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August 2011 Archive for Ask an Agronomist

RSS By: Farm Journal Agronomists, Farm Journal

Have your agronomic questions answered by a Farm Journal agronomist. E-mail us directly at TestPlots@FarmJournal.com, and we’ll respond on this blog to provide an interactive dialogue.

What Causes Corn Leaves To Turn Purple?

Aug 30, 2011

Question: The corn in this area (southern MN) looks very good, but I have noticed some plants have developed purple leaves on the mid to upper portions of the plant. What is this? And should I be concerned about it for next year’s corn?

 
Answer: I would say you may be observing the result of a phosphorus deficiency in your corn. If severe enough, you will see spiraling of the corn kernel rows occur. Along with the potential for a phosphorus deficit in your corn, bear in mind that nearly anything that restricts root growth has the potential to cause corn leaves to purple.  I would be concerned about identifying the exact cause of the purpling so you know exactly what you’re dealing with and can take some actions to prevent it next year, if need be. Soil and tissue tests would be a good investment for you to consider.
 
Soil pH is key to phosphorus availability because if soil pH is too high or too low, the nutrient will not be available to the plant
 
Pest injury becomes evident above ground as areas of yellow and stunted plants develop. Sometimes purpling of the leaves indicates a phosphorus deficiency, along with browning of the leaf tips and edges.
 

Do You Have Soybean Aphids?

Aug 23, 2011

If you have late-planted soybeans, be on the lookout for aphids, according to Ron Hammond, Ohio State University Extension entomologist. The following article, developed by Jennifer Stewart of Purdue University, offers more insights about this pest and what you can do to protect your soybean crop now.

Late-planted soybeans mean aphids in August
Because farmers across the Corn Belt planted crops later than normal this season, scouting for soybean aphids might seem later than normal, according to one Ohio State University Extension entomologist. Even so, the aphids' appearance is right on schedule, agronomically speaking.
 
"We're just hitting the late R4, or early R5 stages of soybean development, and we now have soybean aphids building up in Northern Ohio," said Ron Hammond, OSU Extension entomologist and professor in the Department of Entomology. "We're seeing some fields sprayed for soybean aphids, which would normally be considered pretty late, but because of how late the beans are, this is actually the time we should see aphid activity."
Hammond said the corn crop has reached the stage where insect damage is not as much of a concern, while soybeans are still very much susceptible -- most notably from aphid feeding.
Extension researchers and educators recommend farmers consider spraying for soybean aphids when a field averages 250 aphids per plant. Hammond notes that figure is a field average, not merely a count of 250 aphids on any given plant in a field.
"This is the threshold for spraying," he said, "but the population that really concerns us in terms of injury to the plant is 750 aphids per plant or above."
He said the conservative insect count used in the recommendation is to ensure fields do not experience actual economic injury to the crop.
In terms of pod-feeding insect injury, Hammond's attention is also focused on the second generation of bean leaf beetles.
"The last of the second generation is starting to come out," he said. "There are going to be so many soybean fields that are still green when the second generation comes out, they should really disperse themselves. That means we'll either have very few fields at risk because we'll see low concentrations of insects in any given field, or we'll have a lot of fields at risk because the fields are staying green longer."
The biggest advice Hammond offered to farmers is to continue scouting their fields as August wanes to keep abreast of aphid or bean leaf beetle feeding.
"Growers should scout their fields and take those insect counts so they can make good decisions," he said. "Soybeans are later than normal, so they could be susceptible, and we need to keep on top of our scouting."
 

Where Can I Learn To Calibrate A Yield Monitor?

Aug 19, 2011

Question: Where can I find out how to calibrate a yield monitor?

Answer: A calibrated yield monitor is unbeatable. It’s one of the most valuable tools for a farmer. In 2010, farmers were reporting 100 bu. swings through the field, and we can’t have that when we’re calibrating. The following article was written by Robert Nielsen, Extension corn specialist at Purdue University, and provides a detailed overview of the value of yield monitors and how to calibrate one.
 
Yield Monitor Calibration: Garbage In, Garbage Out
Grain yield monitors have been in vogue for more than 10 years and can provide valuable spatial yield information to growers. Yield monitors offer a visual diversion from the boredom of harvest. They provide a source of historical yield records more detailed than that offered by elevator weigh tickets. They provide a viable alternative to weigh wagons or farm scales for measuring yields in on-farm research trials. When connected to a DGPS receiver, yield monitors generate a source of geo-referenced yield data that can enable growers to document the extent of spatial yield variability within fields.
 
