Oakes Irrigation Research Site
Carrington Research Extension Center * North Dakota State University
P.O. Box 531, Oakes, ND 58474-0531, Phone: (701) 742-2744, FAX: (701) 742-2700, E-mail:										Blaine.Schatz@ndsu.edu
										Kelly.c.Cooper@ndsu.edu
										Leonard.Besemann@ndsu.edu
Defining Glyphosate and Dicamba Drift Injury Thresholds in Potatoes
H. Hatterman-Valenti, A. Robinson, C. Auwarter, A. Crook, and E. Brandvik
A field study was conducted to correlate plant injury in potatoes to results a producer would receive from lab analysis of leaf tissue when off-target movement of glyphosate, dicamba, or the combination of both herbicides is suspected. Russet Burbank seed pieces were planted May 22. Simulated drift doses of glyphosate at 0.2, 0.04, 0.007 lb ai/acre, dicamba at 0.09, 0.02, 0.004 lb ai/acre; and glyphosate + dicamba at 0.2+0.09, 0.04+0.02, 0.007+0.004 lb ai/acre were applied to plants at the tuber initiation stage (July 7) using a CO2 sprayer equipped with 8002 nozzles at 40 psi and an output of 20 GPA. Visual injury ratings and tissue sample collection occurred 10 and 20 days after application. Tissue samples were sent to South Dakota Agricultural Laboratories for residue analysis. Two of the four treated rows were harvested and graded to evaluate herbicide effect on potato yield and grade.
Summary: The highest dicamba dose (0.02 lb) alone or with glyphosate caused the most visible injury. The highest dicamba dose alone or with glyphosate reduced the total and marketable yield compared to the untreated. More undersized tubers (< 4 oz) were formed when plants received dicamba (0.09 or 0.02 lb) alone or with glyphosate.
Table 1.  Defining glyphosate and dicamba drift injury thresholds in potatoes at the Oakes Irrigation Research Site in 2015.
		Rate	Injury	No. 2	No. 1							No. 2
No.	Treatment	(lb ai/ac)	(20 DAA)	< 4 oz	< 4 oz	4-6 oz	6-10 oz	10-14 oz	> 14 oz	Total	> 4 oz	> 4 oz
			--- % ---	-----------------------------------   cwt/acre   ----------------------------------
1	Untreated		0	5	48	79	152	50	14	403	294	57
2	Glyphosate	0.2	10	37	44	65	93	30	7	455	196	178
3	Glyphosate	0.04	0	5	56	108	139	43	7	421	297	63
4	Glyphosate	0.007	0	3	56	84	140	41	17	413	283	71
5	Dicamba	0.09	49	119	16	16	5	0	0	321	21	165
6	Dicamba	0.02	31	73	32	30	22	4	1	396	57	235
7	Dicamba	0.004	30	15	63	89	109	40	6	426	244	104
8	Glyphosate	0.2	50	148	12	5	4	1	0	306	10	137
	Dicamba	0.09
9	Glyphosate	0.04	28	65	36	32	29	3	0	400	64	236
	Dicamba	0.02
10	Glyphosate	0.007	30	11	60	81	127	42	7	431	257	103
	Dicamba	0.004
	LSD (0.05)		4	24	20	28	49	20	7	63	87	66
Oakes Irrigation Research Site
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