After the recent years of drought, thistles have taken advantage of weakened grass stands and full-bloomed plants are visible in many fields through the area.
"Many tracts of land in Southwest Missouri are inundated with heavy populations of musk and bull thistles," said Tim Schnakenberg, an agronomy specialist with University of Missouri Extension. "Some landowners have taken extra steps this year to keep the problem in check, while others have done nothing."
As a reminder for all Missouri landowners, section 263.190 of the Revised Statutes of Missouri reads: "It shall be the duty of every owner of lands in this state to control all Canada, musk or Scotch thistles growing thereon so often in each and every year as shall be sufficient to prevent said thistles from going to seed."
"Thistle control can be very difficult but it is not impossible," said Schnakenberg.
Think before you mow
What is to be done at this point in time? Since the majority of the seed for the growing season is already produced, control measures at this time are after-the-fact. Most thistles are biennials, meaning they germinate in the fall, bolt with a seed head in the spring, produce seed and die by mid-summer.
"Since the plants that have seeded out are almost dead because of the proximity to the end of their lifespan, spraying is almost fruitless now," said Schnakenberg.
Mowing is the first impulse of many to control it now, but one risk of mowing is the spreading of the seed to other areas on the mower deck, making matters worse for the fall germination period. Sometimes this is what it takes however to clean up a mess.
Using biological controls
More than 30 years ago, University of Missouri Extension and USDA introduced the flower head weevil and rosette weevil to Missouri fields. These weevils specifically target thistles.