ECONOMICS OF ROUNDUP READY VS CONVENTIONAL
WEED CONTROL IN NO-TILL BEANS
by D.E. Null, Regional Agronomy Specialist
Summary: Various Roundup treatments were made to no-till
Roundup Ready soybean and compared to a standard weed control
treatment. Yields were taken and profitability of treatments
calculated. The most profitable treatment was a single treatment of
Roundup made 4 weeks after planting.
Objective: A study to determine the economic advantages, if
any, of using delayed burndown treatments in no-till programs using
Roundup Ready soybeans, and to compare Roundup weed control treatments
to a standard conventional treatment.
Situation: Some producers in northwest Missouri are using delayed
burndown treatments in their Roundup Ready soybean weed control
program. They are doing this to try to reduce the number of
applications of Roundup needed and to reduce overall weed control
costs. Little yield data is available to indicate whether the
producers doing this are suffering yield reductions.
Methods: The study will be conducted at the Hundley-Whaley Farm at
Albany. It will consist of five weed control treatments. They are:
Treatment 1. One application of Roundup Ultra alone as a burn-down
herbicide.
Treatment 2. One application of Roundup Ultra alone at four weeks
after planting (4WAP)
Treatment 3. One application of Roundup applied as a delayed burndown
treatment 2 weeks after application (2WAP) and one
application of Roundup three weeks later (5WAP).
Treatment 4. One "at-planting" burndown application of Roundup
Ultra followed by Roundup four weeks later (4WAP).
Treatment 5. A standard treatment consisting of 1 pint of 2,4-D
ester, 2.5 pints of Prowl and 8 ounces of Canopy per
acre, broadcast applied seven days prior to planting
(7EPP).
Each Roundup Ultra application was broadcast at the rate of 1 quart
per acre. No additives were used.
The study was designed around the assumption that the crop variety
used had no effect on the final results of the work. Asgrow 3701RR
soybeans were used in all treatments in order to eliminate the risk of
killing the soybeans planted in the non-Roundup treatment number 5.
This variety has performed in the top group of the Missouri Soybean
Performance Tests.
The study is designed as a randomized complete block with six
replications.
The 7EPP treatment (T5) was made May 3 and became a 23EPP treatment in
fact. An extended period of rainfall was the reason for the delay.
Weed pressure in T5 plots consisted of a moderate pressure of
flowering corn gromwell and 3-4" tall marestail on May 3.
The soybeans were no-till drilled (10" rows) on May 26 at the rate of
220,000 seeds/acre. The standard treatment (T5) was weed free at
planting time. The pre-emergence burndown applications were made the
same day to plots containing a moderate to heavy infestation of 1-2"
giant foxtail and just emerging to 12" tall sunflower. There were
also scattered to light infestations of little barley (heading stage),
4-10" tall marestail and various species of blooming stage mustards.
The 2WAP, delayed burndown treatment (T3) was made on June 10 to
unifoliate stage soybeans and 2-6" giant foxtail, 1-8" shattercane,
4-12" sunflower, 8-12 marestail, 12-18" giant ragweed, 6-12" annual
smartweed and 4-8" lambsquarters. There was considerable variability
in pressure of these weeds within the replications.
The 4WAP application, a very delayed burndown treatment (T2) , was
made on June 24 to plots containing 3' sunflower, 2' marestail and 1'
giant foxtail and shattercane. These weeds could be described as
moderate to heavy within the plots. Soybeans were in the V3 or second
trifoliate growth stage.
The second Roundup Ultra application on T4 (4WAP) was made to V3
soybeans on June 24. Shattercane (4-8") was the dominant weed but
there were also scattered 4-6" cocklebur in the plots.
The second Roundup Ultra treatment on T3 (5WAP) was made on July 6 to
V6 (8-12" tall) soybeans. Weed pressure was light to moderate and
consisted of shattercane and giant foxtail.
Results: Weed control ratings on August 18 showed the following
overall weed control averages:
T1 66% only a pre Rup treatment and lots of weeds came up after
application.
T2 96% only shattercane has come through this treatment in any
substantial way.
T3 100% no weeds in these plots
T4 98% some shattercane made it through but it was small and
spindly
T5 84% some shattercane survived this treatment but sunflower
and waterhemp were only controlled at the 50-60% level.
The plots were harvested on October 14. The table on the following
page provides the yield data. The actual economics of the treatments
is also show, not adjusted for statistical significance.
Discussion: There was no statistical difference in soybean yields
between treatments 2 through 5. Treatment #1, the pre-emergence
burndown treatment alone, suffered from a second flush of weeds that
was detrimental to crop performance. The highest yielding treatment
was the treatment most agronomists would recommend. It was a
pre-emergence burndown followed by a Roundup treatment to 4-8" tall
weeds made 4 weeks after planting.
The most weed-free treatment was the two week after planting,
delayed burndown treatment, followed by another treatment of Roundup
three weeks later (T3).
Surprisingly, the soybean performance in the very delayed, 4 week
after planting treatment of Roundup (T2) did not seem to suffer yield
reduction from the early weed competition that was present in the
plots. Even the very large weeds in the plots were controlled with
the Roundup application.
The most profitable treatment in the study was treatment #2.
Due to the prolonged wet spring, the soybean planting into the
conventional herbicide treatment was delayed from a planned 7 days
after treatment to an actual planting made 23 days after the treatment
was made. There is always the chance that early pre-plant treatments
will be delayed and this is an example of that. It is impossible to
accurately estimate what the crop performance and weed control would
have been if the delay in planting had not occurred. We can speculate
that both weed control and crop performance was adversely affected by
the delay.
Profitability of Soybean Weed Control Programs
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Net after
Seed Tech Fee and
Treatment SB Yield Value of Herbicide Technology Herbicide
Number (Bu/acre) Yield(1) Cost(2) Feet Costs
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1 18.8 $94.00 $15.17 $10.40 $68.43
2 33 $165.00 $15.17 $10.40 $139.43
3 33 $165.00 $30.34 $10.40 $124.26
4 33.9 $169.50 $30.34 $10.40 $128.76
5 28.6 $143.00 $38.50 $0.00(3) $104.50
LSD 0.05 9.5 XX XX XX XX
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(1) Based on $5.00/bushel soybeans
(2) Includes a $5.00/acre application charge for each herbicide
application
(3) This does not mean that A3701 soybeans were without a technology
fee in treatment 5. It does assume, right or wrong, that you
could select a standard variety, that would have the same
yielding potential as A3701, at a similar cost per bushel and
that it would not include a technology fee..
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