There have been several calls over the past couple of days on how to destroy partial corn stands in order to replant back to corn. We conducted a good deal of research on this topic back in 2007 and 2008. This was initiated due to all the questions we had on this subject when the widespread Easter Sunday freeze in 2007 led to the replanting of about 200,000 acres of corn in Tennessee. Limited research was available at the time on effective herbicide to control undesirable stands of glyphosate-tolerant or Roundup ReadyTM (RR) corn where replanting to corn was desired. Therefore in 2007 on three undesirable freeze-damaged corn stands (10,000 plants/A) and in 2008 on two non freeze-damaged corn stands (32,000 plants/A), studies were initiated to determine how to control the unwanted stand while not harming subsequent replant corn.
The results from this research clearly showed that producers have several effective options to manage undesirable RR corn that will allow a producer to replant to corn. The two main take homes from these 5 studies were that; first Select Max at 5 oz/A (applied 7 days before replanting) and Gramoxone at 40 oz/A plus a PSII inhibitor applied pre emergence of the replant corn provided very good control of the original corn stand without effecting the yield of the replanted corn. Second, was that Gramoxone should be applied at rates no lower than 40 oz/A (higher is better) to obtain consistent control of an undesirable corn stand.
One final point I will make has been from walking fields the past 5 years where partial corn stands have been treated with one of the above applications. It has been my experience that those applications work best when they are applied to an undesired corn stand at the 1 to 2 leaf stage. Applications earlier or later will not perform as consistently. Below is the summary of the 5 studies conducted in 2007 and 2008 (Tabel 1).
Table 1. Roundup Ready/Herculex undesirable corn control, final stand after treatment with herbicide admixtures and replanted grain yield.
|
Control of Undesirable Corn |
Replant Corn | |||
| Herbicide |
5 DAA |
15 DAA |
Stand |
Grain Yield |
|
% |
plants/m-1 |
bu/A |
||
| *Select Max 5 oz/A |
31 |
76 |
0.5 |
159 |
| Gramoxone 40 oz/A |
72 |
77 |
2 |
141 |
| Gramoxone 40 oz/A+ Atrazine 16 oz/A |
84 |
92 |
2 |
154 |
| Gramoxone 40 oz/A+ Diuron 16 oz/A |
91 |
98 |
1 |
157 |
| Gramoxone 40 oz/A+ Linuron 16 oz/A |
93 |
96 |
1 |
153 |
| Gramoxone 32 oz/A + Simazine 16 oz/A |
68 |
69 |
6 |
129 |
| Gramoxone 40 oz/A + Simazine 16 oz/A |
91 |
93 |
1 |
159 |
| Not Treated |
0 |
0 |
10 |
124 |
| LSD |
10 |
12 |
1.5 |
11 |
*Corn maybe planted 7 days after up to a 6 oz/A Select Max application
