Dodder (Cuscuta campestris) parasitic weed in Alfalfa
Dodder is an annual total stem (obligate) parasite weed that causes serious problems in many plants. The parasitic weed C. campestris is by far the most important among the dodders, perhaps because of its wide host range. Once introduced, it is almost certain that there will be suitable host plants on which it can thrive and be damaging, whether they are crops or wild species. It also has a wide tolerance of climatic conditions i.e. warm temperate to sub-tropical and tropical. It has slender, twining or threadlike stems that vary from pale green to yellow or bright orange in colour. As the plant do not have any leaves and chlorophyll to live from-they therefore must obtain all of their growth requirements by attaching themselves to other living green plants (host plants). Dodder seeds germinate near the soil surface and send up slender which rotates slowly until it touches the stem or leaf of another plant and begins to wind around it. On a host plant, the dodder stem will immediately form small appendages called hustoria. Soon after attaching to a host plant, the lower end of the dodder withers and break its connection with the ground, while the upper of the stem grows rapidly. Dodder stems that have attached to a host plant have been known to survive for several days after being detached from the host plant. As dodder plants grow, they continually reattach to the host. When other suitable hosts are nearby, dodder shoots spread from host plant to host plant, often forming a dense mat of intertwined stems.
Damage caused by Dodder :
Field dodder (Cuscuta campestris), the most damaging annual obligate stem parasite causes serious problem in forage legumes like lucerne (Medicago sativa L.) and Egyptian clover (Trifolium alexandrinum L.). During the seed production of these economic crops, dodder seeds are harvested with the crop seed and being similar in size and density to the crop seeds, it is extremely difficult to separate from the crop seed (Dawson et al., 1994). Cuscuta species do contain functional chlorophyll, but numbers of chloroplasts are very low and photosynthesis is only 1-2 per cent of that in a normal green plant, i.e. C. campestris is almost totally dependent on the host for growth and survival (Hibberd and Jeschke, 2001). Crop yields can be significantly reduced as it parasitises and shades out the host plants.
– Plants infested with field dodder gradually weaken, their lush growth dwindles and they have very small vegetative and generative yield (Fathoulla and Duhoky, 2008).
– Reducing the biological yields of plants parasitized by field dodder. The damage consists mainly of reduced fresh biomass yield and significantly reduction in crop seed production.
– It may reduce seed yield by 60 per cent. For certified seed production of Lucerne, its population should be <0.05 per cent (20 Cuscuta seeds/kg lucerne seed) (Cudney et al., 1992) and (Mishra, 2009).
– As the dodder is a powerful sink for metabolites, causing a severe drain on host resources and often completely prevent flowering, normal fruit development and death of the host plant after establishment of contact with the host phloem (Wolswinkel, 1974).
– Hay (fresh biomass of legumes, primarily alfalfa and clover) containing 50-60 per cent dodder fed to livestock caused reduction in body weight of livestock and miscarriages are more frequent along with indigestion occurs.
– Dodder consumption in bulk feed causes diarrhea, vomiting, palpitation and heavy breathing in rabbits and horses The C. campestris can be poisonous to animals if it exceeds 5 per cent of the total roughage (Movsesyan and Azaryan, 1974).
– Some Cuscuta species carry viruses such as the cucumber mosaic virus or tobacco rattle virus, thus causing additional difficulties for crop growing and indirectly reducing yields (Marcone et al., 1999).
– It is also a contaminant of hay and threatens the small seeds industry through seed contamination
– Reducing the biological yields of plants parasitized by field dodder. The damage consists mainly of reduced fresh biomass yield and significantly reduction in crop seed production.
– It may reduce seed yield by 60 per cent. For certified seed production of Lucerne, its population should be <0.05 per cent (20 Cuscuta seeds/kg lucerne seed) (Cudney et al., 1992) and (Mishra, 2009).
– As the dodder is a powerful sink for metabolites, causing a severe drain on host resources and often completely prevent flowering, normal fruit development and death of the host plant after establishment of contact with the host phloem (Wolswinkel, 1974).
