Natural Weed Control

Growers are only limited by their imaginations in implementing non-toxic weed control methods on their farm. The most obvious way is to take the chemical farming approach and find an organically approved material to do the killing. Very strong vinegar has been the most marketed material. The important factor in vinegar formulas is to have a surfactant that strips away any waxy protective coating on the plant surface and that allows the desiccation or drying out of the plant. Salt provides the same mode of action and may be included in the formula.

Natural weed control

Flame is an even more modern and harsher approach. The mechanical approach is the most widely used by growers around the world. Cultivators are a modern version of hoe, hoe, hoe or hand pulling. Rotary hoes or spiked harrows are special adaptations of the cultivation approach. Using plastic films, whether degradable or not, is a form of smothering that is similar to mulching by any material. Here the weed is denied sunlight to prevent nature’s germination response.

Repeated cuttings in a fallow situation of a perennial weed may weaken a plant over time by using up any stored energy. Every attempt is also made to prevent the reseeding of an offending species. Treating isolated patches is worth the effort to keep them from spreading. If a field is overwhelmed to a point of not having an economic crop worth harvesting, be sure to take the whole field down before the offending weeds go to seed. Keep in mind that there are seeds in your fields that may have been there for years. Just lime or activate the calcium in your soil and watch clover appear in uncultivated ground that you haven’t spread clover on since you bought the farm.

By the same token, there are all kinds of weed seeds that are just lying there, waiting for you to damage your soil to a point where they will come into play or waiting for you to use a herbicide that will suppress one of your current weeds that has been keeping another weed you weren’t even aware of under control. Nature knows what she is doing!

A more natural way is to activate the forces of nature by crop rotation which allows the allopathic properties of each subsequent crop to affect the soil. Cover cropping is usually a more direct attempt to apply the specific allopathic properties of a given cover crop to the specific weed problem. Online sources of research are readily available to match specific cover crops to specific weeds. This author has always recommended the use of a mixture of two or three plant species for cover cropping and now articles are appearing by farmers that are reporting that mixtures of 10-15 species are providing more weed suppression and soil health properties in general.

The allopathic effect of the economic crop can be amplified by cross drilling of small grains. During my organic farming days I used a little more than half the normal seeding rate and then drilled a north-south pattern followed by an east-west pattern. This increased the soil area impacted by the allopathic properties of the economic crop to almost total coverage within the field. The results were spectacular considering the previous corn crop had been well infested with redroot pigweed that had gone to seed.

Since all weed or grass germination or the spreading by rhizomes is a function of soil and weather conditions, the most natural way to accomplish weed control is by soil mineralization and bioactivation.

Discounting simplistic NPK research, the accumulation of knowledge from the last 100 years or more of research has provided us the standard Cation Exchange Capacity (CEC) model to aim for on our fields. You will find variations between labs and consultants, but don’t let that discourage you from taking tests and using them as a guide to begin balancing your soil for the purpose of production of nutrient-dense crops with the added benefit of discouraging weed and grass pressure.

We know from experience that bioactivity can help overcome soil mineral imbalances and bring low levels of minerals into play for awhile with resulting crop response. That hardly qualifies as soil balancing, if you are too low in boron to effectively move adequate calcium into your crop, your yield will be decreased.

Achieving a soil that is so perfectly balanced and biologically active as to not have any weed or grass pressure is difficult, but not impossible. Let’s look at Dr. Ream’s teachings in detail. He taught that the main situation which promotes broadleaf weeds is the ratio of available phosphorus to available potassium as shown by a LaMotte soil test. The further you deviate from a 1:1 ratio, the stronger the broadleaf pressure. In the 1970s, an associate of mine, Joe Scrimger, had a place on his farm where the usual herbicides totally failed to control the typical weeds he had in other fields. We performed LaMotte tests and compared the bad spot to a typical field. In his fields where the herbicide gave reasonable control, the ratio of P:K was 1:4. In the area where the herbicides failed, the ratio was 1:8. The weeds in that area were so healthy and strong that they could overcome the toxic effects of an herbicide applied at the usual rates.

In current GMO situations, we also have to add the factor of herbicide resistance. According to the March 2013 issue of The Furrow, Arkansas farmers had to hand hoe up to 52 percent of the state’s cotton acreage at a cost of $30 per acre.

Another way of verifying that you are fertilizing for weeds would be to take measure the Brix of the weeds and the economic crop. If the Brix of the weed is higher than the economic crop then obviously the weed is healthier/stronger than the economic crop. The logical conclusion is that your fertilizer program favored the weeds rather than the crop you were trying to harvest and sell. If you were intending to make corn silage, it could turn out that the feed value of your silage would be higher with more high-Brix broadleaf weeds present than with less.

