The Downside of the Roundup Price Decline
March 12, 2010
This year, there has been a sharp decline in the price of Roundup. This price decline might tempt you to go to a Roundup only approach by cutting out the use of a relatively “expensive” pre-plant or pre-emerge herbicide on your corn and soybeans just purely based on cost savings. However, this approach carries a lot of risk.
The main risk th
at comes with a total post program such as Roundup only, is that the timing of the application is critical. Now, you may say to yourself that you can get things applied as quickly as you need to, but there are many factors such as soil conditions, wind, temperature, and overall crop condition that can hinder proper application timing. This does not mean that you may not or cannot get done, what it means is that you have greatly increased your risk. With all of the large investments you have today from machinery, land, fertilizer, seed investment, and so on, it is very risky to not have weeds properly controlled. In reality, there are many methods to control weeds and it is relatively simple and inexpensive to do. So remember to look at the big-picture this year and not get caught-up in a few dollars per acre of cost savings compared to potentially hundreds of dollars in potential lost income.
Corn Requires Protection
The best method is having an aggressive early crop protection system in corn that keeps the field as weed free as possible all year long. Obviously
, weeds directly compete with the crop for water, sunlight, and expensive nutrients. This can harm the crop in many ways. As an example, corn begins to determine ear size as early as stage V6 (2-3 weeks after emergence) as the ear shoots are formed. Therefore keeping weed competition away from the plant at this time is crucial to yield potential.
Weeds affect the plants in less obvious ways. In a study done by Dr. Clarence Swaton at the University of Guelph, Ontario, corn plants with early season weed pressure grew 17% taller and had 10 to 15 percent less root mass. The results showed that the top growth came at the expense of root bio-mass. Later in the season when stresses are present this reduction in root growth restricted the ability of the corn plant to take up sufficient amounts of nutrients and water which ultimately sacrifice kernel fill and thus yield.
In a similar study on the effects of early season weed pressure done in corn fields similar results were found. Aside from the competition for required nutrients, space and water,
there is also the competition for light. Zea Maize (
Corn) is a photo-sensitive plant that responds to changes in the wavelength of the sunlight it receives. Some people believe that once the corn is taller than the weeds it’s in the clear and will shade out the weeds. The trouble with this belief is that when corn is in its early vegetative growth stages, biomass both above and below ground is directly dependant to the wavelength in light. When sunlight reflects off weeds below the corn to the corn leaves the wavelength of light shifts slightly more to the far-red in the spectrum. This causes biological changes in the plant that generate growth patterns to shift slightly. At this point the plant changes from producing equal amounts of above and below ground vegetation to producing more above ground and less root mass, not to mention the change in leaf orientation among the rows.
These studies highlight the impact on the corn plant itself, what they show is the hidden cost of weed competition. At the end of the day, the field may look clean after it is sprayed, but it is difficult to quantify how much yield and productivity were affected. So the key is to control these weeds all season long.
Don’t Forget About Soybeans!
In a study done in southern Illinois, researched showed that in soybean fields, for every inch of weed growth you can lose up to 0.7 bushel per acre. If you are timely on your first round of Roundup and spray when weeds are only two- three inches tall you already decreased your yield potential by 1.4 to 2.1 bushels an acre. That being said, at market prices around $10.00, that’s $14.00 to $21.00 an acre for making a timely application of Roundup.
Use pre-plant/pre-emerge products
Pre-emergence and pre-plant herbicides have added value to farming operations both economically and agronomically. The goal of these early season herbicide options is to provide multiple modes of action to prohibit the growth of weeds. These options also allow a larger window for application of post emergence chemicals. The class of pre-herbicides offer a systemic mode of action that prevents weed seeds from germinating and also attacks weeds already emerged through the roots to kill weeds. Roundup by itself has contact only control which limits the effectiveness to only emerged weeds.
There are many ways to easily and effectively control weeds and lack of proper control will lead to potential large yield decreases and increase your risk. The uses of pre-herbicides have a place both economically and agronomically in your operations. Proper weed control is a must for maximizing yield, and by applying pre-plant and pre-emergence herbicides you can reduce your risk and have a better chance in the weed battle this upcoming year. These herbicides allow great early season weed control along with increasing your window of opportunity and the effectiveness of post-emergence herbicides.
For more information on specific pre-plant and pre-herbicide programs contact your local FCS agronomist.
Nate Mayer
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