– Hay (fresh biomass of legumes, primarily alfalfa and clover) containing 50-60 per cent dodder fed to livestock caused reduction in body weight of livestock and miscarriages are more frequent along with indigestion occurs.
– Dodder consumption in bulk feed causes diarrhea, vomiting, palpitation and heavy breathing in rabbits and horses The C. campestris can be poisonous to animals if it exceeds 5 per cent of the total roughage (Movsesyan and Azaryan, 1974).
– Some Cuscuta species carry viruses such as the cucumber mosaic virus or tobacco rattle virus, thus causing additional difficulties for crop growing and indirectly reducing yields (Marcone et al., 1999).
– It is also a contaminant of hay and threatens the small seeds industry through seed contamination
Management in Lucerne :
Dodder is a difficult weed to eradicate. It grows rapidly and can set seed after only a few weeks of growth. Its seed can survive in the soil for long periods. Preventing entering in new areas and being vigilant in spotting and destroying new outbreaks before they set seed is the best way of control.
Prevention :
Preventive is better than control and is one of the most important and fundamental activities in any field dodder control strategy, which focuses primarily on prevention of field infestation by:
– Use of clean crop seed is vital, and seed should be inspected and cleaned if necessary, or obtained from a source known to be reliable.
– Cleaning all nearby field, field margins and waste grounds at recurrent intervals;
– Maintaining irrigation channels dodder-free;
– Spreading well decomposed and rotten manure;
– Crop rotation of at least of 4-5 years is an important preventive measure even though it may be difficult to find an adequate replacement for some crops and so avoid dodder parasitism in that new crop. Cereal crops such as wheat, barley, oats, triticale and cereal rye are less susceptible to dodder, along with Kharif grain crops such as maize and sorghum.
Contaminated hay can introduce dodder to a clean property. Hay containing dodder should be destroyed as mature seed is often present.
– Machinery used for reaping and other intercultural operations in infested areas should be cleaned before moving to other areas.
– Controlling the preferred alternate weed hosts for dodder reduces the risk in new infestations and the extent of current infestations.
– All host and dodder plant material must be burnt, preferably on the infested site. Cut the host plant as close as possible to ground level and burn it. Burning can be carried out after cutting and drying.
– Deep ploughing can help reduce the seed burden by burying dodder seed. Most dodder seed will not germinate from a depth of more than 7.5 cm.
– Quarantine with seeds and plant material denied entrance. Strict quarantine regulations with sufficient and effective and enforcement and vigilance will be needed.
Mechanical methods :
– Separation of Cuscuta seeds from lucerne by equipment comprising felt or velvet covered rollers to which the rough seeds of Cuscuta stick while the smoother crop seeds pass over.
– Manual removal and frequent inter-row cultivation before the parasite attaches the host plant are the usual control measures. However, these methods are laborious and often not effective.
– Cuscuta can be pulled out and buried.
– The seed of lucerne are to be treated with 5 to 10 per cent solution of common salt for five minutes. The light seeds of Cuscuta will float on the surface of water.
– The young seedlings with rudimentary roots are readily destroyed by shallow tillage before or after crop establishment.
– Hand-pulling is suitable only for scattered infestations as the infested crop plants have to be removed with the parasite.
– More extensive infestations in lucerne are also sometimes treated with overall flaming, as the crop is able to recover.
– Grazing by sheep can result in significant suppression of dodder by their grazing habits.
Cultural control :
– Crop rotation is highly effective against parasitic weeds however careful crop selection is essential. Rotation with non-susceptible crops can be helpful. Cereals are virtually immune from attack, and some broad-leaved crops may also be sufficiently resistant, including soybean, kidney bean, squash, cucumber and cotton. – Postponement of sowing or replanting is also considered an important cultural measure.
– Dense crop canopy is a valuable component because deep shade suppresses the coiling and attachment of Cuscuta.
Biological control :
– Use of bio-herbicide (mycoherbicide) like Lubao II Colletotrichum gleosporioides f. sp. Cuscutae for Cuscuta sp. (Parker and Riches, 1993).
