CORN
Crop Observation and Recommendation Network

September 11 - 17, 2000
C.O.R.N. 2000-30

In This Issue:

A) Harvest Aids in Corn and Soybeans
B) Managing Winter Annual Weeds Are Fall Herbicide Treatments Necessary?
C) Watch for Poor Kernel Set in Corn
D) Corn Stalk Rots; Anthracnose and Gibberella:
E) Corn Borer Injury Observations
F) Identification of Soybean Aphid in Ohio Confirmed
G) Yield Monitor Calibration Tips
H) Precision Agriculture Topics Highlighted at Farm Science Review
I) Visit the OSU Agronomic Crops Team at the Farm Science Review and Receive a Free Gift

A) Harvest Aids in Corn and Soybeans - Jeff Stachler CORN Questions

Many corn and soybean fields have scattered weeds to thick patches of weeds, due to factors such as ALSresistance, frequent rainfall, and thin crop stands. These weeds will slow down harvest, cause added mechanical stress to the combine and increase risk for breakdowns. There are only two ways to reduce the weed biomass in the field for easier harvest: 1. A hard freeze (less than 25 degrees F for several hours) 2. Herbicides.

Waiting at least a week after the freeze will allow the weeds some time to decay and become more brittle, allowing easier harvest. For soybeans, Glyphomax Plus, Roundup Ultra and Touchdown can be applied to soybeans after pods have set and lost all green color. Glyphomax Plus and Roundup Ultra may be used at rates of up to 6.0 quarts per acre for ground application and up to 1.0 quart per acre for aerial applications. Touchdown can only be used up to a 1.6 pint per acre rate. For these products add ammonium sulfate (AMS) and use as high of a rate as possible to achieve more rapid and effective control, since the weeds are very large. Wait at least 7 days after application, but additional time will help to dessicate the weeds. Gramoxone can be applied when at least 65 % of the pods have reached a mature brown color or when seed moisture is 30 % or less. Apply up to 11.0 fluid ounces per acre of Gramoxone Max and add crop oil concentrate at 1.0 % v/v or surfactant at 0.25 % v/v. Wait at least 15 days after application before harvesting. The better the coverage the better the control, since it is a contact herbicide.

In corn, Roundup Ultra can be applied after the corn has reached physiological maturity (blacklayer) and grain moisture is 35 % or less. Roundup Ultra may be applied up to a rate of 3 quarts per acre for ground applications and up to 1.0 quart per acre for aerial applications. Harvest must be delayed at least 7 days after application.

• Other Considerations
  The greener the weeds, the more effective the treatments (including a freeze) and greater likelihood of reducing weed seed viability.
  
• The warmer the temperatures, the better and more rapid the kill.
  
• The sunnier the weather, the better and more rapid the kill.
  
• Glyphomax Plus, Roundup Ultra and Touchdown can provide more longterm control of perennial weeds as compared to Gramoxone Max.
  
• No herbicide treatment or freezing weather will completely get rid of eastern black nightshade berries.
  
• Do not apply harvestaid herbicides to soybeans or corn grown for seed!

B) Managing Winter Annual Weeds Are Fall Herbicide Treatments Necessary? - Mark Loux and Jeff Stachler CORN Questions

Populations of winter annual weeds seem to have been at an all time high over the past several years. Weeds such as common chickweed, henbit, purple (or red) deadnettle, and marestail (horseweed) have been difficult to manage in the spring in some fields, and have interfered with tillage, and crop establishment and earlyseason growth. A major complaint about chickweed is that it keeps soil from drying in the spring. Winter annuals can also harbor insects and possibly soybean cyst nematode. Will the fall/winter of 2000 and 2001 provide us with yet another bumper crop of winter annuals? At this point in time, we would have to say yes. We have already observed winter annuals in a number of fields, and relatively wet conditions should promote emergence and growth. Some questions and answers follow to help you sort through management strategies for winter annuals:

