CULTURALWEED

CONTROl\By Allah Dad Khan

What is Cultural Weed Control?

Cultural weed control includes non-chemical crop management practices ranging from variety selection to land preparation to harvest and postharvest processing. Cultural weed control is a part of integrated weed management which involves the integrated at is Cultural Weed Control?

Cultural weed control includes non-chemical crop management practices ranging from variety selection to land preparation to harvest and postharvest processing. Cultural weed control is a part of integrated weed management which involves the integrated at is Cultural Weed Control?

Why Control Weeds?Prevent yield loss due to weed competitionMaintain purity and/or quality and market price of harvested grainPrevent build-up of weed seeds in soilPrevent weeds that may attract insects or rodents (rats) or act as a host for diseasesPrevent clogging of field irrigation channels to facilitate water flowReduce time and cost of land preparation and weeding operations

Why Use Cultural Control of Weeds?Cost effective and easy to practice: Acceptable and accessible to small & large farmersNon-chemical and ecologically soundPrevention is better than cure.

How to Use Cultural Practices to Control Weeds?Several cultural practices like tillage, planting, fertiliser application, irrigation etc., are employed for creating favourable condition for the crop. These practices if used properly, help in controlling weeds.

1.Field preparation: The field has to be kept weed free. Flowering of weeds should not

be allowed. This helps in prevention of build up of weed seed population.

2. Summer tillage: The practice of summer tillage or off-season tillage is one of the

effective cultural methods to check the growth of perennial weed population in crop cultivation.

3. Maintenance of optimum plant population: Lack of adequate plant population is prone to heavy weed

infestation, which becomes, difficult to control later

4. Crop rotation: The possibility of a certain weed species or group of species

occurring is greater if the same crop is grown year after year. 5. Growing of intercrops: Inter cropping suppresses weeds better than sole cropping and

thus provides an opportunity to utilize crops themselves as tools of weed management.

6. Mulching: Mulch is a protective covering of material maintained on soil

surface. Mulching has smothering effect on weed control by excluding light from the photosynthetic portions of a plant and thus inhibiting the top growth.

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7. Solarisation: This is another method of utilisation of solar energy for the

desiccation of weeds. In this method, the soil temperature is further raised by 5 – 10 ºC by covering a pre-soaked fallow field with thin transparent plastic sheet.

8. Stale seedbed: A stale seedbed is one where initial one or two flushes of weeds

are destroyed before planting of a crop. This is achieved by soaking a well prepared field with either irrigation or rain and allowing the weeds to germinate.

9. Blind tillage: The tillage of the soil after sowing a crop before the crop plants

emerge is known as blind tillage. 10. Crop management practices: Good crop management practices that play an important role in

weed management.Vigorous and fast growing crop varieties are better competitors with weeds

11.Timing: Weeds need to be controlled within the first 20-40 days to avoid yield loss.12. Reduce weed entry into fields: Prevent the introduction of weeds into fields by: 1) use clean good quality seed; 2) keep seedling nurseries free of weeds to make sure weeds are not planted with the rice seedlings; 3) keep irrigation channels and field bunds free of weeds to prevent weed seeds or vegetative parts entering the fields; 4) use clean equipment to prevent field/crop contamination; and 5) rotate crops to break weed cycles13. Fallow management: Kill weeds in fallow fields (e.g., use tillage or herbicides) to prevent flowering, seed-set and the build-up of weed seeds in the soil (remember: “1 year seeds, 7 year weeds”).14. Water management: Water is the best ‘herbicide’ to control weeds. Many weeds cannot germinate or grow under flooded conditions (e.g. most grasses and some sedges). Maintain a 2 to 5 cm water level in the field to minimize weed emergence and lower weed pressure. Fields should be continuously flooded from the time of transplanting to when crop canopy covers the soil completely. Good land leveling is critical to avoid high spots where weeds can become established.

15. Lowering Area under Bunds:Reduction in area under bund and water channels of crop fields is essential to minimize weed infestation as weeds on bunds and channels are often ignored by the farmers since they do not complete directly with crops.16. Intercropping:Many a time intercropping with crops like soybean , cowpea, red gram, green gram , groundnut etc. helps in suppression of secondary growth of weeds e.g Intercropping of soybean or cow pea in sorghum or pearl millet is helpful to suppress secondary growth of weeds as the inter row space is covered by intercrop at latter stage of crop growth. In this method at initial stage of crop growth it is necessary to control the weeds by mechanical or chemical methods.17. Smothering:A quick growing dense crop can successfully complete with weeds. Past growing and fast shading crop is called smother crop. Sweet potatoes, Lucerne, soybean, sun hemp, etc are good smother crops. These crops cover the field within short period due to higher plant density, fast growth and canopy coverage suppress weeds by fast shading effect and also make the under ground parts of weed feeble. The smother crops are sown at close spacing with high plant population to suppress weeds.

18. Use of Fertilizers or Selective Crop Stimulation:Many crops get fillip from the fertilizers applied before sowings or as top dressing. The band application ( near to crop roots) of nitrogen for cereals, sugarcane and Sugar beet etc is said to result in their vigorous growth that carries them beyond weed competition. Some fertilizers like calcium Cyanamid and ammoniums sulphate directly destroy the delicate weeds.19.Soil Condition :-There are certain situations where amending soil conditions may help to reduce the competitiveness of weeds for e.g. some weeds such as Wild oat , prefer low pH soils and increasing the pH on these soils will give crops a better chance against wild oat. Other weeds may grow better in high pH soils .20. Cover crops. Year-round vegetation limits weed opportunities, adds to soil health and can provide allelopathic properties.21. Delayed planting. Warmer soils in late May and early June will promote more vigorous crop growth and can have corn and soybeans emerge in five days. Delayed planting can also provide an opportunity to till the first flush of weeds.

