Glyphosate and SC-0224 at 75 or 150 g ae/ha, applied to alfalfa foliage after field dodder and largeseed dodder were parasitically well established, controlled dodder selectively. Glyphosate applied at any time over a range of developmental stages stopped the growth of dodder. Control was best when the herbicides were applied when alfalfa was 20 to 30 cm tall, when maximum length of dodder shoots was 30 to 60 cm, and while host and parasite were both vegetative and growing vigorously. Later application allowed dodder to injure alfalfa before being controlled, and earlier application sometimes allowed dodder to recover and suppress alfalfa before the hay was cut.

A heavy, uncontrolled infestation of field dodder and largeseed dodder suppressed newly seeded alfalfa severely and killed many of the plants. Glyphosate at 75 or 150 g ae ha-1, sprayed over the top of the dodder-infested alfalfa, stopped the growth of dodder and did not injure alfalfa significantly. Treated dodder began to grow normally again 2 to 3 wk after treatment. This regrowth injured the alfalfa severely in spite of earlier control. Glyphosate at 75 or 150 g ha-1 applied two or three times controlled dodder effectively and protected the alfalfa. A rate of 40 g ha-1 was not effective.