WEED CONTROL TECHNOLOGY OF WHEAT
Weed control play vital role for higher wheat yield
By Dr. Shamsuddin Tunio
Associate Professor Department of Agronomy
Sindh Agriculture University Tandojam.
Feb 19 - 25, 2001
Wheat is a major cereal grain crop of Pakistan, which meet food needs of growing human population of the country. Wheat is grown in rabi season. This crop needs cool season for emergence or growth and warm season for the maturity. Whereas, most of the broad leaved weeds also make growth during the cool season and compete with wheat crop for nutrition and other inputs.
The use of pure seed, proper land preparation, balanced fertilizer and proper irrigations along with weed control play vital role for higher wheat yield. Weeds emerge as un-invited plants, which are harmful not only for whole eco-system but for the environment where are grown. Some weeds are poisonous and some are useless plants exists on the land and compete crop plants by taking food nutrients, water, sunlight and other elements and weakens the main crop, which results in low crop yield.
For achieving higher wheat production, new wheat varieties, modern methods of sowing and control of harmful insect pests and diseases are important but yield target may hardly be accessible. The main reason behind it is that the growers are paying little attention to the weed control or using eradication practices of weeds, due to that yield loss may occur. This sort of loss of wheat grains due to weeds may be 15 to 25 per cent.
Timely control of weeds is most essential for better wheat production, weeds are crop pests of destructive nature, which need continuous strategy to eradicate them. Weed competition with crop for food, water, sunlight, air etc. extends from 3 to 8 weeks. Thus, weeds must be controlled during the period of their competition for better crop and increase in its production. If not doing so, and weeds were left to grow during full season in the crop land, the yield would decrease at drastic level.
Weeds of wheat: There are about thirty weeds of wheat found in Sindh, which are spreaded over in a few or large numbers under different wheat growing areas. Whereas, twelve to sixteen weed species come up and grow in wheat fields, which induce losses upto economic threshold level (Table 1). Such weeds lower the production capacity of land, by competing in irrigation, plant nutrients, sunlight, air and growing space, and left wheat crop devoid of those inputs. The result is that wheat plants turn weak and produce low grain yields.
Table 1: Weeds of wheat
White sweet clover
Nettle leaf weed
Sedge nut grass
Deep root grass
Growth losses of weeds in wheat
* Weeds reduce growth by making share in water, food, light and sir.
* Weeds reduce tiller production and survival, which may result in low production.
* Weeds grow fast and shade over the wheat plants, which may result in weak crop stand.
* Weeds reduce growth, production and grain quality of wheat by mixing at the time of harvest.
* Weeds make hinderances and reduce water flow applied to the wheat.
* Some weeds induce lodging of wheat crop by binding climbing over the plants.
* Some weeds due to spines and thorns make trouble or difficulties in the crop harvest.
Production losses of weeds in wheat: Weed losses in wheat may occur from initial stages to the last stage of maturity, harvest, Threshing, winnowing and storing of wheat grains. Weeds of wheat such as, wild oat and phalaris minor have close resemblance to the wheat crop, which could not be identified during early growth stages, affect crop growth and reduce wheat yields. Weed plants are more resistant, hardy and making faster growth than wheat. Because, until when, wheat plants establish before that weeds bind over the plants and wheat crop receive less time for growth, which result in reduction in production of the crop. Some weed species, nourishes insect pest and diseases and provide shelter to them.
In wheat weeds, there are species of weeds, which bear thorns (such as camel thorn, prickly poppy etc.) and create difficulties in harvest and produce losses in grain quantitatively. Whereas, Bind weed is such a species that binds over the wheat and therefore, the losses of crop growth and yield occur. Some weeds of wheat (such as wild onion and white sweet clover) produce odourful seeds, which spoil the quality of flour.
Weed control methods: There are different methods of controlling weeds of wheat, including traditional to improved weed control methods. The collectively weed control methods depends upon cropping pattern, economic status of the farmer, technology adopted, crop growing area and its climatic conditions.
The weed control methods by and large consists of cultural, mechanical, biological, chemical and integrated weed management practices. The forming communities of Pakistan both due to small holdings prefer to use cultural and chemical methods, which are the most common, effective and important weed control methods in our conditions for the control of weeds of wheat.
