WEED MANAGEMENT IN MAIZE.
Department of Agronomy
Institute of Agriculture and Animal Science
Maize (Zea mays L.) is the second most important cereal crop in the world in terms of total food production. It is grown for fodder as well as for grain. The grains of maize are used in a variety of ways by the human beings. Recently, with the release of improved cultivars and hybrids, the grain yield has been increased but still the maize crop faces many problems. Weeds are one of the most important factors in maize production. They cause important yield losses worldwide with an average of 12.8% despite weed control applications and 29.2% in the case of no weed control (Oerke and Steiner, 1996). Therefore, weed control is an important management practice for maize production that should be carried out to ensure optimum grain yield.
Any plant growing where it is not wanted is called weed. weed, common term for any wild plant, particularly an undesired plant, growing in cultivated ground, where it competes with crop plants for soil nutrients, light and water.
Farmers usually give prime importance to few cultural practices and neglect other factors like seed rate and weed control. As the maize is usually grown during the hot summer months of May, June and August, when manual method of weed control is difficult to imply therefore, other methods of weed control are more feasible, less laborious, cost effective and economical. Several weed species that are strong competitors, compete with the maize crop and thus the yield is decreased. Weed management strategies attempt to limit the deleterious effects of weeds growing with crop plants. These effects could be quite variable, but the most common is competition for available resources. The quantities of growth factors used by weeds are thus unavailable to the crop. Some of the grass weeds found in maize are Cynadon dactylon, Dactyloctenium aegypticum, Echinocloa crusgalli.similarly Amaranthus viridis, Chenopodium album, Parthenium hysterophorus, Trianthema portulacastrum are broad leaved weeds found in maize. Cyperus rotundus and Cyperus deformis are common sedges in maize.On the other hand, the perennial weeds like Cyperus rotundus and Cynodon dactylon which are among the worst weeds of the world, infest the maize crop and thus increase the cost of production, as hand weeding is not effective against these weeds. Presence of weeds in maize crop decreases the yield drastically. As there are limitations of every weed control method therefore integrated weed management is a good option for sustainable agriculture. It involves the combination of all the possible methods to suppress the weeds below economic threshold level. Although some methods are effective against weeds but they prove uneconomical for the farmers or pose environmental hazards.
To know the different methods of weed control in maize.
To know the optimum time of weeding in maize.
REVIEW OF LITERATURE
Several experimental findings with regard to weed management in maize have been found. some previous findings on these directions are as such:
Triplett and Lytle (1972) have shown that maize may be grown with no tillage for 7 years or more with yields equal to those of the cultivated crop if weeds are controlled. They found that in Ohio, paraquat plus simazine gave the most consistent weed control.
Intercropping of maize and other cereals with low growing crops such as cowpea, mungbean, and other beans, sweet potato and melon (Colocynthis citrullus) is effective in smothering many weed (Bantilan et al.,1974; Moody, 1980; Akobundu,1980a; Wahau,1985).
In a similar study Akhtar et al. (1984) reported that maximum leaf area was recorded in manually weed-controlled plots at tasseling. These results are in agreement with Shakoor et al.(1986), who reported that dry biomass of weed from the weedy control plots was significantly greater than chemical and manual weeded plots.
Weed control in maize in Poland was reported problems such as resistant weeds, contamination of water supplies and the limitation of following crops.(Rola and Rola,1990)
In Nepal, maize needs weeding twice. (Mazek, 1991 unpubl)
Harvey et al. (1997) reported that it is logical to expect that weed management should improve if the row spacing of corn is narrow.
Hafeezullah (2000) also reported similar results. He concluded that dry weight of weeds was significantly affected by different herbicidal treatment.
Khan et al. (2002) reported that chemical weed control as well as hand weeding significantly increased the grain yield of maize.
Khan et al. (2002) concluded that maximum leaf area of maize was noted in those treatments where weeds were controlled.
Malik et al. (2006) reported that herbicides proved effective in controlling weeds and produced relatively more weight of cobs, number of grains cob-1, 1000-grain weight, biological yield and grain yield. Similarly plant population and row spacing also affect the weed population.