Most yield monitor systems operate on the same general principles. Typically, a grain flow impact sensor is located at the top of the clean grain elevator. Grain flow hits the impact sensor on its way to the loading auger. The impact of the grain flow is translated to electrical signals by the sensor. The electrical signal data are translated to estimates of grain flow rate by the yield monitor's internal software. If equipped with a DGPS receiver, the yield monitor matches the individual yield estimate data points to geographic locations in the field.
 
Yield estimates on a whole field or individual load basis made by a well-calibrated yield monitor are accurate in the sense that they often very closely match yield estimates calculated from weigh wagons or commercial weigh scales. However, to achieve a satisfactory level of accuracy, yield monitors must be "trained" to correctly interpret the electrical signals generated by the impact sensor into estimates of grain flow rate. Some background information may help you better understand the nature of and importance of faithfully and regularly calibrating yield monitors.
 
Calibrating a yield monitor simply requires the harvest of individual “loads” of grain that represent a range of grain flow rates (i.e., a range of yield levels) expected in the field(s) to be harvested.The amount of grain required for each calibration “load” ranges from 3,000 to 6,000 lbs (50 to 100 bu grain) depending on the manufacturer's recommendations for the specific model/make of yield monitor. The grain weight of each “load” is estimated by the yield monitor as the grain is harvested. The grain for that specific "load" is then offloaded from the combine hopper and weighed on weigh wagon or commercial scales. The actual weight is then entered into the yield monitor console and the yield monitor firmware makes adjustments to curve.
 
Conceptually, the calibration process is about fitting a response curve between grain flow rate and flow sensor signal strength in order to estimate low, medium, and high yields. Makes of monitors appear to differ in the nature of the calibration curve that is determined.
 
Some manufacturers suggest that only one grain load is necessary to perform an accurate calibration. The need for only one grain load implies that the calibration response curve is a straight-line or near-linear relationship between grain flow rates and flow sensor signals. While the standard recommendation is for only one grain load, the "fine print" in the owners' manual suggests that additional calibration loads may be added to fine-tune the accuracy when necessary.
 
Other manufacturers recommend between 3 and 6 grain loads to perform a satisfactory calibration of the yield monitor. This suggests that the calibration response curve for these yield monitors is not a straight-line, but is rather some sort of non-linear response curve that requires a number of calibration points to best "train" the yield monitor how to interpret the flow sensor signals.
 
The goal here is to "capture" the full range of grain flow rates (aka yield levels) you expect to encounter during the harvest of your fields. Capturing a range of grain flow rates can be a nuisance because it typically requires harvesting individual full header width "loads" at different speeds or partial header width "loads" at a constant speed. This headache plus the time it takes to off-load and weigh the individual grain loads are among the most common reasons why growers do not faithfully calibrate their yield monitors.
 
Yield monitor accuracy can be excellent if well-calibrated. Yield estimates by calibrated yield monitors that I use in my field-scale research trials are typically within 1 % of the actual grain weight measured with a weigh wagon or farm scales. Conversely, yield estimates can be very poor if yield monitors are not well-calibrated. The error in accuracy can be as much as 100 % if the yield monitor is taken “off the shelf” and put into service without any calibration. Errors in accuracy can easily range as high as 7 to 10 % late in harvest season if the yield monitor was calibrated only at the beginning of the harvest season. Errors in yield estimates are especially likely if the full anticipated range of harvested grain flow rates are not included in the calibration of the yield monitor.
 
Well, you may ask... who cares whether or not your yield monitor is providing you with accurate yield estimates. After all, growers are typically paid at the point of sale according to the weights printed on the scale ticket and not according to a yield map. Quite honestly, it also may not matter for simple farm record-keeping purposes.
 
However, if you want to USE the information that an accurate yield dataset provides, then you should strive to ensure accuracy in the yield estimates made by your yield monitor. Common uses for yield monitor data include comparisons of one field to another, one specific spot in a field to another, one hybrid's performance to another, early versus late harvest season, and experimental treatments in on-farm field trials.
 
