Frequent inquiries about the response of small grains to atrazine (2-chloro-4.ethylamino-6-isopropylamino-s-triazinc) have been made, but research in this area has been very limited. If atrazine carryover is expected, harley (Hordeum vulgate L. emend Bowden) and spring wheat (Triticum aestivum L. em Thell) might be more suitable small grains to grow if they produced more grain and straw in residual atrazine than oats (Avena sativa L.). The objectives of this research were to evaluate the response of barley and spring wheat to atrazlne, to compare the response of these two small grains to the response of oats, and to test for genotyplc differences for grain yield response to atrazine in barley and spring wheat.
Atrazine applications of 0, 1.12, 2.24, 3.36, and 4.48 kg/ha were applied postemergence to corn (Zea mays L.) in 1975, and the small grains were sown during the spring of 1976. This procedure was repeated in 1976 and 1977. The soil was a silt loam (Typic Arguidoll, finesilty, mixed, mesic) with 3.5 to 4.0% organic matter.
Grain and straw yields of all genotypes were reduced by atrazine carryover, and species differences were evident. Barley produced higher grain and straw yields in residual atrazine than spring wheat in both 1976 and 1977. Oats, which were not included in 1976 comparisons, also had higher grain and straw yields than spring wheat in 1977. Oats did not yield as much grain and straw as barley in high levels of residual atrazine in 1977, but on the basis of tolerance (yield in soil containing atrazine/yield in soil with no atrazine), there was little difference between barley and oats. However, barley was significantly more tolerant of atrazine than spring wheat on the basis of seedling dry matter production in a greenhouse test. Variation among genotypes for response to atrazine in the 2 years of testing was limited in both barley and spring wheat.
The results of this research indicate that if small grains are grown in soil with an anticipated atrazine carryover problem, barley would be preferable to oats. and both harley and oats would be preferable to spring wheat.