Weed Science Component PDF

CPRT41 Principles of Crop Protection WEED SCIENCE COMPONENT BAHALLA, SM WEED SCIENCE It is one of the fields of crop protection that deals primarily on the weeds and their control. The field is an off-shoot of plant physiology, having evolved f...

CPRT41 Principles of Crop Protection WEED SCIENCE COMPONENT BAHALLA, SM WEED SCIENCE It is one of the fields of crop protection that deals primarily on the weeds and their control. The field is an off-shoot of plant physiology, having evolved from the discovery of the organic and selective herbicide, 2,4-D which also happens to work as a growth regulator (auxin type) when used at a very low concentration. BAHALLA, SM WEED Weeds are referred as plants out of place. This means that weeds grow where we either want other plants to grow or where we want no plants at all. A wild plant growing where it is not wanted and in competition with cultivated plants. Weeds are unwanted and undesirable plants which interfere with utilization of land, sunlight and water resources and thus adversely affect the crop yield. All the above definition points out that word weed has a negative connotation and its definition is based on how man perceived it. BAHALLA, SM WEED Weeds can outcompete crops because they have one or more of these qualities: Produce lots of seeds, which often can survive buried in soil for a long time and grow when conditions become favorable. Have roots that spread quickly Adapt to sites that have been disturbed by people, such a plowed fields or vacant lots. They cause problems because they: Rob crops of light, water, and nutrients, Grow faster than crops and crowd them out, Can produce certain chemicals that are toxic to crops or grazing animals. BAHALLA, SM NOXIOUS WEEDS Reduce yields even at low populations because they are very competitive. They persist and resist weed control measures Scientific Name: Chromolaena odorata Common name: Hagonoy, Devil weed BAHALLA, SM VOLUNTEER CROP A plant that grows on its own, rather than being deliberately planted by a farmer or gardener. Scientific Name: Zea mays Common name: Maiz, Corn BAHALLA, SM ESCAPE PLANTS Ornamental plant out of place, those that are not originally native to an area, and due to their dispersal strategies, have escaped from cultivation and have settled in the wild and bred there, whether intentionally or unintentionally Scientific Name: Lantana camara Common name: kanding-kanding BAHALLA, SM COMMON WEEDS Are weeds commonly seen in the fields and are relatively easier to control. Less destructive. Scientific Name: Imperata cylindrica Common name: Cogon grass BAHALLA, SM COMMON WEEDS Are weeds commonly seen in the fields and are relatively easier to control. Less destructive. Scientific Name: Ipomoea triloba Common name: Morning glory BAHALLA, SM COMMON WEEDS Are weeds commonly seen in the fields and are relatively easier to control. Less destructive. Scientific Name: Mimosa pudica Common name: Makahiya BAHALLA, SM COMMON WEEDS Are weeds commonly seen in the fields and are relatively easier to control. Less destructive. Scientific Name: Cyperus rotundos Common name: Purple nutsedge BAHALLA, SM  CHARACTERISTICS OF WEEDS THAT MAKE THEM UNIQUE AND DISTINCT FROM ECONOMICALLY IMPORTANT PLANTS: 1. They have rapid vegetative growth and profuse root production 2. They produce early and efficiently 3. They adapted to competition and adverse environmental conditions 4. Their seeds and vegetative propagules are usually dormant or can be induced to become dormant. 5. They cause significant damage even at low population densities. 