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Tech Tuesday
It's the Site, Not the Mode

It's the Site, Not the Mode

I guess I've had it wrong about battling weed resistance.

Okay, mea culpa, but for years I've kind of harangued readers about the importance of battling resistant weeds and the phrase I always use is "mode of action" as in, you need to be sure your weed control program involves different modes of action.

Of course during Commodity Classic a few weeks back BASF showed me that it's "site of action" not "mode of action" that really matters. In fact you could be changing up mode of action only to keep hammering the same part, or site, in the weed. It's kind of amazing.

SITE OF ACTION: Avoiding resistant weeds - like these Palmer amaranth - will require you to choose crop protection products in new ways.

If you spend some time looking up site of action on the Web, there are some great resources. Our friend Bob Hartzler has a good one that details the site of action and the herbicide. For example, you may think changing from a sulfonylurea to an imidazolinone - say from Classic to Lightning - means you're mixing it up. In fact, both are ALS inhibitors, so you'd be attacking the weed at the same site with two different products. That's how resistance is born.

BASF recently redid it's jug design to include the group number for the site of action for each of its herbicides. That information is available for any product you buy, perhaps in the product label, but putting it right up front is a different approach.

So Armezon, a new product for 2013, carries a 27 on the front, which means it is an HPPD inhibitor, with a "pigment inhibitor" mode of action. You'll find that Balance Flexx and Callisto are also in the 27 group.

So why should you care?

Hammering away at the same site of action with different chemicals is only going to broaden your resistance worries. Sure glyphosate gets a lot of attention, but there are waterhemp plants with three- and four-way resistance that have been found in southern Missouri - they resist ALS inhibitors, glyphosate and PPO inhibitors.

This never-ending weed resistance management issue is just that - never-ending. Doesn't mean you can't control weeds, it just means you'll want to quiz your agronomist and crop protection supplier to make sure you're mixing up those sites of action as much as you can.

BASF, which is promoting its range of sites of action offered,  has information at its site You can learn more there. Crop protection companies are telling this story and many have a range of products to offer you site-of-action options. Talking with that agronomist early will help with your 2013 control program.

It's a tech lesson we can all pay attention to. So I got it wrong in the beginning, but this old dog is learning new tricks every day.

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