Weed Science: Concepts, Characteristics, and Classification

MODULE 3 WEEDS MODULE OVERVIEW In this course, the different components connected to the biology/ecology and management of weeds in both crop and non-crop ecosystems are examined and discussed. Weed management is critical in agricultural crop producti...

MODULE 3 WEEDS MODULE OVERVIEW In this course, the different components connected to the biology/ecology and management of weeds in both crop and non-crop ecosystems are examined and discussed. Weed management is critical in agricultural crop production because it affects yield targets and production. The precise identification of flora, as well as the traits that make weeds particularly competitive and/or undesirable in a specific habitat, are given special emphasis. In general, this module covers the biological, ecology, and ecological aspects of weeds, as well as their integrated management. LESSONS COVERED: 1. Concepts, Characteristics and Classification of Weeds 2. Effects, Reproduction, Establishment of Weeds, Crop- Weed Competition, and Change in Weed Population LESSON 1: CONCEPTS, CHARACTERISTICS AND CLASSIFICATION OF WEEDS I. INTRODUCTION According to Jethro Tull, a weed is a plant growing where it is not desired but a plant can also be desirable in one place and undesirable at another place. When it comes to weeds and weed control, it's crucial to know what constitutes a weed. One must understand its basic concepts, and the most basic concepts of weed science is encapsulated in the word weed. Knowing its concept, characteristics and classification can help us came up into a more efficient management techniques when it comes to weed control. II. LEARNING OUTCOMES: The main aim is to be able to identify and understand the concept, characteristics and classification of weeds as well as the biological factors and ecological principles that influence weed growth, population dynamics, invasiveness, and survival At the end of the lesson, the students must be able to: 1. Define weed science and understand weed science as a discipline 2. Learn the characteristics and importance of weeds 3. Classify and identify weeds associated with crops III. PRE-COMPETENCY CHECKLIST Weeds are naturally growing everywhere and we always encounter and live with them every day. From the day we are born up to present – we saw countless of what we call “weeds”. Can you give at least 3 examples of weeds you've seen in your years of existence and explain why you considered it as a weeds?  IV. CONTENT FOCUS WEED SCIENCE DEFINED Weed science is described as the study of weed establishment, dispersion, impacts, characteristics, identification, as well as their control. CONCEPT OF WEEDS A weed is a plant that is one of the most important components of agro- ecosystems. Weeds would not exist without man since they flourish in a man-made environment. A weed can be defined in a variety of ways, but the following are the most common: Weeds are no strangers to man. They have been there ever since he started to cultivate crops about 10, 000 BC and undoubtedly recognized as a problem from the beginning. Hence, it is considered that many weeds principally originated from two important and major arbitrarily defined groups – by man’s conscious effort – by invasion of plants into man created habits In conclusion, a plant is regarded a weed in terms of human attitudes, therefore it is called a weed if it is unwanted in a certain location and period. Activity 1: Things to ponder: Watch the “Parable of the Weeds” to gain some inspiration and wisdom in weeds. Share this in your FB account and write your reaction or thoughts about it in your caption. https://www.youtube.com/watch?v=XuMYt-aOT1w&t=44s CHARACTERISTICS OF WEEDS Weeds' invulnerability is attributed to them by the prevalent belief that they are noxious. Weeds have developed adaptive features that improve their persistence or competitiveness, despite the fact that weeds and crops share many of the same properties. Some of their secrets of success are: Note: While weeds in their widest sense may be defined as unwanted plants, not all unwanted plants become major weed problems. There are certain characteristics that serious weeds often have. You can watch this video for additional information about the characteristics of a “weed”. https://www.youtube.com/watch?v=hcFh--lia5s WEEDS, CROPS AND OTHER PESTS Relationship of weeds, crops and other pests Weed is a pest just as insects and disease organisms. It can be found everywhere infesting lawns, clogging waterways, filling up ponds, invading gardens and growing in pastures