Authors: Respectively, Extension Weed Specialist/Assistant Professor and Research Assistant, Department of Extension Plant Sciences, New Mexico State University.
There are over 150 species of dodders (Cuscuta spp.) worldwide. Belonging to the Convolvulaceae plant family, dodders are annual parasitic plants that reproduce by seed and do not have any leaves or chlorophyll to live from-they therefore must obtain all of their growth requirements (water, minerals, carbohydrates) by attaching themselves to other living green plants (host plants). Host plants include those grown for agricultural purpose, ornamental plants, range plants, and weeds.
Description and Life Cycle
In the spring, dodder seeds germinate near the soil surface and send up slender, thread-like twining stems varying in color from pale green to yellow or orange and without any cotyledons (seed leaves). The slender, leafless, thread-like stem sways or rotates slowly until it touches the stem or leaf of another plant and begins to wind around it (Figure 1). On a host plant, the dodder stem will immediately form small appendages called haustoria (tiny sucker-like roots), which penetrate the stems or leaves so that dodder can extract its necessary growth requirements. Soon after attaching to a host plant, the lower end of the dodder withers and breaks its connection with the ground, while the upper part of the stem grows rapidly, often forming dense stringy masses. However, if the dodder seedlings are unable to contact a susceptible host plant soon after germination, they will not survive.
Figure 1. Dodder parasitizing a tomato plant. Picture from Weeds of California and Other Western States. (Photo by J.M. DiTomaso; used with permission.)
Dodder flowers are numerous, tiny, whitish to pinkish, and form in small clusters along the stems, generally from May to October, depending on the species and location. Each flower forms a small, globular seedpod with 2 to 4 seeds (Figure 2). The seeds have rough coats and vary in size, depending on the species, and may be able to survive over 20 years in the soil.
Figure 2. Dodder flowers in small clusters along the stems. Pictures from Weeds of California and Other Western States. (Photos by J.M. DiTomaso; used with permission.)
Although there are several species of dodder distributed throughout North America, the most common species in Western United States are largeseed dodder (C. indecora) and field dodder (C. campestris). These species have become a major economic concern in alfalfa, clover, tomatoes, and potatoes. Dodder infestations reduce crop yield and increase harvesting costs. The damage of dodder to the host plant varies from moderate to severe depending on the growth of the host plant and on the number of haustoria attachments to the host plant.
Dodder management is only achieved using combined preventive, cultural, mechanical and chemical methods that aim at control of existing populations prior to seed production and control of subsequent seedlings. Fields with dodder history need to be monitored frequently, and new dodder plants must be removed as soon as possible.
Preventive management includes planting dodder-free crop seeds, cleaning agricultural machinery before moving from an infested area to a non-infested area, and managing existing populations prior to seed production so as to not spread dodder seeds. While small infestations can be removed by hand to prevent the production of the seed, the recommendation for controlling extensive infestations is to remove the host plant and, if possible, replant with non-host crops.
Planting non-host grass crops (e.g., corn, sorghum), winter crops (e.g., winter wheat, broccoli, legumes), and transplanted trees with bark (e.g., pecan) can be effective in managing dodder in an infested area. However, certain broadleaf weeds such as pigweeds, lambsquarters, Russian thistle, and field bindweed serve as dodder host plants and will need to be controlled as part of a successful dodder management strategy. Furthermore, due to the longevity of dodder seed, once a host crop is planted again fields need to be monitored regularly, and new dodder plants must be removed immediately.
Dodder infestation can be decreased by hand-pulling, burning, cutting, or close mowing of the infested plants. If growers decide to use cultivation for dodder control, cultivation should be done prior to dodder's attachment to the host plant.
Several post-emergence (POST) and pre-emergence (PRE) herbicides are effective for dodder control/suppression. Common PRE herbicides (applied prior to dodder emergence) for dodder control include Kerb (pronamide), Treflan (trifluralin), and Prowl (pendimethalin). POST application (applied after dodder emergence) of Dacthal (DCPA), Scythe (pelargonic acid), Raptor (imazamox), Pursuit (imazethapyr), and Gramoxone (paraquat) have been shown to be effective in dodder control/suppression (Table 1). Broadcast or selective (spot treatment) application of Roundup (glyphosate) also has been shown to provide good control of dodder; however, spot treatments of Roundup will result in crop injury in non-Roundup Ready crops.
