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Response of Oats to Atrazine¹

The popularity of atrazine [2-chloro-4-(ethylamino)-6- (isopropylamino)-s-triazine], a persistent corn (Zea mays L.) herbicide, has caused problems for oats (Avena sativa L.) grown in rotation with corn. Despite frequent inquiries about the response of oats to atrazine, very little testing for cultivar differences to atrazine has been conducted. Therefoxe, the objective of this study was to evaluate the response of current oat genotypes to atrazine.

Twenty oat genotypes were evaluated for response to atrazine for 2 years. Five atrazine treatments, 0, 1.12, 2.24, 3.36, and 4.48 kg/ha, were applied postemergence to corn land during each of the years prior to growing the oats. Atrazine damage to oats grown in 1976 was light because of wet conditions during the last half of 1975, while damage to oats grown in 1977 was more severe because of dry conditions during the last half of 1976.

Grain and straw yield responses of the genotypes were evaluated on the combined data from the 2 years of testing with a regression procedure. Tolerant genotypes were expected to have a high mean and a regression coefficient less negative than –1.0, while intolerant genotypes were expected to have a low mean and a regression coefficient more negative than –1.0. There was significant genetic variability for grain yield response to atrazine. Froker, Lang, Mackinaw, X2078-1, and X1839-1 were more tolerant of atrazine than Dal, Lyon, Otee, and Allen. There also was significant variability for straw yield response to atrazine, but grain and straw yield responses (regression coefficients) were not significantly correlated. Straw yield response to atrazine was closely associated with plant height.

The influence of atrazine on kernel quality was evaluated in a subset of eight genotypes. Groat protein percentage was increased by higher levels of residual atrazine, but groat protein yields were reduced because of the grain yield reductions. Groat percentage and 100-seed weight were not reduced in 1976 when atrazine damage was light, but both were reduced in 1977 when damage was severe.

Although there was significant genetic variability for response to atrazine among the 20 genotypes tested, the variability probably is not sufficient to warrant intercrossing them in an effort to develop genotypes with improved tolerance. A thorough search of the World Oat Collection for more tolerant genotypes is recommended.

Key Words: Grain yield • Straw yield • Protein • Regression • Avena sativa L.

² Assistant professor, former graduate student, and professor, Dep. of Agronomy, and assistant scientist, Dairy Science Dep., Univ. of Wisconsin, Madison, WI 53706.

Received for publication June 23, 1979.