– Mark Loux, OSU Extension Weed Specialist
Photo: uwyo.edu
We have had reports of dodder in some red clover fields. Dodder is a parasitic plant without any leaves or chlorophyll to produce its own energy. It lives by attaching to a host with small appendages (called ‘haustoria”), and extracting the host plant’s carbohydrates. The stems are yellow-orange, stringlike, twining, smooth and branching to form dense masses in infested fields. Although neither toxic nor unpalatable to some livestock, dodder can weaken host plants enough to reduce yield, quality, and stand. If infestations are severe enough, dodder may kill host plants.
Dodders are annuals that spread by seed. Seed may be able to survive in the soil over 20 years. Controlling dodder with herbicides depends on the crop in which you wish to control it. Some herbicides may affect dodder, but also may affect the crop, or not be labeled for that use. In many cases, dodder control may be more effective if herbicides are applied before the plant attaches to the host. PRE applications of Kerb have provided good control of dodder in ornamentals and turf. Trifluralin and pendimethalin have also been reported to suppress dodder germination, but in most cases PRE applications will not retain enough residual activity to provide control for the rest of the season.
Glyphosate has sometimes been reported to control dodder POST. It can be applied as a 1 to 2-percent spot treatment in alfalfa, but non Roundup Ready alfalfa will be injured or killed. A broadcast foliar application would be possible in Roundup Ready alfalfa. Raptor® applied at 5 oz/A can suppress dodder when applied after dodder emergence, but before it is three inches tall. Pursuit also can suppress dodder after emergence, but as soon as dodder attaches to the host plant, becomes less effective. The Pursuit label recommends using it with COC or methylated seed oil when trying to suppress dodder.
Other resources:
http://ucce.ucdavis.edu/files/repositoryfiles/ca4304p30-68548.pdf
http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9331
https://www.btny.purdue.edu/WeedScience/2005/Dodder05.pdf
https://www.naaic.org/Meetings/National/2002meeting/2002Abstracts/Reisen.pdf