In this article we will discuss about the herbicides used in plantations of India.
In India, plantation crops like tea, coffee, and rubber are infested with difficult weeds like Chromolaena odorata (= Eupatorium odoratum), Imperata cylindrica, Pennisetum clandestinum, Paspalum conjugatum, Mikania micrantha, and Oxalis spp., besides several other common weeds.
Among the parasitic weeds, dodder (Cuscuta spp.) is common in coffee and black pepper and Loranthus sp. in tea plantations. Both in tea and coffee, the weed problem arises largely after the pruning of their bushes when the sunlight hits the ground. In nursery stage also, all plantation crops suffer badly with weeds.
Manual weeding has been the rule in plantation crops eversince these were planted by man. But in recent years the planters prefer to use herbicides to avoid unnecessary labour disputes and reduce weeding costs at the same time.
In fact, our plantation owners are the main customers of herbicides in India, particularly of paraquat, diuron, dalapon, glyphosate, 2,4-D, and simazine. On sloppy lands, usually it is wiser to use postemergence herbicides to leave behind a cover of dead weeds in the inter-row spaces of the plantation crops.
Tea (Camellina sinensis) and Coffee (Coffea arabica):
Dalapon (1-1.5 % spray):
It is one of the more common postemergence herbicides used in India in tea and coffee plantations, particularly for the control of perennial grasses. The grasses are treated when these are about 10 cm high. The herbicide treatment should be followed 4-6 weeks later by a hard, inter-row cultivation. The regrowth, if any, should be retreated with dalapon to obtain round the year freedom from the weedy grasses. Use an effective wetting agent in the spray to wet the weeds, thoroughly.
Simazine (2.25-3.35 kg ha-1):
Simazine has proved a very safe preemergence to weeds herbicide in tea and coffee plantations even during the summer months when otherwise the weed growth becomes dense. It can also be used in nurseries either 6 months after seeding or 2-3 weeks before planting the clones.
Napropamide (1-2 kg ha-1):
Napropamide has been recently found an effective preemergence (to weeds) herbicide for weed control in established tea plantations. It is applied after an initial physical cleaning of the inter-row spaces during the summer months.
Diuron (2.62-3.40 kg ha-1):
Diuron, when used with a suitable wetting agent, will kill up to 5 cm tall weeds, and at the same time provide residual weed control. Diuron is not to be used in freshly pruned bushes. At this stage even a drift of diuron can damage the plantation.
Avoid using diuron on light and erodable soils.
Paraquat (0.1% spray or 0.25-0.4 kg ha-1):
In established plantations, paraquat can be applied through non- drift type flood nozzles to destroy young weeds growing in the inter-row spaces.
Glyphosate (0.6-1.0 kg ha-1) and Glufosinate (0.3-0.5 kg ha-1):
The two herbicides are chosen for use in tea plantations for the control of deep rooted perennial weeds like Imperata, Arundinella, Polygonum, and Pennisetum spp. These herbicides are applied as directed and spot sprays.
Oxyfluorfen (0.12-0.25 kg ha-1):
Both pre- and postemergence (to weeds) application of oxyfluorfen have been found effective in tea plantations.
Rubber (Hevea brasiliensis):
Paraquat (0.42-0.56 kg ha-1):
It is applied as directed spray for weeding the rubber tree rings, 2-3 times a year. Use lower rates around immature trees and higher rates around the mature ones. First spray can be attempted 2-3 months after starting a new plantation. Diuron can be mixed with paraquat to obtain residual weed control.
Amitrole-T (0.2-1.0%):
Amitrole-T and paraquat are most commonly used herbicides in rubber plantations. Like paraquat, Amitrole is also applied as a directed spray.
DSMA (2-2.5 kg ha-1):
DSMA is applied as directed aqueous sprays in orchards, using a wetting agent.
Other Herbicides:
Dalapon, triclopyr, picloram, and glyphosate are recommended for weed control in rubber in Indonesia. The choice amongst these depends upon the weed flora and crop age. In each case cultural method of suppressing weeds, including growing of a smothering crop like kudzuvine (Puriaria spp.), should be encouraged.
Mentha and Mints (Mentha spp.):
Terbacil and bromacil are the most common herbicides recommended in mentha and mint plantations. These are applied on young weeds after about a month of planting these crops. Terbacil is also applied after a pre-dormancy breaking cultivation, preferably in an isoparaffinic oil carrier.
Other Herbicides:
Other herbicides under recommendation in mentha in different situations are prometryn, propanil, bentazon, metoxuron, and terbutryn.
In banana plantations diuron has proved a very selective preemergence (to weeds) herbicide. Its effective rates are 0.5-1.0 kg ha-1. More recently, besides this herbicide, oxyfluorfen (0.15 kg ha-1) has proved very effective in banana. Glyphosate (1.64 kg ha-1) can be used for protected spot treatment of perennial weeds.
Cardamom (Elettria cardamomum):
Directed applications of paraquat and glyphosate in established grooves during the off-season (non-flowering period) have been found to provide effective control of young weeds in cardamom plantations.
Soil application of fluchloralin, pendimethalin, and thiobencarb in initially weeded plantations have been found to withhold weeds for considerable period. The germinated weeds can be killed with directed sprays of paraquat in cassava plantations.
Soil application of oxyfluorfen, pendimethalin, and oxadiazon prior to the germination of new weeds has proved very effective in established tapioca.