Azolla

Description

Azolla, Azolla pinnata, is an aquatic fern belonging to the plant family Azollacea which is grown primarily as a fodder for livestock. Azolla is a small branching plant with a main stem and pinnate side branches. The side branches are longer at the base of the stem than at the top giving the fronds a roughly triangular shape. Each frond is composed of many overlapping rounded leaves which are covered in tiny hairs on their upper surface. Fronds are bright green in color but exposure to bright sunlight may result in a reddish hue. Fronds float on the water surface giving the appearance of red velvet. Individual fronds can reach 1.5 to 2.5 cm (0.6-1.0 in) in length. Azolla may also be referred to as red azolla, feathered mosquito fern, water velvet or African azolla and has a native range extending from Africa to India, Southeast Asia and Australia.


Uses

Azolla is grown as a fodder for animals and is also commonly grown as a companion plant for rice as it fixes nitrogen and suppresses weeds


Propagation


Basic requirements
Azolla must be grown in fresh water or wet mud in order for the plant to thrive as the plants will die within a few hours if allowed to dry out. Azolla plants can be cultivated in ponds or purpose-built pits and will spread rapidly. If grown in water, there should be little to no current as strong water currents can damage the fronds of the plants. Azolla will grow best in standing water which is between 5 and 12 cm (2.0-4.7 in) deep with a pH between 4 and 7. The roots of the plant should not be able to come into contact with soil at the bottom of the pond or pool as this can cause nutrient deficiencies. Plants will grow optimally at temperatures between 20 and 28°C (68-82.4°F) in partial shade or full sunlight. Heavily shaded areas should be avoided.

Propagation
Azolla is initially grown by inoculating a prebuilt pit or pond with seed. The azolla will quickly colonize the water and become self propagating. Some of the harvest should be held back to allow the plant to recolonize. Plant matter should be harvested every day to every other day to prevent the pond becoming overcrowded.


References

CABI Crop Protection Compendium. (2008). Azollo pinnata datasheet. Available at: http://www.cabi.org/cpc/datasheet/8120. [Accessed 06 November 14]. Paid subscription required.

Directorate of Animal Husbandry and Veterinary Services. (2010). Azollo as Livestock Feed. Directorate of Animal Husbandry and Veterinary Services, Cuttack, India. Available at: http://orissaahvs.com/File/FeedFodder.... [Accessed 06 November 14]. Free to access.

Ferentinos, L., Smith, J., Valenzuela, H. (2002). Azolla. College of Tropical Agriculture and Human Resources (CTAHR), University of Hawaii at Manoa. Available at: http://www.ctahr.hawaii.edu/oc/freepu.... [Accessed 06 November 14]. Free to access.


Common Pests and Diseases

Azolla weevil (Water Fern Weevil)
Stenopelmus rufinasus

Symptoms
Weevil feeds on Azolla and result in complete eradication of fern. So generally it is used as biocontrol agents to control Azolla in ponds and lakes.
Cause
Insect
Comments
The insect is very small measure 2.1 mm (1.8-2.3 mm) which originated in North America.
Management
No known control measures available.

Golden apple snail
Pomacea canaliculata

Symptoms
The snails feed during the night and at dawn on young succulent plants such as newly transplanted rice crops, weeds and Azolla.
Cause
Mollusc
Comments
The golden apple snails are fast growing and females can lay egg masses of up to 500 eggs per week.
Management
Deep ploughing and harrowing during off-season kills all the snails in the soil. One must make sure that Azolla is free from apple snails and their egg when transferring from one location to another. Cayuga black ducks can use as a biocontrol agent to control snails.