> The recent ERS report requires a careful reading. In a nutshell,
> no one (including Monsanto) ever claimed that inserting RR
> resistance genes in soybeans would raise their genetic yield
> potential, other things being equal.
It all depends on the degree and type of weed pressure. It wouldn't
surprise me if there were a small yield penalty in the absence of weed
pressure. After all, seed companies were scrambling to get RR varieties on
the market. Even with marker-assisted backcrossing, it is impossible to
completely recover the recurrent genotype in just a few generations. So
"junk" DNA from the background of the original transformed line contaminates
the new variety. It doesn't necessarily mean that the RR gene itself is
doing anything deleterious (although that wouldn't surprise me either).
> Most farmers not using a Roundup based system are applying either
> sulfonylureas or imidazolinone herbicides which are known to
> cause some stunting/damage to soybeans earlier in the season
Farmers are very sensitive to the esthetics of the crop. It doesn't matter
how many times the salesman says "it'll grow out of it, trust me." Even if
it really does, farmers don't like that yellowish burned look they get from
many postemergence soybean herbicides.
> First, growers switch from a acetanilide (alachlor, metolachlor) or
> other "old" chemistry herbicides that are applied at .75 to 1.5 pounds
> a.i. per acre to Roundup-based system involving maybe .5 to .7 pounds
> a.i. per acre.
> This is not a reduction in reliance, it is a switch to more
> biologically-active and persistent chemistry effective at
> lower use rates.
Huh? Roundup is LESS persistent in the environment than these other
herbicides. In a practical sense, it has almost zero persistence. It is
accurate to say that RR beans reduce the use of environmentally persistent
herbicides.
> If the goal is/was use reduction, a RR bean system averaging in
> 1998 about 1 pound a.i. per acre entails almost 10 times the
> herbicide as some sulfonylurea systems,
So, you are saying that you would rather use highly active and persistent
sulfonylurea herbicides, which, BTW cause carryover problems, than Roundup
which never has any such problem? Really?
> ...So any claims that RR beans reduce herbicide use always are
> incomplete without the phrase "...reduced COMPARED TO WHAT??"
Again, RR beans reduce the use of persistent herbicides.
> Second, growers plant RR beans and spot treat fields where weeds get out
> of control, using non-chemical alternatives in other parts of field,
> like cultivation.
The biggest environmental benefits of the proliferation of herbicide
resistant cultivars are increased flexibility in rotation of weed management
strategies, and possibility of reactive versus preventative application.
For example, a farmer might plant RR beans and decide later, after he sees
what weed threats are out there, what weed control strategy, sulfonylurea,
Roundup, or cultivation, to use. With preemergence chemicals, farmers are
locked into high rates of persistent chemicals before they see any weeds in
the field.
> As projected by many weed scientists, the average rate of
> application and average number of applications will probably
> incrementally rise until weed shifts and resistance render
> RR soybeans not economically attractive.
I hope people are not that stupid. Long rotation of weed control modes of
action is now possible in the corn-soybean system. Clever farmers will
exploit this to control the distribution of weed species in their fields and
reduce chances of resistance arising.
> What is really needed is an "impact adjusted" measure of use and
> reliance
I agree. The criteria should include environmental contamination,
propensity to elicit herbicide resistant weeds, and long term stability of
the cropping system. I don't think raw numbers such as pounds of a.i. used
are that relevant, since the various herbicides differ so much in biological
activity, selectivity, time of application, and persistence in the
environment.
It is apparent that farmers really like RR beans, more so than the seed
industry expected. I'll bet the reason is flexibility. It may be hard to
capture this in data, but flexibility is probably a stabilizing factor.
Dale
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