Even though harvest is around the corner, doing a few root digs before you combine this year’s corn crop is a helpful way to check for CRW and evaluate the performance of your hybrids.
At a root dig in Janesville, WI, we compared the root masses, ear sizes and stalk strength of
Golden Harvest hybrids both with and without the
Duracade® trait for CRW control. The samples represented below were pulled from a field that has been continuous corn for the past 6 years and experiences consistent CRW pressure.
The plants and ears on the left side of each photo represents a Golden Harvest hybrid with the Duracade trait, while the plants and ears on the right are the same Golden Harvest hybrid without a CRW trait. It is apparent the hybrids with the Duracade trait are more productive.
- The root balls are fuller and more developed.
- The stalks are thicker and stand straighter.
- The ears are larger.
Golden Harvest hybrid G06Z97-5122 brand is on the left and contains the Duracade trait, while Golden Harvest hybrid G06Z97-3120 brand, is to the right and does not have any CRW protection. 
Golden Harvest hybrid G03C84-5122 brand is on the left and contains Duracade protection, while Golden Harvest hybrid G03C84-3120 brand is on the right without the CRW trait. A question farmers often ask is just how much of a difference planting hybrids with the CRW trait makes. From the 2 examples pictured above, we estimate there will be a 20 to 25 bu/A yield difference. Over the past 6 years in this field, Golden Harvest hybrids with the Duracade trait have yielded as much as 40 to 50 bu/A more than hybrids without CRW protection.
CRW assessment by the numbersTo see how your hybrids are holding up to CRW pressure, Iowa State University developed a resourceful
node injury scale to help assess feeding levels:
| Value | Root Description |
|---|
0.00 | No feeding damage |
1.00 | 1 node/circle of roots, or the equivalent of an entire node, eaten back to within about 1½ inches of the stalk/soil line on the 7th node |
2.00 | 2 complete nodes eaten |
3.00 | 3 or more nodes eaten |
Note: Damage between complete nodes eaten is considered as the percentage of the node missing, i.e. 1.50 = 1 ½ nodes eaten, 0.25 = ¼ of one node eaten, etc.
Source: Iowa State University; (Oleson, J.D., Y. Park, T.M. Nowatzki, and J.J. Tollefson. 2005. J. Econ Entomol. 98(1): 1-8) |
If you see more severe damage, it’s likely there will be additional signs of corn rootworm injury in your field, including:
- Root lodging: When stalks are leaning at an angle instead of standing upright, it could be a sign of damaged roots.
- Stalk rot: When split open, stalks should be white, and not show brown or black discoloration along the nodes.
- Yield reduction: Corn rootworm feeding can lead to significantly smaller ears.
Northern CRW eggs can remain
dormant for 2 winters, a practice referred to as extended diapause. Once the eggs are laid in a cornfield, they overwinter and remain dormant through the soybean crop, overwinter again and hatch into the next corn crop. As pictured in the figure at bottom left below, rotating to non-host crops disrupts the CRW lifecycle. As you'll see from the illustration in bottom right, even in areas where northern CRW exhibit extended diapause and the western CRW is laying eggs in soybean fields, rotation still reduces CRW populations.
The most effective CRW management tool is planting hybrids equipped with traits to control CRW. Duracade contains 2 modes of action to help reduce pressure.
Contact your
Golden Harvest Seed Advisor about doing a root dig on your farm and making a plan for CRW management next season with Golden Harvest hybrids containing the Duracade trait.
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