|Table 1. Recommended POST and PRE Herbicides (Based on Dodder Emergence and Their Crop Registration) for Dodder Control in New Mexico*|
|Kerb (pronamide)||PRE (3-4 lb)||PRE (3-4 lb)||NR**||NR||
Required rates depend on type of irrigation. Excessive amounts of irrigation water following Kerb herbicide application may adversely affect the herbicide activity.
|Treflan (trifluralin)||PRE (1-4 pt)||NR||PRE (1-2 pt)||PRE (1-2 pt)||For optimum dodder control, the highest labeled rate should be used. Due to the lower registered rates in tomato and potato, herbicide could only provide partial control.|
|Prowl H2O (pendimethalin)||PRE (1-4 qt)||NR||PRE (1.5-3 pt)||PRE (1.5-3 pt)||For optimum dodder control, the highest labeled rate should be used. In seedling alfalfa, application rate is 1-2 pt of Prowl/acre.|
|Roundup 4S (glyphosate)||POST (4 pt)||NR||NR||NR||Broadcast application is only recommended on Roundup Ready alfalfa. However, in conventional alfalfa, Roundup may be applied as a spot treatment or with wiper applicators. Applications may be made in the same area at 30-day intervals; however, no more than 10 percent of the total field area should be treated at one time.|
|Dacthal (DCPA)||NR||NR||PRE (6-14 lb)||NR||Tomato plants should be well-established prior to Dacthal application. For optimum dodder control, the highest labeled rate should be used.|
|Raptor (imazamox)||POST (4-6 fl oz)||POST (5 fl oz)||NR||NR||Raptor suppresses dodder prior to its attachment to the host plant. For optimum dodder control, the highest labeled rate should be used.|
|Pursuit (imazethapyr)||POST (3-6 fl oz)||POST (3-6 fl oz)||NR||NR||Pursuit suppresses dodder prior to its attachment to the host plant. For best results, Pursuit should be applied with crop oil concentrate or methylated seed oil. For optimum dodder control, the highest labeled rate should be used.|
|Gramoxone Extra (paraquat)||POST (12.8 fl oz)||POST (13-24 fl oz)||NR||NR||Gramoxone is a restricted-use herbicide, so the applicator is required to be certified. Apply between cuttings but before regrowth for dodder suppression. Gramoxone will damage emerged or green plants. The rate of 12.8 fl oz of Gramoxone/acre is registered for between-cutting applications.|
|Scythe (pelargonic acid)||POST (Variable, 3-7%)||POST (Variable, 3-7%)||NR||NR||Apply between cuttings but before regrowth for dodder suppression. Scythe will damage emerged or green plants.|
*Other trade names of the active ingredients alone or in combination may be available in the market. When considering the use of an herbicide, nothing can take the place of reading the label and making applications according to label directions. Most labels can be accessed at either http://greenbook.net or http://cdms.net.
The critical reviews of this article by Dr. Jill Schroeder, Ms. Cheryl Fiore, and Mr. Mike Cowbrough are acknowledged.
Alex, J.F. 1998. Ontario Weeds (Publication 505). Guelph: Ontario Ministry of Agriculture, Food, and Rural Affairs.
Cudney, D.W., S.B. Orloff, and J.S. Reints. 1992. An integrated weed management procedure for the control of dodder (Cuscuta indecora) in alfalfa (Medicago sativa). Weed Technology, 6, 603-606.
Dawson, J.H., and A.R. Saghir. 1983. Herbicides applied to dodder (Cuscuta spp.) after attachment to alfalfa (Medicago sativa). Weed Science, 31, 465-471.
DiTomaso, J.M., and E.A. Healey. 2007. Weeds of California and Other Western States (Publication 3488). Davis: University of California Agriculture and Natural Resources.
Lanini, W.T., D.W. Cudney, G. Miyao, and K.J. Hembree. 2002. Dodder. Davis: University of California Agriculture and Natural Resources. Accessed April 2, 2009 at http://www.ipm.ucdavis.edu/PDF/PESTNOTES/pndodder.pdf
Whitson, T.D., L.C. Burrill, S.A. Dewey, D.W. Cudney, B.E. Nelson, R.D. Lee, and R. Parker. 2006. Weeds of the West (9th Edition). The Western Society of Weed Science in cooperation with the Western United States Land Grant Universities Cooperative Extension Services.
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Printed and electronically distributed in January 2010 Las Cruces, NM.