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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2011-33

Dates Covered: 
September 27, 2011 - October 3, 2011
Justin Petrosino

Weather Update

Well, the trend is your friend. Clearly, our pattern has shifted toward a cooler and damper pattern. Even though the weather models have consistently suggested not as cool or damp, Mother Nature has a different mind.

As updated last week, a stubborn low will influence our weather this week with below normal temperatures and some light showers. However, heavier showers can be expected near Lake Erie. Rainfall will range from 0.10 south to 1.00 inches north on average this week, but that is after 1-4 inches of rain Sunday night and Monday. The heaviest rain early this week was near the I-75 corridor.

Looking ahead, this weekend into most of next week will see temperatures return to near normal with little or no rain and high pressure.

However, it looks like more rain chances starting around Oct. 7-9, with potential rainfall of 0.50 to 1.50 inches.

Overall, temperatures will be near or slightly cooler than normal for the next 2-3 weeks and rainfall will be normal to above normal.

This could now affect harvest when combined with recent rains.

We will monitor this since this is a change from our climate models earlier indications.

No widespread freeze is forecast.


Soil Compaction Management at Harvest Time

Farmers are eager to harvest soybeans and corn but the fields are very soggy in much of Ohio. The danger of causing soil compaction is therefore high.  Let’s look at ways to increase the resilience of the soil to compaction, to avoid compaction, and ways to alleviate compaction.

1) Make soil more resilient to compaction.

Resilience is a term used by ecologists to describe the ability of an ecosystem to resist perturbation or disturbance by resisting damage and recovering rapidly. Soil can be made to resist compaction by eliminating tillage, increasing organic matter content, and maintaining a living root system in the soil for as much time as possible. Any long-term no-till farmer will testify to the fact that tires do not sink as deep as in tilled soil. Soil that was tilled this spring or even in last year’s spring, will be more susceptible to compaction than a soil that has been in no-till continuously. Increasing organic matter content will also increase the resistance of the soil to compaction, because the spongy humus maintains porosity and also increases aggregate stability. Finally, a living root system at time of traffic would increase the resistance of the soil to compaction. While it is uncommon to see living root systems at harvest time, some exciting work is being done at Penn State University with establishment of cover crops into standing corn or soybean, combined in one pass with herbicide application and side-dressing.  Resilience also includes the concept of kicking back after disturbance. To make soil kick back from the effects of compaction, it is important to try to establish a cover crop after harvest. The roots of the cover crop will help alleviate compaction that has been caused. It is also a practice that helps increase biological activity in the soil – the mycorrhyzae and bacteria growing in the rhizosphere of cover crops produce glomalin and other organic substances that improve aggregation of the soil. If manure is available to give the cover crop a boost and supply additional food for soil microbes that will also be helpful. It should also be noted that without soil disturbance and leaving soil covered with mulch smaller and larger organisms such as nightcrawlers will be much more prevalent and active than if soil is tilled and left bare. Therefore, fall moldboard plowing should be avoided especially, and even chisel plowing in the fall will reduce the activity of these organisms that can help soil kick back from the effects of compaction while also improving drainage of the soil.

2) Avoid compaction

It is advised to stay off the field until conditions are fit for traffic, but sometimes we never reach those conditions! At least, try to avoid creating ruts. If you have different soil types on the farm, start harvest on the better-drained soil types first. Although this is a bit early yet, a little frost in the soil will also help to make the soil much less sensitive to compaction. I assume all of you Ohio farmers are aware of the great importance of increasing tire foot print by using flotation tires, duals and reducing tire pressure because key research in this area was done by Bob Holmes and Randall Reeder at OSU. Their research also showed that tracks can do a very good job as long as the weight of the vehicle is equally distributed along the whole length of the track. The effectiveness of flotation tires is all determined by inflation pressure – inflated at high pressures they will cause much more compaction than at low pressures. Check inflation tables to determine what the minimum allowable pressure is for your tires. If you need to get new tires, ask your equipment representative about tires that cause less compaction. Radial tires have a bigger footprint than bias-ply tires and are therefore recommended to avoid compaction. As far as harvest traffic: Keep those trucks with road tires out of the field. Axle load also plays a role, with axle loads above 10 tons being able to cause subsoil compaction that will be virtually permanent and very difficult to alleviate. Also, try to limit repeated traffic to certain areas of the field. Although these will be more compacted, it will be possible to correct compaction here without having to do remedial action on the whole field.

