Weed competition in sugarcane is much greater than in other short season row crops, because of the wider row spacing and slow initial growth phase. More than 200 weed species have been reported to infest the sugarcane fields, and among them, 30 are of economic importance. The composition of the weed species varies depending upon the climatic conditions, soil type, cropping systems followed and management practices adopted for controlling weeds and cultivation of the crop. Studies have shown that if weeds are not controlled adequately in the initial stages, the loss in cane yield could be anything between 17.2 and 35.4 t/ha.
Pre emergence weed control
Practices adopted to control weeds after planting of the crop but before its emergence is known as pre-emergence weed control. In this exercise, weeds are controlled at the germination stage itself, and there is no chance for them to compete with the crop. The only root absorbed selective herbicides, which do not cause any harm to the plant, could be used. Simazine (1.5 – 2.5 kg a.i./ha), atrazine (2.0 – 2.5 kg a.i./ha), metribuzin (1.0 – 2.0 kg a.i./ha), ametryne (2.0 kg a.i./ha), diuron (1.25 – 2.50 kg a.i./ha), oxyfluorfen (0.3 kga.i./ha), oxadiazon (0.4 kg a.i./ha) and pendimethalin (2.0 kg a.i./ha) have been found to be useful for pre-emergence weed control in sugarcane.
Of them, atrazine has been found to be the most suitable given its efficacy in a wide range of conditions, low cost and easy availability. It has to be applied on the soil surface like a blanket spray on 3rd or 4th day after planting Sugarcane using a deflector (flat fan) type of nozzle. The recommended dosage range from 1.5 to 2.0 kg a.i./ha depending upon the type of soil. For the herbicide to be effective, spraying should be followed by irrigation. Atrazine can be used even in standing crop or ratoon crop in situations when the weeds are in emerging or in germination phase.
Overgrown weeds are not affected by atrazine. Atrazine controls both broadleaf weeds and grasses germinating from seeds. It does not control weeds like Cynodon and nut grass that emerge from vegetative parts. Atrazine cannot be used in intercropped sugarcane, as many of the common intercrops are susceptible to atrazine. In intercropped Sugarcane, metribuzin (0.5 kg a.i./ha) or oxyfluorfen (0.3 kg a.i./ha) or pendimethalin (2.0 kg a.i./ha) or oxadiazon (0.4 kg a.i./ha) can be used as pre-emergence herbicide.
Post emergence weed control
Practices adopted to control weeds after the emergence of the crop is known as post emergence weed control. Weeds can be removed manually (hand pulling or hand hoeing or by both) or controlled mechanically by using animal/power tiller/tractor drawn inter-cultivation implements or by use of post emergence herbicides. Manual hoeing and weeding thrice at 30, 60 and 90 days after planting has been found to be an effective post emergence weed management practice in sugarcane. Use of inter-cultivation implements is less costly but the weed control efficiency is lower, and the weeds along the crop rows are not monitored.
At times, it may not be possible to carry out the intercultural operation in time, and the only option is the use of post emergence herbicides. Only foliage absorbed selective herbicides could be used. A commonly used post-emergence herbicide in sugarcane is 2,4-D. The recommended dosages vary from 1.0 to 2.5 kg a.i./ha depending on the intensity of weeds.
However, it controls only broad-leaved weeds but not grasses. Non-selective contact herbicides like paraquat and foliage absorbed translocated herbicides like glyphosate are useful as a directed spray for controlling weeds in the inter-row spaces in sugarcane. This will be of much use even in fields with the problem of perennial weeds like Cynodon and nut grass. The directed post emergence application is to be done using a Knapsack or Backpack sprayer with the hooded nozzle. As these are non-selective herbicides, extra care must be taken to avoid spray fluid from falling on sugarcane stem and leaves. The weeds present along the rows have to be removed manually.
