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August 05, 2020

Agronomy Update: Managing Gray Leaf Spot, Goss’s Wilt and IDC

BY Dairyland Seed
Gray Leaf Spot

Overview: Gray leaf spot, caused by the fungus Cercospora zeae-maydis, leads to leaf tissue loss, a decrease in plant sugars and decreased grain production. It is considered the world’s most yield-limiting disease in corn, causing yield losses from 5-40%. All corn hybrids have some susceptibility to the disease.

What you should know:

Action steps:

  1. Manage residue: Crop rotation and clean plowing are effective methods to control fungus levels. A two-year crop rotation away from corn is effective under reduced tillage. A one-year rotation is sufficient with clean plowing.
  2. Apply fungicides early: Fungicides are recommended when susceptible hybrids are planted in fields with a history of gray leaf spot. Apply fungicides early in the season before significant leaf damage occurs.
  3. Select tolerant hybrids: Using tolerant hybrids provides an earlier, more extensive source of inoculums for gray leaf spot development.

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Goss’s Wilt

Overview: Goss’s wilt (Clavibacter michiganensis subsp. nebraskensis) is a bacterial disease that affects corn plants. Goss’s wilt has been prevalent in areas of the Western Corn Belt for decades and has expanded in recent years to additional areas of the Central and Eastern Corn Belt.

What you should know:

Action steps:

  1. Reduce residue: Rotate crops and utilize tillage to bury residue and reduce the probability of infection. Infected fields should be tilled or harvested last to prevent infected material from spreading to uninfected fields.
  2. Select appropriate hybrids: The best way to control the disease is to plant hybrids with strong Goss’s wilt tolerance.

30-Second Summary:

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Iron Deficiency Chlorosis or IDC in Soybeans

IDC symptoms are interveinal chlorosis of the leaves with leaf veins remaining green as shown in the photo below. These yellow leaves tend to show up when the soybean plant is in the first to third trifoliate stage. IDC is more prevalent in poorly drained soils containing high pH or calcium carbonate, high salt or saline soils.

Soils in most instances have enough iron (Fe) for production, the issue that arises is that as pH increases the soluble form of Fe decreases due to high pH especially those with high calcium carbonates and in some instance’s salts. As air space reduces in soils (wet soils) the respiration of carbon dioxide from roots and soils increases, when that happens you increase bicarbonate levels at the same time. Higher bicarbonate levels (I always think higher soil pH in this instance) correlates with higher IDC.

Other factors that may increase bicarbonate levels are crop residues and manures. As soil microbes are breaking down organic matter from the crop residue or manure, they release carbon dioxide which again raises bicarbonate levels. Higher soil nitrate levels and increased IDC, in my opinion, is very complex, as a soybean root takes in nitrate it exchanges it with bicarbonate ion, again increasing bicarbonate soil levels. Another aspect is as the plant brings in nitrate it converts it to ammonium in the leaves which increase leaf sap pH levels and then reduces the level of usable Fe available to the leaf and plant.

Best Management Practices for IDC:

Other factors that may reduce IDC severity:

As always, if you have questions about this or other agronomic issues, please contact your local Dairyland Seed Agronomist.

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Corteva Technology Use Agreements

All growers with orders for any Corteva Agriscience brand seed product, regardless of crop or trait (including non-GM products) need to have a signed Corteva Technology Use Agreement in place by September 1. Growers should sign the Corteva Technology Use Agreement electronically at www.agcelerate.com. Signing electronically is preferable, however, paper copies are available at www.traitstewardship.com.

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Brian Weller
Western Region
507.456.3034
Dan Ritter
Central Region
219.863.0583
Branden Furseth
Northern Region
608.513.4265
Rod King
Eastern Region
574.596.6721
Terry Jones
Eastern Region
419.630.3115

enjoying our Agronomy Updates?  suggestions for topics you'd like us to weigh in on?  Drop us an email at dairylandseed@dairylandseed.com.  We'd love to hear from you!
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