Gundhi (Chard) which occurs in kharif paddy fields in stagnant water, can be controlled by broadcasting 50-100 kg freshly plucked karada leaves in August. The algae consumes oxygen from water of the rice field and produces carbon dioxide, which results in yellowing and dwarfing of rice plants. The toxicants present in karada leaves damage chlorophyll of green algae. This practice has been in use since time immemorial in Panipila village of Nayagarh district in Odisha.
Results and discussion
The experiment conducted during the kharif season of year 2002 to 2004 and results from both the sets of experiment, i.e. at CRRI and farmers fields revealed that though one application of karada leaves reduced the population to below 50% level, another application was needed after 20 days of first application to make the rice plants completely free from gundhi.
The vegetative stage of gundhi was reduced 100% at 5 g and by 85% in 3 g leaf treatment. Results also clear that the gradual decrease of dissolved oxygen as well as chlorophyll content in Chara after karada leaf application. The oxygen content varied from 9.8 mg/ litre on first day of treatment (DAT) to 0.7 mg/litre on 4 DAT. Biochemical analysis revealed high phenol content of karada leaves, which was 16.4 mg/g fresh weight in comparison with 2.3-2.4 mg in rice leaf. Perhaps this high phenol content is responsible for killing gundhi so effectively.
Conclusion
Karada leaf proved effective in controlling Chara spp. harmful green algae in rice field and increasing the yield of rice. It is effective due to its efficacy in reducing the chlorophyll content in Chara, which may be attributed to high phenol content in karada leaf. Application of karada at the vegetative stage of Chara was relatively more effective.