Cultural weed control: The cultural weed control method is more effectively used in wheat growing areas, due to the reason that it is observed as environment friendly method of weed control and it is farmer's method who uses their various agricultural practices to eradicate weeds. This method may be used with stirring soil through weeding and interculturing practices by using Hoe (khurpi), Pick axe (chanjour) and spade etc. In normal course, the farmers in a majority control, prevent or eradicate weeds through cultural practices including deep tillage, flooding, crop rotation, hand pulling, hoeing, weeding and interculturing with tools and implements. The cultural weed control method has its scope, by means of that weeds could be uprooted, the soil be opened and pulverized through breaking up of hard pan, weeds after removal may be incorporated in the soil for adding organic matter, which would enhance fertility and water holding capacity of the soil.
In wheat, the control of weeds may necessarily be done before first irrigation application by cultural method i.e. Interculturing practice. It would not only clean wheat field from the weeds but such stirrer soils would retain moisture for longer periods for proper crop growth.
Bar harrowing is one of the important practice under cultural weed control, which may be done by Bar harrow that run after first or second irrigation when soil comes into condition using bullocks to drag this implement. Bar harrow would perform the function of interculturing alongwith uprooting weeds.
Wheat grown on large areas needs harrowing operation to control weeds, which is an economical cultural practice by the use of Bar harrows. Such practice may be employed to break hard pan of soil and to control weeds in wheat. Bar harrow opens root zone of wheat during early growth stages of the crop, which would result in better root establishment of wheat. Harrowing would bring better environment for wheat through retaining moisture for longer time. This would maintain vigorous growth and increase in crop yields. It is to be noted that Bar harrow could only be used when crop is grown by drilling method. By this means, wheat crop may be kept clean from annual weeds such as lamb's quarter, white sweet clover, nettle leaf weed, wild onion, shepherds clock, vetch weed etc.
However, the pre-sowing practices such as clean seed, proper land preparation, increasing seed rate, timely sowing, crop rotation and competition may bitterly adopted to control weeds of wheat.
Chemical weed control: The chemical weed control is one of the improved method and recent technology to have control over weeds. In wheat, the most easy and cheap method is use of weedicides, which take less time and is effective input to control weeds on large scale. There are number of weedicies, which have been effective and profitable while controlling weeds of wheat. Because, chemical weed control is more efficient to control weeds in wheat when it is grown on large area.
The use of herbicides/weedicides for the control of weeds is rapidly increasing. In technical terms, the control of weeds through herbicides is known by chemical weed control technology. For this purpose, specific or many kinds of weedicidies are formulated and are under use, which have been very effective to control annual and perennial weeds (Table 2).
The weedicides are considered effective and efficient in terms of their selection, volume, application on specific weed and/ or crop. It also be remembered that weedicides are poisonous and must be handled carefully, which may be dangerous to plant or animal life, human health and life, all living beings and environment as a whole.
The weedicide application would be essential when the losses of weeds increase at economic threshold level. In wheat, weed density and species, which cause production losses must be monitored before application of weedicides. The time and method of herbicide application may be classified in three categories:
The herbicides applied before sowing of wheat crop.
Thus, pre-planting herbicides are used on the prepared land before growing crop, which would kill newly emerging weeds.
One herbicides applied before emergence of either crop or weed species which may be effective to control weeds, In this case, spray is to be done after sowing of crop and before emergence of weeds.
The herbicides applied after emergence of both either crop or weed species. In this case, weeds would have been emerged and are sprayed on their leaves.
Weeds must come under farmer's target to be controlled during early stages of crop growth for the decrease of yield losses. Thus, weed control technology of wheat must reflect in terms of its benefits and losses on crop productivity. If weeds are controlled upto first 4, 6, 8 and 12 weeks after sowing, there would be yield increase of 21.5, 39.5. 46.5 and 55.0% and if weeds are kept clean from wheat crop for full season, there would be yield increase of 65.5% .
Table 2: Weedicides used in wheat
Buctril - M
Kurund, Naro, Matri.
Wild oat, Phalaris
Jhil, Senjh, Naro
and Wild oat, Phalaris minor.
Jhil, Senjh, Naro, Matri
Jhil, Senjh, Naro,
and Phalaris, minor
Wild oat and Phalaris minor
Wild oat and Phalaris minor
Jhil, Senjh, Naro, Matri and Wild oat or phalaris minor.