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To Fertilize and Spray For Weed Control, Or Not To, That Is The Question

Posted Sep. 1, 1996

Many years ago Gary Simmons, then a NF Soil Fertility Specialist, reported some relative yields from common bermudagrass with weed control and nitrogen (N) application (Table 1). Later we did a more comprehensive research trial that included nitrogen rates, dates, and sources (Tables 2 & 3). Jerry Rogers and Wadell Altom also have other N response data.

The production benefits of 34-0-0 versus 28-0-0 are well illustrated by the fact that 28-0-0 produced only 38% the efficiency (lb. of grass/lb. N) in the study of Table 2 whereas it produced 80% of 34-0-0 in the study of Table 3. The 34-0-0 won in all cases.

Weed control with a water solution plus surfactant was 100% whereas weed control with 2,4-D mixed in the 28-0-0 liquid ranged 93% to 98%. The grass production benefits of using 2,4-D (or other modern herbicide) are well shown. Where there is a serious weed problem, as in these cases, the elimination of weeds plus the application of nitrogen fertilizer on the introduced grass produces tremendous results. 2,4-D weed control added an average of 22% to bermudagrass production when coupled with a nitrogen application. 34-0-0 at 50 N/acre with 2,4-D produced 82% more grass than the fertilizer alone. Weed control sharply increased nitrogen efficiency. There are numerous post-emergence herbicides for pasture available today: 2,4-D formulations, Banvel, Weedmaster, Grazon P+D, Amber, and other special use ones.

Where is our mind set? What are these things called weeds? What if they are nutritious and edible by beef cattle? Are they then forage? Yes! Is "weed" production bad then? Maybe not.

The study reported in Table 1 was with western ragweed. Table 2 results reflect marestail, western ragweed, poorjo, bitterweed, and bagpod. Only bitterweed and bagpod are relatively inedible or toxic. So, they probably do need the "deep six." But, the others can be biologically controlled, over time, by timely high density rotational stocking (grazing). We have done it many times. A few "weeds" in the paddocks is not aesthetically displeasing – if we understand the biological and economic dynamics of it.

It costs $8.00/acre, plus or minus $5.00/acre, to spray for weed control. I challenge you to put your own costs to the treatments and response. It is proven that most weeds can be used and controlled by rotational grazing. However, it is often best, in introduced intensive grass production situations, to control the weeds, fertilize to get thicker grass, and then manage production and grazing without herbicides, or at least very limited herbicides, thereafter.

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