Tailor your weed control in 2013

A new crop year is a chance for clean fields

Now that grower meetings have slowed down and you gear up for field work, let me review a frequently asked question about weed control options for 2013. My first response to questions about what to do this year is a question in itself. I ask what weed control program was used the previous year. The common response is: a preemergence herbicide applied at planting followed by glyphosate and an in-season contact herbicide. Of course, the drought had major effects on the performance of your preemergence herbicides in 2012. But whatever let-downs we might have suffered last year, we have to recognize that managing herbicide resistant weeds in the future will rely heavily on the proper use of preemergence herbicides. So if your preemergence herbicide was a flop in 2012 please don’t give up in 2013.

For weed control in 2013, I have a few themes for you to consider. With corn or soybean we must start clean with herbicides or tillage. If you plant your crop into weeds you will have weeds all year. Our options for weed control after the crop is planted are limited. Controlling annual weeds like marestail and giant ragweed before we plant our crop can save you a headache during the growing season. To combat these two problematic weeds, 2,4-D or Dicamba can be used prior to planting either corn or soybeans. 2,4-D or Dicamba provide challenges in themselves. Plant back restrictions following these herbicide range from 7 to 30 days (consult label for specific restrictions).

If you are not willing to use 2,4-D or Dicamba in a burndown situation, there are a few other options. Paraquat can be effective on small weeds. Paraquat is a contact herbicide and needs to have excellent coverage of the weeds to get control. Sharpen (BASF) herbicide can also provide excellent control of marestail and giant ragweed. The organic matter of your soil affects the plant-back intervals following an application of Sharpen. Regardless of what herbicide or tillage option you choose, make sure that you start clean.

Choosing the right preemergence herbicide for your farm will depend on the weed spectrum you have in your fields. Just because you have a program that works on one field doesn’t mean that it will be the right program on another field. Programs need to be developed on a field-by-field basis. The Today’s Farmer Agronomy Guide can be very useful for determining which preemergence herbicide you would like to use in corn or soybean based off of the weed spectrum in your field. However, our local agronomist can help you develop a whole-farm weed resistance plan, which will be tailored to your needs.

When we talk about soybeans we must talk about overlapping our residual herbicides to get ahead of the glyphosate-resistant waterhemp and Palmer amaranth. We must get in the mindset of applying our herbicides on bare ground. Generally, most of the commonly used preemergence herbicides will be effective for around 30 days. There are a lot of factors that influence the degradation of herbicides and can vary their effectiveness. So we need to have another preemergence herbicide applied before the first residual herbicide is ineffective. For example: if we apply our first preemergence herbicide on May 1, by June 1 we need to have our next preemergence herbicide applied and hopefully activated by a rain before the first preemergence herbicide is no longer effective. This will provide weed control further into the growing season giving you a greater chance of success.

In corn, a lot of growers talk about using a one-pass program. That is fine if you are scouting your fields and willing to come back with another postemergence application. However, I find that a lot of people plan on a one-pass program and never scout their fields. We had several calls last fall that corn was clean for eight weeks, but when the combines pulled in the field it was weedy. This could have been avoided by scouting. If you are planning a one-pass program scout your fields every seven to 10 days for escaped weeds and other pests that may be present. I like a two-pass program: a preemergence herbicide applied at planting and, 30 days later, another preemergence herbicide applied to extend weed control further into the season.

Regardless whether it’s a corn or soybean crop, it is critical that we keep the crop weed-free early in the season. Early season weed completion is detrimental to your yields.
Scouting your fields every seven to 10 days can save you a lot of headaches later into the season. Getting in the field means you see weed escapes and can treat for them, but it also means you see the disease and insects that can really affect yield. There is no replacement for scouting your fields. MFA’s CropTrack is a scouting program that helps you determine pests that are present and when crop management tactics are needed. Visit your local MFA and see if this program is a fit for your operation.

Dr. Weirich is director of agronomy for MFA Incorporated.

Read more by Dr. Weirich HERE.

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Type and timing for sidedress

Nitrogen sidedressing corn is a balancing act

Each year we get a lot of questions regarding sidedress applications of nitrogen. Sidedress applications allow growers to maximize profits. However, each growing season has varying precipitation and different environmental conditions that can prohibit producers from applying nitrogen in-season.

For each bushel of corn removed, 1.5 pound of nitrogen is required. However, one pound of nitrogen is in the corn and half a pound is in the stover. For example, you want to grow 200 bushels of corn, you would need 300 pounds of nitrogen. Some of the nitrogen would come from a credit from previous crop and nitrogen from the soil to reduce the total amount of nitrogen needed for application.

If the corn crop were following soybeans, a 20- to 30-pound nitrogen credit would be applied. Depending on soil type and cropping history, 60 to 70 percent of your nitrogen should be applied at or before planting if you are planning on sidedressing your corn crop. This allows you to evaluate growing conditions and maximize profit.

