Groundnut

Weed Management

Introduction Common Weeds Methods Of Weed Control Herbicide and Climate

Introduction

  • Groundnut the kingpin among the oilseed crops of India ,alone occupies about 9.0 million hectares of land (45%0f the oil seed area ) and accounts for 8.2 million tonnes of oil seeds (55% of the total production ) and are claimed to be world's largest.
  • Paradoxically, India is the one of the largest importers of edible oil because of the fact that groundnut is predominantly grown as rainfed crop under various biotic and abiotic stresses resulting in low yield.
  • Minimizing the crop-weed competition particularly at early stage of growth Groundnut usually encounters with diverse weed flora ,the yield could improved upon by about 20-30%.

Yield losses

  • Reduction of pod yield owing to competition with weed depends on the duration of the crop weed competition in general and the stages of crop growth in particular.
  • The yield losses are more pronounced in rainfed crop and Spanish Bunch varieties are much affected as compared with the Virginia types.
  • When the groundnut fields are kept weed free for a period of atleast first 6 weeks there is no significant reduction in pod yield.
  • On the other hand, when groundnut competes with weeds at 4 - 8 weeks the reduction in pod yield is substantial.
  • With the increased crop - weed competition the pod as well as fodder yield decreased proportionately.
  • The average loss of yield owing to crop weed competition under ordinary management condition turns out to be 34% whereas under poor management the loss is as high as 60%.
  • Once the weeds are established in the row it is difficult to remove them because of the growth habit of groundnut and ultimately the interfere with the harvest resulting in substantial pod loss in the soil.
  • In unweeded field, depletion of fertility status is also substantial and removes about 40 kg 9 kg and 24 kg N, P and K per hectare respectively in a rainfed crop of Spanish Bunch groundnut.
  • Improvement of economic yield demands effective integration of each of the recommended cultural practices for the given zone, besides the use of high yielding varieties.
  • In groundnut both intra and inter-genotypic competitions are very much prevalent, since the regulation of interplant spacing within the row is difficult to maintain in the absence of groundnut planter and the crop has to compete with a wide array of weeds for light moisture and nutrition at various stages of crop growth.
  • As in the case of other crops, timely and effective weed control is necessary to realise the maximum yields in groundnut.

Crop-weed competition

  • Groundnut being mainly grown during rainy season encounters several weeds since the annual grasses and seasonal broad leaf weeds grow luxuriantly and dominate during this season as compared to rabi/ summer season.
  • The weed competition in early stages of groundnut is maximum because of slow initial foliage growth depending upon the degradation of food reserve in the cotylendons.
  • Although emergence of radicle in groundnut is fast (24 hr for Spanish and 36 - 48 hr for Virginia types), root development is slow (5-10 days).
  • Only when the root is capable of absorbing nutrients the epicotyl is exposed to light in groundnut whereas the situation is reverse in the case of weeds which emerge faster and grow rapidly as compared with groundnut and consequently take a lead in crop - weed competition.
  • The critical period of weed competition is estimated to be 2 - 6 weeks after sowing.

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Common Weeds

  • A variety of weeds are associated with groundnut cultivation which comprise diverse plant species of annual grasses and seasonal broad leaved weeds either erect or prostrate in nature.
  • Groundnut encounters with the following major weeds which appear in different flushes at different stages of crop growth.

Dicots

  • Celosia argentea, Leucas aspera, Alysicarpus sp., Portulaca oleracea, Lindernia crustacea, L. procumbens, Alysicarpus monilifer, Borreria articularis, Cleome sp., Digera arvensis, Corchorus olitorius, Solanum nigrum, Argemone mexicana, Abutilon indicum, Euphorbia parviflora, Vernonia cinerea, Brachiaria eruciformis, Euphorbia geniculata, Acalypha indica.

Monocots

  • Arachne racemosa, Digitaria sanguinalis, Echinochloa colonum, E. crusgalli, Cynodon dactylon, Commelina benghalensis, Dactyloctenium ageyptium, Cynotis sp., Eragrostis tenella, Paspalums distichum, Setaria glauca, Eleusine sp.,

Sedges

  • Cyperus rotundus, C. iria, C. defformis, C. compressus, Eleocharis sp.,

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Methods Of Weed Control

  • Effectiveness of weed control is largely dependent on the weed species prevalent, its life cycle and method of propagation.