3) Correct compaction

When compaction has been caused, remedial action may be needed. This is especially the case if ruts have been created. If no ruts are seen it is probably not needed to do tillage – instead plant a cover crop to use the living root system to alleviate compaction. Ruts need to be smoothened out to be able to plant the next crop successfully, however. If ruts are uniformly distributed across the whole field, some type of tillage may need to be done on the whole field. In many cases, however, ruts are localized and only need localized repair. Remember the negative consequences of tillage! It will be necessary to till deeper than the depth of compaction. Shallow ‘vertical tillage’ tools that only do tillage in the top 4 inches will not be sufficient to manage soil compaction. Very tough shanks are needed that will penetrate instead of bounce on top of the compacted layer. New subsoilers can do maximum fracturing without doing much surface disturbance with straight or bent-leg shanks. Parabolic shanks do much more surface disturbance and will need more secondary tillage for seedbed preparation and are therefore not preferred. Deep tillage may be what you could use in the fall, and then come back in the spring to smoothen the field up with a field cultivator or disk harrow. However, it may be tough to find the right soil moisture conditions this fall for deep tillage. Deep tillage should fracture the soil and it therefore needs to be performed in relatively dry soil. With the temperatures coming down now the soil is not likely to dry out sufficiently, and it may be necessary to wait until spring to do deep tillage. Deep tillage can be performed in a living cover crop in the spring – if you use the modern, low disturbance subsoilers.  So let subsoiling not deter you from planting a cover crop. The more tillage you do, however, the more you set yourself up for increased compaction problems in the future.

Fall Herbicide Treatments

Fall Herbicide Treatments

Consider this your annual reminder on fall herbicide treatments.  We have published this same type of information fairly frequently in C.O.R.N., and our suggestions for fall treatments have not really changed much.  Links to previous articles are listed at the end of this article.  Herbicides are applied in the fall primarily for control of an existing infestation of winter annuals or marestail, volunteer wheat, biennials (wild carrot, poison hemlock), or cool-season perennials (dandelion, quackgrass, Canada thistle) that are most susceptible to herbicides in the fall.  It should be an interesting fall to get herbicide applied, based on the extended harvest season.  We have already been asked a number of times how late in the fall herbicides can be applied and still be effective.  In our research, herbicides seem to be effective for control of winter annuals and biennials well into December.   The rate of plant death can slow considerably, but this is not a problem since weeds just have to die by early spring.  Control of perennials typically declines in late November or early December though, depending upon weather. 

We consider the fall herbicide application to be an essential component of an effective marestail management program, although fall is not where the majority of the money should be spent on managing this weed.  Even where the herbicides lack residual, the fall treatment seems to enable more effective control of marestail the following season.  In some cases, it’s probable that you don’t even know how much the fall treatment helps out, but our research shows that more often than not it does.  For most other weeds, a field that appears fairly weed free following corn or soybean harvest may not require fall treatment, especially given how late harvest is this year.

There is a core group of herbicide treatments that make sense to use in the fall based on their effectiveness and cost, as follows.

Glyphosate + 2,4-D – can be used in the fall prior to any spring crop.  It is the most effective of the treatments shown here on grasses, biennials, and perennials.  The combination of 0.38 lb ae/A of glyphosate plus 0.5 lb 2,4-D ester is effective for most winter annuals, and rates of both herbicides can be increased for perennials and biennials or large weeds.

2,4-D + dicamba (premixes = Weedmaster, Brash, etc) – can be used prior to corn or soybeans.  This combination controls most broadleaf weeds, but is not as effective as glyphosate-based treatments on dandelion or Canada thistle.  In OSU research, application of dicamba alone has not typically provided adequate control when applied in November, but the combination of the two herbicides seems to work.

Canopy EX or DF + 2,4-D – can be used prior to soybeans.  The only one of the treatments listed here that provides residual control into the following spring/early summer.  The lower labeled rates of Canopy are adequate for control of emerged winter annual weeds.  Canopy DF may not adequately control chickweed unless mixed with glyphosate, metribuzin, or Express.  Canopy treatments have been the most effective for control of dandelion.