– Among pathogens, Alternaria cuscutacidae is reported to have been used successfully on C. campestris.
Integrated weed management
Broad geographic distribution and spectrum of hosts make field dodder, Cuscuta campestris, one of the most widespread and most harmful pests among flowering parasitic plants. Different measures are available for controlling field dodder, from preventive to mechanical to biological treatments. The most successful control of field dodder requires a systematic approach ensured through integrated protection, which contributes to a more effective control of parasitic cuscuta plants.
Integrated methods involve the all important use of clean seed; good field hygiene to eradicate scattered infestations before they get out of control; good control of other weeds which might act as reservoirs of infestation; timing of tillage and planting to maximize destruction of parasite seedlings before sowing; and optimum planting arrangement and growing conditions for a good crop canopy to suppress development of the weed.
Best Management Practices for managing weeds
- Choose a weed-free field and avoid introducing weed seeds via seed, machinery or vehicles.
- Use a long fallow cultivation
- Use weed-free seed.
- Use maximum sowing rate of Lucerne for the situation.
- Keep Lucerne healthy and competitive by managing nutrition, diseases and insects.
- Control weeds when they are small to prevent them from setting seed.
- Monitor stands closely for emerging weeds.
- Weeds are killed or suppressed and light penetration allows re-growing Lucerne to compete
- Allow time for the root reserves to regenerate after early cutting—delay the second cut.
ORGANIC WEED MANAGEMENT
Organic farms rely on multiple tactics for their weed management. Ecological weed management promotes weed suppression, rather than weed elimination, by enhancing crop competition and phytotoxic effects on weeds. Specific methods include the following:
Crop Rotations
Crop rotations are the foundation of organic farming. Organic certification requires that a small grain and/or legume be planted after row crops to maintain soil health and biologically based pest management. As an example, if the legume is plowed under as a cover crop in the fifth year, four years of row crops could be grown prior to the green manure crop year. The same crop cannot be grown in sequential years.
Maintaining soil fertility through crop rotations, cover crops, intercrops, and biologically-based fertilizers will enhance the competitiveness of the crop plant and inhibit weed growth. Reports indicate that Humic and Fulvic acids in compost may mitigate weed seed germination.
Production Practices
• Cultivar or variety selection.
Organic farmers select crop varieties that compete well with weeds. Quick canopy-forming varieties assist the crop competitiveness over weeds within and between rows.
• Crop density. Planting at the maximum adapted population will provide the crop an increased competitive edge over weeds.
• Row spacing. Closer row spacing generally leads to greater crop competition with weeds in row middles. Some organic farmers have drilled soybeans with rye and obtained excellent weed control but lower yields.
• Seed grade. High germination rates are critical for a rapid canopy.
• Sowing date. To provide a competitive advantage, warm season are planted when the soil is adequately warmed to facilitate rapid germination. Warmer soils allow quicker emergence and a more competitive crop without major losses in yield.
Physical Tactics for Organic Weed Management
Physical controls are a key factor for weed management on all organic farms. Physical methods of control include cultivation, propane flame burning, and mulching.
Mechanical Cultivation
Depending on the crop, cultivation offers the least labor-intensive weed control method. A harrow or field cultivator with a drag- or spring-tooth harrow attachment can be used in the spring to kill weeds before planting. Cultivation then is timed with the pulses of weed seed germination and growth.
The initial cultivation occurs when the weeds are at the most vulnerable stage. Fields are rotary hoed at a slow speed (5 mph) three to five days after planting to kill weeds in their initial development or white-thread stage. A harrow also can be used at this stage. One week later,
after plants have emerged, fields are hoed again but at a slightly faster speed (7–9 mph). A 6-row cultivator, at speeds of 6–7 mph, can cover 100 acres in 11 hours.
