C.O.R.N. Newsletter 2008-18

Dates Covered: 
June 16, 2008 - June 24, 2008
Jonah T. Johnson

Armyworms on Wheat and Their Movement

Authors: Ron Hammond, Pierce Paul, Andy Michel, Bruce Eisley

With the large number of wheat fields being hit by armyworm and with the wheat well into grain fill or beginning to mature, we should begin to turn our attention to adjacent fields where the armyworms might migrate to. As the wheat begins to mature, the need for spraying diminishes. It is true that the health of the upper two leaves and the spike is important to maintain good yields and test weights; however, the importance of keeping these plant parts healthy with chemical applications diminishes once grain fill is complete. For those fields that have been completely defoliated by armyworm, the damage has already been done unless significant head cutting is occurring. The extent of the yield loss resulting from defoliation depends largely on when defoliation occurs relative to grain fill, the variety involved, and the weather conditions. Losses resulting from damage to the upper two leaves tend to be highest when defoliation occurs shortly after pollination (which coincides closely with flowering), before grain fill is complete. If defoliation occurs toward the end of grain fill, losses will likely be much lower. If leaves are destroyed at such a late growth stage, sugars will be redistributed from other greens plant parts such as the spike and stems to compensate for the loss of the upper leaves.

Because of our weather, the grain fill period here in Ohio is usually relative short, and tends to be even shorter as it gets warmer. Since flowering occurred between 10 and 15 days ago in northern Ohio and because we have had warm temperatures during this period, most of the grain fill probably occurred before plants were heavily damaged by armyworm. To determine the growth stage of your crop, remove and examine a few kernels from the tip, middle, and based of 15 to 20 spikes. If the content of the kernels is milky, the wheat is at Feekes growth stage 11.1 (milky ripe); if it is soft but dry, the wheat is at Feekes growth stage 11.2 (mealy ripe); if it is hard and difficult to divide with the thumb-nail, then the wheat is at Feekes growth stage 11.3 (kernel hard). Fields that were defoliated close to Feekes 11.3 will likely suffer less yield loss than those that were defoliated at an earlier stage during grain fill. Remember, this all depends on the variety. For a very similar level of defoliation and a similar growth stage, yield and quality losses may be higher in one variety compared to another.

As the wheat becomes less succulent, larvae will often move in large numbers and continue to feed on an adjacent crop; thus the term “army” worm. Larvae will not feed on soybean and is not considered a pest on that crop, although you might see nibbling on the soybean leaf edges as larvae search for a new host plant. The crop of concern is corn. The main area in a corn field that will see significant feeding will be along the edge adjacent or nearest the wheat. If you have contour strips of wheat and corn, the entire corn area MIGHT be of concern. If greater than 25% of the corn shows significant feeding injury, an insecticide treatment might be warranted. In a large corn field, you can usually spray the edge, perhaps going 10-20 rows into the field, and control the insect. If the larvae are already in the corn, you will definitely want to go a spray pass or two beyond that area. If larvae are fairly large, you should probably use the higher rates of the insecticides. Growers should pay close attention to this movement because significant feeding can happen in just a few days. Spraying the wheat is not the best way to prevent the armyworms from moving. They no longer will be feeding on the wheat, and more than likely, the pre-harvest intervals usually cancel out the ability to spray wheat.

Double-Cropping Soybeans Following Wheat

Authors: Jim Beuerlein

Ohio farmers have an opportunity to increase their productivity by double-cropping on one million acres of wheat each year. The 10 to 12 weeks of growing season that remain after wheat harvest are enough to grow a second crop of soybeans. Although yield potential for double-crop soybeans is reduced by late planting, the value of the combined soybean and wheat crop makes this practice economically competitive with full season corn and soybean crops.

Careful management is required for production of a profitable second crop. The soybean planting date is critical in determining productivity of the system. At the time of wheat harvest, the potential yield of soybeans is decreasing by at least one bushel per acre for each day that planting is delayed. Thus every effort must be made to get the wheat harvested and the soybeans seeded as early as possible. Selecting an early maturing wheat variety can allow for harvest 5 to 7 days before the late varieties are ready. Wheat can be harvested when grain moisture is 18 to 20 percent with no loss of quality and will permit soybean planting to be advanced from 3 to 5 days. Planting the wheat immediately after the fly-safe date often hastens its development, leading to a slightly earlier harvest. If planting cannot be completed by July 10, double-cropping should not be attempted.

