War against musk thistle requires new weapons

Marion County Noxious Weed Office

Sometimes it seems never ending, and in some ways it is. But there is very good news. Not only now but on the horizon.

I have been fighting the musk thistle battle for more than 25 years. Nothing has changed with the plant. It is still as prolific as in 1950 with a possible 10,000 seeds with over 90 percent viability per plant.

But I have seen infested acres decrease in Marion County in recent years due to new chemicals, insects and aggressive operators.

As I view large infestations, I am continually encouraged and amazed by the damage to the rosettes and seeds in the heads by the bugs.

Next time you see the purple heads nodding at you, look inside the head. Many of them will appear ?rotten,? which is the result of the insect. An infested rosette will appear healthy at first, then slowly yellow and die as if sprayed with chemical. The tap root will be ?rotten,? having been eaten by the insect.

In the early 1980s, Dow Chemical introduced a Picloram (Tordon 22k) label, which has proven to be a godsend against thistles. Being a restricted use herbicide, applicators were required to be licensed making it an ally in education, safety, stewardship and awareness of pesticide implications.

But with so many years of use comes the dreaded ?resistance? equation. We?re seeing more and more plants survive the traditional applications of 2,4-D, Dicamba (Banvel) and now Picloram (Tordon 22k).

It’s time to make use of new ammo for control. DuPont?s Metsulfuron Methyl (Escort & Ally) gets little attention but is extremely effective on musk thistle, shows no resistance and is a non-restricted use pesticide.

It can be used at the same rate of application from rosette to heads and works as a super ?rescue? treatment for areas that have gone to seed. It is available through the Marion County Noxious Weed Office at cost-share prices.

Two years ago Dow Chemical introduced a new formulation called Milestone (Aminopyralid). It is a non-restricted-use herbicide. Last year I did two test plots with very impressive results.

A fall application of Mile?stone was applied on an infestation so thick there was little grass. When returning in spring for follow-up no thistles were found.

Milestone is not available for cost share through Marion County at this time because of the high cost per gallon.

DuPont is also coming out with a new herbicide formulation which looks very promising for musk thistle. So as you can see, there are many weapons for the war on musk thistle, which are welcomed in these trying economical times and keeps you on the ?good neighbor? list.

Rollin Schmidt is the director of the Marion County Noxious Weed Office.

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