Measurement mistakes add up

Throw away old tubes used to measure dry flowable pesticides. Invest in an inexpensive scale.

“When you’re measuring product in ounces per acre, a 20% error either way is a big deal,” says Fred Whitford, Purdue University coordinator of Pesticide Programs. If the error means you apply less product than required, you risk not controlling weeds. You may need a follow-up treatment. And if the error means you’re applying too much, you’re wasting money and putting extra pesticide into the environment.

Key Points

Pesticide measurement tubes can be off as much as 20%.

Don’t use tubes intended for one dry product to measure another dry product.

A simple scale for measuring products could be a wise investment.


Whitford discovered most tubes shipped with dry flowables aren’t 100% accurate. If you’re using a tube designed for liquids to measure a dry product, you won’t even come close.

Why a scale?

Manufacturers make tubes specifically for each dry product. However, Whitford is aware of instances where the manufacturer didn’t include enough tubes in shipments. Insist on receiving a tube shipped with that product.

Measuring dry products is all about weight, Whitford insists. A tube for one dry product will give different results with a different dry product. Think of flour and sugar. The same volume of both products won’t weigh the same. If you poured the same weight of each into the same tube, they would be at different levels.

Tubes bear the product name and instruct you to use it only for that product. This year’s tube may not work for the same product next year.

“My advice is to throw out tubes and invest in a scale,” he says. “When you’re dealing in ounces per acre, it’s easy to be off unless you weigh it. Even the manufacturer indicates on tubes ‘for accurate measurement, use a scale.’ ”

Perfect storm

Whitford knows herbicide resistance is an issue. Bill Johnson, Purdue weed control specialist, has clearly shown it’s a problem. However, Whitford says every case of poor weed control isn’t due to resistant weeds.

“If you don’t measure the amount of product correctly, and you’re light on ounces per acre of product, you’re setting yourself up for subpar control,” he notes. Suppose environmental conditions aren’t favoring weed growth, your calibration is off and you don’t choose nozzles that deliver necessary coverage. More trouble brews.

Then add in water quality, Whitford notes. With pH and water hardness being less than ideal, one error builds upon another. “You can have the most expensive sprayer, but it’s negated if little things that affect what’s in the spray tank aren’t addressed,” he says.

You could have a “perfect storm.” A string of factors could line up that all favor poor control or more costly control of weeds. Then if you’ve got weeds that the product controls marginally anyway, even though they’re not resistant, the scales could tip toward poor control and weed escapes.

Whitford’s point is simple. Don’t automatically assume a weed breakthrough ties back to resistant weeds. Retrace every step of the application process. A good place to start is making sure the pesticide was measured correctly, he concludes.

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Right tube: Use the right tube for the right product, Whitford says. Better yet, use a scale instead.

This article published in the February, 2012 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.