The straw remaining after wheat harvest must be considered. While excessive amounts of straw can interfere with the soybean planting operation, some wheat stubble (12 inches) should be left on the field to provide mulch cover for the soybean crop. Straw passing through the combine should be chopped and spread widely or baled and removed. Using a stripper header is also an ideal way to leave the wheat straw in the field without it interfering with soybean planting

Soil moisture present at the time of wheat harvest is the critical factor for determining the potential yield of the soybean crop. If soil is quite dry at the time of harvest, double-cropping should not be attempted. Soybean seed planted into dry soil will not germinate until enough rain falls to allow germination. This may occur too many days after harvest for satisfactory crop growth and yield. If the subsoil has been depleted of moisture by the wheat crop, soybean growth will depend totally on rainfall. Usually rainfall amounts during July - September are inadequate to support adequate growth of the second crop. Most failures can be avoided by not planting when the soil is dry at the time of wheat harvest. "If June is dry, do not try". The soybean crop should be planted without tillage to save all available moisture.

Selection of the proper soybean variety is critical. Varieties that are extremely early maturing for an area do not yield as well as later maturing varieties. In general, a variety with a mid season maturity rating for the area is usually the best choice. For fields near I-70 that can be planted on July 4th a variety with relative maturity of 3.4 to 3.8 will be suitable most years.

Narrow rows (7 inch) are required for maximum yield of double-crop soybeans. Because of late planting, the soybeans flower about 30 days after emergence resulting in small plants. Since the plants will be small, the planting rate should be increased to 4 seeds/ft. in 7-inch rows.

With no tillage planting, weed control with herbicide is essential for satisfactory production of the second crop. Wheat stubble ordinarily contains many weed seedlings that must be controlled. When competition from the wheat is removed, these weed seedlings will develop rapidly and compete severely with soybeans. Herbicides selected and rates of application used for weed control in double-crop soybeans should kill the weeds present at planting time and provide residual control of weeds emerging from seed. The use of Roundup Ready soybean varieties and Roundup Ultra for weed control almost guarantees perfect weed control.

Adequate amounts of phosphorus and potassium may be applied for both crops when planting the wheat.

Double-cropping is not a practice for everyone. Unless producers are willing to closely follow management procedures outlined above, they should not attempt double-cropping. By adding the value of 20 to 30 bu/A of soybeans to the value of the wheat crop, double-cropping soybeans after wheat becomes quite competitive economically with other cropping practices. In fields where soybean diseases are a major problem, double-cropping soybeans will make those problems worse and should not be attempted.

Some other general comments, there is very little seed available for double cropping and it is typically lower in germination and seed quality than is normally acceptable. So, a buyer should look at the seed before buying and be sure to note the germination percentage and when the germination was determined, as it will likely be lower now than previously. Seeding rates should be adjusted for the reduced germ percentage; the seeding rate will likely be very high and expensive.

Soybean Aphid Pipe

Authors: Ron Hammond, Andy Michel, Bruce Eisley

Many of you are familiar with the soybean rust PIPE website where you can follow the presence and movement of soybean rust across the U.S. (http://sba.ipmpipe.org). Included in this website is the ability to go to the soybean aphid PIPE website, which provides some of the same information for the soybean aphid. You can get weekly updates as to where the aphid is occurring, and also obtain information on other insects and scouting needs.

As of this year, there are new domain names that can take you directly to the soybean aphid PIPE website. These are 1) http://sba.ipmpipe.org or 2) http://soybeanaphid.ipmpipe.org . This should make getting to the soybean aphid information much easier. However, as in the past, you can still get to the aphid website by going through the soybean rust site.

Currently, there are no reports of soybean aphids in Ohio, which is already reflected in the PIPE system. As of now, only Ontario is reporting having found aphids at the PIPE site, although there are the reports of aphids on soybeans in Michigan. See last week’s C.O.R.N. newsletter for information on the aphid and how to sample for it. For even more information on soybean aphid, see the report written by the North Central Soybean Research Program (NCSRP) that is available at the Ohio Soybean Council office.