When corn is in its early vegetative stages to V5, little nitrogen is needed. The largest portion of nitrogen uptake occurs during the V8 to VT (tasseling) development stages. Corn takes up very little nitrogen after pollination.

Thus, it is critical to apply your sidedress nitrogen application before the V8 development stage. Most research indicates that if the nitrogen application is made around the V6 stage, yield loss due to nitrogen stress is rare.

Soil injection or dribbling nitrogen between the rows is the best ways to sidedress nitrogen. This type of application can reduce volatilization of urea and protect the crop from foliar damage. If you are sidedressing with ammonia, it is critical that you watch soil conditions and make sure the knife track closes properly to avoid foliar damage from the ammonia escaping.

Applications of ammonium nitrate, SuperU and urea “over the top” can result in foliar damage. However, this damage is an aesthetic concern and rarely result in any yield loss.
For broadcast applications, UAN can be applied up to one-foot plants, ammonium nitrate up to two-foot plants, and urea or SuperU up to four-foot plants or the V8 stage. Broadcast applications of UAN or ammonium nitrate are the least desirable way of applying N due to the cosmetic burn. You can reduce this cosmetic burn by applying the dry nitrogen sources when the foliage is dry.

Sidedressing corn can help you apply nitrogen when the crop needs it most. Also, sidedressing allows you to evaluate current-growing conditions to determine yield potential and the proper amount of nitrogen needed to reach your yield potential. When it comes to sidedress applications, apply earlier than later in crop development. By waiting until later in the season, you have the risk of wet weather. Wet weather can sometimes delay timely applications of nitrogen and cause significant yield loss.

Visit your local MFA location for more information on sidedressing corn or to visit with an agronomist about sidedressing corn on your farm.
Dr. Weirich is director of agronomy for MFA Incorporated.

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New weed control technologies on the way

Management to prevent resistant weeds will still be critical

For the past three months, I have been traveling MFA’s trade territory participating in grower meetings. As you can imagine, the main topic of conversation was poor weed control and the drought we faced in 2012. I hope that the 2013 growing season is more forgiving than the hot and dry days of 2012, and, while I may not be able to provide any future direction on the weather, I can provide some insight on upcoming crop technologies.

There are several new technologies in the pipeline. Crops bred to tolerate Dicamba, 2,4-D and HPPD will be available in the near future. We’ve also heard about additional technology breakthroughs that will be on your farm before 2025. These technologies will arrive with several challenges for growers and applicators (drift, tank contamination etc.).

In the near future, you will see Monsanto’s Roundup Ready 2 Xtend. This latest Genuity soybean trait gives crops tolerance to dicamba. Roundup Xtend is an enhanced dicamba-and-glyphosate herbicide premix. Monsanto plans to have a follow-up introduction for cotton with Bollgard II RR Xtend with LibertyLink. Pending regulatory approvals, Monsanto will launch the first Roundup Ready 2 Xtend for the 2014 growing season.

The Enlist Weed Control System is Dow AgroSciences’ newest corn, soybean and cotton trait. Enlist crops are tolerant to Enlist Duo herbicide with Colex-D technology. Enlist Duo is a proprietary blend of glyphosate and new 2,4-D choline. The Enlist system will combine herbicide-tolerant traits that will allow producers to apply the new 2,4-D choline, glyphosate and glufosinate (in corn and soybeans), and FOP chemistries (in corn). Pending regulatory approvals Dow AgroSciences will launch the Enlist weed control system in 2013 for corn, followed by soybeans in 2015, and cotton in 2016.

Bayer CropScience and Sygenta will bring soybeans tolerant to HPPD (Balance or Laudis) herbicides to the market in 2015, pending regulatory approval. HPPD herbicides are already being used in corn with great success.

As I mentioned above, these technologies still need regulatory approval. But once they receive approval, and you have them on your farm, you will still have a few management concerns to consider. You will need to get the right crop protection product aligned with the right seed technology. The dicamba and 2,4-D formulations you are currently using are not the same formulations suggested for new herbicide-tolerant crop lines. Monsanto and Dow have done extensive research and testing to develop a formulation that reduces potential for drift and volatilization. Having said that, I want to remind you that using common drift reduction practices is a must for application of all herbicides. The new technologies I’ve mentioned will require another management step to avoid tank contamination or misapplication of the wrong herbicides. Dicamba and 2,4-D are two different herbicides. If you apply dicamba to a 2,4-D tolerant crop it will be desiccated and visa versa.

New technologies are not a stand-alone system. We must continue to use multiple modes of action and preemergence herbicides. Overlapping residuals will still be recommended for all future technologies. The concept of placing a preemergence herbicide and following 21 to 30 days later with another residual herbicide is gaining acceptance. The best chance we have at controlling weeds is controlling them before they emerge. Remember, if you don’t manage your weeds they will manage you.

Dr. Jason Weirich is director of agronomy for MFA Incorporated.

