P&PDL Picture of the Week for
August 21, 2006

Clubbed Roots in Corn

Glenn Nice, Weed Diagnostician, Department of Botany & Plant Pathology, Purdue University

I often come across things that I have not seen before.  I would be fooling myself to think that I have seen it all, I wonder if anybody has.  These oddly formed brace roots on a corn plant were sent in to the P&PDL.  Some of the brace roots were showing clubbed secondary roots coming off of the brace roots (Figure 1). 

If I were to see this on the primary and secondary underground roots I would have suspicions that a dinitroaniline (Treflan, Sonalan, Prowl) that had been incorporated into the soil might have been involved (Figure 2).  However, I have not seen these particular symptoms on the brace roots before.  The dinitroaniline herbicides are a group of herbicides that are generally used preplant incorporated, preemergence on the soil surface.  The dinitroaniline herbicides inhibit a plant’s cells ability to go though mitosis and form cell walls.  If the developing roots come in contact with the dinitroaniline this can lead to swollen stubby secondary roots (Figure 2) or other wise known as “clubbed roots”.  This can sometimes lead to lodged corn because the root cannot brace the corn plant into the soil.

There has been some mention of corn lodging suspected to be a result of pendimethalin injury.  The University of California recommends Post applications of pendimethalin as a culti-spray after brace roots have formed; warning that it may cause lodging1.  This might be recommended to assure that the brace roots are already pegged down into the soil to minimize contact with the herbicide.  Michigan State University reported that in coarse textured soils with low organic matter after heavy rains that pendimethalin could move in the soil to the root zone and cause injury and lodging2.  The Cornell Integrated Crop and Pest Management Guidelines for Vegetable Crops mentions that in sweet corn applications or pendimethalin in wet conditions may lead to poor brace root development leading to lodging3.  In the 2005 Iowa State University Weed Control Results, a study looking at postemergence applied pendimethalin reported brace root malformation4.

Excluding the information previously discussed above, there was not much in the diagnostic and scientific literature regarding the malformation of brace roots due to dinitroaniline herbicides, suggesting that it is not a common occurrence.  However, the symptom seen on this corn’s brace roots is suggestive of dinitroaniline injury. If the secondary roots were to come in contact with a high concentration of dinitroaniline when they reached the soil it might lead to the “clubbed root” symptoms typically seen in injury situations from dinitroaniline herbicides.  In this situation, it is possible that pendimethalin was postemerged applied just prior to the brace roots reaching the soil.  Thus the brace root tips were exposed to a high concentration of pendimethalin and these injury symptoms resulted.

References:

1. Corn Herbicide Treatment Table.  Accessed on August 21, 2006. 

2. Jim Kells.  Accessed on August 21, 2006.  Excessive rain and soil-applied corn herbicides.

3. Cornell Integrated Crop and Pest Management Guidelines for Vegetable Crops.  Accessed on August 19, 2006.

4. Owen, M.D.K., R. G. Hartzler, J.F. Lux, and D.D. Franzenburg.  Iowa State University Weed Control Results, 2005

Click image to enlarge

Figure 1. Corn plant with clubbed primary and secondary brace roots.

Figure 2. Dinitroaniline injury on underground roots.

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service