Estimating Soybean Stands

Authors: Dennis Mills

Soybeans have emerged now and evaluation of the stand maybe needed. Poor stands may occur at one time or another and producers need to be aware of the potential yield loss from those deficit stands and the cost of replanting. Soybeans have a high capacity to compensate for low plant populations and gaps in the row.
If a poor stand does occur producers should investigate. Was the poor stand the result of poor seed quality, cold wet soils, hot dry soils, planting too deep or shallow, soil crusting, herbicide injury, insect feeding, poor soil to seed contact, or disease infection? Determine if the cause can be corrected to avoid a similar situation.
One popular method to determine plant population is by using a hula hoop. This involves placing a circular measuring device such as a hula hoop on the ground and counting the plants contained within. Use the table below, listing various sizes of hoops, to determine the number of plants per acre.

Hula hoop method for determining drilled soybean populations.

Inside Diameter of Hula Hoop
No. of plants 30 in 32 in 34 in 36 in 38 in
Plants (1000/acre)
6 53 47 41 37 33
10 89 78 69 62 55
14 124 109 97 86 77
18 160 140 124 111 100
22 196 172 152 136 122
26 231 203 179 160 144


Early season diseases and replanting

Authors: Anne Dorrance, Jim Beuerlein

Soybean stands are either really good or marginal in the state this year; if they are planted. The wet soil conditions have been great for many early season seedling diseases. To assess the stands this year, look at both the number of plants per acre but also look at the health of those plants that made it. To do this, first look to see how many seedlings died shortly after emergence. This is an indication that either Pythium or Phytophthora sojae may have been active. Pythium and P. sojae are both watermolds; they are both favored by saturated soil conditions. Both are easily managed with seed treatments and of course P. sojae is best managed by choosing the best variety. Rhizoctonia can also infect young seedlings and tends to have a brick red lesion at the soil line. Dig up a few plants (unifoliate or first full leaf stage) and check the roots after you remove wet soil. If plants are white, they are healthy. If they have light tan to brown color, then they are infected with one of the pathogens above and may not make it through the year; or the yields will be negatively impacted by 5 to 10%.

For replanting, we are now in late June. For planting at this time of year, it is important to get the plants to full canopy as soon as possible. To do this, narrow rows (7.5”) and higher you must remember that seeding rates are important. Seeding rates should be bumped up to 200,000 to 250,000 plants per acre. In addition, varieties with a later maturity should be planted to stall the flowering time by a few days. The bigger the plants get before flowering then the more nodes will be set and more pods developed. However, if the plants are too late in maturity, they will get caught in the fall with a freeze. Some general guidelines for Ohio for replanting decisions:

Ohio Region Planting Date Suitable Relative Maturity Yield Potential
Northern June 1-15 3.2-3.8 20-45
June 15-30 3.1-3.5 15-35
July 1-10 3.0-3.3 10-25
Central June 1-15 3.4-4.0 25-48
June 15-30 3.3-3.7 20-40
July 1-10 3.2-3.5 15-33
Southern June 1-15 3.6-4.2 30-50
June 15-30 3.5-3.9 25-45
July 1-10 3.4-3.7 20-40


Nutrient Value and Removal of Wheat Straw

Authors: Robert Mullen, Edwin Lentz, Keith Diedrick

Due to the increasing fertilizer and straw prices across Ohio in recent times, some producers are curious about the economics of baling wheat straw versus leaving it in the field as residue. This leads to the question – what is the nutrient value of the straw being removed and should removal lead to increased fertilizer applications in subsequent years?

From a pure fertilizer value, wheat straw contains very little in the way of phosphorus (P2O5) but moderate amounts of nitrogen (N) and potassium (K2O). The actual amounts of N, P2O5, and K2O contained in a ton of wheat straw are 11, 3, and 15 pounds, respectively. A sixty bushel wheat crop might produce upwards of 2.7 tons of straw per acre, removing 30 pounds of N, 9 pounds of P2O5, and 41 pounds of K2O. Thus, straw does have some fertilizer value especially with regard to potassium and may require some additional fertilizer input in subsequent years, but, soil testing should be conducted to validate the need for additional nutrients.

