Bradbrook - 2012 - Rice Farming complete with methods to increase ric

Weed management is very important during the vegetative stage of the rice plant. The
first 30 to 40 days after sowing or transplanting is when competition from weeds is the
highest and great reductions in yield can occur if proper crop and cultural management
practices are not undertaken. To ensure that weed growth is kept to a minimum,
inspect nursery beds and remove weed seedlings that germinated with the rice seeds.
For lowland rice culture, maintain a water depth of about 5 cm after transplanting to
discourage weed seed germination on the field. In both upland and lowland rice
culture, manual or mechanical weeding may be done. If the soil is to be flooded, the
water depth must be kept shallow 7 to 10 days after transplanting to allow the
mechanical weeder to pass through each row crosswise. The weeder pushes the weed
seedlings into the mud, and the shallow water depth is maintained for another two
days to keep the seedlings buried. After two days, the water depth is brought back to
5 cm.
In cases where severe weed infestation has occurred or when problematic (i.e. difficult
to eradicate) weeds are present, either prior to or during the growing cycle, it may be
advisable to use herbicides. However, herbicide use varies from region to region and
from country to country. What is allowed in one country might be banned in another.
Several rice varieties have been bred for herbicide resistance to facilitate the removal
of weeds using herbicides without damaging the rice plant. If weeds are a major issue
in the area to be used for rice production, using herbicide-resistant rice varieties can
help alleviate the problem.
Although weeding is not necessary during the reproductive and ripening stages, the
presence of weedy rice necessitates their removal before they mature and produce
seeds that can infest the field in subsequent growing cycles. Removing weedy rice is
costly if they have infiltrated the rice field, especially because they are genetically
related to rice and resemble its physical characteristics in many ways. They can be
taller, shorter, or of the same height as the rice plant. They can also have the same
growth cycle. During the reproductive stage, they develop panicles and spikelets and
produce grains. The difference is that weedy rice grains fall off easily and cannot be
harvested. The seeds however remain on the ground and may germinate in the next
growing cycle. To prevent the introduction of weedy rice into the field, it is important
to make sure that the rice seeds purchased are pure and do not contain weed seeds.
Machinery that has been used in weedy rice-infested fields must be inspected and
cleaned of residues before being used in the next growing cycle. Irrigation canals and
ditches must be kept weed-free. If infestation is not severe, and weedy rice can be
easily distinguished, cutting off the panicles or removing them by hand before they
flower can be an effective preventive measure. After harvesting an infested field, the
straws can be left on the ground and burned to destroy weedy rice seeds. During the
next land preparation, allowing weedy rice seeds to germinate then incorporating them
into the soil can help break the cycle of infestation.
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