Around that same time I regretfully discovered that excess wood ash, which is high in available K, was a sure way to have uncontrollable weeds in my farm garden. I also noticed that areas receiving raw manure also were prone to redroot pigweed and lambsquarter, aka “fertility weeds.” It is now generally understood that broadleaf weeds thrive on highly available nitrates and potassium diets. Even when P is included in the NPK fertilizer, the potassium is much more available than the phosphorus due to its dependence on biological activity to make it available and its propensity to chemically bind with calcium. That bonding reduces the available calcium in your soil, increasing the pressure for Mother Nature to germinate a sour grass such as quack or crabgrass to bring calcium to the surface. In other words, NPK farming promotes weeds and grasses, increases your “rescue chemistry” costs and lowers the feed or food value of your crop.

Organic and sustainable growers can fall victim to the same phenomenon when they apply raw or partially composted manures, organically approved Chilean Nitrate (NaNO3) or any other soluble nitrate, sodium or potassium source. Even if they have applied a natural phosphate, failure to insure mycorrhizal inoculation and general bioactivation can lead to Mother Nature thinking that the ratios are still off.

Most of the weed problems in farming are surface problems. Each time the soil is disturbed, new weed seeds come to the surface, rays of sunlight strike them and that is their signal to germinate if the other soil signals tell them it is their turn to come into play. This relation to sunlight exposure led to another weed control approach, cultivating or planting at night with hooded or red head lights to avoid the sunlight triggering response.

Weed Control: Results in the Field

I first learned of the successful use of liquid calcium and molasses for surface weed control in the early ’80s. At about the same time I learned that oats were a good accumulator of phosphorus and winter-killed oat crop residue provided both allopathic suppression as well as additional bio-available phosphorus. After writing about that in my newsletter, a Pennsylvania farmer reported a very successful and weed-free, no-till corn crop by planting a heavy fall crop of bin-run

oat seed, letting it winter kill and then no-till drilling his corn seed into the residue. He also added the liquid calcium and molasses spray right after planting. The net effect was a weed-free field of organic corn.

The next report we received was from a strawberry grower. For those of you who have come by our booth at an Acres U.S.A. conference, the sequential pictures show the same amazing total suppression of weeds and grasses in what amounts to an open soil between the rows of strawberries for an entire season. The grower planted a heavy crop of fall oats in Pennsylvania. Naturally, they winter-killed. After tilling them in, he planted his rows of strawberries. Following the correct procedure, he sprayed a liquid calcium molasses mixture at a slightly reduced rate. Since this was a U-pick operation, he repeated his calcium molasses spray at about one-quarter rate every few weeks as he was getting soil disturbance from customers. The net effect was almost perfect weed control without the use of any mulch, any mechanical removal of weeds or any toxic spray (see Figure 1).

Since the early 1980s, scores of growers have tried the concept on every imaginable crop. At first the 2-gallon liquid calcium part of the formula was applied as non-organic chelated calcium nitrate or organic chelated calcium chloride with the 2 gallons of molasses (see Figure 2). The molasses was critical to the formula as it feeds/activates the phosphatase bacteria which breaks the bonds of tied up phosphorus. A few years ago, two alternative sources of calcium became available. One was limestone ground to 500 mesh and the other was TN Brown phosphate that contains both calcium and phosphorus ground to 500 mesh. Both are available as liquid suspensions, Premium Cal 33 and Phos Cal 22, for easy mixing and blending.

The latest test of the formula or concept came in 2013 on California organic rice. One of the Lundberg Farms contract growers used the following procedures and materials to achieve control of water grass on 92 acres of short grain rice: The last disturbance of soil was leveling, so that was the timing point for applying the weed suppression formula of 2 gallons of molasses and 42 ounces per acre of Phos Cal 22 (we had recommended 64 ounces per acre, but the final use rate was more of a factor of, “we have this much product and this much acreage to cover.”) in 20 gallons of water applied by ground rig. They took the additional step of using drop nozzles to insure a uniform coating on the soil. A few days later, the field was flooded and then seeded by air. The results were excellent.

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The local flying service reported that the organic field had equal or better control than the chemical fields in the area. The yield was 5,000 pounds per acre. The weed control cost was less than $20 per acre!

Not to confuse anyone, but the same rice farmer had tried the formula the year before by flying it on after flooding.

Due to atmospheric conditions, the spray drifted to an adjacent field and was still quite effective as a water grass control on the field hit by the drift. That just shows you how little material or infrared signals from a material it takes to affect nature.

By Philip A. Wheeler, Ph.D. This article appeared in the March 2014 issue of Acres U.S.A.

Philip Wheeler is a crop consultant and lecturer who has worked with growers all over the world. He can be contacted at Crop Services International Inc., phone 616-246-7933. The Non-Toxic Farming Handbook, by Philip A. Wheeler and Ronald B. Ward, is available from the Acres U.S.A. bookstore.

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