Wheat straw residue also contains organic matter that when returned to the soil does have value, but it is difficult to put a dollar value on it. Continued removal of the above-ground biomass may have negative repercussions in the long-run in the form of decreased organic matter, especially if some organic residue is not returned to the soil.

Nutrient Removal and Topdressing of Hayfields

Authors: Keith Diedrick, Robert Mullen

For hay growers, nutrient removal is a little different, since most of the plant material is removed as the crop, not a choice as the wheat straw above. As it was described in last week’s C.O.R.N. article on hay economics, grass hay will remove 40 lbs of nitrogen, 13 lbs of phosphate (P2O5) and 50 lbs of potash (K2O) per ton harvested. Alfalfa removes similar amounts of phosphate and potassium per ton, but supplies its own nitrogen by fixation in the roots. Forages cropped intensively respond to adequate fertility, and topdressing is recommended when soil tests show marginal levels of nutrients.

For legume and grass hay crops, phosphate and potash topdressing is not terribly time-dependent if soil test levels are near optimum. Most producers prefer to apply these products in a split fashion; one half of the fertilizer after the first cutting, and the other half in late summer to early fall. If soil test values are marginal or low, an early fall application of phosphate and potassium (before the plants go dormant) is very helpful for the crop to store nutrients in their roots and overwinter more successfully.

Nitrogen is still a necessary input for grass hayfields and mixed hay with less than 35% legumes (alfalfa, clover, etc), and should be applied after each cutting. The usual recommendation from the Ohio Agronomy Guide is 70-80 pounds in early spring for green-up, and 50 pounds of N per acre after the following cuttings. Those producers with pastures may modify these timings and rates to assure forage biomass at the right time for grazing.

Keep in mind that some N fertilizers are volatile and can be lost to the atmosphere. Hot summer temperatures as well as soil pH above 6.5 accelerate the N losses, especially when unstabilized urea is on the soil surface. Urea can enter the soil profile with a little rainfall (0.25 to 0.50” of rain will suffice in low residue situations). If you limed a field in the spring, or if lime is on the surface, urea will volatilize even more quickly. Ammonium nitrate and ammonium sulfate are alternatives with low volatility, but they may be hard to find.

Control of common pokeweed

Authors: Mark Loux

While some perennial species have become less of a problem due to the use of glyphosate in Roundup Ready crops, reducing pokeweed populations has proven to be more difficult. Pokeweed is inherently difficult to control due to its perennial life cycle and ability to regrow from a well-established root. Successful control during the growing season depends upon use of the appropriate herbicide(s), herbicide rate and timing, and spray boom height. Pokeweed can be fairly large at the time of postemergence herbicide application, and the spray boom should be high enough to ensure coverage of the entire plant with spray.

In non-GMO corn, the best control is usually results from a combination of the full rate of an ALS-inhibiting herbicide (Spirit, Permit, or Equip) with Status at 2.5 oz/A or dicamba at 6 to 8 oz/A. Apply when pokeweed plants are at least 8 inches tall, but before 24 inches tall. Other herbicides with substantial activity include NorthStar, Yukon, Callisto, dicamba (1 pt/A), and Status.

In non-GMO and non-STS soybeans, the combination of Synchrony XP at 0.38 oz/A, Harmony GT at 1/24 oz/A, and MSO can suppress pokeweed for the season. This treatment can injure soybeans but will provide greater control than Synchrony XP alone. In STS soybeans, use Synchrony XP at 0.75 oz/A with MSO.

In glyphosate-resistant corn, apply glyphosate at 1.1 lb ae/A when pokeweed are in the bud to flower stage for a single application. Where two postemergence glyphosate treatments are planned, apply 1.1 lb ae/A when the pokeweed plants are 12 to 24 inches tall and make a second application after 12 inches of regrowth. The same recommendation should be effective in Roundup Ready soybeans. However, if using the single application strategy in soybean, the 1.5 lb ae/A rate will provide more effective control. The effectiveness of pokeweed control with glyphosate is tied very closely to rate and timing, so multiple applications of at least 1.1 lb ae/A will typically provide more effective control than a single application.

