It’s time to fight resistant pigweed

Residual herbicides should become a part of your weed-control

If you have attended a grower meeting recently, you have probably heard a lot about herbicide resistance—whether you wanted to or not. Herbicide resistance is not going away any time soon. As we move in to the growing season, we should all ask ourselves one question, “Do I want to be proactive or reactive?”

Since the introduction of Roundup-Ready crops in the mid- to late-1990s, glyphosate made weed control too easy. Farmers were able to plant crops, follow with one, or sometimes two, applications of glyphosate, and then they were finished.

In 2005, we started seeing and hearing about reduced control and weed escapes resulting in yield loss and reduced profit. Things got worse. And now, the days of efficient glyphosate-only weed control programs are gone.

If you don’t have glyphosate-resistant weeds yet and continue to use only glyphosate, it is a matter of time before resistance reaches your farm. And when that happens, residual herbicides will become a part of your weed-control program, if they aren’t already. Make sure to choose a residual herbicide that fits your weed spectrum. The MFA agronomy guide provides an excellent breakdown of each herbicide by weeds controlled.

Read more: It’s time to fight resistant pigweed

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Late fall tillage could mean big spring weed flush

I know its February and weed control for the upcoming field season is probably the last thing on your mind. It is not uncommon to already have your plant food and seed inputs planned and purchased by now. Even though integrated pest management is reactionary by nature, planned pest management is often a very good idea.

Over the past several years, weed control systems have changed appreciably. Now is the perfect time to address those changes and prepare for the field season. Let’s discuss a few key components of a planned progressive weed control program.
Fall weed-control strategies have increased over the past decade. Many of these programs use residual products designed to keep weed pressure low through spring planting. We noticed a large downturn in fall herbicide use in 2010. The main reason given for less fall herbicide use was that the early harvest combined with dry weather allowed some much needed fall tillage to be done. Environmental conditions in 2008 and 2009 were not conducive to tillage.

As a result, many fields were severely rutted. Additionally, terrace work, grass waterway construction/maintenance, and drainage improvement projects, which were put on hold for several years, were finally initiated. All the ground work kept fall weeds in check. Don’t be lulled into a false sense of weed control security, as we often experience a weed flush following tillage. I expect to see that flush in full force this spring.

Be prepared to use an aggressive burndown program. In many cases, that burndown should include a full-rate residual product. If a residual is not used in the burndown, I recommend a planned residual as a preemerge or early post-emergent application.
Even with a residual herbicide, plan on an additional post application of glyphosate on tolerant crops once the weeds reach a height of 4 to 6 inches. Where resistance is an issue (almost everywhere in Missouri), the glyphosate needs to be applied with an appropriate tank-mix partner.

I am a big supporter of agronomy programs designed to slow weed, insect and disease resistance. I have discussed resistance as the key message in this column many times in my tenure. For obvious reasons, glyphosate resistance has received the most attention. However, as of 2010, the Weed Science Society of America lists 348 herbicide resistant weed biotypes present in over 50 countries. The United States alone accounts for 123 of those biotypes. To fine-tune those numbers, they represent 194 weed species and have been documented in over 400,000 fields.

Weeds developing resistance to glyphosate is part of a long list that includes resistance to seven other herbicide modes of action. In Missouri, 12 weed species have developed resistance to herbicides since 1992. They include common cocklebur, barnyardgrass, common sunflower, horseweed/marestail, common ragweed, Palmer amaranth, giant ragweed, annual bluegrass and most impressively, common waterhemp, which has developed resistance to four different herbicide families.

The society lists the following general principals of weed resistance management as:
•    Apply integrated pest management practices. Use multiple herbicide modes-of-action with overlapping weed spectrums in rotation, sequences or mixtures.
•    Use the full recommended herbicide rate and proper application timing for the hardest to control weed species present in the field.
•    Scout fields after herbicide application to ensure control.
•    Monitor site and clean equipment between sites.
For annual cropping situations they also suggest you consider the following:
•    Start with a clean field and control weeds early using a burndown treatment or tillage in combination with a preemergence residual herbicide as appropriate.
•    Use cultural practices such as cultivation and crop rotation where appropriate.
•    Use agronomic principles that enhance crop competitiveness.
Weed control strategies are constantly evolving. Even when the most aggressive herbicide programs are required, the return on investment is very positive, especially with today’s commodity values. Don’t let the season sneak up on you. Take time during a cold February day to visit with your local MFA Certified Crop Adviser. They can help develop a custom weed control program for each of your fields.
Dr. Paul Tracy is director of agronomy for MFA Incorporated.

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Agronomy 2010

Calendar year 2010 was filled with environmental stresses, new product releases, non-traditional pest invasions—but more importantly—great opportunity for our farming community.
For the third straight year, excessive early season rainfall dominated our spring. Like last year, the wet spring forced delayed planting or caused many fields to be replanted. Unlike last year, our dry September and October created excellent harvest conditions.