1) What is the life cycle of winter annual weeds? Chickweed, deadnettle, mustards, and most other winter annual weeds emerge in the fall, survive the winter with little or no further growth, resume growth in latewinter or early spring, and flower and go to seed in latespring or early summer. However, some winter annuals can demonstrate summer annual weed characteristics under certain environmental conditions. We have occasionally observed mustard and marestail emerging with the foxtail, lambsquarters and other summer annual weeds over the month or so following corn or soybean planting. The growing season of 2000 provides a good example of the ability of marestail to emerge over much of the year. When chickweed gets an early start in late summer, it may set seed in late fall or early winter.

2) Why have winter annuals populations increased? Several factors may have caused the increase in winter annual weeds. Most winter annuals emerge in the fall, and the warm weather in late fall during the past several years has resulted in higher populations. Warm weather in late winter of 2000 also promoted growth of winter annuals that had emerged the previous fall. Winter annuals have been more of a problem in the southern half of Ohio, and we assume this is due to warmer soil temperatures later in the fall compared to farther north. Notillage tends to promote winter annual populations, since there is no tillage in fall to disrupt their emergence. However, winter annuals can emerge after an early fall tillage, and have been a problem in tilled as well as notill fields. Early soybean harvest in 1999 allowed earlier than typical fall tillage in some fields, providing a window after tillage for winter annual emergence. Another factor may be the switch from preplant/preemergence herbicide programs (Squadron, Canopy etc.) to Roundup Ready and other postemergence programs, since we have observed winter annual weed problems showing up more often following postemergence programs. If so, this may indicate that the preplant herbicides are either: 1) preventing seed production by these weeds in the spring, or 2) persisting into the fall at rates that are high enough to reduce winter annual emergence. Continued problems with winter annuals may warrant reconsideration of the utility of total postemergence programs.

3) Can winter annuals be controlled with spring burndown treatments? Yes, but control is often more variable and more difficult than in fall, due to weed size and weather conditions. Herbicides are more active under the warmer temperatures in late spring, but winter annuals should probably be controlled in early spring to allow maximum time for soil drying and herbicide activity that can be very slow. Because they generally are completing their life cycle in late spring, one management strategy when winter annual populations are low is to till or apply burndown herbicides around the time of planting, and plant the crop regardless of how effective the tillage/herbicides were on the weeds. This can be an adequate strategy, since the winter annuals are most likely reduced in vigor and are unlikely to interfere with early crop establishment. However, as crop planting is moved earlier and winter annuals increase in density and size, a more aggressive management strategy will be needed and fall or early spring applications should be considered.

4) How effective are fall treatments? In general, herbicide treatments or tillage in late fall (November) seem to be much more consistently effective than spring treatments, especially in dense stands of winter annuals. Weeds are smaller and more susceptible to herbicides in the fall, and weather may be more conducive for herbicide activity. Soil conditions may also be bettersuited to sprayer traffic.

We conducted research at three sites in 1999/2000, with a number of fall and springapplied herbicide treatments. Fall treatments were applied in midNovember, and spring treatments in mid to lateMarch. One site had a dense chickweed population and the other two had moderate to dense populations of purple deadnettle. Most treatments included 2,4D amine, but it contributed essentially no control of chickweed and poor control of dead nettle (but 2,4D ester is cheap enough that it should probably be included in any treatment of this type). Results varied by weed species, making it somewhat difficult to develop a single management strategy for both weeds.

Fall treatments providing at least 90% control of chickweed included Steel, Command, glyphosate (1 pint), and Banvel (1 pint). Note: Command are not currently labeled for fall application. Fallapplied Sencor and Sencor+Python combinations were more variable, with control ranging from about 60 to 80% depending upon rate (the 8 oz rate of Sencor provided close to 80% control). Spring treatments providing the most effective control included glyphosate (94%), Gramoxone (80%), and Sencor (74%).