Organic farms rely on multiple tactics for their weed management. Ecological weed management promotes weed suppression, rather than weed elimination, by enhancing crop competition and phytotoxic effects on weeds. Specific methods include the following:
Crop Rotations
Crop rotations are the foundation of organic farming. Organic certification requires that a small grain and/or legume be planted after row crops to maintain soil health and biologically based pest management. As an example, if the legume is plowed under as a cover crop in the fifth year, four years of row crops could be grown prior to the green manure crop year. The same crop cannot be grown in sequential years.
Maintaining soil fertility through crop rotations, cover crops, intercrops, and biologically-based fertilizers will enhance the competitiveness of the crop plant and inhibit weed growth. Reports indicate that Humic and Fulvic acids in compost may mitigate weed seed germination.
Production Practices
• Cultivar or variety selection.
Organic farmers select crop varieties that compete well with weeds. Quick canopy-forming varieties assist the crop competitiveness over weeds within and between rows.
• Crop density. Planting at the maximum adapted population will provide the crop an increased competitive edge over weeds.
• Row spacing. Closer row spacing generally leads to greater crop competition with weeds in row middles. Some organic farmers have drilled soybeans with rye and obtained excellent weed control but lower yields.
• Seed grade. High germination rates are critical for a rapid canopy.
• Sowing date. To provide a competitive advantage, warm season are planted when the soil is adequately warmed to facilitate rapid germination. Warmer soils allow quicker emergence and a more competitive crop without major losses in yield.
Physical Tactics for Organic Weed Management
Physical controls are a key factor for weed management on all organic farms. Physical methods of control include cultivation, propane flame burning, and mulching.
Mechanical Cultivation
Depending on the crop, cultivation offers the least labor-intensive weed control method. A harrow or field cultivator with a drag- or spring-tooth harrow attachment can be used in the spring to kill weeds before planting. Cultivation then is timed with the pulses of weed seed germination and growth.
The initial cultivation occurs when the weeds are at the most vulnerable stage. Fields are rotary hoed at a slow speed (5 mph) three to five days after planting to kill weeds in their initial development or white-thread stage. A harrow also can be used at this stage. One week later,
after plants have emerged, fields are hoed again but at a slightly faster speed (7–9 mph). A 6-row cultivator, at speeds of 6–7 mph, can cover 100 acres in 11 hours.
Propane Flame Burning
Many organic farmers have included propane (LP) flame-burners as an additional tool in their weed management toolbox. Flaming is used particularly during times of high field moisture when tillage with large machinery is not feasible. In drier weather, flaming is used in conjunction with cultivation. Flame weeding of corn can be accomplished when corn is less than 2" in height and when corn is 8" to 1.5' in height. Other growth stages are considered potentially damaging to the corn meristem (growing point).
Soil Solarization
Soil solarization is a method of hydrothermal disinfection accomplished by covering moist soil with transparent polyethylene (TPE) film during the hot summer months. Solarization during the hot summer months can increase soil temperature to levels that kill many disease-causing organisms (pathogens), nematodes and weed seed and seedlings. It leaves no toxic residues and can be easily used on a small or large scale. Soil solarization also improves soil structure and increases the availability of nitrogen and other essential plant nutrients.
The basic phenomenon helping weed control upon soil solarization is build up of lethally high temperatures in top soil where most of the dormant and viable weed seeds are present. The possible mechanisms of weed control by soil solarization are breaking dormancy of weed seeds and solar scorching of emerged weeds and direct killing of weed seeds by heat. Soil solarization increases soil temperatures by 8-12°C over the corresponding non-mulched soil. Rhizomes of perennial weeds may be controlled by solarization, if they are not deeply buried. Solarization for two successive years was most effective in suppressing the perennial weeds.
Soil solarization with the use of 0.05 mm transparent polyethylene sheets for 40 days was effective in controlling weeds than the use of 0.1 mm thickness polyethylene sheet and the lesser duration of soil solarization. Soil solarization with 0.05 mm thickness for 40 days recorded significantly higher pod yield of ground nut and least weed seed reserves in the top 5 cm soil.
