Get the lowdown on herbicide breakdown

Written by Dr. Jason Weirich on .

Now that you are likely done with harvesting, take a moment to reflect on your fields from this past growing season. When you were spending countless hours in the combine, did you notice areas that had better weed control than other parts of the field? Did you have fields with better weed control than others, yet you had the same weed control program across all of them? This is a common theme. While I would like to tell you that every field will respond the same or that each program will work every time, that’s just not the case.  

Herbicides break down in many ways. Microbes, water and sunlight are the main environmental factors that influence herbicide breakdown. Each herbicide family—and sometimes products within the family—respond differently to each process.  

Microbial degradation is the dominant factor that breaks down herbicides. Certain bacteria, fungi and algae use herbicides as a food source. Microbes are herbicide-specific, and populations are dependent on the rate of the herbicide application. Repeated use of the same herbicide year after year can cause more rapid degradation of the specific herbicide, resulting in shorter efficacy windows from that herbicide.  

Several factors can influence this process, such as soil composition, soil pH and climatic conditions. Soil organic matter influences microbial activity and provides habitat for the microbes to exist. When we look at pH, each microbe favors a certain level, but we see very little microbial activity in the extremes.

We all remember the drought of 2012 and concerns about herbicide carryover into the 2013 growing season. Length of herbicide activity is very dependent on soil temperature, soil moisture and rainfall, just to name a few influential conditions. You’re likely aware that microbes are not very active when soil temps drop below 50 degrees. That’s why a lot of fall-applied herbicides provide weed control well into spring. Very little herbicide breakdown occurs in the fall and winter from microbial degradation.

Water also has a negative effect on herbicide activity. Areas where water pools on the field and low spots are typically the first areas to break down herbicides when we have moisture or excess moisture. This chemical breakdown is a process called hydrolysis.  

Finally, sunlight is a factor in breaking down herbicides, but this photosynthetic decomposition is not as prevalent as it was 20 to 30 years ago. You probably remember having yellow-stained boots, pants, shirts and hands. The Treflan and Prowls of the world would break down relatively fast by light. That’s why I remember, as a kid, following the sprayer with the field cultivator to incorporate Treflan into the soil.   

These factors emphasize why we have to continue overlapping residuals. I can’t predict how long these residuals will provide weed control because it varies from year to year and field to field. This past year, depending on rain, the two-pass weed control program was the cleanest.  

I hope you will take time to evaluate this past year’s successes and failures to make weed-control plans for the upcoming year. These insights will provide us with some of the knowledge we need to make proper recommendations. If you have questions or want to develop a weed-control program, contact your nearest MFA or AGChoice location.

What did your harvest remove from the soil?

Written by Dr. Jason Weirich on .

 This has been another year with variable yields across our trade territory. You are probably hearing about higher-than-expected yields in corn and soybeans and even record yields in some areas. Weather is one factor in that variability, with wide fluctuations from one corner to the other. Areas along I-70 to the west saw significant rain events that caused some flooding, and areas to the northwest and northeast had prolonged periods without precipitation.  

With these variable yields come variable nutrient removals, whether it’s the bottom part of your field or the old clay knob that sits up high. So why do most producers apply the same amount of P and K to those areas? Most of the time the answer is, “Because it’s easy.”  

There are a couple ways we can address these issues through our Nutri-Track program. One is by using grid soil sampling, which captures the nutrient levels in specific parts of your field. At MFA, we use a 2.5-acre grid and pull soil samples in each subsection of the field. This allows us to apply variable-rate fertilizer according to varying needs of the soil. Just picture your field broken down in 2.5-acre sections and treating them differently to maximize your fertilizer dollar.

Another way that Nutri-Track can help you manage variability is by using your yield monitor. It’s more than just a screen showing current yields as you drive through the field. We can take the information from your yield monitor and apply variable-rate P and K based on your actual nutrient removal. When we couple this with our grid-sampling service, you can get on a program to stabilize P and K levels in your fields.  

Over the past few years in our trade area, producers have been removing more nutrients from their fields than they have been replacing. You might not see a yield drag immediately, but at some point you will. MFA’s Nutri-Track program is focused on putting your fertilizer where it is needed and not over-applying where it is not. I can’t promise that Nutri-Track will decrease your fertilizer cost, but I can say that the program helps put those nutrients in the right areas.  

When we look at nutrient removal, we know that 1 bushel of corn removes 0.45 pound of P and 0.25 pound of K, while 1 bushel of soybeans removes 0.9 pound of P and 1.5 pounds of K. Look at your farm’s yields, and do the math. You can see what type of P and K applications are needed to replace the nutrients you just removed. If you have any questions, please feel free to contact your local store for more details.

Going Viral

Written by Jason Worthington on .