Control of deadnettle varied by site and size of the weeds at the time of application. Plants were considerably smaller in the spring at our site near South Charleston (1 inch), compared to our site near Amanda (6 inches). At South Charleston, fall application of Python+Sencor, Canopy (2 or 4 oz), Steel, Command, Sencor (8 oz), or glyphosate provided good to excellent control (although Sencor was somewhat more variable than the other treatments). At Amanda, good to excellent control occurred with fallapplied Canopy (4 oz), Command, or Sencor (8 oz). Fallapplied glyphosate and lower rates of Canopy and Sencor were more variable at Amanda, but still provided at least 80% control. For spring treatments at South Charleston, adequate control resulted from Sencor (98%), Canopy (89%), or Python+Sencor (88%). At Amanda, the most effective springapplied control was 79% with Sencor or Canopy. Gramoxone applied in the spring provided some control at both locations (59 to 69%). Glyphosate was much less effective in the spring than in the fall for deadnettle control.

We did not include Canopy XL in these studies it apparently has excellent activity on deadnettle and star of Bethlehem but no activity on chickweed. Dupont has data showing good chickweed control with mixtures of Canopy or Canopy XL with low rates of Express in the fall. We also did not test Princep, but a fall treatment of Princep + 2,4D should be fairly effective on a number of species where corn will be planted next spring. Our standard rate of glyphosate in these studies was 1 pint/A, and control of deadnettle may be improved with higher rates (Monsanto recommends at least 1 1/2 pints/A for fall control of winter annuals).

5) Fall herbicide recommendations for a mixture of winter annual species We assume that a number of fields will have both chickweed and deadnettle. Fall application of glyphosate + 2,4D, where the glyphosate rate is at least 1 1/2 pints/A, should be effective except possibly where deadnettle is more than a few inches tall. Where winter annuals are less than a few inches tall, application of Sencor or Gramoxone plus 2,4D may be sufficient. Our data seem to show little benefit to Python/Sencor mixtures, compared to 8 oz/A of Sencor alone. For control of larger plants,combinations of Sencor or Canopy/Canopy XL plus Gramoxone or glyphosate (with 2,4D) should also provide broadspectrum control. Herbicides should be applied with surfactant or crop oil to maximize activity.

6) Will fall treatments eliminate the need for a spring burndown treatment? A latefall herbicide treatment that controls all of the weeds present at that time should often provide near complete winter annual control through spring crop planting, regardless of whether the herbicide(s) has residual activity. Some emergence of winter annuals can occur in spring, but this seems to be minimal. However, a number of other weeds can emerge in early spring and reach considerable size by planting, including ragweeds, smartweed, atriplex spp, quackgrass, and Canada thistle. If any of these weeds are present in the spring, a burndown treatment should be applied at or before planting. Where Roundup Ready soybeans are planted, glyphosate could be applied after planting if earlyemerging weeds are not too large. Weeds that emerge in early spring should not be allowed to coexist with soybeans until the time of a typical postmergence treatment (4 weeks after planting), or yield loss may occur. In nonRoundup Ready soybeans, fall applications of herbicides with residual (Canopy, Canopy XL, Scepter, etc.) may provide sufficient control to avoid the need for a burndown treatment at planting, but fields should be scouted at that time to make sure weeds are not present. Weeds that emerge in early spring can be extremely difficult to control with postemergence herbicides in nonRoundup Ready soybeans.

C) Watch for Poor Kernel Set in Corn - Peter Thomison CORN Questions

I've received several reports recently related to poor kernel set, along with some ear samples documenting the severity of the problem. In the worse cases, the ears contained just a few scattered kernels or were totally barren of kernels. The ears were also characterized by tight husks, with silks bunched up inside the husks at the tip of the ear. In sampled problem fields, over 10% of the plants were affected. Although a number of factors can cause incomplete kernel set, including drought conditions during pollination, pollen feeding and silk clipping insects, nutrient deficiencies, leaf blights, etc., the kernel set problem described above, is most likely due to a phenomenon commonly referred to as "silk balling." Silk balling describes a type of silk elongation and emergence failure caused by the silks simply "balling up" or "knotting up" inside the husk leaves. For more information on silk balling, consult the July 24, 2000 issue: http://www.ag.ohio-state.edu/~corn/archive/2000/jul00/0024.html for an article that contained a good overview of silk balling written by Dr. Bob Nielsen at Purdue.

