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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2012-16

Dates Covered: 
June 5, 2012 - June 11, 2012
Glen Arnold
Why Won’t Marestail Die?

There seems to be an abundance of fields where preplant burndown treatments did not adequately control marestail.  This can be because the burndown was applied early in spring and any residual used at that time did not adequately control later emerging plants, or because the burndown just was not effective enough.

We speculate the inability to get herbicide applied to fields last fall resulted in overwintering marestail that have just generally been tough to kill.  We have received a number of calls asking about postemergence herbicide options for control of marestail in emerged soybeans.  The news here is not good.  The best available treatment is a high rate of glyphosate with either Classic or FirsRate, which can suppress larger plants and control small plants in populations that are not ALS-resistant.  The frequency of populations that are both glyphosate- and ALS-resistant is increasing so expect this approach to have much variability both within and among fields.  None of the other postemergence soybean herbicides have significant activity on marestail, and we advise against spending a lot of money for postemergence treatments that won’t work.

We have also observed that in many fields, there is a greater difference in size between the giant ragweed and the soybeans, compared with most years.  In other words, while giant ragweed might typically reach a size of 8 to 12 inches when the soybeans are in the V3 stage or larger, this year the ragweed are approaching this size when soybeans are in more like the V1 stage. This has relevance for those growers who delay postemergence glyphosate applications as long as possible, in the hope of avoiding a second postemergence application.  Following this strategy will be more risky this year due to the small size of the soybeans relative to the ragweed.

Postemergence herbicide treatments should be timed for the size of the weed, not the size of the soybeans.  The more effective strategy would be to apply when the ragweed plants are still small, even if soybeans are small, and make a second application 3 to 4 weeks later.  Our research has shown two postemergence applications to be a more effective approach anyway, and especially where the giant ragweed population has developed any resistance to glyphosate (see also the article on giant ragweed in the April 24 issue of C.O.R.N.).

Dry Weather is Holding Back Soybean Seed Germination

Dry Weather is Holding Back Soybean Seed Germination

Soybeans that were not planted to moisture are sitting there in the ground just like they were still in the bag!  They will continue to rest in the soil until they receive adequate moisture for germination.  Soybean is an amazing crop and it will continue to sit until conditions are right.  At the Wooster location, we planted into marginal conditions for some seed treatment tests the week of May 14th.  Seedlings are in 3 different growth stages, and more keep emerging with every rain.  The one challenge will be if the seed has swelled and germinated to the point that with dry weather the cotyledons get too dry.  This will take quite a while and the cool weather that is forecast may hold this off until Ohio receives the next rain shower.

Before you start pulling the planter out again, run a germination test on the seed that has been sitting in the ground, collect a few from different parts of the field and place them on some moist (not sopping wet) paper towel, cover them with a second – moist paper towel and wait 48 hours to check.  Don’t let the towels dry out.  If the seed is healthy – it will germinate and produce a nice white root.  If it is struggling the seed will shrink.

Under these conditions, we are not too worried about pathogens during this dry spell.  This will also have an effect on inoculants.  The viability of those is compromised under these conditions and we will be relying on the native Rhizobium that is very prevalent in Ohio production fields.  The fungicide seed treatments that were applied will be good as long as the seed coat is still on the seed. 

How long should we wait?  One week after the next saturating rain, this is the length of time it takes for seed to germinate and emerge from the soil.  If you replant now, you could end up doubling your stand population which will further reduce yield due to the competition among all of these plants.  With the low levels of rain in the long-term forecast, we should avoid high populations to limit the competition among the plants for water, which this year may turn out to be a precious commodity.

Double Crop Soybeans versus Modified Rely Intercrop Soybean in 2012

Double Crop Soybeans versus Modified Rely Intercrop Soybean in 2012

Modified Relay Intercropping (MRI) is the planting of soybeans into standing wheat and double crop soybeans are planted after wheat is harvested. Vyn et al, found that relay intercropping of soybeans yielded better than double cropping of soybeans north of I - 70 in Indiana (   In 13 years of replicated trials in North Central Ohio on the MRI system, yields have averaged 75 bu/acre for wheat and 31 bu/acre for soybeans. Wheat yields in favorable growing seasons have exceeded 90 bushels per acre and while soybeans have yielded well over 40 bushels per acre.