Mechanical / cultural control

  • In India, weeds are controlled mostly either manually or mechanically.
  • Hand - pulling of individual weeds although primitive, is most vital and effective method of weed management particularly when there is no dearth of manpower.
  • Pulling out of weeds at regular intervals must be attended to so that the weeds do not enterr the reproductive phase and consequently dispersal of seed is prevented.
  • Hand hoeing is another effective method adopted widely to control weeds in the inter - row spaces of a line - sown sole crop.
  • This method provides excellent physical condition to the crop growth by way of soil aeration through stirring of the soil. The manually operated implements like star weeder and push hoe are also used.
  • Star weeder is found to be more economical as compared with manual weeding.
  • Time requirement for weeding one hectare of land twice with star weeder is much less (300 man hours) whereas the same operation by hand weeding is much more time consuming (536 man hours).
  • First weeding should be attended to at about 20 - 25 days after sowing and should be repeated at fortnightly intervals up to 45 days.
  • Beyond that soil should not be disturbed which may affect peg penetration and pod development leading to yield loss.
  • Blade harrowing,in relatively dry and loose soil within the inter - row spacing of groundnut, is a widely followed method for effective weed control since it cuts the root system and weed die owing to desiccation.
  • Harrowing also loosens the soil considerably and thus has good impact on peg penetration and pod development.
  • Weeding must be completed before peg penetration and pod development.
  • Mulching practice loosens the surface soil to form a soil mulch and also facilitates infiltration of rain water to the root zone.

Chemical control

  • Since mechanical / cultural method alone does not ensure weed - free condition, the use of herbicides in combination with cultural methods should be adopted.
  • In areas where agricultural labour is scarce and costly, herbicides may be used there as pre - and post - emergence application to weeds which provides good control of weeds.
  • The use of herbicides in India is still very scanty and unorganised although its use is known since long.

  • There is scope to educate the farmers on the judicious use of herbicides which are selective in action and can be used in groundnut for high economic returns.
  • Depending upon the time of application of the herbicides they are grouped as (i) pre - planting (followed by incorporation), (ii) pre - emergence (after planting but before emergence of seedling), and (iii) post - emergence (after emergence of weed along with the crop).
  • All - India Co - ordinated Research Project on Weed Control has identified certain useful herbicides, viz., Alachlor, Nitrofen and Fluchloralin, which effectively control various weeds of economic importance throughout the country.
  • Details of few mportant herbicides suitable for weed control in groundnut are described below:

Amides group

Alachlor (Lasso)

  • It is usually applied to the soil surface within 48 hr after sowing as a pre - emergence treatment @ 1.5 - 2 kg a i / ha.
  • The compound is water soluble and is formulated either as emulsifiable concentrate or as granules.
  • Under low soil moisture, incorporation is considered advantageous. Rain or irrigation within a week after application is necessary for best results.
  • Alachlor is effective in controlling annual grasses and partial control of weeds belonging to Acalypha, Amaranthus and Eleusine spp.

Diphenamid

  • It is formulated as wettable powder or as a water dispersible concentrate.
  • Diphenamid is ordinarily spread on the soil surface but shallow soil incorporation improves weed control under dry condition.
  • It may be applied at planting @ 2.25 to 3.40 kg a i / ha for effective control of annual and perennial grasses and partial control of broad - leaved weeds.
  • Absorption is mainly through root and leaches rapidly in sandy soil but slowly in clay loam soils.
  • The herbicidal action persists for longer time (more than 6 months) under low rainfall than under moist warm - soil condition.

Aniline group

Fluchloralin (Basalin)

  • This is a selective herbicide most commonly used both as pre - plant (10 days before sowing) as well as pre - emergence.
  • The herbicide does not directly inhibit weed germination but it inhibits lateral and secondary root development.
  • Fluchloralin gets photo - decomposed easily and, therefore, it has to be incorporated in the soil. If incorporation of the herbicide into the soil is not done, immediate irrigation is necessary after the application.
  • The rate of application varies from 1.25 to 1.50 kg a i / ha. Fluchloralin is effective in controlling majority of broad - leaved weeds.

Trifluralin

  • It is formulated as an emulsifiable concentrate and also as granules.
  • The weeds are controlled effectively when the herbicide is incorporated in the soil as pre - emergence application. It affects both seedling emergence of weed and its associated physiological process.
  • The recommended dose is 0.5 kg a i / ha at which dose herbicidal action persists for 4 - 6 months.
  • Trifluralin is not easily leached out but adsorbed strongly on organic matter and clay colloids. This herbicide is recommended for ‘Spanish Bunch’ groundnut varieties.

