Farm Horizons, June 2012

It’s spraying time

By Myron Oftedahl, Farm Business Management Instructor, South Central College

It is that time of the year when the corn and soybeans need to be sprayed for weed control. By now, many fields have been sprayed already. With the advent of glyphosate-ready crops ,spraying became really easy, didn’t it?

There are some basics that we need to keep in mind. What weeds or insects am I actually trying to control? What size are the weeds? What stage are the insects in? What can I do to control drift or off-target movement? What is the cost? What are the benefits?

Let’s look at what weeds you are trying to control first. You need to walk or take a four wheeler out into the field to see what weeds are present. While glyphosate and all of its various forms seems like a miracle product, there are some weeds that it doesn’t control, such as dandelions or wild buckwheat. It may set them back, but they are still alive.

Now you need to know what size the weeds are, because this will determine the rate of product or what mixture of products you will need to use. I don’t usually carry a tape measure with me, but I know that the top of my instep is between 3 and 4 inches, my fingers are 3 inches long, and it is 8 inches from fingertip to my wrist. What are your measurements? Now you have something to compare to instead of looking at the weed and thinking that is only 3 inches tall when it is actually closer to 6 inches. Size matters when it comes to weed control.

Insects are something that you may not feel comfortable identifying, so get some examples and put them in a jar so that you can take them to your retailer or extension agent to identify. You need to know if this insect will do economic damage to the crop that you found it in. Aster leafhopper in alfalfa is not an economic concern, while potato leafhopper at sufficient levels can do a lot of damage. So, you need to know what insect it is, and you also need to know at what population you need to begin treatment. The threshold for soybean aphids remains at 250 per plant over 80 percent of the field.

Controlling drift can be done a number of ways; slowing down, reducing pressure, using drift control nozzles, lowering the boom height, using drift control agents, and just not spraying when the wind speed is over 10 mph.

One of the pieces of management information that you must know is the cost of the product and what surfactants need to be added. How can you control your crop budget if you don’t know the cost of the product per acre? Is it a justifiable cost? Is there yield data to back up the yield claims? With prices of corn and soybeans at these levels, you will see a lot of additive-type products claiming two- to six-bushel increases while costing a bushel per acre. Do you know why they typically cost a bushel per acre? Because the company knows that you will risk a bushel.

Sometimes it is not the direct cost that you need to be concerned with, but the indirect cost. Did you know that if you spray your soybeans with fungicide, your soybean crop is now at a greater risk for soybean aphid?

There is a naturally occurring fungus that will attack soybean aphid. If you sprayed a fungicide, you have just removed this natural control. Now you have added expense that you may not have budgeted for.

As you walk your fields this summer, pay attention to what is out there, what size is it, how many are there? Know what your options are; the decision is yours.

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