Musk Thistle Management Action List

Calendar of thistle and Weevil Activity

 

January

Musk thistle head weevil overwinter in rosette

 Rosette weevil larval damage can be detected in the thistle rosettes.

 

February

Biennial musk thistle begin to emerge.   These plants will not begin their reproductive (bolting) until next spring.

 

 

March/April

Thistle that have overwintered begin their upright reproductive growth (bolting).

Now is the time to control problem areas with herbicides

 

Now is the time to control problem areas with herbicides

 

 

May

Purple to red flowers  indicate musk thistle is in full bloom.

Head and rosette weevil adults emerge and feed on thistle. Head weevils are laying eggs.  Collect weevils now for redistribution in other fields.

 

June

  Head weevils are feeding on the seeds in thistles heads.

 

July / August  

Musk thistle seeds are being dispersed by the wind.

Head weevil pupae and empty pupae chambers can be found in the thistle heads.  New adult weevils have moved into the ground until spring.  If at least half of the thistle heads in the fields have four to six pupae per head, there will be enough adults to collect and in the spring. 

  

September

Annual musk thistle begins to emerge. these plants will not flower until the spring.

 

October

Rosette weevils are laying eggs on the thistle seedlings 

 

November

Musk thistle overwinters as a rosette.

 

December 

Rosette weevils (eggs , larva, adults) and adult head weevils are hibernating until late February.

 

 

Table 1 Herbicide recommendations for control of invasive thistles in Oklahoma.

(Recommendations for controlling Thistles)

^a 2,4-D, GrazonNext®, Grazon P+D and Weedmaster® are labeled for pastures and rangelands. Escort®, Transline® and Vanquish® are labeled for non-cropland. Grazon P+D is a restricted use pesticide. Read labels for specific information and guidelines prior to using the product.

^b Check your dealer for updated prices.

^c Control includes killing the actively growing plant and preventing it from producing seed. Best results are obtained with spring applications, so that fall and spring emerging seedlings are actively growing at the time of treatment. B = bull thistle, M = musk thistle and S = Scotch thistle.