The open fall allowed us time to start replenishing the negative nutrient balance that has occurred via a combination of plant food prices, high crop yields and restrictive application weather over the past several years. If you haven’t already addressed this issue, please plan to do so before spring planting.

How did our crops respond to the weather patterns? Generally, corn yields were more adversely affected than soybean yields. Aside from the obvious flooded areas, much of the lost yield this year came in the form of nitrogen deficiency. Preplant nitrogen just couldn’t hold up to the loss pathways associated with the wet weather. Once again, split nitrogen performed much better than applying all nitrogen up front. Slow release or nitrogen stabilization products helped, but for the third straight year, they were inferior to a planned split nitrogen program.

If decades of preaching the benefits of sidedressing nitrogen onto corn, combined with environmental conditions over the past three years doesn’t generate interest in this management operation, then I guess nothing will. I fully understand the equipment, logistics and timeliness issues associated with sidedressing, but still highly recommend considering it as a planned, standard component of your corn production system.

Unlike corn, I was pleasantly surprised with soybean yields this fall. Obviously, nitrogen loss is not critical with beans, but other factors like adequate moisture, improved genetics and better adoption of residual herbicides, foliar fungicides and foliar insecticides played a role.

Soybean fields that received foliar fungicides, insecticides and fertilizers applied between growth stages R1 (flowering) and R3 (pod set) performed very well. A common denominator with yield increases was the positive response to the fungicide. The insecticide and foliar fertilizers increased crop growth and yield in some situations. Late season disease pressure, thick canopies and high humidity conditions stimulated diseases like Septoria brown spot, Frogeye leaf spot and Cercospora blight.

I believe that soybean insect pressure was much higher than normal and response to insecticides was from insect control and not a function of plant health, that is so often claimed as a benefit.

We had high podworm pressure in several areas. One hundred percent yield loss was reported at some western and northern Missouri locations. I have not seen this in 24 years of walking soybean fields in our region.

We had mid-season garden webworm and late season stinkbug problems this year. Both required treatment and the stinkbugs led to “green bean syndrome” and appreciable yield loss.
Soybean aphid pressure was much less than last season. These insects have been known to cycle in large numbers every other year. Therefore, we need to be prepared to address them next season.

Foliar fertilizers have been the rage the past few years. Higher commodity values and increased crop yields have driven these phenomena that cycle through about every 7 to 10 years. What, if anything, is different this time around? First, crop yields are much higher. A shot of needed plant food mid-season may help top-off a good crop. Second, since we are already going across fields with mid-season fungicides and insecticides, a good situation for piggy-backing crop nutrients is already present. Third, is the glyphosate-chelation theory that has generated quite a buzz.

With increased demand, comes misinformation. It also generates a myriad of new products, many of which are unproven. My advice to anyone considering foliar fertilizers is to check out the products thoroughly and buy them from a reputable source.

Forage yield (especially tall fescue) was down this year. With adequate moisture, this should not have happened. I believe in many situations, that years of neglect in plant food applications and weed control strategies were the primary causes. As commodity prices continue to stay high, pressure on forage will continue. Let’s not overlook the management required to reap the most benefit from our forage acres.

The optimist in me predicts a strong agronomic 2011. As we enter the holiday season, remember the important role we play in feeding, clothing, and fueling the world. It is a mission to be proud of.

Paul Tracy is Director of Agronomy for MFA Incorporated.

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Crop sulfur fertilizer choices

Last month, I discussed why we are seeing increased demand for crop sulfur fertilization. The four main reasons are 1) higher crop yields; 2) depleted soil organic matter; 3) lower amounts in atmospheric deposition; 4) less sulfur contained as impurities within modern fertilizers and crop protection products.
The increased demand for sulfur is undeniable. This demand has stimulated numerous new products, new marketing campaigns and new “expertise” on how to address crop sulfur fertilization programs.

{gallery}Nov10/chart:210:270:1:2{/gallery}MFA’s sulfur message has been consistent for many years. Our soil test recommendations for sulfur are aggressive and based upon a combination of targeted crop yield, soil organic matter and soil texture. We know that sulfur pathways through the soil/plant/air/water environment are extremely dynamic. I often compare sulfur’s dynamics to those associated with nitrogen. In fact, since both nutrients are basic building blocks of amino acids and proteins, they are closely related in terms of biological pathways and fertilization requirements. In general, the nitrogen-to-sulfur ratio in soils, plants, animals and organic residues is relatively constant at approximately 10:1. A rule of thumb concerning sulfur fertilization is to apply one pound of sulfur for every 10 pounds of nitrogen. How many crop producers in our region adhere to this ratio rule?
Sulfur fertilizers generally come in two major chemical forms, sulfate (or sulfate derivatives) and elemental sulfur. Organic waste products can also contain a fair amount of sulfur, but their consistency, analysis and nutrient availability is extremely variable. The nearby table lists the major sulfur fertilizer compounds used in our region.