The cause of this problem is not clear, but seems related to cold nights during silk emergence/pollen shed. Early silk growth may have been slowed during cold periods followed by rapid elongation as conditions warmed that could have resulted in the silk balling problem. Hybrids usually vary in the severity of this problem, as those with relatively tight husks seem to display the most silk balling. I have observed silk balling in Ohio during previous cool summers, 1992 and 1994, and the 2000 growing season has also been unusually cool. In Ohio, temperatures in July ranged from 2.5 degrees below average for the week ending July 2, to nearly 7 degrees below average for the week ending July 23. As for differences among hybrids this year, in the cases I've heard about the problem has been limited to specific hybrids with other hybrids growing in near proximity not showing silk balling or abnormal kernel set.

D) Corn Stalk Rots; Anthracnose and Gibberella: - Pat LippsCORN Questions

The potential for corn stalk rots and lodging appears to be relatively high this year in different parts of the state. Weather conditions have varied greatly across the state during the growing season with some locations receiving adequate to surplus moisture and others being quite dry. The potential for stalk rot will vary according to several factors including weather and other stresses. Severe leaf damage due to leaf diseases like common rust, gray leaf spot or Stewart's bacterial leaf blight will predispose plants to higher levels of stalk rots. Other stresses can include high plant populations and nitrogen deficiency. Regardless of the stalk rot disease affecting the field, the relative damage is the same: premature death of plants and weakened stalks prone to lodging.

So far this year we have seen damage from both Anthracnose stalk rot and Gibberella stalk rot. Anthracnose causes premature death of the plants and frequently causes top dieback' on certain susceptible hybrids. Anthracnose stalk rot is more common in continuous corn fields, especially those in reduced tillage. The anthracnose fungus survives in old corn residues and infects the leaves of the plants. Spores are rain splashed onto stalk surfaces where the fungus infects the stalks. Shiny black streaks or spots on the surface of the stalks is characteristic of anthracnose stalk rot. Like the antrhacnose fungus, the Gibberella fungus survives from one crop to the next on corn residues. However, it enters the stalks via the roots and moves into the stalks when plants become stressed. The pith inside the stalks begins to disintegrate causing weakened stalks. Gibberella stalk rot can be identified by the pink discoloration of the pith when the stalks are split open.

As corn growers prepare for harvest, scouting fields is just as important as getting the combine ready. Plants that die prematurely are most prone to lodging. Look for plants with stalks that loose their green color before other plants in the field. Tear off the lower leaf sheaths to examine the stalk surface and squeeze stalks above the brace roots to see how rotted they may be. Fields should be assessed for stalk rot by examining a hundred or so plants throughout the field. Randomly select plants, bend over and squeeze one of the lower internodes on each stalk. Record the number of soft stalks and plan to harvest those fields with the highest percentage of soft stalks before they lodge. Management of stalk rot diseases is through selecting hybrids resistant to the disease or to lodging, crop rotation, destroying old corn residues, avoiding stress through water and fertility management, and planting proper plant populations for the available fertility.

E) Corn Borer Injury Observations - Hal WillsonCORN Questions

During the month of September, we split many corn stalks comparing various treatments for European corn borer. Most of the stalk splitting is focused on evaluation of Btcorn trials run on OARDC research stations and various onfarm trials conducted in cooperation with a number of OSU Extension agents. Last week, we evaluated trials at the Western branch station comparing Bthybrids to comparative isolines. Corn borer injury observed in the nonBt hybrids averaged 0.48 cavities per stalk which is equivalent to the average level of corn borer injury of 0.41 cavities per stalk observed in similar trials conducted at the Western branch over the previous three years. In brief, it appears that we are experiencing another year of relatively low corn borer injury. While working in our Btcorn plots last week, we found a few milkweed plants in the plots. In the process of sampling corn stalks, we observed a big healthy Monarch butterfly larvae on one of the milkweed plants. For the record, the Monarch butterfly infested milkweed plant was located in the middle of a Btcorn plot.

