Submerged aquatic weeds have been posing a new threat to the paddy cultivation in various districts in the State.
These weeds include aquatic plants like vallisneria , najas as well as utricularia . “Recently a weed shift has been observed in the paddy fields of Palakkad district, the rice granary of the State,” noted P. Prameela, Professor & Principal Investigator, All India Coordinated Research Project (AICRP) on Weed Management, KAU , Thrissur.
Kannur, Ernakulam, Kottayam and Idukki districts have also recorded cases, though the incidence is less severe, she said.
Vallisneria also known as eel grass or tape grass is a common submerged aquatic plant. This has been introduced to the country as an ornamental aquarium plant. The genus is widely distributed in tropical and subtropical regions of Asia, Africa, Europe, and North America. In Malayalam it is known as thalayattippullu,vazhakala and mudipayal .
Another one is Najas commonly known as rice field water-nymph, a species of aquatic plant found in freshwater habitats, especially still or slow-moving waters, like ponds and in rice fields.
Utricularia , a carnivorous aquatic plant, is now common in rice fields, but the problem is more severe in the second crop season.
“These plants may seem harmless at initial stage, but can grow as a major rice weed. The incidence is very severe in many parts of Palakkad District like Mankara, Alathur, Kannadi, Pattambi and Thasrak,” said Savitha Antony, Assistant Professor, AICRP.
- Liming of field on 15th day after transplanting (DAT).
- Apply post emergent herbicides like bispyribac sodium against vallisneria by 20-25 DAT
- Remove Vallisneria plants before flowering to avoid seed propagation.
- Unscrupulous spraying of pesticide will affect natural enemies of vallisneria and other aquatic plants.
- Direct seeding or wet seeding of rice can reduce the problem as interspaces will not be available for weed growth.
The problem is severe in transplanted crops where these weeds get the ideal condition of a standing water column and sufficient inter-space and sunlight. Moreover, as other common rice weeds are absent at this stage, these new groups of weeds are at an advantage, she pointed out.
The fertilizers applied to the crop by 60 days become totally ineffective as weeds absorb the nutrients forming a thick mat over the soil, she added.
In parts of Palakkad, hand weeding is still a common practice and farmers find it very difficult to control it as these new groups of weeds cannot be handpicked easily like grasses, sedges or broad-leaved weeds of rice. According to the farmers, these weeds have been seen in paddy fields for the last 4-5 four or five years.
“Currently many aquarium plants / propagules / seeds are available online. Public awareness on safe disposal of these is important to avoid them reaching our water bodies and become invasive. This has happened in the case of Cabomba furcata at Perambra in Kozhikode,” noted Dr. Prameela.