METHODS AND METHODOLOGY
For the study about the subject, various journals, books and newsletters were concerned in the IAAS library. Similarly, web surfing was also found helpful. Google and encyclopedia were of special help. Many e- papers were consulted.
RESULTS AND DISCUSSION
Weed control in maize is carried out by mechanical and/or chemical methods. Weeds between plant rows are removed generally by mechanical cultivation, while weeds on the rows are controlled by hand hoeing or by herbicides. Although both methods are effective in controlling weeds, they increase production costs and have some disadvantages or side effects when applied intensively. Low efficacy against perennial weeds, short duration, soil erosion and crop injuries are the main disadvantages of intensive mechanical weed control, whereas the intensive use of herbicides is mostly associated with soil and water pollution. Weed infestation drastically reduces the grain yield of maize. Crop responds very well to mechanical weeding done by bullocks or tractor drawn implements between the rows and hand weeding with in the rows. The weeding operation may be repeated two to three times but not after knee high stage of the crop. Losses caused by weeds are more during the early stages than in the later stages. Mechanical weeding is good for root aeration but continuous rains in kharif season posses a serious problem in which the soil becomes wet and any agricultural operation cannot be done. Under such conditions weed grow luxuriantly and they do permanent harm to the crop before they are controlled. Therefore integrated weed control measure is essential for taking care of weeds from initial stage of growth. Mechanical weeding in any case should not be done after knee height stage as it damages the leaves.
Methods of Weed Control
Maize is most sensitive to weed competition during its early growth period. The growth of maize plants in the first week is rather slow and it is during this period that weeds establish rapidly and become competitive. Maximum weed competition in maize occurs during the period of 2 to 6 weeks after sowing. This suggests the importance of maintaining the field weeds free during this critical period of weed competition. The integrated weed control measures are to be followed for efficient weed control.
- Weed Control through efficient Seed bed preparation
Two to three ploughings by country or mould board plough or ploughing by disc or mould board plough followed by 2 to 3 harrowings not only brings desired tilth but makes weed free seed bed preparation. Ridge and furrows layout further reduces weed intensity.
- Weed Control through Seed treatment
Soaking the maize seed for 24 hours in water and sowing after shade drying makes the seed to germinate early compared to weed seed and gives upper hand to maize crop over weeds. This practice besides providing optimum plant stands reduces crop duration.
- Weed Control through improved fertilizer practices
Chemical fertilizer application in bands 5 to 10 cm. from the seed instead of broadcasting, makes it available more to the crop and less to the weeds and hence more dominance of crop over weeds. Top dressing of fertilizer at knee high stage after inter culture 15-20 cm. from crop rows, with holding irrigation for a week and covering the fertilizer by operation of ridger also reduces crop competition from weeds.
- Chemical Weed Control
Incessant rains and dry spells prevent weed control on time by traditional methods. Non-availability of manual labour due to competition from other crops or high wages of manual labour also come in the way of timely weed control in maize. Weed control by mechanical means is possible only when crop grows up to certain stage and crop has to compete with weeds till such period. Chemical weedicides are boon in such a situation.
Preplant, preemergent herbicides are applied to the soil surface and mechanically mixed in the soil before the crop is planted. Herbicides applied before the corn emerges offer the advantage of controlling weeds before they compete with the corn when it is in the seedling stage; this is the most critical time in regard to yield reduction. Preplant herbicides such as EPTC (Eradicane), alachlor (Micro-Tech), or metolachlor (Dual Magnum) can be applied broadcast on flat ground and incorporated by discing before beds are formed and the corn is planted, or they can be applied in a band on preformed beds, then incorporated with a rolling cultivator or power tillers.
To maximize the performance of preplant incorporated herbicides, the following are important:
- Pre irrigate where feasible.
- Disc in manures before incorporating the herbicide.