The most consistently effective strategy for controlling pokeweed is the cut-stump method. Cut the pokeweed stems off with a pruner or a sharp corn knife and apply concentrated (not diluted) herbicide to the cut surface until it begins to run off the cut surface. Glyphosate may be the most appropriate herbicide when using this method in a crop, but other non-crop herbicides are also effective in situations where they can legally be used. This method may not kill every plant, but can be considerable more effective than a single postemergence application.

Modified Relay Intercropping Field Day - June 19

Authors: Steve Prochaska

Farmers in Crawford and Wyandot have planted soybeans into headed out wheat fields with modified equipment. This planting of soybeans into standing wheat is called Modified Relay Intercropping (MRI). A field day will be held on June 19, 2007 at the OSU Unger Farm in Bucyrus (go to http://crawford.osu.edu for directions to the farm) to exhibit and discuss this alternate cropping method. The program will begin at 7:00 PM,

This system of intercropping does not use coated soybeans and wheat rows may vary from 10 to 15 inches. Interseeding occurs in late May or early June as opposed to planting in early to mid May for other systems of intercropping done in wider rows.

The MRI system offers producers many benefits. Because two crops with vastly different growing seasons and cultural requirements are produced in the same field in the same year, MRI offers producers both a production and marketing hedge. Thus, farmers in the MRI system utilize their time, equipment, land and labor during a period (normally late May or early June) to grow a second crop. The MRI system is also very favorable from an environmental perspective in that soil erosion is minimized with the small grain crop and often very little herbicide is needed to grow soybeans sown into the standing wheat.

Soybeans in the MRI system are generally sown into wheat around the pollination time period, with a grain drill, or tool bar planter. The wheat has a tramline to facilitate soybean planting. Light or the lack of it, has a profound effect on the growth of intercropped soybeans. This year, farmers have started to plant soybeans into wheat around May 20. MRI can be employed until wheat stems begin to break over. The soybean yield of this system is highly dependent on timely rains in July and August.

The wheat plant, by virtue of its wide adaptability, is able to tolerate slightly wider row spacing and the stress of soybean planting with minimal yield loss. Six years of replicated field trials on the MRI system have resulted in favorable average soybean and wheat yields (73 bu/acre for wheat and 28 bu/acre for soybeans). Wheat yields in good years have exceeded 80 bushels per acre and soybean yields over 40 bushels per acre.

Weather Update

Authors: Jim Noel

A pattern change has occurred which will allow for an overall cooler and drier pattern for a week to two weeks at least.

The outlook this week is for below normal temperatures and below normal rainfall except some areas of normal rainfall in the eastern half of the state mainly from Monday rains. Rains after Monday of this week will be light and mainly in the east with cool air aloft and afternoon heating. Temperatures will be below normal this week, highs mainly in the 70s and lows in the 50s. Some lows in the 40s are possible in the north and valley areas.

Next week should be near normal temperatures and rainfall.

Gradually we will see a ridge build across much of the U.S. with the storm track in the north. This likely will set up a ring of fire but not as strong as we saw in past week. This will result in above normal temperatures and normal rainfall with some strips of above normal rainfall especially in western Ohio by week 3, which pushes us into the 4th of July week. We will keep you up-to-date on this.


Archive Issue Contributors: 

Pierce Paul, Anne Dorrance, and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel and Bruce Eisley (Entomology), Jim Beuerlein (Soybean & Small Grain Production), Robert Mullen (Soil Fertility), Mark Loux (Weed Science) and Jim Noel (NOAA). Extension Agents and Associates: Jonah T. Johnson, Howard Siegrist (Licking), Glen Arnold (Putnam), Harold Watters (Champaign), Mike Gastier (Huron), Mark Koenig (Sandusky), Wes Haun (Logan), Marissa Mullett (Coshocton), Ed Lentz (Seneca), Bruce Clevenger (Defiance), Les Ober (Geauga), Steve Bartels (Butler), Steve Prochaska (Crawford), Gary Wilson (Hancock), Todd Mangen (Mercer) and Woody Joslin (Shelby).

About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.