Plant roots can only adsorb sulfur when it occurs in the sulfate form. This leads to a dilemma when choosing the appropriate fertilizer material.

Elemental and organic sources of sulfur must go through microbial-driven processes that convert them into sulfate. This conversion is moisture, time and temperature dependent, and can take from a few weeks to several months.

Sulfate-containing materials provide an immediate plant available form. However, since sulfate is water soluble and soil mobile, it can leach below the root zone with rainfall and irrigation events, and thus become unavailable to the growing crop.

We recommend sulfate-containing materials be applied near planting, as starter fertilizers or even post-emergent. These timings give us the best opportunity for crop uptake before leaching losses can occur.
The time delay for elemental sulfur to convert to plant available sulfate makes it an optimal product for fall or winter applications in front of a summer crop like corn or soybeans. It works extremely well when applied off-season with phosphorus and potassium fertilizers. If elemental sulfur must be applied near planting, a slightly higher rate is recommended.

Conversely, when sulfur response needs are immediate (at spring green-up for fescue and wheat, near planting, as a planting starter or post emergent with corn, soybeans or alfalfa), then the sulfate sulfur form is preferred.

Most sulfur products that contain micronutrients are applied in rates sufficient to satisfy crop micronutrient needs. Since these rates generally account for an extremely small amount of the crop sulfur needs and are relatively expensive.

An example of a new type of sulfur product that attempts to eliminate timing as a major factor is the MicroEssential line from The Mosaic Company. These materials contain half the sulfur as elemental, and half the sulfur as sulfate. They also conveniently place sulfur within phosphorus fertilizer granules to help obtain a more unified material spread pattern.

I expect that we’ll see many more attempts to create sulfur products that reduce the timing risk of the current materials used. As these products enter the market, please evaluate them for consistency, efficiency and compatibility.

Dr. Paul Tracy is director of agronomy for MFA Incorporated.

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A better way to fertilize

Recently, I compiled soil test data that came through MFA's West Central AGRIServices office in Adrian from 2000 to present. The first set of tests were from 2000 through 2006. The second were from 2007 through 2009. When I looked at soil tests in the "low" to "very low" range, the results in the older data group showed 52 percent were low on phosphorous and 18 percent were low on potassium.

The later group showed that 51 percent were low on phosphorous and 27 were low on potassium. As for soil pH, the older set of samples showed 29 below a pH level 6. In the more recent collection, some 38 percent of samples were below a pH level of 6. Our MFA home-office agronomy staff agrees that this is not just a local trend in our area, they are seeing this all across the MFA trade territory.

I'm sure that by now you are thinking that this is a fertilizer sales pitch, but that is not my goal. My goal is to develop a fertilizer recommendation based on all information available to us. The only true way to do this is based on current sampling, taken in an unbiased and random pattern and combined with yield data from each field.

{gallery}Nov10/maps:210:270:1:2{/gallery}The majority of combines running now have yield monitors in them, and I would like you to think about what that monitor is showing while you move through the field. In my limited time spent in a combine, I have yet to see a yield monitor display a constant number. It is always moving around, and sometimes by a pretty good percentage. As this is going on, you are looking at the crop in front of you searching for the cause.

Sometimes you see the thin stand, or an area that is always wet. Or, you may be on the thin ground from which you borrowed to fill a ditch or build terraces. Often times, though, you are in the good dirt—maybe where the beans used to be 5 or 10 bushel better, or the corn is the same as it was years ago. You think about the cause, and consider insects or a disease. You know you are fertilizing the same as always, and you are using the best genetics. Still your yields just barely improve.

We all know that most fields have inconsistent soil types and yield capabilities. So could it be that most areas of the field have shown a slight yield increase as you bring a better genetic package with your seed purchase. Meanwhile, it could be that the very best soil yields the same because the fertility has fallen off. In an attempt to increase yields we put on more fertilizer, and as we would expect, slowly the yields increase. But, if you identify the low-soil-test areas, especially the ones that happen to be the best ground and fertilize it to its highest potential, you'll be giving those seed genetics the means to perform as expected.

Now, just like the effect of a few drowned-out spots that drag your average yield, you can see it the other way around with your best soil boosting yield to its potential. I illustrate this to point out that as we continue to plant better genetics and expect more yield from every acre, the fact is our soil fertility is not keeping up with demand. All of the new technology you put in a tractor cab (yield monitors, auto steer and even Internet on your smartphone) may or may not make you money, but my read on the data is that we are neglecting the proven technology available to put each fertilizer dollar in the most needed spot.

We don't always need to crank up the fertilizer rate to get the best return; we just need to apply it wisely. I would like to suggest that you soil test your fields in a grid-sample method and use variable-rate application to apply your fertilizer and lime.

Doing this will place the right amount of fertilizer where it is needed most and not waste fertilizer in places that don't need it.

Dale Guss is the branch manager of MFA-owned West Central AGRIServices in Adrian, Mo.


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