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Our “experiments” were routine agronomic glyphosate sprays in spring and other seasons, followed by stormwater runoff sampling. There has been no specific spraying simply to trace glyphosate. Most spraying has been to eliminate competing plant types from plots that were intended to house a single grass species, and in one case the spraying was to change crops without cultivation. Since the crop species are not engineered to be glyphosate resistant, the spring spraying must happen before the desired crop begins to grow again, thus is effective against only earlier-emerging plants. Three tables below present the plots, the recent spraying history of the site through spring 2018, and sampling history.

The various plots are:

Plot ID	Crop	Area (ac)	Frac in watershed
A	Control	0.833	0.983
B	Switchgrass	0.837	0.985
C	Reed-Canary, then Switchgrass	0.837	1.000
D	Switchgrass	0.837	1.000
E	Reed-Canary, then Switchgrass	0.833	0.975
F	Switchgrass	0.848	0.888
G	Switchgrass	0.875	0.845
H	Switchgrass	0.901	0.818
I	Control	0.915	0.802
J	Switchgrass	0.930	0.761
K	Switchgrass	0.928	0.727
L	Reed-Canary, then Switchgrass	0.970	0.700
M	Switchgrass	1.025	0.655
N	Switchgrass	0.933	0.696
O	Reed-Canary, then Switchgrass	1.091	0.673
P	Control	1.083	0.641
Q	Miscanthus	0.400	0.423
R	Miscanthus	0.400	0.308

We sprayed glyphosate each year at least once:

Year/ season	Plots sprayed	kg AI in watershed	Comments
2014 May	B,D,G,H,J,K,M,N	4.08
2015 May	B,D,G,H,J,K,M,N,Q,R	2.85
2016 April	B,D,G,H,J,K,M,N,Q,R	4.28
2016 July	C,E,L,O	2.14	Killing reed-canary grass for crop change
2016 October	C,E,L,O	2.85	Killing reed-canary grass for crop change
2017 April	C,E,L,O,Q,R	2.34
2017 June	C,E,L,O	2.14
2018 spring	All except controls (A,I,P)	6.4

The glyphosate sampling campaigns in these years were as follows:

Year and season	Number of samples	Comments
2014 spring	CRC Weir: 226	Pilot year, few samples analyzed
2015 spring	CRC Weir: 104 CRC Tile: 94	First round with USGS collaboration
2016 spring	CRC Weir: 124 CRC Tile: 126
2016 fall	CRC Weir: 49
2017 spring	CRC Weir: 84
2018 spring	CRC Weir: 175 CRC Tile: 1 Freese: 2
2018 summer and fall	CRC Weir: 166 CRC Tile: 3 Freese: 69