From the results of experiments at different sugarcane growing areas in India, it is estimated that weeds take away about 160 N, 25 P2O5 and 200 K2O kg ha-1.
Under tropical conditions of south India, the following weeds predominantly infest sugarcane fields:
Under subtropical conditions, the following weeds are common in sugarcane fields:
A species of morning glory (lpomoea hederacea) causes around 25 per cent loss in case yield in Bihar by twining round the clumps. Orobanche (Aeginetia indica), a root parasite is capable of producing certain enzymes that cause degeneration of sucrose in cane plant to the extent of 75 per cent.
Critical Period of weed Competition:
In sugarcane fields, weeds get adequate time and space to germinate and establish well before the crop is able to compete. Hence, weeds pose tough competition to crop until the grand growth phase (150 days after planting) sets in.
Generally, sugarcane is most sensitive to weed infestation during tillering. Sugarcane crop should be kept weed free during its tillering phase, which under north Indian conditions falls between 60 and 120 days after planting for spring planted crop.
Autumn planted cane crop in central, eastern and western parts of Uttar Pradesh requires weed free environment from November to June. Sugarcane, in general, requires weed free environment for the first 90 to 100 days before the rapid close in of the cane canopy.
Cultural Management:
Deep summer ploughing and inclusion of short duration crops in intensive cropping systems arc effective in minimising the weed infestation. Inclusion of lowland rice in sugarcane based cropping systems can effectively checks the Cyperus rotundus.
Hand weeding, digging with spades and intercultivation using three-tined cultivator are commonly used for weed control in sugarcane crop. Removal of weeds by hand at 30, 60 and 90 DAP is the best among all the cultural and mechanical methods of weed control. Sugarcane trash mulch at 7.5 to 10 t ha-1 to an average thickness of 10 cm over the soil surface is effective against many weeds besides soil moisture conservation.
Optimum stage for trash mulching is 45 DAP which does not create hindrance to germination and tillering of sugarcane and also suppress excessive tiller. Intercropping bengalgram and peas in autumn planted crop also reduces competition from weeds.
Use of Herbicides:
Most commonly used herbicide is PRE spray of Atragin at 2 kg ha-1 in 100 l of water followed by 2,4-D 1.0 kg ha-1 60 DAP. This controls almost all the weeds and provide weed free environment for required duration.
Other herbicides for weed control in sugarcane crops are:
The effectiveness of Metribuzin and Diuron can be enhanced by giving a light irrigation either in advance or just after herbicide spray. Commonly used other herbicides are Asulam, Cyanazin, Ametryn, Trifluralin and Hexazinone. PPI of Fluchloralin or Trifluralin and PRE spray of Alachlor provides effective weed control in the common intercropping systems of sugarcane.
Integrated Weed Management:
Plant cane:
(i) Weeds should be controlled during most critical period (planting-120 days) of crop growth.
(ii) Under manpower availability, three manual hoeings or intercultural operations at 30, 60 and 90 days after planting should be done.
(iii) Under limitations of manpower availability, pre-emergence application of either atrazine (2.0 kg ha-1) or metribuzin (1.0 kg ha-1) in 800 litres water ha-1 followed by either post-emergence spray of (Na salt) 1.0 kg ha-1 (800 litres water ha-1) or one manual hoeing at 60 days after planting can successfully be done.
(iv) Under heavy infestation of Cyperus rotundus, a blanket spray of glyphosate (1 kg ha-1) in 625 litres water ha-1 after 15-20 days of cane planting (before emergence of cane) followed by one hoeing at 60 days of planting should be done.
(v) After 150 days, earthing-up should be done to suppress the weeds.
Ratoon cane:
(i) Weeds in ratoon crop should be controlled within 60 days of crop initiation.
(ii) With the availability of manpower, three hoeings at 1, 4 and 7 weeks after ratoon initiation should be adopted for effective control of weeds.
(iii)Under limitations of manpower availability, pre-emergence application of either atrazine (2.0 kg ha-1) or metribuzine 1.0 kg ha-1 (800 litres water ha-1) followed by either spray of 2, 4-D (Na salt) at 1.0 kg ha-1 (800 litres water ha-1) or hoeing at 45 days after ratoon initiation should be practiced.
(iv) Trash mulching in alternate rows and hoeing in unmulched rows at 1 & 6 weeks after ratoon initiation is also a good option.
(v) In the standing crop, during or after monsoon, weeds should be removed manually.
(vi) Crop should be given earthing-up at 120 days to suppress the weeds.
Ratoon Crop Weed Management:
Perennials pose serious problem in ratoon compared with annuals. This aggravates the problem and shifts critical phase of crop-weed competition towards early stage. Hence, unhindered presence of weeds after initial 30 days causes significant reduction in number and yield of millable canes whereas keeping the crop weed free after 60 days of initiation does not bring about conspicuous increase in the above parameters.
This indicates that crop-weed competition during the initial 30 to 60 days is most critical for weed control in sugarcane ratoon.
Initial ploughing and off-barring with trash mulching just after first irrigation provides highest magnitude of weed control in ratoon sugarcane crop. Three manual hoeings at 30, 60 and 90 days after ratoon initiation also bring about similar effect.
As far as herbicides are concerned, PRE spray of Atrazine (2 kg ha-1) just after initiation of ratoon provides weed free environment comparable to manual hoeing. Broad spectrum nonselective, systemic herbicide Glyphosate (1.0 1 ha-1) can be used as blanket spray 15 days after ratoon initiation for good weed control in ratoon sugarcane.
Integrated weed management involving PRE spray of Atrazine (2 kg ha-1) followed by 10 cm thick trash mulch 35 days after planting (DAP) onwards is an ideal method for weed control in plant crop. Integration of herbicide use with manual weeding 60 DAP gives best results in plant crop and its residual effect in succeeding ratoon.