For effective full-season control of dodder in alfalfa produced for seed, herbicides applied to soil in late winter or early spring should remain active through June. Pendimethalin or prodiamine at 2.2 kg ai ha-1 applied in mid March controlled 97 to 100% of dodder through May and 92 to 100% through June. At 3.4 kg ha-1, both controlled 96 to 100% of dodder through June each year, and control of 95 or 96% persisted through July in 1 of 3 yr. In the greenhouse, trifluralin was only about 1/8 as active against dodder as pendimethalin and prodiamine. In the field, trifluralin at 2.2 kg ai ha-1 controlled dodder satisfactorily through May in 3 of 4 yr and through June in 1 of 4 yr. At 4.5 kg ha-1, trifluralin controlled 99% of dodder through May in each of 3 yr; control was satisfactory through June in 2 of 3 yr. Oryzalin was less effective than the other three dinitroaniline herbicides. A standard herbicide, chlorpropham at 6.7 kg ai ha-1, controlled 97 to 100% of dodder through May, but control usually did not persist through June. Another standard herbicide, DCPA at 11.2 kg ai ha-1, controlled 97 or 98% of dodder through June in 2 of 3 yr. Pendimethalin and prodiamine at 3.4 and 6.7 kg ai ha-1 did not affect the yield or quality of seed produced by established alfalfa. Heavy sprinkler irrigation (15 cm of water) after application did not diminish dodder control from pendimethalin or prodiamine.

Chlorpropham (isopropyl m-chlorocarbanilate) at 6.7 kg ai/ha controlled a mixture of field dodder (Cuscuta campestris Yunck. ♯3 CVCCA) and largeseed dodder (Cuscuta indecora Choisy ♯ CVCIN) for 3.0 and 4.3 weeks in two greenhouse experiments. The insecticide carbaryl (1-naphthyl N-methylcarbamate) at 0.8 kg ai/ha applied with chlorpropham extended control by 0.7 and 1.8 weeks, and PCMC (p-chlorphenyl N-methylcarbamate) at 0.8 kg ai/ha extended it by 2.7 and 2.8 weeks. Both additives also improved dodder control by chlorpropham in the field, with carbaryl having less effect than PCMC.