22.PIanting MethodSowing of clean crop seeds without weed seeds should be done. It is a preventive method against introduction of weeds. Sowings are taken up one to three days after rainfall or irrigation depending on soil type. Weeds already present in the soil start geminating within two or three days. Sowing operation with seed drill removes some of the germinating weeds. Transplanting is another operation which reduces weed population. Since, the crop has an additional advantage due to its age.23. VarietiesShort statured, erect leaved varieties permit more light compared to tall and leafy traditional varieties.Weeds continue to germinate for long time in 'dwarf varieties resulting in high weed growth.24. Fertiliser ApplicationPlants differ in their capacity to respond to fertilizer application.Crops like sorghum, maize, pearl millet and rice grow at a faster rate when nitrogenous fertilisers are applied and cover the soil earlier.Weeds like Cynodon dactylon, Cyperus rotundus do not respond to nitrogen application and they are suppressed by fast growing crops.25. Irrigation and DrainageDepending on the method of irrigation, weed infestation may be increased or decreased.Frequent irrigation or rain during initial stage of crop growth induces several flushes of weeds.In lowland rice, where standing water is present most of the time, germination of weeds is less.Continuous submergence with 5 cm water results in reducing weed population whereas under upland situation, weed population and weed dry matter is very high

23. Crop EstablishmentAs a general rule, the first plants to germinate and emerge in an area tend to exclude all others. Therefore, it is critical when considering plant competition as a weed management tool to establish a vigorous dense crop. Important factors that affect germination and emergence include the viability of the crop seed (percent germination), soil temperature, availability of moisture, and physical resistance to seeding emergence by the soil. These factors are influenced by the soil type, physical condition of the soil, depth of planting, the firmness of soil around the seed, the degree of soil compaction above the seed, and the formation of surface crusts after planting. The final stand will also be influenced by post-emergent stress due to weeds, diseases, insects and adverse weather conditions. Crop germination, if planting has been correctly done, is generally rapid and predictable. If pre-seeding weed growth has been killed, at least a temporary advantage has been gained for the crop. This initial advantage can be lost however, if effective post-seeding herbicide application or tillage is not undertaken to control late emerging weeds.

Plant Competition

As a general rule, for every pound of weed growth produced, about one less pound of crop growth is produced. Usually, early weed competition reduces crop yield far greater than late season weed growth. It naturally follows then, that early weed control is exceptionally important. Late season weed growth may not seriously reduce yields, but it can make harvesting difficult, lower crop quality, and add to the reservoir of weed seeds in the soil.

FACTORS LEADING TO MAXIMUM CROP COMPETITION1.Prepare Good Seedbed - Stale Seedbed Technique: A good seedbed is prepared, but no seeds are planted. After a good growth of weeds have emerged, they are killed using a non-selective herbicide with no residual effect in the soil. The crop is then planted with as little disturbance of the soil as possible to avoid bringing fresh weed seeds to the surface. This technique controls the all important first flush of weeds.2.Rate of Seeding: Heavier seeding rates can be used to reduce weed competition in areas where sufficient moisture is available. This applies to seeding completed at the regular time, as well as in a delayed seeding program. The recommended heavy seeding rate varies from 25 to 100 percent more seed, depending on the crop and the location. However, it should be remembered that heavy seeding rates should be used together with other cultural and chemical control measures to be most effective.3.Date of Seeding: Different weeds have different preferences for germination. Weeds such as many of the mustards and wild oats germinate best in cool conditions and are therefore more of a problem in early sown crops. Redroot pigweed and green foxtail prefer warmer soils and therefore germinate later. Late seeding allows for tillage or pre-seeding herbicide control of early germinating weeds. Early seeding results in crop competition with later germinating weed species. By varying crop seeding dates weeds have difficulty adapting.

4.Crop Variety: It is important to choose a variety of crop plant that is well adapted to local conditions of soil, water, climate and disease resistance.5.Fertilization: The fertility of the soil affects both the vigour of crop plants and the vigour of weeds. Many weeds can utilize fertilizers as well as or better than crop plants. Nevertheless, if most of the weeds are suppressed or killed by tillage or herbicides, the extra vigour given to the crop by fertilizers will make them better competitors. Placement of the fertilizer in the crop rows has an advantage over broadcast fertilization because most of the fertilizer is directly available to the crop.6.Smother Crops: A smother crop is defined as a thick stand of rapidly growing crop that competes with weeds to such an extent that their top growth is drastically suppressed and their roots are severely weakened. Alfalfa, when it becomes well established, is an excellent smother crop. Its extensive root system enables it to compete with most weeds for water, and its dense top growth smothers new weed growth.

The principle value of smother crops in weed control is that they severely weaken the underground parts so that weeds are readily killed by the cultivation that follows.7.Soil - Water Relationships: Water relations, particularly the quantity of rainfall and its distribution, are critical to growth. Soil type, texture and the height of the water table are also important. Most land cropped with cereals and vegetables is sufficiently drained that any improvement of the overall drainage would have little effect on weeds.8.Soil Reaction: Certain weeds tend to be associated with alkaline and acid soils. For example, wild barley and arrowgrass are more prevalent on alkaline soils. Wild oats do better on acid soils than most cereals. Amending soil reaction is suggested where indicator weed species prevail.