Julie Jones  |   December 5, 2011

Waterhemp has reported resistance to these 5 modes of action:

1)      Photosystem II inhibitors (Atrazine)

2)      ALS-inhibitors (Pursuit and Classic)

3)      PPO-inhibitors (Flexstar and Cobra)

4)      Glycines (glyphosate)

5)      HPPD-inhibitors (Callisto and Laudis)

 

Now, 2,4-D has become the sixth herbicide that waterhemp has become resistant to.

a)      In 2009, this resistant waterhemp population was 10X more tolerant to 2,4-D than non-resistant waterhemp

b)      In 2011, the resistant waterhemp was treated with a 64X rate of 2,4-D, and initially showed injury symptoms, but some plants recovered and produced seed

 

Some waterhemp facts:

a)      It is later emerging, sometimes after herbicide applications have been made

b)      Male and female flowers occur on separate plants, which allows resistance genes to quickly spread

c)      A single plant can produce over 1 million seeds

 

6)      To minimize the risk of herbicide resistant weeds:

a)      Rotate herbicides

b)      Tank-mix herbicides

c)      Use effective rates

d)      Use effective crop rotations

e)      Consider tillage

f)       Monitor changes in weed control

g)      Remove surviving plants

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