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Dodder |
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Glenn Nice, Weed Diagnostician , Botany & Plant Pathology, Purdue University
Dodder is a unique plant in the fact that it is parasitic. The relationship with dodder and its particular host is absolute parasitic, meaning that there is no benefit afforded the host whatsoever, and dodder must have its host to survive. Dodder does not have any leaves or, for that matter, any chlorophyll to produce its own food. It lives by attaching to a host plant and extracting the host plant’s carbohydrates. It does this by penetrating the host plant with small appendages called “haustoria.” Through the haustoria, dodder will extract the carbohydrates. Although not toxic or even unpalatable to some livestock, it can weaken the host plant to reduce yield, quality, and stand. It is not to the advantage for a parasite to kill its host, thus dodder generally will not kill its host, but if the infestation is severe enough, it may result in the death of the host plant. Work done in southern California reported that yield dropped from 2235 lb/A to 1576 lb/A when untreated for dodder (Cudney et al. 1992). In the same study alfalfa plant number was reduced from 5 to 2 plants/ft2. Once thought to belong to the morningglory family, it is now being placed in a family of its own, called cuscutacease. Dodders belong to the genus Cuscuta. The USDA plant data base lists approximately 47 species (http://plants.usda.gov). Some of the differences in species are the different species that the specific dodder will parasitize. Examples of this are Cuscuta epithymum, clover dodder and Cuscuta polygonorum, smartweed dodder. As the common names suggest these species of dodder generally parasitize clovers and smartweeds. Without leaves, identification can become a little more difficult. All the plant identification keys I have seen use the flowers to identify specific dodders. Differences in flower corollas and the way the capsules open are often used. An Illustrated Flora of the Northern United States and Canada Vol. 3 by N. Brown and A. Brown has a key and descriptions of 12 dodder species. Single dodder plants may be missed when looking at broadleaf plants. It appears as yellow string winding up the stems or over the leaves of another plant (Figure 1.). It might be missed if you don’t look close enough. However, if dodder gets bad enough, then it can look like a mat of these yellow strings covering the plants they parasitize. Dodders are annuals and are spread by seed. Having a hard seed coat, it is suspected that gas and water levels control dormancy. How long the seed can survive appears to be variable. This may be because of different environmental conditions and differences between species. Seed may be able to survive in the soil over 20 years. One article I read wrote about seed collected from herbarium specimen that was over 60 years old and still germinating. However, it should be noted that conditions sitting in a herbarium are not like the conditions a seed would experience sitting in the soil. Work done studying germination with five angled dodder in California (1980) reported that the majority of seed germinated near the surface; however, seedlings could reach the soil surface even when buried an inch deep below the soil surface. Seedling survival decreased when buried deeper. Several approaches to control have been investigated. Flail mowing and burning were investigated in Southern California. Flail mowing increased dodder infested alfalfa yield 32% from an untreated. The use of burning not only decreased alfalfa yields, as might be expected, but also decreased dodder emergence when soil was moved into a greenhouse when compared to untreated. This most likely was a result of decreased seed production. When considering the possible longevity of seed dormancy and an already established seed bank, burning may not make for a viable solution. Control of dodder with herbicides is dependent on the crop that you wish to control it in. Some herbicides may have an effect on the dodder, but may also either have an effect on the crop or may not be labeled for use in that crop. Always read and follow herbicide labels. In many cases, control may be more effective before attachment to the host. PRE applications of Kerb have provided good control of dodder in ornamentals and turf. Treflan and Prowl have also been reported to suppress dodder germination. However, PRE applications often do not retain enough residual activity to provide control for the rest of the season. POST applications to control dodder after it has attached to the host plants can be more variable. Suggestions for control of dodder POST are few and inconsistent. Dawson and Saghir (1983) reported Dactathol (DCPA) controlled dodder 100% three weeks after application. However, Dactathol is not labeled for either alfalfa or clover, crops in which dodder is often a problem. Glyphosate has been reported to control dodder post attachment and can be applied as a spot-treatment of a 1-2% solution to alfalfa. However, be aware that there will be damage to the alfalfa where the glyphosate is applied. Raptor can suppress dodder at 5 fl oz/A when applied after dodder emergence and before dodder reaches 3 inches. Pursuit DG can also suppress dodder after emergence, but as soon as the dodder attaches to the host plant, suppression drops. It is recommended on the label to use COC or methylated seed oil with Pursuit when trying to suppress dodder. For more information on Dodder, click here For more information on this unique plant see the sources below. Sources:
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Site last updated:
5 February, 2010