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• Submerged aquatic weeds have been posing a new threat to the paddy cultivation in various districts of Kerala.
• All India Coordinated Research Project (AICRP) on Weed Management, Thrissur has observed weed shift in the paddy fields of Palakkad district, the rice granary of the State.
• These weeds include aquatic plants like vallisneria, najas as well as utricularia.
• Kannur, Ernakulam, Kottayam and Idukki districts have also recorded cases.
• 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.
• The fertilizers applied to the crop by 60 days become totally ineffective as weeds absorb the nutrients forming a thick mat over the soil.
• 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 four or five years.
• Public awareness on safe disposal of these plants is important to avoid them reaching our water bodies and become invasive. 

Additional Details

Vallisneria

• 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.

Najas

• Najas is commonly known as rice field water-nymph, a species of aquatic plant found in freshwater habitats, especially in still or slow-moving waters, like ponds and in rice fields.

Utricularia

• Utricularia, a carnivorous aquatic plant, is now common in rice fields, but the problem is more severe in the second crop season.

Reference:

1. https://www.thehindu.com/sci-tech/agriculture/submerged-aquatic-plants-a-new-threat-to-paddy-cultivation/article36336505.ece