Yield monitor calibration accuracy can be influenced by yield levels outside the range of grain flow rates used for the yield monitor calibration, by seasonal changes in temperature, by grain moisture content early in the season versus late in the season, by hybrids in terms of their differences for grain weight, grain shape, and grain moisture, and by field topography. Calibrating your yield monitor once a season will typically not be satisfactory. Check the accuracy of the yield monitor calibration occasionally by harvesting and weighing additional calibration loads. Recalibrate the yield monitor when necessary to maintain an acceptable accuracy. You can read more about calibrating monitors from Nielsen at the following link.

Calibrate Your Yield Monitor

What Can We Do To Control Japanese Beetles?

Aug 15, 2011

Question: This is the first year we have had trouble with Japanese beetles.  We keep checking the silks on corn and they are OK. We pulled back the shucks, and they are eating the kernels on the stalks that are still green.  Anyone else having this problem? Nothing we can do, but it sure is depressing. Guess they might move to soybeans when all of the corn dries, and then we need to spray. How long will they continue to eat and lay eggs? They are doing more damage than an earworm.

 
Answer: We are seeing quite a few Japanese beetles this year across the eastern and western Corn Belts. Erin Hodgson, Department of Entomology, Iowa State University, says, "In corn, Japanese beetles can feed on leaves, but the most significant damage comes from clipping silks during pollination. Consider a foliar insecticide during tasselling and silking if: there are three or more beetles per ear, silks have been clipped to less than ½ inch, AND pollination is less than 50% complete."
 
At this point in the season, a majority of fields are probably beyond 50% pollination, so Japanese beetles may not be economically important anymore. As you’ve indicated, however, soybeans are at risk as well and require careful scouting. Traditional defoliation levels suggest economic thresholds are 30% before bloom and 20% between bloom and podfill. Because the soybean crop is so valuable this year, growers may want consider lower thresholds.
 
Notes Hodgson, "There are many insecticides labeled for Japanese beetle control; however, do not expect season-long control from a foliar application. Adults are highly mobile and move frequently in the summer. Japanese beetles release a strong aggregation pheromone and are commonly seen feeding and mating in clusters. Beetles present during the application will be killed, but beetles migrating into sprayed fields may not be controlled. If soybean defoliation continues, additional applications may be necessary to protect the seed-filling stage."
 
More information is available in Hodgson’s newsletter article Japanese Beetle Control.

How Useful Is Test Plot Information?

Aug 11, 2011

Question: I know you like and reference test plot information a lot, but I question how useful that information really is for farmers?

Answer: I understand what your concern is and there certainly is some validity to it. There is a difference between what I call show plots and test plots. Show plots have value in demonstrating higher-end genetics, but they are typically planted next to a road to show off hybrid performance in ideal conditions. Show plots may have received extra nitrogen and two fungicide applications. Show plot results may be meaningless. Actual test plots are another matter, and they do deserve your consideration. These are plots that are able to help guide your seed choices for the next year. But you have to know how to use that information and whether it’s worth considering. The ones you want to key into are the ones that were planted with soil, climate and management practices similar to your own. Taking factors like these into account may add another 15 to 20 bushels per acre for you, compared with picking hybrids based on general plot performance. Also, look at regional plot data over a period of years. It will tell you if a hybrid is or isn’t suited to your conditions. I also recommend that farmers test-drive new hybrids by planting their own test plot or teaming up with a neighbor. If you don’t plant your own test plot, pay close attention to other local plots. Also, tell your seedsman what you want to see in hybrid comparisons and management practices. He may be able to set up some test plots that will be helpful to you.
 
The Farm Journal Test Plots were founded by Ken Ferrie and Charlene Finck to help farmers raise more bushels. Twenty years later, that mission is the driving force behind the effort.
 
One of the goals of the Farm Journal Test Plots is to stay up-to-date with emerging technologies that can help you farm more efficiently and take yields higher. In the past five years, one of the biggest technologies to come on the scene has been NDVI (Normalized Difference Vegetation Index) mapping.

What Is Goss's Wilt?

Aug 08, 2011

During the past couple of weeks we have received numerous reports from farmers concerning the presence of Goss's wilt in the eastern Corn Belt.  Farm Journal Crops Editor, Pam Smith, covered the topic of Goss's wilt for AgWeb earlier this month, and we believe the information she shared with our readers bears repeating. Do consult with your local agronomist, Extension specialist and seed supplier, if you believe you have this problem in your fields.   

Goss’s Wilt Finds Illinois Cornfields
Goss’s wilt has infiltrated the eastern Corn Belt. Prior to this year, the bacterial disease has mostly been a west of the Mississippi phenomenon.
 
