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June 2012 Archive for Ask an Agronomist

RSS By: Farm Journal Agronomists, Farm Journal

Have your agronomic questions answered by a Farm Journal agronomist. E-mail us directly at, and we’ll respond on this blog to provide an interactive dialogue.

When Do Corn Roots Stop Trying to Find Moisture?

Jun 25, 2012

Question: At what growth stage do (corn) roots stop going deeper to find moisture?
Answer: If there’s no obstruction to the corn roots – no compaction and no horizontal layer – corn roots will grow and move down until they reach the water table. The roots will continue to grow as long as they have access to water and oxygen. If the water table drops, the roots will follow the water. Typically, during rapid growth stage, a corn plant will put on 1" to 1.5" of root growth a day, while your water table drops in only a few centimeters per day. 
If there is compaction or a horizontal layer, the roots will typically grow horizontally once they hit that layer until they can find a crack in the soil that allows them to grow vertically again.  The common problem at that point is if the water table has dropped very far, the roots will not be able to keep up with it even though they’re growing vertically again.  If temperatures get too high, roots begin to die due to the heat and lack of water. In a drought situation the roots typically die from the top down and not the bottom up. 
If you have compaction or density layers in your fields, you have to get them out of there.  That’s one reason why we talk quite a bit about vertical tillage.  Anther option, if you don’t have irrigation and your fields drain off water quickly, is to entertain the idea of installing gated tile to slow down how quickly your water table drops. That will take some planning and help from someone who specializes in this type of work, but it could be a good investment for future corn crops.

What Can I Do to Prevent Frogeye Leaf Spot?

Jun 20, 2012


Question: What can I do about frogeye leaf spot in soybeans?
Answer:Cool, wet conditions and early planting can set the stage for seedling diseases and for frogeye leaf spot. Carl Bradley at the University of Illinois has detected fungicide-resistant strains of Cercospora sojina, the causal agent of frogeye leaf spot, which suggests the disease should not be taken for granted. Bradley found the strobilurin fungicide–resistant strains in plant samples from a Tennessee soybean field.
Several popular fungicide products include a strobilurin fungicide in the formulation. So far, the fungicide-resistant strains have not been found to be widespread. But their existence reaffirms the importance of planting varieties resistant to frogeye leaf spot. If you planted a susceptible variety and are considering applying a fungicide, choose a triazole fungicide rather than a strobilurin product. If you need to spray a strobilurin fungicide for other foliar diseases as well as frogeye leaf spot, apply a product or a tank mix containing both classes of fungicides.
Know what conditions can foster each disease, select resistant or tolerant varieties and be prepared to apply a fungicide if necessary.


Top 10 Tips for Scouting This Season

Jun 14, 2012


Everything is showing up early in the field this season, including crop diseases, weeds and pests. Farmers need to gear up earlier than usual, too, to get on top of these agronomic challenges, says Missy Bauer, Farm Journal associate field agronomist.
Here are 10 scouting tips she recommends farmers use as they check fields. While she says the 10 tips are in no way comprehensive, using them this season is sure to add more bushels to your yield outcome at harvest.
  1. Be proactive and timely. Know when to anticipate specific weeds, insects and diseases for your area and plan to scout accordingly.
  2. Track your local weather conditions. Environmental factors can significantly influence when and whether weeds, diseases and pests develop in your fields.
  3. Walk through fields using a zigzag or "W" shaped approach. This will help you get a more comprehensive overview of what potential problems each field you scout contains.
  4. Take good notes. Record the types, numbers and locations of weeds, disease or pests you have in each field as well as the time and date. Hang onto this information so you can reference it next year.
  5. Assign the job of insect scouting to a specific individual, a bug boss, who will make the scouting process a #1 priority in their day-to-day activities.
  6. Take action if insect threshold numbers are met, using sound integrated pest management (IPM) treatment practices.
  7. For disease scouting, check for plants that show signs of stunting, lesions, discoloration, yellowing and senescence. Get a laboratory diagnosis if you are unsure of the correct identification of the disease.
  8. For weed scouting, check your fields during early pre-plant and post emergence as well. Be vigilant to check fields for weed growth during the first three weeks following crop emergence to evaluate weed pressure and to determine whether you need supplemental control measures.
  9. If you find weeds, disease or insects you do not recognize, consult your agronomist, Extension personnel or a pest-identification guide.
  10. Take a pest kit with you to the field. Helpful tools include: pollen hat, safety glasses, scouting guides, tape measure, digital camera, hatchet, pocket knife, hand lens, vials or sandwich baggies for collecting samples, change of clothes, water to drink.
For more help in identifying weeds, diseases and pests, visit AgWeb's Online Field Guide.


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