CULTURAL WEED CONTROL IN COTTON
By Dr. Shamsuddin Tunio
Sep 18 - 24, 2000
The cotton is important fibre and cash crop of Pakistan and major source of foreign exchange earning. The crop is always at risks and suffers production constraints due to insect pests, diseases and weeds. Weeds offer great risks in decrease of cotton yields through reducing crop efficiency. Weeds are un-invited guests and most of the weeds are competent to induce losses during crop growth and development in terms of poor growth by making greater share in the uptake of soil moisture, nutrients, sunlight, Co2 and space; and weeds serve as an alternate host to many of the insect pests and disease pathogens. The question is how cotton crop makes itself efficient and competent to cover such risks, which is again farmers job to monitor time by time growth and yield affecting crop risks and hazards.
The crop does speak about risks and damages but it is farmer who must have spoken regarding crop risks and select right direction towards yield loss reduction.
Weeds have serious negative factor in crop production and result in markedly great losses in crop yields, despite the use of costly inputs i.e. seed, fertilizer, pesticides, irrigation water and improved cultural practices. Weeds also act as reservior for multitude of pests and diseases, which use them as alternate hosts for food and shelter during the off season periods, when crop plants are not in the field.
The cotton crop grow and respond betterly under its specific environment with specific crop growth habits — as it has deep root system, profusely branching and heavy feeding crop which utilizes resources such as nutrients and water more efficiently. The sunshine, Co2 and space are upcoming resources, which cotton crop also utilize at the most.
But, such resources might be shared if weeds ate left in the cotton fields. Traditional farming, may allow weeds to be grown in the interest of the farmer to achieve and/or receive green fodder for animals. Is this not a injustice of the farmer with the crop to infuse many risks for cotton crop growth and yield potentialities?
The cotton crop weeds may be classified into two categories i.e. Annual and perennial weeds, which might be active in the season during which cotton is grown. Thus, such weeds may further be classified as summer or kharif annual weeds and summer or kharif perennial weeds of cotton (Table 1).
Table 1:Important weeds of cotton
Amaranthus polygamous viridis
Deep root grass
Weed species which increases the risks of losses during crop growth, development and maturity especially at the time of picking that may affect lint quality and may be of versatile type growth habits and life cycle.
The most weeds of cotton are annual in nature, which include dicot weeds or broad leaved weeds such as Carpet weed, Amaranths, Digeria arvensis, Purselane, Niruri, Ubat Kanderi etc. But, perennial weeds of cotton must not be ignored, which may induce both dicot and monocot weeds of perennial in nature or life span. Such weeds may emerge in-cotton and produce drastic losses in crop. Perennial weeds of cotton may include lawn grass, sedge grass, Johnson grass, Tick trefoil, Jimson weed, Bind weed etc.
The cotton crop needs environment friendly methods of weed control. The weeds may be minimized in their population and losses through methods like prevention, eradication and control. Where as, control of weeds may be cultural, mechanical, biological and chemical etc. The cotton pest control technology extends use of chemicals which have increased environment pollution problems. Because, we use not only pesticides including insecticides, fungicides and herbicides but a huge amount of chemical fertilizers, which may also be added in the soil. That's why such chemicals create air, soil and water pollution problems for the farmers and the growers of cotton belt. Though, chemical weed control technology may be most effective to control cotton weeds. But, there are alternatives of chemical weed control in cotton such be biological weed control and cultural weed control methods. The former weed control method i.e. biological weed control is seemed uncommon amongst the farmers and cotton growers due to unawareness with regard to its handling and sorting out the ways and means, which include insect species and pathogens those might feed upon weed species that may be regarded as biological weed control method.
The cultural control method may be regarded as farmers practice of controlling weeds from the crop field. The cotton crop needs frequent weed management practice during its early growth. However, delayed stages of both crop and weed itself may create difficulties in the removal or eradication of weeds by cultural methods. There are reports that above 75% farmers control weeds by manual or cultural methods. But, the best method is one which may be cheap, effective, easy to adopt, environment friendly and finally helpful in increasing crop yields. However, in cotton for proper weed control purposes, platting patterns such as row spacing and planting methods including flat bed or ridge bed method play important role in checking weeds.
The reasons for low yield in cotton are many, but one of the most serious but less noticeable cause of the low yield is the presence of weeds. The crops in Pakistan suffers an average losses to the extent of 10-15% due to weeds where cotton crop suffers loss of 31-41%. However, the problem of weed control in cotton should not considered in isolation. In fact, there are some weeds (may be perennial in nature) which are carry-over from the previous crop. Thus, there should be a year round check over the weeds.
The weed problem is becoming more and more serious with every passing season and it seems to be getting out of hand, which must not be ignored any more.
Thus, cultural weed control practice in cotton is very important. Before first irrigation, one thorough hoeing is very necessary and subsequent irrigations should be followed by a hoeing. This practice would not only keep the field free from weeds, but would conserve soil moisture to a great extent. Hand tools like spade and Hoe (Khurpi) may be used for dry hoeing it cotton. However, local plough and triphali may also be used for weeding and interculturing purposes in cotton, after each irrigation. Hoeing, weeding and/ or interculturing should not be done when the plants have attained sufficient growth, to avoid breaking of the branches of cotton plant. But, early growth weedings and interculturings may be beneficial to better root establishment and vigorous crop growth that may led to higher seed cotton yields.
Weeds may also be controlled adequately by cultivation but no tillage or zero-tillage strategies for cotton planted alone may show promising results in the subtropical or semi-arid environment. The effect of integrated weed management on cotton yield with pre-emergence spray, both alone and in combination with one weeding and hoeing at 50 days after sowing, or weeding and hoeing at 25 and 50 days after sowing, results were effective in controlling weeds and increasing the seed cotton yield in both cases, in combination with one weeding and hoeing. However, a weed free check has the maximum weed control efficiency and seed cotton yield.
Associate Professor Department of Agronomy Sindh Agriculture University, Tando Jam.