However, double crop soybean systems may have commensurate or better yield/profit potential than MRI systems this year.  The following factors may suggest double cropping of soybeans a better option than MRI in 2012:

1.    Wheat harvest is anticipated to occur perhaps 7 to 14 days earlier in 2012; thus the growing season advantage of MRI soybeans may be mitigated. 

2.    Soil moisture levels are variable. One of the challenges of MRI is planting soybean seed at appropriate depth and with adequate soil cover to ensure seed to soil contact and uniform germination.  Planting soybeans after wheat harvest with conventional seeding equipment may mitigate the above issue often faced by farmers interseeding.  

3.    Combine wheel damage to intercrop soybeans can be significant depending upon the size of the soybean plant (smaller plants are better able to withstand wheel traffic) and the width of the combine grain table and tires.  Narrow tires and wide combine header will partially limit soybean plant damage.

4.    Not any damage/yield loss to wheat from interseeding of soybeans into standing wheat. 

5.    Better plant stands may occur in double crop soybeans because of precision seed placement, good seed to soil contact and not any combine wheel traffic damage.

6.    Double crop soybeans may permit the baling of straw after wheat harvest (a good commodity now) immediately prior to sowing of soybeans.

In either system, early harvest of wheat is recommended (around 20% moisture) to not only limit shading of MRI soybeans but also to increase  the growing season of double crop beans. Both wheat stubble height and residue require management in both systems.  In MRI soybean systems, wheat should be cut just above soybean plants.  In both systems (if not baling straw in double crop soybeans), chop wheat residue finely and spread evenly behind the combine.

True Armyworms in Grass Pastures

True Armyworms in Grass Pastures

Last week we received a number of reports of true armyworm feeding in grassy pastures, removing almost all of the leaf material in parts of the fields.  Following this heavy feeding, the armyworms were observed “marching from the field” into adjacent areas or fields.

If this type of activity is observed, growers should pay attention not only to the pastures, but also the adjacent crops areas with special emphasis on corn fields.   The only types of crops they do not appear to feed on are soybeans, although they might appear to be feeding as they nibble on soybean plants to determine whether it is an acceptable host plant.

Past observations suggest that true armyworms will not continue to feed on them, although the initial nibbling might suggest otherwise.

Western Bean Cutworm Monitoring to begin June 1

Western Bean Cutworm Monitoring to begin June 1

For the 6th straight year, OSU-Extension and OARDC will be trapping for western bean cutworm (WBC).  This is a pest of only corn and dry beans (note: NOT a pest of soybean), and has rapidly expanded its native range in Colorado and western Nebraska across the eastern Great Lakes.  In the past, our trapping began by June 15th.  Given the impact the warm spring has had in causing early emergence of most insects, we anticipate WBC to begin flight early as well.  Monitoring WBC adult emergence is critical in knowing when and where to scout for corn.

Our trap counts will be updated weekly on our Agronomic Crops Insects website:  Traps can be easily constructed from milk jugs, or using commercial “bucket-traps.”  These traps use pheromone lures, which are relatively inexpensive (lures cost about $2, and are good for about 4 weeks, so over the course of 4 months, the total for lures is $8).  Both traps and lures can be purchased from Great Lakes IPM (, and for more information see our WBC fact sheet (

What do we expect to see this year? While Ohio has not yet seen economic damage in corn from WBC, Michigan and Ontario reported heavy damage last year.  Our total counts increased last year, and we have noticed egg deposition in northwest Ohio for the past 2 years, so there is risk of damage from WBC.  However, the good start to the planting season may limit some of the potential damage.  WBC prefers to oviposit in corn that has not tasseled.  Despite the anticipated early emergence, if most of the corn has tasseled before peak flight, then feeding and damage will be minimal.  Trapping and scouting remains our best option to determine the impact of WBC. 

Weather Outlook

Weather Outlook

The overall pattern remains in place for this summer of above normal temperatures and below normal precipitation.

In the short-term, the first full week of June will feature a shift from below normal temperatures through Thursday to above normal temperatures from Friday into the weekend. Rainfall will be very spotty with a few showers possible Tuesday and Wednesday with coverage under 10-20 percent of the area and totals from a trace to a few hundredths. A few more spotty showers could occur on the weekend but overall it will be a dry week.

The second week of June will feature above normal temperatures and still normal to below normal rainfall.

Normal highs are 75-80 with normal lows 55-60. Normal rainfall is about 0.75-1.00 inches per week.








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Crop Observation and Recommendation Network

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.