6. They persist and resist control measures BAHALLA, SM Because the concept of weed is based on how man looks at it, their effects could be of two types: A. HARMFUL EFFECTS 1. Reduce yield quantity and quality 2. Increase the cost of crop production or maintenance of an area 3. Act as alternate host for harmful insects, disease causing organisms and other pests 4. Clog waterways and irrigation canals 5. Release harmful chemicals (allelochemicals) that affect the growth of adjacent crops, including the next season crop BAHALLA, SM Because the concept of weed is based on how man looks at it, their effects could be of two types: B. BENEFICIAL EFFECTS 1. Food for man and animals 2. Aesthetic value to beautify areas 3. Prevent/minimize soil erosion in hilly places 4. Return organic matter and nutrients into the soil after decomposition 5. Source of possible medicine and pesticide 6. Source of exotic gene for crop improvement. BAHALLA, SM CLASSIFICATION OF WEEDS BAHALLA, SM  BASED ON LIFESPAN Annuals – these are weeds that grow and complete their lifespan in a single growing season or in a year. Ex. Amaranthus spinosus, & Rottboella cochinchinensis Perennials – these are weeds with indeterminate lifespans, that is, their growth period is more than 1 year. Ex. Imperata cylindrica, Chromolaena odorata & Cyperus rotundus BAHALLA, SM  BASED ON HABITAT Upland/Terestrial – These weeds are well- adapted in a well-drained soil. Ex. Cyperus rotundus, Mimosa pudica, Euphorbia hirta Lowland/Aquatic – These weeds thrive best under saturated or flooded conditions. Further classified into floating, submerged and emerged. Ex. Ipomoea aquatica, Ludwigia octovalvis BAHALLA, SM  BASED ON GROWTH HABIT Erect – These weeds grow vertically with a single or multiple stem. Ex. Ageratum conyzoides Creeping/prostrate – these weeds grow horizontally on the ground. They can be sub- classified as procumbent and decumbent. Ex. Digitaria sanguinalis Twining/Climbing – these plants need support for grow vertically. Ex. Ipomoea triloba BAHALLA, SM  BASED ON STEM STRUCTURE Herbaceous – stems are soft and succulent ex. Cynodon dactylon, Cyperus difformis Woody – stems are hard and with a bark: are usually perennials ex. Amaranthus spinosus, Euphorbia hirta BAHALLA, SM  BASED ON GROSS MORPHOLOGY GRASSES They belong to Family Gramineae (Poaceae) and usually creeping annuals or perennials. The stems which are succulent have well-defined nodes and internodes. The leaves are arranged in two rows. It is thin and narrow with parallel venation. The roots are fibrous and have shallow penetration to the soil. Eleusine indica Echinochloa glabrescens Ischaemum rugosum BAHALLA, SM BASED ON GROSS MORPHOLOGY BAHALLA, SM BASED ON GROSS MORPHOLOGY BAHALLA, SM  BASED ON GROSS MORPHOLOGY SEDGES They are members of Family Cyperaceae. They closely resemble grasses except that their stems are triangular (angular) and the internodes and nodes are not easily distinguishable. Leaves are parallel-veined, thin and narrow, and the root systems are fibrous. Please see photo below. BAHALLA, SM  BASED ON GROSS MORPHOLOGY SEDGES Creeping growth habit, spreading by above ground Root system with spreading by underground stolons tubers rhizomes. BAHALLA, SM  BASED ON GROSS MORPHOLOGY BROADLEAVES These weeds belong to other families of monocots and dicots. Identified because of their fully expanded leaves. Most have netted venation, tap root systems, although a number of them have fibrous roots. Many of them have succulent stems, but there are those which are woody. See photos below for sample weeds under broadleaves. Centella asiatica Euphorbia hirta Lantana camara Chromolaena odorata BAHALLA, SM REPRODUCTION AND WEED ESTABLISHMENT  TWO GENERAL METHODS OF PLANT PROPAGATION Sexual (seeds) In flowering plants involves the production of male and female gametes, the transfer of the male gametes to the female ovules in a process called pollination. After pollination occurs, fertilization happens and the ovules grow into seeds within a fruit. Weeds are capable of producing easily thousands of seeds per plant every season at the time of their vegetative phase. BAHALLA, SM  TWO GENERAL METHODS OF PLANT PROPAGATION Asexual (vegetative propagules) In vegetative (asexual) reproduction, a new plant develops from a vegetative organ such as a stem, root, or leaf. Several modifications of these organs are common in perennial weeds, such as underground stems (rhizomes), above-ground stems (stolons), bulbs, corms, and tubers. Although vegetative structures generally do not survive as long in the soil as do seeds, very small structures can result in a new plant. Vegetative reproduction can be as prolific as seed production. BAHALLA, SM DISPERSAL Dispersal determines weed