Mike Rankin
Crops and Soils Agent - Fond du Lac County
University of Wisconsin - Extension
"What do you think of those Roundup soybeans?" I've been asked this question a lot over the past year. We have now had two years to see how Roundup Ready (RR) varieties perform in farm fields and research plots.
Figure 1 shows the performance of 70 conventional soybean varieties and 40 RR varieties in the 1998 UW central region performance trials (includes the Fond du Lac site). On average, conventional soybeans out-yielded the RR varieties by 2 to 3 bushels per acre. However, a "top 5" RR variety was 10 bushels per acre better than an "average" conventional variety and a "top 5" conventional variety was 15 bushels better than an "average" RR variety. This again points to the importance of selecting soybean varieties based on BOTH performance and associated traits.
There are many herbicide programs that will do an excellent job controlling weeds. However, in situations where a problem weed exists that is best controlled with Roundup (e.g. Canada Thistle), a top performing RR variety is an obvious best choice. Overall, a Roundup based program may also have a slight advantage in terms of application window for providing excellent weed control. I have not seen too many RR fields or plots with anything close to what I would consider poor weed control.
Table 1 shows an example partial cost budget comparing RR versus conventional soybean variety use for both conventional tillage and no-till. In both systems it costs about $10 per acre less for the RR program. An easy decision? Not really. Remember that conventional varieties currently have a relative performance advantage of 2 to 3 bushels per acre. The decision to shift to a top performing RR variety might be more obvious if your typical weed control costs are significantly higher than the post-emerge program used in Table 1.
| Table 1. Comparing Roundup Ready vs. Conventional Soybean Costs | |||
| SEED: | |||
| Roundup Ready | Conventional | ||
| Price/50 lb. bag | $22.50 | $16.00 | |
| Price/lb. | $0.45 | $0.32 | |
| Seeds/lb. | 3000 | 2850 | |
| Lbs. seed @ 200K/ac. seeding rate | 67 | 70 | |
| Lbs. seed @ 225K/ac. seeding rate | 75 | 79 | |
| COST BUDGET COMPARISON OF RR vs. CONVENTIONAL SOYBEANS IN TWO TILLAGE SYSTEMS: | ||||||
Conventional Tillage |
No-till |
|||||
Roundup Ready |
Conventional |
Roundup Ready |
Conventional |
|||
--------------------------- cost per acre --------------------------- |
||||||
| SEED: | $30.15 |
$22.40 |
$33.75 |
$25.28 |
||
| WEED CONTROL: | ||||||
| Roundup (1.5 pt. PRE) | ----- |
----- |
$7.75 |
$7.75 |
||
| Raptor (5 oz. - POST) | ----- |
$24.60 |
----- |
$24.60 |
||
| Adjuvants | ----- |
$1.50 |
----- |
$1.50 |
||
| Roundup (1.5 pt.) | $7.75 |
----- |
$7.75 |
----- |
||
| Application costs | $7.00 |
$7.00 |
$14.00 |
$14.00 |
||
| TOTAL COST/ACRE | $44.90 |
$55.50 |
$63.25 |
$73.13 |
||
In summary, a RR program offers the advantage of low cost and nearly "sure bet" weed control with a well-timed application. However, a top-yielding variety needs to be selected or these advantages are quickly lost. Conventional weed control systems offer more high-yielding varieties to select from but herbicide costs must be kept competitive. Currently, more profit stands to be lost from variety selection than from herbicide program.
For
more information contact Mike Rankin