Control of Volunteer Potatoes in Field Corn

J.M. Jemison, Jr., and H.J. Wilson

Volunteer Potato Control in Corn (PowerPoint slide show)

Introduction

For the second year out of the past three, volunteer potatoes (VP) have been a management issue for potato growers in central Maine. These untreated VP are a potential source of innoculum for late blight and a competitive weed. Solanaceous weeds are generally difficult to control. Volunteer potatoes are particularly difficult to control as they emerge from the ground at different times and are frequently at different stages of development when one needs to control them. 

A post-emergence weed control trial was established on a farm in Exeter, Maine to provide data on VP control. We evaluated standard control measures (Banvel and Marksman) compared to using Callisto a new low rate postemergence weed control product for field corn. We were also interested in evaluating different stickers and adjuvants to assess increased or decreased effectiveness on VP or potential injury to corn. The treatments applied to the corn are presented below:

1. Check

2. Banvel – 16 oz/ac rate + NIS (0.25% v/v)

3. Banvel + Atrazine – 16 oz/ac + 32 oz/ac + NIS (0.25% v/v)

4. Callisto - 3 oz + Crop Oil Concentrate (1% v/v)  (COC)

5. Callisto - 3 oz + COC (1% v/v) + Urea ammonium nitrate  (UAN) solution (2.5% v/v) 

6. Callisto - 3 oz + COC (1% v/v) + UAN (2.5% v/v)  + 8 oz/ac atrazine

7. Callisto - 4.5 oz + COC (1% v/v) + UAN (2.5% v/v) 

8. Callisto - 4.5 oz + COC (1% v/v) + UAN (2.5% v/v)  + 8 oz/ac atrazine

9. Callisto - 6 oz + COC (1% v/v) + UAN (2.5% v/v) 

10. Callisto - 6 oz + COC (1% v/v) + UAN (2.5% v/v) + 8 oz/ac atrazine

11. Callisto - 3 oz/ac + Banvel (16 oz/ac) + NIS (0.25% v/v)

12. Callisto - 3 oz + Banvel and Atrazine (16 + 32 oz/ac) + NIS (0.25% v/v)

Methods

Prior to our establishing this herbicide study, a preemergence application of Prowl (3 pts/ac) and Aatrex (16 oz/ac) were applied to the field at the spike to 1 leaf stage of development. Thus, some potatoes that had already emerged had been slightly injured by the preemergence application while others that emerged after that spray application did not show any damage.  Based on our observations of damage on the check plots, the preemergence herbicide did very little damage to VP. Postemergence herbicides were applied on 20 June 2002, and ratings were taken four, ten, and 21 days after application (DAT). Note: this field is in a 3-year rotation (potato followed by corn followed by barley). So, this application of atrazine did not conflict with label guidelines. At four DAT, corn injury and a rating of herbicide effectiveness on VP was made.  Corn injury is defined as the percentage of plants exhibiting chlorosis. Herbicide effectiveness on VP was made as a 1 – 10 rating:  the lower the number the more effective the herbicide. At 10 and 21 DAT, we also rated corn injury and injury to VP. We also counted the number of live potato plants potentially able to spread late-blight or other diseases. 

Results

We found significant differences in corn injury and VP control at all ratings taken after application of herbicides. Data for each rating period are presented below.

Table 1.  Herbicide Effect on Field Corn Injury and Volunteer Potato Control – 4 DAT

Crop Injury and VP Control at 4 DAT

From this first set of data, it appears that VP were most impacted by higher rates of Callisto or Callisto combined with a growth regulator.  But, this rating was made early after application and it generally takes more time for an herbicide’s impact on VP to be evident. With the higher rates of Callisto and the combination of COC and UAN, corn was injury was significantly higher.  While the corn did grow out of this injury, keeping rates of Callisto at 3 oz/ac with COC and UAN appears to keep injury to field corn to an acceptable level. Callisto was significantly more injurious to VP than either Banvel or Banvel and atrazine. The addition of a quarter pound of atrazine significantly increased activity on the VP. From the first evaluation, use of 3 oz/ac Callisto + 0.25 lbs/ac atrazine and COC (1% v/v) and UAN (2.5%  v/v) seems to be as effective as any other treatment evaluated in this study.  

Table 2.  Herbicide Effect on Field Corn Injury and VP Control – 10 DAT

Crop Injury and VP Control at 10 DAT

With the 10 DAT rating, corn injury was evident only at the 4.5 and 6.0 oz/ac Callisto rates. While this injury was common on plants, the degree of injury was slight at 10 DAT. From this data, it appears that keeping Callisto rates at 3 oz/ac with COC and UAN is safe to corn, but higher rates, particularly with adjuvant and crop oil concentrate was injurious to corn. Use of Banvel or Marksman (atrazine and Banvel) did not provide adequate control of VP. At both ratings (4 and 10 DAT), VP appeared significantly healthier and the number of live potatoes were significantly higher than those treated with Callisto. The most effective treatment from the perspective of cost and efficacy appears to be the 3 oz/ac rate of Callisto + crop oil + UAN and ¼ lb of atrazine. Corn injury was slight (7%), and VP health was statistically similar to the 4.5 and 6.0 oz/ac rates of Callisto. There were very few live potatoes in these plots. 

Table 3.  Herbicide Effect on Field Corn Injury and VP Control – 21 DAT

Crop Injury and Volunteer Potato Control at 21 DAT

Corn injury was not rated at 21 DAT because the producer had applied UAN as a sidedress application to the entire field.  Between the 11 days between applications, a few additional VP emerged which is somewhat disturbing because these potatoes could potentially spread late blight if innoculum were present.  However, by the time of this rating, the corn was thigh high and starting to significantly compete with VP.  By the final rating, VP vigor rating has increased.  This was in part due to the fact that the newly emerged VP did not show the impact that the treated VP did, and in part due to the fact that the plants were recovering slightly from the spray.   

Based on this one-year, one-location project, Callisto applied at 3 oz/ac with UAN (2.5% v/v) + ¼ lb of atrazine + crop oil concentrate (1% v/v) appears to be a very effective treatment to control VP.  Crop injury in this study was low, VP control was excellent, and the amount of chemical used is minimal.  In some years with possibly more challenging weather conditions, the addition of UAN and COC could be more injurious to some corn varieties.  But VP are difficult to control, and the combination of the adjuvant and oil was needed to get optimum control.