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   Striga asiatica (herb)     
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         Management Information

    Integrated management:: The CDFA (2006) suggests that light infestations can usually be controlled by hand pulling before seed is produced. For heavier infestations, an integrated management plan is required. Options include: 1) growing trap-crops (those that stimulate S. asiatica seed germination but do not host the parasite) such as cotton or catch-crops (susceptible crops that are harvested before S. asiatica seed is produced) for 3 or more years; 2) allowing land to lay fallow for several years; injecting the soil with ethylene (a germination stimulant); 3) enhancing soil nitrogen fertility; 4) growing the most tolerant cereal varieties; 5) utilizing herbicides known to prevent S. asiatica emergence or seed production (CDFA, 2006).

    Research conducted by Mohamed et al. (1998) suggests evaluating the efficacy of ethylene treatment before application. Their research has shown that if seeds buried in the soil have moisture content above their threshold, then application of ethylene will not cause suicidal germination. The authors state that, "One does not need to condition the seed to observe readiness to germinate but need only measure moisture content. When the seeds reach a certain moisture content they will fail to germinate, so inducing this high moisture content by pre-watering the soil in irrigated fields or by delaying the sowing date in areas with a long rainy season could be a strategy for an integrated approach to control. This could easily be managed if weed scientists or extension officers measured the seed moisture content. When certain moisture content is reached, they can recommend a sowing date for farmers in Striga-infested areas (Mohamed et al. 1998).

    Biological: Elzein and Kroschel (2004) have found that the fungal pathogen Fusarium oxysporum abbreviated as Foxy 2, isolated from diseased S. hermonthica plants from Ghana, proved to be highly pathogenic against all developmental stages of the parasite, including seeds. Foxy 2 was found to be very effective in reducing the seedbank of S. asiatica by destruction of the seeds and prevention of emergence and subsequent reproduction, however, no severe disease symptoms or death were observed on the emerged S. asiatica shoots but its potential application as a biological control agent for this species is still a possibility for early developmental stages of S. asiatica (Elzein and Kroschel, 2004).    