 When it comes to disease control in wheat, the focus is often on fungus. Fusarium head scab, leaf rust, stripe rust and even powdery mildew receive a lot of attention from growers and crop advisors as they inspect fields through the growing season. They select appropriate fungicides and time applications to optimize disease control.

However, viral diseases in wheat are just as important—and potentially just as harmful—but more commonly overlooked. This tendency stems in part from the fact that once viral infections are discovered in wheat nothing can be done to treat them. True, but there is plenty that can be done to prevent them.

Prevention methods, of course, depend on the particular virus you are facing. For example, soil-borne mosaic and spindle streak mosaic viruses can be averted, or at least limited, by selecting resistant varieties and avoiding planting wheat into poorly drained soils. The impact of wheat streak mosaic virus can be reduced by planting late or controlling nearby volunteer wheat and other grassy weeds. This limits exposure to wheat curl mites that transmit the disease.

Among all diseases, not just viruses, barley yellow dwarf is one of the most prevalent and damaging problems in wheat grown in MFA territory. Fortunately, with proper management barley yellow dwarf virus can be avoided.

Aphid species such as corn leaf aphid, greenbugs, English grain aphid and, most commonly, the bird oat cherry aphid can all transmit the barley yellow dwarf virus. Symptoms of this disease include stunted plants and yellow or red leaf tips. Depending on the amount of infection and vector populations, infected areas are generally found in patches that are 1-foot to 5-foot in diameter, with the worst symptoms near the center of the affected area. As the wheat matures, infected heads tend to be darker than their healthy counterparts. Grain from infected heads is often shriveled. Yield losses can be as high as 35 percent.

This past spring, visual signs of barley yellow dwarf virus were seen quite frequently throughout Missouri, more commonly in northern areas. While last year once again proved that all areas of the state are vulnerable, typically the potential for infection is worse in the south. Later freeze dates and milder winters allow for greater aphid activity in the fall. Though the disease can infect wheat plants at any point of their life cycle, fall and winter aphids cause infections that provide much more time for the disease to develop than a spring infection.

So why were infected fields more prevalent in the north this past year? There was no shortage of infected fields in any part of the state, and aphids were prevalent far into a mild winter. The difference appears to be seed treatments. Insecticide seed treatments were much more commonly used in the southern areas, where growers are more accustomed to growing wheat and managing for barley yellow dwarf control.

 Though there are some varieties with limited resistance and delayed planting can be helpful, effective control of aphid vectors is—by far—the most reliable way to prevent barley yellow dwarf virus. Scouting and foliar-applied insecticides can help control aphids, but even then some level of infection has likely occurred. Preferably, systemic insecticide seed treatments should be used to keep aphid populations from developing in the fall. Wheat fields with insecticide-treated seed showed an obvious advantage to fields planted with untreated seed.

It is also important to note that not all seed treatments are equal. The majority of available seed treatment packages offered for wheat do not contain an insecticide. Those that do often contain an insecticide rate that’s too low to be effective against aphids. However, products like MFA’s Crop Advantage Cereals Aphid blend ensure effective control with high use rates of the systemic insecticide, imidicloparid. Products that do not have these rates need additional imidicloparid if control of aphids and, in turn, barley yellow dwarf virus is desired.

While all potential challenges in the next growing season are easier to overcome with proactive planning, when it comes to barley yellow dwarf virus control, that foresight is not just beneficial but crucial. The old saying that “an ounce of prevention is worth a pound of cure” is surely an understatement in this case. If that ounce ensures the full rate of a seed treatment, then its worth is measured in bushels rather than pounds.

What we're learning from the dicamba dilemma

Written by Dr. Jason Weirich on .

As expected, the launch of XtendiMax and Engenia came with a few headaches. We have been preparing for the introduction of the dicamba- tolerant trait for the past few years. Since I joined MFA almost six years ago, we have had numerous employee trainings, producer meetings and special applicator sessions. For a while, I didn’t know if we would ever see this technology reach the farm gate with all the additional requests made by numerous government agencies.

Little did I know that my first complaint call on dicamba would come in early May. I also didn’t think the complaint would be failure to control 3- to 4-inch waterhemp. Looking at this technology in trials, we had decent control when timely applications were made. While the early-emerged waterhemp was a problem, I was overly impressed with what was happening with our giant ragweed and marestail. Quite often, I would get a picture and a text that said, “Look at what it can do!” I would respond, “Roundup used to, too.”

What I noticed to be different about the waterhemp that had emerged in late April and early May was that these plants had already put on a seed head. This is not typical of waterhemp for that time of year. However, we have new technology with new adjuvant requirements we were trying to figure out on the fly. We quickly noticed some of the issues and made a labeled change to meet the requirements for both XtendiMax and Engenia applications. We needed to do a better job on coverage and penetration of the target species. That’s why we included Xpond and Impetro II in all of our applications for better weed control.