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Resistance is not futile

As you plan for next season’s weed control, think preemergence

In my April column, I visited about the use of preemerege herbicides and their need in assisting producers’ battle against herbicide resistance. Over the past few months, I have had several calls claiming residual herbicides had no value on growers’ farms, while other growers stated that residual herbicides were the best thing since sliced bread. I learned through visiting with a particular customer that he applied the residual herbicide behind the press wheel and started clean. However, the first rain on the field didn’t come until nearly four weeks after application. The activating rain was too late. It is likely the herbicide was already degraded by the first rain and the weeds were already emerging with the crops. Unfortunately, that situation was all too common this year.

Another all-too-common issue for 2012 was to plant first and then later attempt to clean up the field. Once the crop is planted, the options for controlling weeds such as giant ragweed, marestail and waterhemp are limited. Tillage is a viable herbicide option before the crop is in the ground.

I am talking about the failures of weed control this year to remind you that there are no silver bullets. As much as I would like to inform you that using glyphosate the same way you always have used will deliver the same results, that just isn’t the case.

As we move into the planning process for the next growing season, let’s prepare for success. Residual herbicides must continue to be a foundation for any cropping system. Even though we need moisture to activate the herbicide, it is still our best option to controlling weeds. Our best chance to control tough weeds is to never allow them out of the ground. The use of residual herbicides adds another management step to our programs, but we must be willing to manage the weeds or they will manage us.

If you planted LibertyLink soybean this year, I hope enough Liberty was available to cover your acres. The shortages of Liberty were global, making it a very stressful year across all the crop growing areas in the United States. As we progress into preparing for next year, go ahead and book your Liberty for the next season with your local MFA. I often get the question of how much Liberty a particular grower will need, and my general response is two full-labeled-rate applications worth. Two applications not only allow you to feel comfortable about the technology, it also allows our stores to plan for the next year’s Liberty supply. Even though Liberty has been very effective, I also recommend the use of residual herbicides at the full-labeled rate. Application of the residual herbicide will not only reduce the amount of pressure you are putting on Liberty, but add another mode of action to the mix.

In May, MFA gained a staff agronomist, Kellar Nelson, who has been tasked with the LibertyLink project. She graduated from the University of Missouri with a Master’s in Plant and Soil Science. This past year, MFA planted ten LibertyLink soybean variety trials across the state. Nelson visited these trials bi-weekly from planting to harvest to evaluate variety placement throughout the state.

Contact your local MFA for Nelson’s and other final variety yield reports or for more information on MorCorn, MorSoy Xtra, or MorSoy LibertyLink crops.

Dr. Jason Weirich is director of agronomy for MFA Incorporated.

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Soil sample pointers

Every year I get questions that focus on fertility. My first response is to ask, “Have you pulled a soil sample?” The typical response I get is, “I think so.”

Just what role should soil testing play in your farming operation?

Soil sampling is not a perfect science. However, it can be a valuable component of your agronomy programs by following a few basic principles.

The standard soil sampling depth is six to seven inches. This depth represents approximately two million pounds of soil—a convenient conversion number. I recommend that you stay close to this depth. Equations that soil testing labs use were developed with that standard depth.

You need a strategy for sampling fields. The general rule of thumb is a “composite” soil sample is not to be greater than 20 acres.

For example: an 80-acre field needs four separate soil samples. Try to divide sampling areas from fields greater than 20 acres into a management zone. These zones can be based upon soil type, history, yield potential, field geography, field use or other logical divisions.

Each composite sample should have 12 to 25 soil cores. This allows you to collect a representative soil sample from that area. Fewer than 12 cores per sample can lead to poor representation if one of the cores is extremely high or low in a given nutrient. If you have banded any fertilizer applications, you must have at least 20 cores per sample.

Another question I often get is, “How often should I resample?”

I suggest every two to four years, depending upon the crop grown, fertilizer utilized, environmental conditions and other agronomic components. Try to resample fields the same time of year, and preferably after the same cropping sequence.

Precision agriculture programs usually sample in a tighter acreage pattern. Some programs use standardized grid samples while others use management zones. Most grid sampling is done on 2.5-acre grids. MFA’s precision program often offers a combination of composite, grid and management zone sampling. This provides producers with the ability to apply the right amount of nutrients to the right acre, and it gives growers a great range of agronomic and economic options. Contact your local MFA to see how MFA’s precision program can help you and your farm increase profits.

Regardless of the collection process you choose, basic soil sampling procedures should be followed. Consistency is the key to an effective soil-sampling program.

Even if you follow these simple guidelines there may be anomalies associated with soil testing. Don’t get frustrated if some of your soil tests come back different than expected or are inconsistent across space or time.

Soil is a complex combination of physical, mineral, biological and organic residue systems working together. Some unexpected measurements will come along.

Soil sampling is just one component of crop nutrient management. On page 10 of this magazine, MFA agronomist Steve Cromley discusses nutrient recommendation programs.

Dr. Jason Weirich is director of agronomy for MFA Incorporated.   See related story on interpreting soil samples HERE.

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