Miscellaneous

Nitrogen (Tok - E - 25)

  • Nitrogen is both a short contact and soil active herbicide.
  • Pre - emergence application of Nitrofen @ 1.5 - 2.0 kg a i / ha controls several germinating as well as young broad - leaved weeds of groundnut.
  • The effectiveness of the herbicide declines with the increase of age and size of the weeds.

2, 4 - D

  • It is another selective pre - and Post - emergence herbicide and is systemic in nature.
  • When sprayed on plants, the herbicide diffuses through the cuticle of leaves and stem and is translocated through the phloem cells.
  • 2, 4-D @ 2 kg a i / ha plus 5% jaggery solution effectively controls the sedge, Cyperus rotundus.

Herbicides and environment

  • Effective control of weeds by using herbicides depends largely on the soil types, soil moisture, humidity and atmospheric temperature at the time of application of herbicides.
  • Sandy - loam soils with low organic matter requires less quantity of herbicides than clay loams.
  • Herbicides may leach down if the soil moisture is in excess or gets photo - decomposed when exposed to sunlight.
  • Hence herbicides should be applied at appropriate field conditions keeping the above points in mind.

Use of herbicide in combinations(Tank mixtures)

  • Herbicidal mixtures are often used to broaden the spectrum of herbicidal action for killing a large number of weeds of different species.
  • A mixture of Nitrofen + Fluchloralin @ 0.7 kg a i and 0.5 kg a i / ha controls various weeds of groundnut effectively under rainfed situation.
  • The effectiveness may be due to the synergistic effect.

Integrated Weed Management (Combinations of herbicides plus cultural practices)

  • There is no evidence so far available to show that application herbicides either as pre - or post - emergence effect the market or organoleptic quality in groundnut.
  • However, precautions must be taken for using right amount in correct time.
  • Recommended doses of herbicides are usually not found toxic to the crop.
  • The first hand - weeding or harrowing in groundnut is usually done at 25 days after sowing and is repeated once or twice depending upon the weed situation.
  • Beyond 45 days of sowing no weedin g is done to avoid damage to the growing peg and developing pods.
  • For controlling fresh flush of weeds appearing relatively at later stages, use of herbicides plus hand - weeding is found effective.

Pre - sowing

  • Application of Tok - E 25 @ 4 kg a i / ha followed by one hoeing and one hand - weeding gave effective control of weeds and increased pod yield.
  • Also pre - emergence application of Alachlor @ 1- 2 kg a i / ha plus one hand - weeding, 30 days after sowing, effectively controlled weeds in rainfed groundnut and gave higher returns.

Actual requirement of chemicals

Calculation of quantity of chemical required based on recommended dosage

  • The doses mentioned interms of active ingredients (a i) in case of granules / powder and acid equivalent (a e) for liquid need working out of actual quantity of chemicals.
  • The following example may be considered to find out actual chemical requirement:
    • If 1.5 kg a i / ha at 75% concentration is to be applied then the amount required for 1.5 ha of land would be
    • 1.5 x 1.5 x 100/75 = 3Kg.

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Herbicide and Climate

  • Effective control of weeds of herbisides depends on soil type, soil moisture, humidity, temperature at the time of application. In sandy loam soil which contains less organic matter requires less amt of weedicide than fine loam soil.
  • When there is excessive moisture in soil herbisides drain down the root zone and get wasted.

Use of mixed herbisides

  • Mixed herbisides are used to destroy the large range of weeds.
  • Mixed use of nitrophen 0.7kg ai + fluchloralin 0.5kg a.i. control many weeds of groundnut crop.
  • This happens because of sinergetic effect.

Integrated weed management

  • Use of cultural practices with herbisides.
  • Till now there is no proof which shows that use of herbiside before after sowing has any bad effect on groundnut quality.
  • Still the herbiside should be used in recommended quantities at proper time because the recommended quantity of herbisides are hattoxic to plants.
  • In groundnut crop first manual weeding is done 25days after sowing and if required it repeated one or twice more.
  • To avoid loss of pods and pegs manual hoeing is not done after 45 days of sowing.
  • Use of herbiside on late germinated fresh is found very effective.
  • Spray of to k e -25 before sowing followed by one weeding by hoeing give best results.
  • Pre germination application of 1-2kg ai Alachlor and one hand weeding 30 days after sowing controls weeds effectively in rainfed groundnut which results in high yield.

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Uttar Pradesh