PEST RISK ANALYSIS (PRA) TRAINING Group Exercises Manual

GROUP EXERCISE NO. 2
PEST RISK ANALYSIS TRAINING - GROUP EXERCISES MANUAL
Example No. 3 – Water Hyacinth 3
SCENARIO: Nepal has received requests to import nursery stock plants of water hyacinth
(Eichhornia crassipes) for use in water gardens. The NPPO has decided to conduct a PRA.
PEST DATASHEET:
Identity: Eichhornia crassipes (Mart.) Solms (Liliopsida (monocotyledons): Liliales:
Pontederiaceae). Synonym: Pontederia crassipes Mart. (basionym). Common name: Water
hyacinth.
Habitat / Hosts: E. crassipes is a floating weed of tropical and sub-tropical freshwater lakes
and rivers, especially those enriched with plant nutrients. It may also be a weed in flooded
rice. Optimum temperature for growth is 25-30°C. Growth ceases when water temperature is
above 40°C or below 10°C, but short periods at freezing may be tolerated. E. crassipes is very
responsive to nutrients (especially nitrogen and phosphorus) and high growth rates are
always associated with eutrophic, nutrient-rich conditions. Optimum pH is between 6 and 8
and extremes of pH (below 4.5 or above 10) can be damaging. Calcium concentration is
important, with an observed threshold of 5 mg/l, below which growth ceases.
Distribution: Origin: Amazon basin of Brazil. Present: Much of South America, Central
America and the Caribbean; Mexico; the United States (Alabama, Arkansas, California,
Florida, Georgia, Hawaii, Louisiana, Mississippi, North Carolina, South Carolina, Texas);
Europe (Czech Republic, France, Portugal); much of Africa; Pakistan; India; Southeast Asia;
Korea; Japan; China (Fujian, Guangdong, Hong Kong, Jiangsu, Taiwan, Yunnan, Zhejiang );
Australia; New Zealand. Absent: Canada; northern Eurasia; Nepal.
Biology and Dispersal: E. crassipes propagates vegetatively and by seed. After flowering,
the capsules mature and seeds are eventually released below water. The seeds are capable of
germinating immediately but may remain dormant for many years. Germination is
encouraged by aerobic conditions and alternating temperatures. Large populations of
seedlings may become established on exposed mud at the edges of water bodies when water
levels fall. Seedlings are rooted in mud initially but become free-floating as a result of wave
action or rising water levels. From an early stage, the axillary buds of the older leaves of the
seedling are capable of developing into stolons, which grow horizontally and develop daughter
plants. Such vegetative spread can occur indefinitely and very large populations are produced
in this way without any sexual reproduction. Wind will readily move the plant and the upright
leaves act as sails in lakes and canals. Along rivers, water flow is the prime mover of vegetative
material but strong winds may sometimes blow the plant upstream. Seeds are thought to be
transported over long distances by water birds. New infestations may arise via unintentional
human transportation such as canoes and boats. However, the primary means of longdistance
dispersal is the deliberate introduction of plants for use in water gardens.
Damage: E. crassipes is considered the world’s most troublesome aquatic plant, and is a
major freshwater weed in most regions of the world that are free of frost. It has been widely
distributed for ornamental purposes since the 1800s, and has escaped cultivation and spread
with phenomenal rapidity wherever it has encountered suitable environmental conditions. It
forms vast monotypic stands in lakes, rivers and rice paddy fields, reducing water quality and
encouraging the growth of mosquitoes, snails and other organisms associated with human
illnesses (e.g. malaria, schistosomiasis, encephalitis, filariasis and cholera). Dense mats
greatly hinder boating by fishermen and may prevent fishing altogether. In paddy fields,
dense mats affect rice production and in extreme cases of competition between E. crassipes
and rice crops, fields have been abandoned.
Control: It is impossible to eradicate E. crassipes, and often only an integrated management
strategy, inclusive of chemical and biological control, can provide a long-term solution to this
pest.
3 NOTE: This example was developed specifically for use in the IPPC PRA training course. The
scenario is not real. The data sheet is based on the CABI Crop Protection Compendium
(http://www.cabi.org/compendia/cpc).
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