Herbicides approved for use in Sugarcane
Though a large number of herbicides have been found to be effective for weed management in sugarcane, only a few of them have been approved for use in sugarcane crop by the Central Insecticides Board. The details of the approved herbicides are given in Table 1.
| Herbicide name | Dosage/ha) | Waiting period before harvest (days) |
| 2,4-D Dimethyl Amine salt 58% SL | 3.5 kg | – |
| 2,4-D Na salt Technical (having 2,4-D acid 80% w/w) (Earlier Registered as 80%WP) | 2.0-2.6 kg | 300 |
| 2,4-D Ethyl Ester 38 % EC(having 2,4-D acid 34% w/w)
|
1.2 to 1.8 kg | 330 – 330 |
| Diuron 80% WP | 1.6-3.2 kg | – |
| Metsulfuron Methyl 20% WP(Add non -ionic surfactant 0.2%v/v) | 6 g | 346 |
| Hexazinone 13.2% + Diuron 46.8 % WP | 1200 g (264+936) | 282-306 |
Management of creeper weeds
With the extension of Sugarcane cultivation to rice fields, twining weeds or creeper weeds or binder weeds have become a major problem. These weeds twine around Sugarcane clumps, bend the canes, damage the tops and affect cane growth and final yield loss could be as high as 25%. They also interfere with harvesting operations. The major creeper weeds are Convolvulus, Ipomoea, Coccinia, Passiflora, and Cardiospermum.
Management of creeper weeds poses serious problems as they germinate after the earthing up and it is hard to use mechanical methods are take up spraying operations. At Pantnagar, application of metribuzin 1.25 kg a.i./ha + dicamba @ 350 g. a.i./ ha at 70 DAP effectively controlled Ipomoea spp. along with other grasses and non-grass weeds.
Management of Cynodon and Cyperus
Digging, collection and destruction of underground vegetative parts of perennial weeds like Cynodondactylon that are capable of multiplying can be done during the fallow period, to check such perennial weeds efficiently. Puddling is also helpful in reducing the infestation of perennial weeds. Pre-planting weed control using ‘glyphosate’ followed by in-crop weed control with ‘pre-emergence atrazine’ and ‘post emergence ethoxysulfuron’ or ‘directed post emergence paraquat’ or ‘directed post emergence glyphosate’ all were found useful to manage weeds including Cynodon and nut grass.
Pre-emergence application of atrazine at 1.75 kg a.i./ha followed by two post-emergence following applications of ethoxysulfuron at 80 g ai./ha at 15 and 30 DAP has been suggested as an effective weed management practice for fields severely infested with nutgrass. After the spray of ethoxysufuron, nut grass is effectively controlled, and its re-emergence was very slow. However, ethoxysulfuron had no effect on Cynodon as well as the second flush of weeds germinating from seeds.
Management of Striga
Striga (commonly known as witch weed) is a serious parasitic weed that invades host plant’s root system for nutrients, water and carbohydrates, eventually stunting growth and killing the host plant. Striga is most abundant in dry, infertile, marginal soils in semi-arid tropical grasslands and savannahs. When sugarcane cultivation is extended to infertile soils under moisture deficit conditions, Striga becomes a problem for sugarcane.
In recent years, Striga has been reported to be a serious problem in sugarcane in isolated pockets. A multi-pronged approach is needed to manage the Striga problem. The soil fertility has to be improved, and moisture stress should be avoided. To control the Striga after emergence, 2,4-D Na salt has to be applied at 1.0 kg a.i./ha as a directed spray and the spray has to be repeated at 15 days intervals two or three times. This should be done before Striga flowers.
Application of pendimethalin at 2.0 kg a.i./ha as a directed spray to the soil at the base of the sugarcane clumps just before the second irrigation after full earthing up would control Striga at the emergence stage itself. If some escapes are there, they can be controlled by spraying 2,4-D. Pre-emergence application of atrazine 1.0 kg/ha on the third day after planting + hand weeding on 45 DAP with an earthing up on 60 DAP combined with post-emergence spraying of 2,4-D sodium salt 5g / litre (0.5%) + urea 20 g/litre (2%) on 90 DAP is recommended for complete control of Strigaasiatica in sugarcane. The Striga control efficiency is 99.3%. Other management options include:
- Grow fodder jowar or maize and after 45 days pull out the plant.
- Grow cotton in the infested soil which acts as a trap crop.
- Apply adequate FYM or organic manure to improve soil fertility and retention of soil
moisture. - Apply extra dosage of nitrogen and use fertilizers in more splits.
- Give light but frequent irrigations.
Source-
- Sugarcane Breeding Institute, Coimbatore-641 007