Metribuzin + 2,4-D – can be used prior to corn or soybeans.  This mixture controls winter annual weeds only.  The metribuzin can provide some residual weed control into later fall, but residual control does not persist into the spring.

Basis + 2,4-D – can be used prior to corn, and also prior to soybeans south of I-70 at rates up to 0.5 oz/A.  This combination is effective on winter annuals and dandelion, with some activity on biennials.

Simazine + 2,4-D – can be used prior to corn.  It controls winter annuals only.  While simazine is a fairly persistent herbicide, it provides little residual control into the spring.

Autumn + 2,4-D or glyphosate – can be used prior to corn or soybeans.  Controls winter annual weeds and can suppress dandelions, but overall is not as effective as Basis or Canopy treatments.  The 2,4-D or glyphosate carries more of the load for this treatment compared with the others shown here, so higher rates of these herbicides maybe required.

Express + 2,4-D – can be used prior to corn or soybeans.  Controls winter annual weeds and dandelion, but less effective than Basis or Canopy treatments on the latter.
A few additional points:

1.  Speed of plant death is not essential, so avoid spending money on products that result in faster activity without contributing much to control (e.g. Aim). 

2.  Chlorimuron (Canopy) is the only residual herbicide that provides substantial residual control into the spring, and only for weeds that are not ALS-resistant.  While we occasionally observe a small amount of residual control into spring from Valor or cloransulam (FirstRate), these and other residual herbicides should be applied in the spring where they have substantial utility.  It’s largely a waste of money to apply them in the fall.

3.  The bulk of the money spent on weed control should be used in the spring/summer, not the fall.  In other words, fall treatments should not substitute for a comprehensive, in-season herbicide program.

Links to several previous articles that cover fall herbicides, in the event that the information provided here is insufficient: 

“The ABC’s of fall herbicide treatments”

“Should residual soybean herbicides be applied in the fall?”

“Fall herbicide treatments – focus on marestail management”


Picking Your Transgenic Corn Hybrids for 2012

Picking Your Transgenic Corn Hybrids for 2012

An issue facing corn growers this fall and winter when purchasing corn for next summer centers around the recent announcement of western corn rootworms developing resistance to Cry3Bb1. The trait is one of the rootworm-control Bt genes that has been incorporated into various corn hybrids including YieldGard VTRW and YieldGard VT Triple, and in the pyramided hybrid SmartStax.  This was reported on in July and we addressed it in an article in the C.O.R.N. newsletter from Aug 9-16, Issue 26.  Currently, this resistance has possibly shown up in southern Minnesota, northern Iowa, and northwest Illinois.  Reports are that these fields had been in continuous corn for the past 3-4 years, and relied on a single Bt gene, Cry3Bb1, during that time.

While researchers and companies further examine this phenomenon in those states, the question is what should growers in Ohio do IF they plan to use Bt transgenic hybrids for rootworm control.  At this time, we do not see any reason why hybrids containing the Cry3Bb1 gene should not be used.  There are no reports of problems in Ohio of significant injury when using these hybrids, and we need to remember our rootworms populations are not as heavy or widespread as in those states to our west.  And with SmartStax, there are two other Bt genes, Cry34/35Ab1, that would control the rootworm larvae.

However, we do see this concern as a good learning experience on what growers should do to limit the potential for resistance to develop.  1)  Rotate to soybeans or another nonhost crop, 2) use a Bt hybrid expressing a different corn rootworm Bt protein than what has been used the previous year if growing continuous corn, 3) use a pyramided Bt hybrid that expresses multiple Cry proteins targeted against corn rootworms, 4) use one of the corn rootworm soil insecticides at planting which are still very effective, 5) if rootworm problems have not been that heavy in your area, consider a high rate of a seed treatment (although realize they have not been that effective if rootworm populations are extremely high), and finally 5) make use of the appropriate refuges!

For effective corn rootworm management, it is important to use a long-term, integrated approach that includes multiple tactics.  Too many growers have relied on a single tactic for too many years, and unfortunately, resistance is apparently beginning to emerge.

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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.