80 percent mature heads ideal time for pre-harvest glyphosate

Kernels at various times during grain filling. Left to right: kernel at watery ripe, kernel at late milk, kernel at soft dough, kernel at hard dough showing loss of green colour, and kernel ripe for harvest.  |  Michael Raine photos

Standing crops were barely standing Sept. 9 in the Pincher Creek, Alta., region after wet snow fell across the southwestern part of the province. | Tracy Glen photo
Standing crops were barely standing Sept. 9 in the Pincher Creek, Alta., region after wet snow fell across the southwestern part of the province. | Tracy Glen photo
I had an interesting question from a grower this week. The question was “What is the operation that if I screw up, costs me the most money?”

Basically, he was asking for an evaluation of his practices and suggestions on how he could improve. This is different from most questions from farmers.

Most want to know ‘What more can I do?’ rather than ‘What can I do better?’

I had to step back and give the question a little thought. The answer that would have rolled off my tongue, had I not known this grower would have been “Spraying herbicides too late.”

However, I have worked with this grower for a number of years and we had been down this road a number of years ago.

He sprays in a timely manner and, barring adverse, weather, completes his cereal herbicides by the four leaf stage and has both canola applications done before the cabbage stage.

So what other practices could he improve?

The number one place where farmers have hurt their yields over the past 10 years is, from my vantage point, preharvest glyphosate timing.

Early application will cause yield reduction, reduce bushel weight, kernel weight, protein and in extreme cases, reduced grades.

Early applications may also result in residues in the seed. Maximum residue levels (MRLs) usual target is to apply glyphosate at 30 percent moisture.

So what does this look like? Generally, the wheat crop must be in the hard dough stage. This is when the kernel has become firm and hard and a thumbnail impression re-mains on the seed. It is also the stage when the final weight of the kernel has been determined.

The other way of determining the proper staging is when the wheat reach physiological maturity. This stage can be determined when the peduncle changes from green to tan.

So this seems quite straight forward. However, there are a couple of complicating factors.

First, many fields are uneven this year. In many situations, one area of a field may be ready for pre-harvest application and other areas still immature.

The second factor is tillers. De-pending on growing conditions, planting density and varieties, tillering can be extensive. Tillers may come later in the season when some rain follows a dry period.

So how do you determine when the proper stage has been reached? The key is to get a representative sample of a field. I sample 10 areas of a field. I walk into a field past the headlands, double seeding and double fertilizer may give misleading information, and grab a handful of stems.

I examine each head and determine if it is physiologically mature. I then note the total number of heads examined and the number that are mature, for example 33/28.

After repeating this in the other nine areas, I tally the numbers and come up with a percentage of mature heads.

The number that I look for is 80%.

If there is a large area in a field that is immature, you may wish to spray only the most mature area and follow up in a week or so to pre harvest the remaining area.

Remember, you can’t rely on the colour of the field as an indicator.  Walk the field and sample representative areas to determine pre-harvest staging.

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