F) Identification of Soybean Aphid in Ohio Confirmed - Hal Willson & Ron Hammond CORN Questions

In last week's CORN newsletter, it was reported that Ron Hammond (OARDC) had collected aphids from soybeans in Fulton, Lucas and Wayne counties that were suspected to be the new soybean aphid, which had recently be reported infesting soybeans in a number of states in the north central region. Identification of the aphids collected on Ohio soybeans as the soybean aphid was confirmed by taxonomists a few days later.

On Friday (Sept. 8th), we collected aphids from soybeans at the Western Branch Station in Clark county. The aphids collected at the Western Branch Station match the general description of the soybean aphids, but the identification of the aphids has not yet been confirmed. The aphid infestation observed was not economic. The underside of about 10 to 20 trifoliates had to be closely inspected to locate a few aphids. Occasionally, we would find a small colony of adults and nymphs. Given the distribution of initial observations of soybean aphids in Ohio plus reports received from other midwest states, it appears that the geographical distribution of the soybean aphid may be very widespread.

G) Yield Monitor Calibration Tips - Nathan WatermeierCORN Questions

When harvest time approaches it can become time consuming and discouraging to calibrate yield monitors on combines. Improperly calibrated yield monitors can essentially generate useless or difficult to interpret data. However, taking the time and patience to calibrate a yield monitor properly can go a long ways when it comes time to make important decisions from your yield data.

In order to maximize the benefits of your yield monitoring equipment here are a few tips you should know about before you head to the field. For more information see: Yield Monitor Calibration Tips, Making the Most From your Data: http://precision.ag.ohiostate.edu/library/ymonitor.html

Before Operation: 1. Become familiar with your yield monitoring equipment. Information provided by your dealer or manufacturer through onsite support, training sessions, users manuals and videos are all ways to learn about your equipment. Each yield monitor has a specific way to be calibrated which is outlined in the manufacturers calibration procedures manual.

2. Back up any data from the PCMCIA memory cards if you have not done so already from the previous season. After the previous harvest data is backed up delete the files from the memory card.

3. Check all cables, connections, and sensors for wear or damage from mice.

4. Inspect the flow sensor. Look for wear on the grain elevator and missing or worn paddles. Check to make sure that the spacing between the paddles and the top of the elevator meets the manufacturers requirements.

During Operation, Prior To Calibration:

1. Check to see if you are receiving good differential correction from either Coast Guard, WAAS, or your satellite subscription provider. If you have a satellite subscription make sure it is renewed so you will not be caught in the middle of the field during harvest with out service.

2. Make sure to set row width according to number of rows for a row crop header and about a foot less than the width of a cutting platform header.

3. Make sure the combine sensors are working properly. Engage the separator and observe the elevator speed on the monitor. Put the combine in drive and make sure the ground speed indicator is working. Check the header stop height.

4. Before calibrating loads make sure you will be using accurate scales to weigh the grain. Certified scales or calibrated weigh wagons are recommended. If you are using weigh wagons it is recommended to leave the wagon in one location in the field. Moving the weigh wagon through a field causing it to shake and bounce can throw off the calibration of the weigh wagon. Make sure you are also using the same scales throughout calibration.

During Calibration:

1. Harvest calibration loads at different flow rates. Yield will vary throughout the field. Adjusting flow rates will improve accuracy. When calibrating loads it is recommended to use loads between 5,000 to 8,000 pounds. This helps reduce variability with excess grain that may be in the combine.