         Location Specific Management Information
    North Carolina
    Integrated Management:: APHIS (2000) reports that S. asiatica potential for devastating important host crops led to a Congressional decision to eradicate this pest in 1957. The USDA's Animal and Plant Health Inspection Service (APHIS) established a research station and farm where it developed control methods. Since its discovery in North and South Carolina, the spread has been halted, and the acreage supporting it has been reduced by 99 percent (from 450,000 acres to about 3,400).
    Eradication is accomplished in three phases: 1) Survey activities find and map all infestations: APHIS and State cooperators have taken steps to prevent this dangerous weed from spreading from infested areas in North and South Carolina. APHIS is offering a $25 reward to anyone who identifies and reports the weed. After receiving a report, officials remove the plant to stop reproduction. Then they destroy seeds already in the soil. Finding every specimen of the slender, foot-tall S. asiatica is not without obstacles. The cooperation of landowners is essential. Scouts are sent out on foot, in vehicles, and on horseback to find infested sites. People are asked to check their own land and to report the presence of S. asiatica to an agricultural extension agent or S. asiatica personnel (APHIS, 2000).
    2) Quarantine activities prevent human spread of S. asiatica beyond the infested region: Although the tiny S. asiatica seeds can be spread by wind or water, people are the chief means of dispersal. To prevent the spread of this pest, agricultural quarantines specify conditions for moving soil, plants, or machinery out of infested areas (APHIS, 2000).
    3) Control activities seek to prevent existing plants from producing seeds and to destroy seeds already in the soil. These activities involve the cooperative efforts of Federal and State governments as well as the general public: Eliminating S. asiatica requires finding and killing plants before they go to seed and eliminating seeds already in the soil. Herbicides are used on fields infested with S. asiatica. Extensive field research has provided information on the best chemical or combination of chemicals for the given crop, weed species, and field conditions. Eliminating the microscopic seeds is another important part of eradication. Some seeds die of natural attrition or sprout only to be killed by an herbicide. However, since S. asiatica seeds can persist in the soil for a decade, efficient eradication requires accelerating the natural rate of seed germination. S. asiatica seeds can be eliminated from the soil by creating conditions that cause them to germinate when no host is present. This phenomenon is known as suicidal germination. Ethylene gas, a natural ripening agent produced by fruits, vegetables, and flowers, is injected into the soil under proper environmental conditions. It stimulates seed germination, but lacking a host, seedlings die. Soil fumigation is another alternative, albeit an expensive one. Chemicals such as methyl bromide are used on occasion to assure seed destruction (APHIS, 2000).
    The large number of acres involved and the high seed production of this pest have made eradication a slow process. However, this parasite has been eradicated from 99 percent of the infested land. In 1995, the North Carolina Department of Agriculture assumed responsibility for eradication activities in that State. APHIS personnel continue eradication activities on the remaining 400 infested acres in South Carolina. APHIS will continue to provide support to these States for surveys to verify eradication and for post-eradication treatments (APHIS, 2000).
    South Carolina
    Integrated Management:: APHIS (2000) reports that S. asiatica potential for devastating important host crops led to a Congressional decision to eradicate this pest in 1957. The USDA's Animal and Plant Health Inspection Service (APHIS) established a research station and farm where it developed control methods. Since its discovery in North and South Carolina, the spread has been halted, and the acreage supporting it has been reduced by 99 percent (from 450,000 acres to about 3,400).
    Eradication is accomplished in three phases: 1) Survey activities find and map all infestations: APHIS and State cooperators have taken steps to prevent this dangerous weed from spreading from infested areas in North and South Carolina. APHIS is offering a $25 reward to anyone who identifies and reports the weed. After receiving a report, officials remove the plant to stop reproduction. Then they destroy seeds already in the soil. Finding every specimen of the slender, foot-tall S. asiatica is not without obstacles. The cooperation of landowners is essential. Scouts are sent out on foot, in vehicles, and on horseback to find infested sites. People are asked to check their own land and to report the presence of S. asiatica to an agricultural extension agent or S. asiatica personnel (APHIS, 2000).
    2) Quarantine activities prevent human spread of S. asiatica beyond the infested region: Although the tiny S. asiatica seeds can be spread by wind or water, people are the chief means of dispersal. To prevent the spread of this pest, agricultural quarantines specify conditions for moving soil, plants, or machinery out of infested areas (APHIS, 2000).
    3) Control activities seek to prevent existing plants from producing seeds and to destroy seeds already in the soil. These activities involve the cooperative efforts of Federal and State governments as well as the general public: Eliminating S. asiatica requires finding and killing plants before they go to seed and eliminating seeds already in the soil. Herbicides are used on fields infested with S. asiatica. Extensive field research has provided information on the best chemical or combination of chemicals for the given crop, weed species, and field conditions. Eliminating the microscopic seeds is another important part of eradication. Some seeds die of natural attrition or sprout only to be killed by an herbicide. However, since S. asiatica seeds can persist in the soil for a decade, efficient eradication requires accelerating the natural rate of seed germination. S. asiatica seeds can be eliminated from the soil by creating conditions that cause them to germinate when no host is present. This phenomenon is known as suicidal germination. Ethylene gas, a natural ripening agent produced by fruits, vegetables, and flowers, is injected into the soil under proper environmental conditions. It stimulates seed germination, but lacking a host, seedlings die. Soil fumigation is another alternative, albeit an expensive one. Chemicals such as methyl bromide are used on occasion to assure seed destruction (APHIS, 2000).
    The large number of acres involved and the high seed production of this pest have made eradication a slow process. However, this parasite has been eradicated from 99 percent of the infested land. In 1995, the North Carolina Department of Agriculture assumed responsibility for eradication activities in that State. APHIS personnel continue eradication activities on the remaining 400 infested acres in South Carolina. APHIS will continue to provide support to these States for surveys to verify eradication and for post-eradication treatments (APHIS, 2000).


         Management Resources/Links

    3. Elzein, A., and J. Kroschel. 2004. Fusarium oxysporum Foxy 2 shows potential to control both Striga hermonthica and S. asiatica . European Weed Research Society Weed Research 2004 44, 433-438.
    4. Mohamed, A. H., G Ejeta, Butler, and Housley. 1998. Moisture Content and Dormancy in Striga asiatica seeds. Weed Research 38(4):256.

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ISSG Landcare Research NBII IUCN University of Auckland