a four-fold rise - Center for Food Safety

Center for Food Safety – Science Comments – FG72 Soybean
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plots were sprayed with IFT at a target rate of 70 grams ai/Ha and GLY at a target rate of
1060 grams ai/Ha. Herbicide applications were made to the Regimen C plants as a foliar spray
at about the V4-V5 plant growth stage.” (Petition at 59, emphases added). The application
rate of 70 g ai/Ha is similar to the average rate that isoxaflutole is applied on corn today (USDA
NASS 2011). The V4 – V5 stage of soybean development is when the 4 th or 5 th trifoliate leaf
unfolds, and often corresponds to the 4 th or 5 th week after planting, depending on conditions
(Casteel 2010).
APHIS depends on information in Appendix A for isoxaflutole application details (DEA at 30),
taken from a Supplemental Label, EPA Reg. No.: 264-­‐600, “For use on Isoxaflutole-­‐tolerant
soybean grown for research, field trials and seed production only, including USDA regulated
plantings or seed production” (Bayer 2011a, as cited in DEA at 30). This label states that
isoxaflutole can be used from preplant until “early postemergence”, but gives no definition of
the specific soybean stage of development for “early postemergence”. This is unusual, because
labels for herbicides used on HR crops are very specific about plant developmental stages
related to applications. Perhaps this label is meant to imitate the corn label where corn can be
sprayed until the 2 nd leaf stage, for purposes of FG72 soybean experimentation, until a full
review can be made. Or maybe Bayer CropScience gave individual instructions to growers on
when to make the postemergence application in these trials. APHIS then cites an EPA human-­health
risk assessment for isoxaflutole that provides directions for its use, but this source is
also based on growing FG72 soybean in experimental conditions only (EPA 2011b, as cited in
DEA at 102). In any case, APHIS should not assume that the details of application to FG72
soybean if it is approved will correspond to experimental use conditions, particularly since
Bayer CropScience did not explicitly state such details in its Petition, and in fact used a
postemergence application later than “early postemergence” in its tolerance tests that were
said to represent likely practices.
It is important to know the window of application in assessing risks, because herbicides
applied later in the growing season are likely to impact non-­‐target crops and wild organisms in
different ways, as we discuss in more detail later. Many plants are more sensitive to herbicides
during reproductive stages, for example. Also, drift and runoff are affected by weather, likely
to differ later in the season. In the case of isoxaflutole with its residual soil activity, later
applications may push the limits of possible rotation crops.
Use of isoxaflutole in FG72 soybeans will result in later applications than now occur on corn.
First, soybeans can be planted later than corn without as much risk of yield loss (Edwards
2012; Pedersen 2008). In fact, soybeans are often planted a month or more later than corn, so
even preplant or preemergence use of isoxoflutole is likely occur weeks later in the season on
FG72 soybean than on corn. Second, as discussed above, isoxaflutole may be used for over a
month after planting with FG72 soybean (following the tolerance test details in the Petition),
whereas with corn it can only be used for a few weeks after planting, further extending the
difference in application window between FG72 and corn. It is conceivable that with late-­planted
FG72 soybeans the isoxaflutole application would be in mid August, compared to early
July for late-­‐ planted corn, for example. This is a substantial difference in the pattern of use.