spread, Seed structure and its habitat are the key determinants for weed dispersal, Adaptive structures and proper habitat. Together with the activities of man contribute to a great deal to the dispersal process. Dispersal -The movement and spread of a species or individuals Dispersal unit - refers to the structure, usually single-seeded or multi-seeded, together with its accessory parts that is dispersed or separated from the mother plant. BAHALLA, SM  AGENTS OF WEED SEED DISPERSAL Wind – applicable to seeds that are light, flattened structure, with wing-liked outgrowths and with hairy appendages (those with explosive mechanisms or cancer mechanisms). e.g. Dandelion seeds Water – common in seashores and aquatic weeds. These are weeds with pericarps/structures that consist of light tissues with inflated structure that enable the seeds to be buoyant. e.g. Bidens pilosa BAHALLA, SM  AGENTS OF WEED SEED DISPERSAL Animals – seeds that have hard seed coats that can pass through the alimentary tract of animals without losing viability and become dispersed to areas where the animals excrete. e.g. Ruminant animals (cow, carabao), birds, bats), Seeds with spine that may stick to the hairs of animals Man - consider as best agents of dispersal, consciously & unconsciously. e.g. seeds with hooks, sharp & hard spine & sticky substances BAHALLA, SM  EFFECT OF COMPETITION DURATION ❖ Critical Period of Competition - Particular duration during the cropping period when the crop is very sensitive to weed competition - The time that the crop needs to be weed-free to show no detrimental effect on yield (immediately after emergence) ❖ Critical Threshold Level - Level of weed density at which beyond this density will cause significant reduction in yield  EFFECT OF COMPETITION DURATION ❖ Critical Period of Competition  FACTORS AFFECTING THE COMPETING ABILITY OF A CROP AGAINST WEEDS Period of weed growth – The weeds that germinate and grow at the same time as the crop seeds are most successful competitors. Intensity of weeds – There has to be some minimum amount of weed growth in terms of either population or yield in the field to exert a minimum biological stress on the crop performance. Weed species – Different weeds differ in their ability to compete with the crop at similar density levels. This is primarily because of difference in their growth habits as well as due to the allelopathic affects which they may exert on the germination and growth for the crop. Soil fertility – Methods and time of application of fertilizer to the crop fields are important in determining whether the added fertilizers will suppress or increase weed growth in fields.  FACTORS AFFECTING THE COMPETING ABILITY OF A CROP AGAINST WEEDS Allelopathy – is the detrimental effects of chemicals or exudates produced by one (living) plant species on the germination, growth or development of another plant species (or even microorganisms) sharing the same habitat. Allelochemicals – are produced by plants as end products, by-products and metabolites liberalized from the plants; they belong to phenolic acids, flavonoids, and other aromatic compounds, terpenoids, steroids, alkaloids and organic cyanides. Mechanism of action of allelochemicals ▪ Interfere with cell elongation ▪ Interfere with photosynthesis ▪ Interfere with respiration ▪ Interfere with mineral ion uptake ▪ Interfere with protein and nucleic acid metabolism  FACTORS CAUSES SHIFTS CHANGE IN WEED POPULATION Weed Control Method – There is no single control method that is effective for all weeds. One method may control some weeds but may favor the growth of other weeds. Water Management – When water regime changes in an area, weed population will also change because different plants have different water requirement. Ex. Upland area converted to lowland- upland weeds will be reduced and lowland weed will predominate. Fertilizer Management – Fertilization enhances growth of responsive weeds but may suppress the growth of non-responsive weeds. Growth of responsive weed is enhanced, the growth of less competitive weeds is suppressed, thereby changing the weed composition in the field. END OF CPRT41 (WEED SCIENCE COMPONENT)