CORN
Crop Observation and Recommendation Network

April 30 - May 6, 2001
C.O.R.N. 2001-11

In This Issue:

A) Scout for Cutworms and Slugs
B) Wheat Development on Schedule, Disease Level Low - Start Scouting Fields
C) Pre-emergence Herbicide for use on Emerged Corn

A) Scout for Cutworms and Slugs - Bruce Eisley and Ron Hammond CORN Questions

Adult moths of the black cutworm have been collected in pheromone traps at the Western Branch during the past couple of weeks. The moths are laying eggs and the eggs will soon begin hatching. As corn emerges, fields need to be scouted for cutworm both above and below ground injury. Pay particular attention to those fields that had a lot of winter annual broadleaf weed growth as this area might have been attractive for the moths to lay their eggs.

Both eggs and small slugs can be found in fields at this time. As corn emerges, fields need to be watched for slug activity. Scout all parts of the field and check plants for slime trails and typical feeding injury that indicate the presence of  slugs.

B) Wheat Development on Schedule, Disease Level Low - Start Scouting Fields - Pat Lipps CORN Questions

Wheat in southern Ohio is beginning flag leaf emergence (Feekes’ growth stage 8 whereas most of the wheat in northern Ohio is in first node (growth stage 6) or second node visible (growth stage 7).  Overall the wheat crop looks very good with only a few isolated problem fields.  Some fields are still recovering from winter injury due to frost heaving. Frost heaved plants have their crowns pushed up out of the ground during periods of soil freezing and thawing.  The plants that have survived are usually smaller and the crowns are exposed above the soil surface and greenish colored roots attempting to anchor the plants in the soil. On the CORN web site see a photo of a heaved plant showing the crown region above the soil and crown root development.

The dry weather we are now experiencing will limit the development of most foliar diseases. However, powdery mildew has been reported on some susceptible varieties in north central Counties where it over wintered in the field.  These fields need to be monitored over the next couple of weeks to see if the disease continues to develop.  Powdery mildew can be detected as small (eighth inch diameter) white fluffy pustules on the lower leaves of plants at this time..  In some of our field plots disease can be detected on the second leaf above the first node.  This leaf will eventually be the third leaf below the head when the plant is fully developed.  Check your fields for powdery mildew development now then come back when the plants are in flag leaf emergence.  If powdery mildew is moving up the plant rapidly, especially if it starts to attack the leaf below the flag leaf a fungicide application my be warranted on susceptible varieties.  Scout the entire field to confirm the presence of the disease throughout the stand.  Powdery mildew does not need rain to continue to develop, just high humidity which it will receive as the canopy of the crop gets larger.  For more information on powdery mildew and a picture of the disease see Ohio Field Crop Diseases web site http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/mildew.htm.

There are now three fungicide products that can be used to control powdery mildew on wheat: Tilt (propriconazole), Quadris (azoxystrobin) and Stratego (propriconazole + trifloxystrobin).  Of these three materials Tilt (4.0 fl. oz./A) has shown the greatest efficacy against powdery mildew on wheat and is the most economical to use.  Scouting is essential to the successful use of a fungicide and only susceptible varieties should be sprayed.. A listing of most of the common varieties and their reaction to powdery mildew and other diseases can be found on Ohioline (http://www.ag.ohio-state.edu/~ohioline/iwy/tab5.html).

Heaved Wheat

C) Pre-emergence Herbicide for use on Emerged Corn - Mark Loux CORN Questions

As a general rule, pre-emergence herbicides applied at planting need one-half to one inch of rainfall within 7 to 10 days for effective weed control.  Weeds will usually begin to emerge after this period of time if rain is not sufficient for herbicide activity.  Later rain may move herbicide into the soil to control weeds that have not yet emerged, but root uptake by emerged weeds is limited for many pre-emergence herbicides.  All other things being equal, more rain is required when soil is dry compared to moist soil.  Due to differences in their solubility and adsorptivity to soil, herbicides also vary in their rainfall requirement.  Command seems to require less rain than most other soybean herbicides.  Corn herbicides, ranked roughly in order of their rainfall requirement, are as follows:

Balance < Harness=Topnotch < Degree=Outlook < Dual II=Axiom=atrazine=Python=Hornet < simazine < Prowl

Corn planting is proceeding rapidly right now, and much of this is being treated with pre-emergence corn herbicides.  However, it has not rained much in the past week, and there does not seem to be a good chance of rain in the forecast for this week.  This lack of rain is likely to result in some pre-emergence herbicide  failures.  While we recognize the importance and economics of pre-emergence corn herbicides, we question the wisdom of applying herbicides when no rain is in the forecast.  Consider some of the following ideas to reduce the risk of herbicide failure when rainfall is lacking (these comments pertain mostly to atrazine premix products, except where indicated).

Incorporating a herbicide reduces its dependence upon rainfall, and generally ensures a relatively effective level of control.  The effective depth of incorporation, which is about half the depth of actual soil movement by the implement, should be no more than 1 to 2 inches.

Rather than applying herbicides at planting, wait until there is a fairly definite forecast for rain, and apply herbicides a day or two before the rain. Atrazine will control most small weeds that may have emerged, and the rain will allow the herbicide to control weeds not yet emerged. 

Wait until corn and the first flush of weeds have emerged with grasses no more than an inch tall, and apply herbicides at that time as an early post-emergence treatment.  The rate of atrazine in this type of application should be 1.5 to 2 lbs active ingredient per acre to ensure grass control.  If grass is more than inch or so tall, add Accent or a similar product.  Do not apply Balance, Epic, Axiom, Sencor, or simazine after corn has emerged.
 
Switch to a post-emergence program, such as Basis Gold, Accent Gold, or Celebrity Plus.  Apply before grasses exceed 3 to 4 inches in height.  Choosing products with some residual activity, or adding atrazine, will help control weeds that emerge after post-emergence application.

If timely rain does not occur within the first 7 to 10 days after herbicide application, get ready to rotary hoe.  The rotary hoe is most effective on weeds that are just about to emerge from the soil, rather than emerged weeds (this is sometimes called the “white stage”).  A timely rotary hoeing can buy some more time to receive rainfall. 

When it is obvious that rainfall has been insufficient for herbicide activity, be sure to scout fields early enough to see what weeds are emerging.  Applying post-emergence herbicides when weeds are small can allow rate reductions and prevent excessive costs, which is important when considerable money has already been spent on pre-emergence herbicides.

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: Steve Prochaska        Web Editor: Nathan Watermeier

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

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