With vast geographic distribution and a plethora of vulnerable host plants, the irregular looking field dodder (Cuscuta campestris) is one of the most widespread and most harmful pests among the flowering parasitic plants. Field dodder can easily become a problem in flower gardens, vegetable gardens (e.g. tomato, sweet pepper, potatoes and cabbage), or possibly even show up in greenhouse crops. The most devastating damage, however, comes from field dodder outbreaks in newly-established perennial legume crops (alfalfa, clover, etc.), which are generally the preferred hosts of this plant species.
Field dodder may be known by common names such as strangle weed, witch’s hair, or devils’ hair. It is composed of golden yellow, leafless “threads” that twine all throughout and over its victim plant as well as those plants around it. These threads attach themselves with short, suction-cup-like suckers that originate from the base of the dodder stems. The suckers will then penetrate the stems of host plants where it will access all of its needed nourishment.
Because this plant is an annual it must replicate from seed, ergo flowering is crucial to its survival. The flowers of the field dodder are small, whitish, and 1/4 inch in diameter. They appear on the plant anywhere from April to October and will produce a seedpod that is two-celled and four-seeded.
Plants growing in the current season will be killed by the first frost of the fall. The seeds might sprout the following spring, or they may lie dormant for a number of years. Germination for this plant takes place in the soil, but interestingly the field dodder’s roots die as soon as the plant finds and penetrates an acceptable host. After attachment, the field dodder leeches its nourishment totally from the host plant. A single dodder plant can spread by branching and attacking additional host plants.
The field dodder cannot be destroyed by pulling it off the host plants. This is because remaining stem pieces will continue to grow, re-establishing itself once again. Destroying the host plants can control dodder. This method, however, usually is not too favorable a solution for many a gardener nor farmer. Chemical control can be had by using Trifluralin (Preen, Miracle-Gro Garden Weed Preventer, Treflan, Hi-Yield Herbicide Granules Weed and Grass Stopper). It is a pre-emergent herbicide that can be used for control if applied before the dodder seed germinates. This may be your best option. There is always glyphosate (Round-up, Kleen-up, Killzall, etc.), which is quite effective on dodder. However, glyphosate is a nonselective herbicide and will kill whatever it hits, including the host plants.
Rip Winkel is the Horticulture agent in the Cottonwood District (Barton and Ellis Counties) for K-State Research and Extension. One can contact him by email at firstname.lastname@example.org or calling either 785-682-9430, or 620-793-1910.