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Tuesday, June 12, 2012

Donkey thistle control

Using donkeys to reduce plumeless thistle infestations in pastures

Vince Crary and Carlyle Holen, PhD, University of Minnesota

Plumeless thistle is the most common species of thistle infesting NW Minnesota pastures. In overgrazed pastures this plant often forms dense patches that limits cattle feeding and reduces pasture productivity. Plumeless thistle infestations can be reduced over time with annual applications of herbicides; however, access by spray equipment to many pastures is limited by steep slopes, rocks, trees, water and other physical barriers.

The purpose of this research was to evaluate the effectiveness of donkeys in reducing plumeless thistle infestations in established pastures. In 2003, a three year study was established in a grass pasture with moderate to heavy plumeless thistle populations at Deer Creek, MN. Treatments consisted of 1) one donkey and one cow/calf pair and 2) two cow/calf pairs.

Some of the observations about feeding preferences include:

  1. There are differences between donkeys in their preference for consuming plumeless thistle blossoms. All donkeys in the project grazed on plumeless thistle but some donkeys have a greater affinity for consuming thistle blossoms than others.

  2. Donkeys prefer blossoms over stems and leaves of plumeless thistle. Donkeys ignore the younger plants and do not begin grazing on plumeless thistle plants until blooms are present.

  3. Plumeless thistle plants with heavy grazing pressure are stimulated to continue to produce additional blossoms. Many of the later blossoms produced by the plant will not produce seed.

The number of plumeless thistle blossoms in sampling areas was reduced by 74% in 2003 and 87% in 2004 in the donkey treatment compared to the cattle grazing treatment. Plant height was reduced by 10% and 40% in the donkey treatment compared to the cattle treatment in 2003 and 2004, respectively. Some pastures may have plumeless thistle populations that are too high for management by donkeys. For more information, please contract Vince Crary at 218-385-3000 or Carlyle Holen at 218-281-8691.

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