If I had a dollar for every time I shared or heard that old adage “Time is money,” I wouldn’t have been stuck in Iowa all winter. Time is always at a premium during planting season, and I have a feeling this season it’ll be even more valuable.
So what I’m going to say next may seem counterintuitive: Make time this spring to use residual herbicides. With the likely crunch ahead to get fields ready for planting, this advice may be hard to swallow. But in the long run, using a residual — the right way — on early-season weeds will make you more profitable.
I can hear some of the protests now: Why spend precious time applying residual herbicide when there are still crops to be harvested, nitrogen to be applied and new crops to be planted?
Why make two trips to control weeds when we have good postemergence herbicides and crops that can handle the weeds, especially glyphosate- and glufosinate-resistant crops?
Early competition hurts
First, early-season weeds compete with our crops for water and sunlight, and can consume valuable fertilizer intended for our crops. I don’t know about you, but recalling the fertilizer price spikes of the last few years makes me want to unleash herbicide vengeance on any weeds I see in a field. Come to think of it, after the winter we’ve just had, I don’t want to share any sunlight with weeds either.
Second, and perhaps more important, herbicide-resistant weeds are increasing in the Midwest. As she almost always does, Mother Nature found a way to beat our convenient postemergence-only system. Most notably in Iowa, common waterhemp and giant ragweed have documented glyphosate resistance, and we are pretty sure marestail will be added to that list.
We had a pretty tough time dealing with these weeds even before they were resistant to our big hitter. Using a residual herbicide with a different mode of action will help to contain these resistant weeds.
I can still hear some arguing: Why worsen the spring rush applying residuals when, most of the time they’re used, we still clean up with postemergence products anyway?
Reasons to apply residual
There are good reasons to use a soil-applied herbicide. For those of you who are still not convinced, here are two more reasons why residual herbicides are more important than ever:
• Saving time. Postemerge spraying season is now probably more stressful than the pre-emerge season used to be. Applying a residual herbicide, even at the lower “setup” rates promoted in herbicide-resistant crops, will buy you time. Expanding the postemergence spray window by a couple weeks can help with risk management.
Mother Nature is pretty stingy with good spraying days. With residual herbicides reducing weed pressure, the risk of yield loss is greatly reduced while you wait out windy and rainy days to get post herbicides applied. Remember, time is money!
• Better yields. Weeds take vital resources from crops. Residual herbicides reduce weed pressure, which reduces the resources lost to weeds.
Be selective with herbicide
Does every field need a residual herbicide? Probably not. Consider the following criteria to help decide which fields to spend the time and money on applying residual herbicides:
• History of weed escapes. If the field has had high weed pressure the past few years, it is a good candidate for a residual herbicide.
• Herbicide-resistant weeds. If you have them or suspect you do, remember the value of multiple applications and multiple modes of action to keep them in check. Residual herbicides are a cornerstone of managing resistant weeds.
• Problem weeds. Many weeds, even if not herbicide-resistant, are still hard to control. While this list could be endless, waterhemp, lambsquarter, velvetleaf and marestail come to mind. The right residual herbicide will offer valuable help with your problem weeds.
Before and after
With the great control that postemergence products provide, the preemergence products don’t have to perform perfectly. We can often get by with reduced application rates as long as the product has good activity on the dominant weeds.
If you don’t have the time and manpower to apply your own residual herbicides, consider a custom applicator. These professionals can cover a lot of ground with herbicides while you are planting. Remember, time is money, especially in the spring. So save time (and money) this season by making time for a dose of residual in your fields!
McGrath is the partner program manager and Extension agronomist for ISU’s Corn and Soybean Initiative.
This article published in the April, 2010 edition of WALLACES FARMER.
All rights reserved. Copyright Farm Progress Cos. 2010.