CRIMSON CLOVER RESEEDING POTENTIAL AS AFFECTED BY S-TRIAZINE HERBICIDES

Economic savings can result from allowing a crimson clover (Trifolium incarnatum L.) cover crop in no-tillage corn (Zea mays L.) systems to self-reseed and thereby eliminate the need for annual seeding operations. Research has indicated, however, that self-reseeding of crimson clover is variably sensitive to certain residual corn herbicides, depending on growth stage at time of herbicide application. Accordingly, a 2-yr experiment was conducted to evaluate the effects of atrazine, cyanazine, and simazine applied to crimson clover at four growth stages (late vegetative, early bloom, late bloom, and early seed set) on subsequent clover reseeding potential. All successfully reseeded crimson dover plots were sampled in 1990 and 1991 for dry matter (DM) and total N concentration, In 1990, strazine and cyanazine applied at the late vegetative stage and cyanazine applied st early bloom the previous spring prevented crimson clover seed development for fall self-reseeding. Regardless of herbicide, DM production in the spring of 1990 tended to be greater for reseeded clover plots when the respective herbicide was applied at the early seed set stage (3929 to 4912 lb/acre) than when applied earlier (447 to 4286 lb/acre). In 1991, the atrazine/late vegetative, atrazine/early bloom, cyanazine/early bloom, and cyanazine/late bloom treatment combinations did not reseed. Atrazine applied at late bloom resulted in lower DM production than did any other treatment which reseeded. Results indicate that strip application may be necessary in reseeding crimson clover systems where cyanazine and atrazine are used during late vegetative to late bloom growth stages; whereas simazine may be broadcast applied at any growth stage without diminishing reseeding success.