a four-fold rise - Center for Food Safety

Center for Food Safety – Science Comments – FG72 Soybean
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the pattern of application will differ. If FG72 soybean is adopted for use on the same number
of acres as isoxaflutole is used on corn – 7% -­‐ then use of isoxaflutole at the landscape level
will double. (We estimate that adoption of FG72 soybean will be much higher than that, and
that use on corn will also increase, so that 4 times more isoxaflutole is possible, as we have
discussed.) The point here is that even if the amount of isoxaflutole is the same with FG72
soybean as it now is in corn – same number of acres, same application rate, same number of
applications – twice the amount isoxaflutole will be used in regions where both are grown.
This landscape-­‐level increase in isoxaflutole use is likely to have impacts on water quality.
Within a watershed draining corn and soybean fields there will be twice the load of
isoxaflutole entering the system. Basically, the number of agricultural non-­‐point sources for
isoxaflutole pollution will increase (DEA at 12). We discuss all of these impacts later in thesthe
comments: isoxaflutole, and particularly its degradates, enter surface water through runoff
and leaching for quite a while after it is are applied, and can persist and accumulate in water at
levels that are harmful to non-­‐target organisms, including threatened and endangered species.
Biodiversity may thus be diminished. These increased loads may also affect drinking water,
and human health. The propensity of isoxaflutole applications to contaminate water with risk
of harm to non-­‐target plants is the reason for its restricted use status (DEA at 35, 93 – 95). A
greater portion of the landscape sprayed with isoxaflutole may also accelerate weed
resistance. APHIS must assess the cumulative impacts from isoxaflutole use on corn and FG72
soybean in the same landscape.
ii. Isoxaflutole appliations in sequence
Corn – FG72 soybean rotations on the same acreage with isoxaflutole applied in succession
also may have cumulative impacts, as we discuss below: isoxaflutole has residual activity in
soil, killing germinating seedlings after rains for weeks; and requiring waiting periods of
months to a year and a half, accompanied by specified amounts of rainfall, before other crops
can be planted. Drought results in increased soil retention of isoxaflutole residues and its
degradates, possibly increasing the waiting times, too. Under some conditions, isoxaflutole
may be applied in the second year on top of residual isoxaflutole from the year before, perhaps
leading to higher contamination of water, or to unexpected injury in other rotation crops. Non-­target
wild plant populations, including threatened and endangered species, that are
particularly sensitive to isoxaflutole may be more adversely affected by use of isoxaflutole in
successive years than from intermittent applications. Biodiversity may thus be diminished.
Also, use of herbicides with the same mode of action on the same acreage in successive years is
a risk factor for promotion of resistant weeds, including isoxaflutole resistance and resistance
to multiple herbicides. APHIS needs to consider the cumulative impacts of rotating corn with
FG72 soybean.