Todd Thumma, Syngenta agronomy service representative, says he picked up evidence of the disease last year in northwestern Illinois. “It came in late in the season and it looks a lot like anthracnose die back at that stage so some growers may not have recognized it as a problem.” He says the symptoms are sometimes mistaken for Northern Corn Leaf Blight at this time of the year.
 
It’s important to identify Goss’s wilt because hybrid tolerance is the main defense mechanism. “Shredding stalks, burying residue and crop rotation are all management measures,” Thumma says. “However, once Goss’s wilt infects a field, it is present. Hybrid selection is your best defense mechanism.
 
There are no in-season controls. Fungicides have no activity on Goss’s wilt because it is bacterial and not fungal, he adds.
 
Goss’s wilt is carried by storms and overwinters in residue. "Bacterial diseases require some type of wounding to infect a plant," says Suzanne Bissonnette, director of the University of Illinois Plant Clinic. "Goss's wilt, caused by the bacterium Clavibacter michiganense subspecies nebraskensis, finds easy infection from tissue damage after hail, high winds and heavy rainfall."
 
Once infected, the symptoms move rapidly. Large tan to gray lesions that run lengthwise on the leaves with dark flecks or freckles are typical. Lesions may appear shiny in sunlight due to bacteria oozing on the leaf surface. Plant wilt can also be a symptom because the bacteria infect and effectively clog the xylem in the plant. On wilted plants, splitting the stalk may show dark streaking of the vascular tissue. This is easiest to see if you cut the stalk at about a 45-degree angle.
 
Bissonnette says numerous field corn leaf samples have come in over the past two weeks. Repots of the disease have come from Sangamon, Knox, Livingston, Bureau, Edgar, Shelby, Woodford and Piatt counties.
 
Fields that are corn-on-corn, fields that have detected or undetected Goss's wilt from previous seasons, fields with high corn residue and fields with weed hosts such as green foxtail or shattercane are at a higher risk for infection, she adds.
 
Bissonnette says in states where the disease occurs regularly, yield losses of up to 50 percent in very susceptible hybrids have been noted. Research indicates that dent corn inbred A632 and hybrids in which this and related inbreds are used are highly susceptible, she adds.
 
Thumma recommends growers impacted by the disease check Goss’s wilt ratings as they plan for the coming season. “Ask how they’ve conducted the tests too,” he recommends. “We field verify our hybrids in Nebraska under natural and inoculated disease conditions to make sure we put that tolerance to the maximum test.”
 
For more information on Goss’s wilt:
 
 
 
Jennifer Shike contributed to this report.

What Caused My Corn Ear Tips To Not Completely Fill?

Aug 05, 2011

Question: I’ve been checking my corn this week and the ears are filled out pretty decent except around the top; the tips are mostly empty. It’s been hot here, so I’m guessing I don’t have good ear fill because of the heat, but I’m wondering if you can give me any better idea of the cause?

Answer:You’re probably right about it being the result of the heat, if you’re in an area that had a lot of high temperatures hit your area during pollination. Tips of corn ears pollinate last and so are most susceptible to kernel abortion. If you look at the ears and see fairly uniform kernel loss around the top, that’s probably what you’ve experienced. A potassium or nitrogen deficiency is another possibility. Both of those nutrients are mobile and move from the oldest to the newest part of the plant but will look different on the crop’s leaves. Nitrogen deficiency starts at the tip of the leaf and comes down through the mid-rib, so there will be a V-pattern through the mid-rib. A potassium deficiency looks somewhat the same, so you have to look closely. That deficiency starts at the tips but then goes down through the outside of the leaves.
The grain filling period is the final important stage in growth and development of the corn crop. Stress on the crop during this time period can mean lower yields.
 
If you saw abnormal corn ear development in your fields this year, you weren’t alone. A number of farmers across the Midwest reported seeing curved, bent and/or twisted ears in their cornfields.

What Is the Value of Staging Soybean Growth?

Aug 01, 2011
Question: What value is there in staging soybean growth?
 
Answer: Staging soybeans can give you an initial sense of how those soybeans are going to yield come harvest. You also can get an idea of how a specific soybean crop is handling weather-related stress. Check out the following video, featuring Brad Beutke with Crop Tech Consulting, to learn more about how to implement the soybean staging process on your farm.
 
 
 
 
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