- Incorporate to the proper depth: 4 to 6 inches for EPTC and 2 to 3 inches for alachlor or metolachlor. When applying herbicides to beds with a rotary hoe, incorporate two times, once each in opposite directions. Broadcast applications of EPTC require cross-discing for maximum incorporation and effective weed control. Time incorporation according to label: EPTC immediately; alachlor and metolachlor, 7 to 14 hours.
- Chop up perennials such as Johnson grass or Bermuda grass by cross-discing or mulching before planting.
- Use proper incorporation speed.
- Disturb nut sedge by using sweeps or power mulchers before planting.Plant immediately after herbicide application.
- Time the first irrigation to enhance herbicide activity.
Atrazine or Simazine @ 1.5 to 2 kg / ha dissolved in 500-600 litres of water, sprayed uniformly on the soil 2-3 days after sowing and followed by irrigation control most of the weeds efficiently. Moisture in the soil is essential for efficient weed control.
In case of intercropping with legumes Pendimethalin should be used instead of Atrataf in the same proportions
Table: 1 Herbicides used in Maize.
|Weedicide||Tradename||Weeds Controlled||Mode of action||Dosage|
|i)Pre emergence AtrazineSimazine||AtratafTaphizin||Contols several broad leaved and grasses||Abrobed by weeds through rootsActs on Hill reaction and stops the production of oxyzen and thus interferes with photosynthesis and effects the weed grwoth.||2.0-2.5
|Alachlor:||Lasso,Alanex||annual grasses and certain broad leaved weeds.||Absorbs mainly near the first node of germinated shoots, secondarily by roots and translocated throughout the plant and then metabolized within 10 days.||2-3 kg/ha.|
|Linoron||Afalon||Besides annual grasses, it is also reported to suppress the growth of bermudagrass to some extent||—||1 kg/ha|
|ii)Preplant incorporationFluchloralin||Basalin||Effective against commom annual weds||—||05-0.67
|EPTC||Eptam||Effective in the control of cheifly annual grasses||—||3-4 kg/ha|
|iii) Post emergence2,4-D||Weedtrine||Applied as direct spray, it can control sedges and young broadleaf weeds when the crop height is 8.25 cm. Dicamba can be added to 2,4-D to improve control of Trianthema and other difficult weeds||—||0.5-0.8
|iv) Herbicide combinationsTank mixture of Atrazine, alachlor and phytobland oil||—||Effectively control sedges||—||0.25kg/ha
- Weed Control by mechanical and manual means
When maize crop attains Knee high stage (30 days after sowing), weeds can be controlled by working cultivator or blade harrow in between the rows of the crop.
Withholding irrigation for a week after the operation controls most of the weeds. Manual Weeding, only within the crop rows (between the plants) makes weed control efficient and economical.
- Weed Control by intercropping
Slow initial growth nature of crop and wide inter row spacing creates congenial conditions for growth of weeds. Inter cropping of compatible and non-competitive crops like pulses, oil seeds and rooted vegetables not only prevent growth of weeds but also results in profitable utilization of natural and applied resources resulting in higher returns.
- Weed Control by Crop rotation
Maize followed by red gram, groundnut and safflower in rotation not only control weeds but improves productivity of maize.
Maize preceded by green manure crops like Dhaincha and Sun hemp not only exterminates weeds due to rank vegetative growth but also improves the fertility of soil.
- Weed Control by harvesting at physiological maturity
Harvesting of maize a at physiological maturity (as indicated by black layer formation) leaves the soil with moisture content sufficient enough to take up post harvesting ploughing and duration of crops reduced by 8-10 days. Exposure of soil to solar radiation by post harvest ploughing kills most of the deep-rooted weeds and a good seedbed is prepared by natural means.
Control of weed at an early stage avoids the competition of weeds with maize for soil moisture and plant nutrient. Weed can be controlled chemically, mechanically or manually. Weed management is a complex phenomenon. To obtain weed free plot, proper attention should be paid towards integration of cultural practices, mechanical method and proper integration of herbicides. But while applying herbicides proper precaution should be paid towards safety measures and proper dose and time of application.
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