2. Gather loads in well represented areas of the field. Avoid starting calibration loads on turn rows, weed patches, or areas of major topography changes in the field. Hill sides and rolling ground can impact calibration load data because of how the grain impacts the flow sensor. If you are unable to avoid topographical changes make sure you get a good representation of loads going upanddown hill and sidetoside of a hill.

3. It is recommended to calibrate for each type of grain for each year. The dynamics of the combine changes from wear and tear and can influence the outcome of your yield data. On occasion you should also calibrate for different varieties of grains. For example, calibrate for regular corn and high oil corn separately due to the differences in test weight and moisture characteristics of the grain.

4. Calibrate for different moisture levels per type of grain. For example, calibrate differently for corn below 22% moisture versus corn above 22% moisture.

During Harvest

1. Correct any malfunctions or errors indicated by the yield monitor. This can include moisture and flow sensors not working properly and loss of DGPS signal. Make sure the monitor is actually collecting data. Sometimes one can manually switch off data collection on the monitor and forget to turn it back on.

2. If you have a long harvest season it would be wise to do periodic calibration loads through the season to check or improve accuracy. It is suggested to recalibrate if you see more than 5 percent differences in error, 5 lb/bu differences in test weight, or temperature changes greater than 10 degrees.

3. If significant changes are made to the elevator chain, paddles, or flow sensor during harvest you will need to recalibrate. Tightening the elevator chain, replacing old paddles or changing the gap of the flow sensor to the paddles changes the outcome of the previous calibration.

4. If you run into problems with the monitoring equipment during harvest check through the trouble shooting information in the operators manual. Contact technical support if you are unable to solve the problem.

For more tips about yield monitor calibration contact your yield monitor manufacturer or local dealer. Additional resources, information and news about precision agriculture can be found at The Ohio State University's Precision Ag Web Site http://precision.ag.ohiostate.edu

H) Precision Agriculture Topics Highlighted at Farm Science Review - Nathan Watermeier CORN Questions

Several precision agriculture topics will be addressed this year at Farm Science Review with demonstrations and exhibits. These topics include DGPS soil sampling techniques, WAAS (wide area augmentation system) GPS, an interactive display on vision sprayer technology, and yield calibration, monitoring and mapping. The precision agriculture field demonstrations and exhibits will be held in conjunction with the Review's tillage and harvest demonstrations, from 10:00 a.m. to 4:00 p.m. on Sept. 19 and 20, and from 1:00 p.m. to 4:00 p.m. on Sept. 21. Economics of precision agriculture and the future of agricultural technologies will be presented on Sept. 20 at 2:45 and 3:15 p.m., respectively at the main exhibit area.

The Farm Science Review is sponsored by Ohio State University's College of Food, Agricultural, and Environmental Sciences and takes place at the Molly Caren Agricultural Center near London, Ohio. Tickets are $4 in advance and $6 at the gate and can be purchased from agribusinesses and county offices of Ohio State University Extension. Children 5 and younger are admitted free. Hours are 8:00 a.m. to 5:00 p.m., Sept. 1920 and 8:00 a.m. to 4:00 p.m., Sept. 21. For more information about precision agriculture demonstrations at Farm Science Review: http://ohioline.ag.ohio-state.edu/news/08_00/08_08_04.html

I) Visit the OSU Agronomic Crops Team at the Farm Science Review and Receive a Free Gift CORN Questions

The first 35 visitors, each day, to the Ohio State University Agronomic Crops Team tent at the Farm Science Review who bring a copy of this week's C.O.R.N. Newsletter will receive a copy of the popular OSU Extension Bulletin 827 "Corn, Soybean, Wheat and Alfalfa Field Guide" as a free gift. The tent will be located Northeast of the Bailey Building on Farm Avenue, adjacent to the Utzinger Garden. Agronomic Crops Team members will be on hand to answer questions and poster presentations from various team members will be on display.

Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.

Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Editor: Clark Hutson        Web Editor: Tom Rosati

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