How to protect and manage soybean crop

Weed Management: Weeds complete with soybeans for nutrient's, moisture and light and thus, reduce yield. The most effective measure for developing weed control in soybean vary; depending on types of weeds, degree of weed infestation, soil type, weather patterns, crop rotation, tillage methods, row spacing and equipments available. A good weed control program should includes combination of preventive, cultural, mechanical and chemical practices.

Preventive Measures: All these measures taken to prevent the introduction and spread of weeds include the use of weed free crop seed.

·          Weed free soil, seed and farm yard manure

·          Plant certified seed

·          Clean planting/harvesting equipments

Cultural Control

Crop Rotation: Crop rotation reduce the weeds populations of certain weeds common to a particular crop. It results in improved crop yield, quality, improved soil conditions, and reduces the chance of plant disease and insect infestation.

Tillage Practices: Deep and dry ploughing gives a substantial control of perennial weeds. By tillage method, weeds are buried with soil, thrown over and with disruption of the ultimate relationship between the weed, crop and soil.

Mechanical (Physical) Control: Hand weeding is the most common practice and used employed by the farmers, two weedings are recommenced during the growing period. Mechanical weeding by rotary weeder control the annual weeds effectively and economically.

Chemical Control: The experimental results have shown that proper use of pre-emergence herbicides i.e. Pendimethalin 8(Stomp), Trifluralin (Treflan) and Oxadiazon (Ronstar) can be applied after planting before the germination of soybean. These have been found very effective in controlling a wide range of grasses and broad leaf weeds.

Integrated Weed Control : This involves the use of two or more above mentioned weed control techniques. The combined use of more than one weed control technique is advantageous, because one technique rarely achieves complete eradication of weeds.

Diseases: About 35 diseases of economic importance are known to affect soybean throughout the world. Diseases can reduce yield from 10 to 30 percent, depending upon the severity, pathogen and weather conditions. In Pakistan only 6 major diseases have been observed and these are anthracnose, charcoal rot, purple seed stain, pod and stem blight and bacterial blight/pustule. Careful diagnosis is very important for the disease control strategies, because more than one pathogen or a complex may be responsible for final loss in yield and seed quality. Thus, the collection of samples is essential throughout the growing season.

Disease management programme should include the following methods:

Preventive Measures

·         Plant quality and healthy seed, free of mechanical damage.

·          Harvest seed soybeans as soon as they are mature.

·          Avoid planting in wet and poorly drained soils to reduce chances of the development of soil borne diseases (Root rot).

·          Keep the crop free from weeds because they may be the hosts to any diseases.

·          Seeds should be stored at 8 to 10 percent moisture at 15^oC temperature to have more seed viability.

Cultural Control

·         Plough down crop residues

·         Crop rotation with non-leguminous crop.

·         Plant early before the soil temperature rises.

·         Reduce plant population, increase row width and avoid high fertility to prevent a closed canopy, improve aeration and increase drying in the canopy.

Chemical Control

i) Seed Treatment: To protect from soil born diseases, seed should be treated before planting with one of the available fungicides; Captan, Dithane M-45, Benlate and Tecto @ 1.5-2 gms per 1 kg seed.

ii) Foliar Spray: At the appearance of disease symptoms, after field survey foliar spray with one of the systemic fungicides, Dithane M-45 @ 1 kg ha^-1, Benlate and Tecto @ 120-150 gm ha^-1 dissolved in 250 litre of water should be done after 10 to 15 days interval. This process should be repeated 2-3 times depending upon the severity of disease.

Integrated Disease Control

·         Use multi-race resistance varieties or least susceptible cultivars and avoid tall, viney cultivars that may lodge.

·         Use integrated control; combines high tolerate cultivar, good drainage, complete tillage, seed treatment and rotation with cereals.

Insects and their control

Major insects that damage soybean crops are stem fly, white fly, green stink bug, cut worm and larvae. Insects attack on all parts of the soybean plant and feed throughout the growing season. Certain insect can also provide access for disease organism and or transmit them directly to plants. Therefore, understanding the relationships between the insect and the crop will enable farmers to manage pests much better. A new practice to control insect attack is based on knowledge of the economic injury levels of the consequential insects. The economic injury levels is the population of insects that is capable of producing an amount of economic damage which is at least equal to the cost of controlling the insects. Wise monitoring of major insects is required in order to effectively make decision relative to insecticide application.

Bio Control

Many insect predators, parasites and pathogens occur in soybean fields that help in keeping population of pest species below economic levels. However, experience has shown us that beneficial insects and pathogens do not do a complete job, and that chemical control becomes necessary.

Cultural Control

Early planted soybeans tend to receive the majority of the overwhelming adult of flies and bugs, while late planted will alleviate some of the problems with these two insects and cutworm. Therefore, it is still more economical to plant early for high yields and control any potential insect problems with insecticides than it is to plant late for insect control.

Chemical Control

·         For cutworm and termite apply powder of BHC @ 7 kg per hectare or Dieldrin 20 EC @ 5-7 litres ha mixed with irrigation water.

·     For other insects especially flies, thrips and larvae spray; Dimecron 100% @ 600 ml ha or Methyl-Parathion 50 percent @ 800 to 1200 ml ha Somicidin 20 EC @ 400 to 600 ml ha dissolved in 250 litre of water, if attack is severe spray two times with an interval of 8-10 days.

Harvesting and Threshing: Soybean matures in 92 to 120 days depending upon growing season and the variety that was planted. Senescence is the decline in chemical activity associated with aging of plants and maturation is only loss of water from plants or seeds which are physiologically mature. Seeds are physiologically mature when they are no longer synthesizing food. Physiological loss of chlorophyll and acceleration of senescence is characteristics of dry, dehisent fruits (soybean pods). Ethylene and abscisic acid play an important role in abscission and dehiscence of pod and often capsule dry fruits (soybean). Oil and storage protein have reached their maximum dry weight. At this stage seed moisture is 45 to 55 percent, pods and stems are yellow, and leaves are yellow or have dropped. Delay in harvesting not only reduces seed quality but it also reduces harvesting efficiency and increases shattering losses. As soon as the pods are dry enough to open easily, harvest it, thresh after drying within 7-10 days and threshed seed must be cleaned before storage or marketing.

Yield: Number of pods per plant is a function of spacing and intercepted light while leaf N is a principal factor in determining soybean seed yield. The average farmers yield ranges from 1500 to 2500 kg ha. At Agricultural Research Institutes under high level management practices the yields range from 2500 to 3500 kg ha

Storage: Well dried seed should be stored at about 8 to 10 percent moisture content and 15^o C in tropical regions. To maintain dried seed at a low moisture level, two practices are feasible. these are:

i) To grow soybean for seed in an area where relative humidity is low.

ii) To use moisture proof containers for seed storage.

For long-term benefit and effectiveness, air conditioned storage in tropical and subtropical areas are more suitable. Adequately air-conditioned storage should be maintained at a temperature of 20^oC to 22^oC or less and a relative humidity of 60 percent or less when the storage period is of eight-nine months duration. Poor quality soybeans seeds will deteriorate quickly in storage than high quality seeds. In addition, the practice of "Carrying over" soybean seeds should be discouraged because this crop does not store well and the quality of seed quickly diminishes during the second over wintering period.