Early on we had a lot of successes. We had producers and applicators calling in and telling me how well this product was staying put. I also had a producer tell me that I had been wrong about this technology being risky. He had applied the product right next to his house and garden with no issues. Mind you, we are talking about early applications. Here’s where it gets tricky. Maybe we got a little too comfortable with the technology. Maybe the success stories caused some of the applicators to relax in strictly following the requirements.

Then it happened. We got our first off-target complaint early June, and once it started, it didn’t stop. We had call after call after call. We obviously had our fair share of tank contamination, typical physical drift, wrong field, wrong tip, wrong pressure, wrong boom height, etc. We see these issues with other crop protection technologies as well. We also saw a fair amount of damage from our Group 15 herbicides such as Dual, Warrant and Outlook.

Then we saw damage that appeared to be “unexplainable.” In these cases, we had followed the label, tips, boom height, speed, weather, tank mix partners and so on, but still had movement. I wish I had the answer today to tell you what happened, but I don’t. I had several applicators look at me and say, “Doc, I followed the label, and it still moved.” I think it is safe to say that there is still a lot we don’t know about the dicamba molecule.

Overall, from our custom application standpoint, we did a better job than I thought we were going to do. I was expecting to see more mistakes than were actually made. We didn’t just put this in the hands of a new applicator; we put it in the hands of our veteran employees. Some of these applicators have been spraying for more than 30 years. They took the challenge and were successful, in my opinion.

As we move into the next growing season, we have to learn from what went right and what went wrong. We need to get out of our silos and join together to figure out how we can make this work effectively and safely for all of agriculture. I will write about dicamba a couple more times before next spring and will be on the speaking trail talking about the pros and cons that we saw this season.

Will crop rotation still protect against corn rootworm?

Written by Jason Worthington on .

 When discussing insect management with growers, the preferred strategy of management is often a “wait and see” approach. Waiting until insects are found before deciding on a management practice can be effective for some species, if a field is scouted thoroughly and frequently enough. However, this same practice falls woefully short on other species, especially when managing insects that could cause devastating yield losses or pose a predictable threat to a crop. Corn rootworm falls into both these categories.

The most damaging corn pest in North America, corn rootworm pressure is documented almost every year at some level in areas that are in a continuous corn rotation. Over the past two centuries, Missouri corn growers, unless they were in a corn-on-corn rotation, didn’t have to worry much about corn rootworm pressure. That may be about to change.

Crop rotation traditionally controls rootworm. That’s why there has been limited concern in our area about corn rootworm pressure. Beetle eggs would hatch in the spring, but if the larvae did not find a food source (corn), they would quickly perish. The vast majority of Missouri’s corn acres are in a corn/soybean rotation, so growers were putting an insect management plan in place with their crop rotations.

However, in July 2016, MFA Crop-Trak Consultant Kevin Moore discovered the likely presence of northern corn rootworm extended diapause, a longer life cycle in which the eggs remain dormant in the soil for two years or more before hatching. Evidence of larvae and adult beetles were found in numerous corn fields in a corn/soybean rotation in Atchison, Nodaway, Holt and Worth counties in Missouri as well as Page County, Iowa. Many other parts of the U.S. already experience extended diapause rootworm and cannot count on crop rotation for control any longer.

To confirm these findings, MFA partnered with the USDA to conduct lab testing of suspect beetle populations. In these tests, eggs from collected beetles endured a simulated winter. A typical diapause, or period before eggs hatch, is one winter. In an extended diapause, rootworm eggs must endure two or more winters before hatching. After the first winter and spring of testing populations collected from northwest Missouri, only 45 percent of the eggs hatched. While it is unknown what portion of the remaining 55 percent will hatch after a second winter, it is likely a significant number of these eggs are still viable and could threaten a corn crop. At 45-percent hatch after one winter, the numbers closely resemble testing of known extended diapause rootworm populations in South Dakota.

What does this mean for growers in these areas? First, the threat could be much greater in 2018 because it’s an even number year like 2016, when the extended diapause was discovered. Methods other than crop rotation must be used to control rootworm. The most effective plans must be proactively developed along with hybrid selection.

When it comes to managing rootworm, reactive control measures will not be effective. The two real options a grower has to control rootworm are Bt corn traits with multiple effective proteins such as SmartStax, and granular in-furrow soil insecticides such as Force or Aztec. Both of these control options require planning ahead. With few planters in the state set up for dry insecticide applications, traited seed will likely be the preferred method of control. The decision to purchase seed with rootworm control traits often happens before the prior year’s harvest is even complete.

While rootworm can be devastating to a crop and extended diapause situations may keep crop rotation from protecting us, we still have options to control this pest. Just like many of our most important decisions, we will have to plan ahead to ensure success against this emerging threat.


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