Mulching
Many organic operations rely on manual labor and a combination of mulching/cultivation for adequate weed control. Natural mulches and synthetic mulches, including polyethylene film and polypropylene landscape fabric, are used in organic operations. Synthetic mulches have proven their durability in numerous vegetable production systems. Synthetic mulches must remain intact during the growing season and must be removed from the field at the end of the season. Despite the labor-saving aspect of synthetic mulches, most organic growers prefer natural mulches for weed control. Natural mulches are used to regulate surface soil temperatures and moisture, improve soil quality, and suppress weed activity. Organic mulches add organic matter to the soil during decomposition, thus increasing nutrients, soil porosity, water holding capacity, microbial populations, and cation exchange capacity. Straw mulch is commonly used in organic operations to control weeds and protect against harsh environments.
Integrated weed management on organic farms requires extensive planning and management. Crop rotations are the basis for successful organic farming and are necessary for breaking weed,
insect, and disease cycles. Cultivation must be completed with properly set equipment under soil conditions that are not conducive to compaction. Monitoring weed growth stages also is critical in determining ideal cultivation times.
Chemical Control:
Application of Pre planting herbicide : Glyphosate @6-8 liters per ha controls perennial weeds.
Many organic farmers have included propane (LP) flame-burners as an additional tool in their weed management toolbox. Flaming is used particularly during times of high field moisture when tillage with large machinery is not feasible. In drier weather, flaming is used in conjunction with cultivation. Flame weeding of corn can be accomplished when corn is less than 2" in height and when corn is 8" to 1.5' in height. Other growth stages are considered potentially damaging to the corn meristem (growing point).
Soil Solarization
Soil solarization is a method of hydrothermal disinfection accomplished by covering moist soil with transparent polyethylene (TPE) film during the hot summer months. Solarization during the hot summer months can increase soil temperature to levels that kill many disease-causing organisms (pathogens), nematodes and weed seed and seedlings. It leaves no toxic residues and can be easily used on a small or large scale. Soil solarization also improves soil structure and increases the availability of nitrogen and other essential plant nutrients.
The basic phenomenon helping weed control upon soil solarization is build up of lethally high temperatures in top soil where most of the dormant and viable weed seeds are present. The possible mechanisms of weed control by soil solarization are breaking dormancy of weed seeds and solar scorching of emerged weeds and direct killing of weed seeds by heat. Soil solarization increases soil temperatures by 8-12°C over the corresponding non-mulched soil. Rhizomes of perennial weeds may be controlled by solarization, if they are not deeply buried. Solarization for two successive years was most effective in suppressing the perennial weeds.
Soil solarization with the use of 0.05 mm transparent polyethylene sheets for 40 days was effective in controlling weeds than the use of 0.1 mm thickness polyethylene sheet and the lesser duration of soil solarization. Soil solarization with 0.05 mm thickness for 40 days recorded significantly higher pod yield of ground nut and least weed seed reserves in the top 5 cm soil.
Mulching
Many organic operations rely on manual labor and a combination of mulching/cultivation for adequate weed control. Natural mulches and synthetic mulches, including polyethylene film and polypropylene landscape fabric, are used in organic operations. Synthetic mulches have proven their durability in numerous vegetable production systems. Synthetic mulches must remain intact during the growing season and must be removed from the field at the end of the season. Despite the labor-saving aspect of synthetic mulches, most organic growers prefer natural mulches for weed control. Natural mulches are used to regulate surface soil temperatures and moisture, improve soil quality, and suppress weed activity. Organic mulches add organic matter to the soil during decomposition, thus increasing nutrients, soil porosity, water holding capacity, microbial populations, and cation exchange capacity. Straw mulch is commonly used in organic operations to control weeds and protect against harsh environments.
Integrated weed management on organic farms requires extensive planning and management. Crop rotations are the basis for successful organic farming and are necessary for breaking weed,
insect, and disease cycles. Cultivation must be completed with properly set equipment under soil conditions that are not conducive to compaction. Monitoring weed growth stages also is critical in determining ideal cultivation times.
Chemical Control:
Application of Pre planting herbicide : Glyphosate @6-8 liters per ha controls perennial weeds.
