4-D and dicamba (Cimmaron Max). Metsulfuron-methyl is a systemic herbicide with residual activity, known to be effective for controlling perennial species with underground stems or suckers, such as cottonwood. Effective control of the suckers will prevent regrowth of a sprayed cottonwood. Metsulfuron-methyl based products are also safe on grasses.

These results indicate there are few excellent herbicide options for cottonwood control in Nebraska pastures, for both sub-irrigated meadows and higher grounds.