and forests. Weeds compete with crops for materials essential to growth like nutrients, water, sunlight and space. The value of plant and animal products may be lowered due to a weed. Weed also serves as alternate host for insects and disease organisms and may be poisonous to livestock. Human beings may suffer from allergic reactions to pollen produced from noxious weeds. However, a plant commonly described as a weed can be desirable if it grows on hillsides and controls soil erosion and if used as feed for livestock. Being familiar with the beneficial and harmful effects of weeds would bring about greater appreciation of their role in the agro ecosystems. Weeds are beneficial in some other ways to crop production. For example, the spiny amaranth (Amaranthus spinosus) is used as trap crop for the Asian corn borer when planted within the corn plantation. However, apart from being competitor for water, nutrients and light, it can harbor viruses as to the purple nut sedge (Cyperus rotondus) being an alternate host of rice virus. Larvae of various Lepidopterous insects in some instances are used to control some species of weeds. IMPORTANCE OF WEEDS OR BENEFITS OR ADVANTAGES DERIVED FROM WEEDS 1. Weeds add organic matter and nutrients to the soil 2. Weeds check wind, water and soil erosion 3. Some of the weeds used as Fodder for Animal 4. Some of the Weeds are used as Leafy Vegetables 5. Some of the Weeds have medicinal value 6. Some of the Weeds have Economic Importance 7. Some of the Weeds Serves as Ornamental and Hedge Plants 8. Certain Weeds have Nematicidal Properties (Control of Nematodes) IMPORTANCE OF WEEDS OR BENEFITS OR ADVANTAGES DERIVED FROM WEEDS  In conclusion, weeds can be a source of feed, food and medicine. It also serves as fertilizer and hosts for beneficial insects and etc. We just need to look closer, understand deeper and appreciate their purpose. CLASSIFICATION OF WEEDS Weed categorization entails grouping weeds together. They are classified according to the following categories: 1. According to their life cycle a) Annual – weeds having a life cycle of less than a year to one year or within one growing season. Examples: Phyllanthus niruri Phyllanthus niruri Euphorbia hirta b) Biennial- weeds that complete their life cycle within a period of two years. They germinate, emerge, and usually form a rosette in the first year. Example: Wild carrot (Daucus carota subsp. maximus) c) Perennials – weeds that thrive for more than two years and reproduce vegetatively or by seeds. 1. Simple perennials – propagate only by seeds. Examples: Chromolaena odorata Sida acuta (pc)dreamstime.com (pc)en.wikipedia.org  2. Creeping perennials – propagate by seeds and vegetative parts such as rhizomes, runners, stolons, tubers and bulblets. Examples: Centella asiatica Commelina diffusa (pc)en.wikipedia.org (pc)swbiodiversity.org 2. According to Habitat a) Terrestial – weeds living on land. Subcategories: 1. Rice field weeds 2. Garden weeds 3. Grassland weeds 4. Wasteland weeds 5. Forests weeds 6. Weeds in fields  b) Aquatic – weeds living in water. Subcategories: 1. Floating – weeds that are not anchored in the soil. They grow on the water surface. Example: Eichhornia crassipes 2. Emergent – weeds with their roots attached to the soil and the leaves are above the water surface. Example: Monochoria vaginalis 3. Submergent – weeds with their roots attached to the soil and are totally under water. Example: Hydrilla verticillata c. Epiphytic – this group of weeds needs a host plant to support, it has no roots but cling to trees by tiny scales. Example: Lichens, algae, ferns, orchids 3. According to morphology a) Grasses – belong to family Graminae. They have cylindrical hollow stem composed of nodes and internodes. The leaves are narrow with parallel veins. A membranous outgrowth at the junction of the leafsheath and leafblade called ligule varies in length among species. with long leaf blades with parallel veins belong to the Graminae or Poaceae families with distinct nodes and internodes alternate leaf arrangements presence of round stems Eleusine indica (Goose grass) Sedges – belong to family Cyperaceae. Similar to grasses and can be distinguished by a triangular solid stem without node and internode. with long leaf blades with parallel veins no nodes and internodes absence of ligule fusion of leaf sheath forming a tube around the stem with angular or triangular stems. With whorl leaf arrangements Cyperus rotundus (Nut sedge) (pc identify.plantnet.org)  Broadleaves – belong to other families. They have expanded leaves that are net vein with various size, shape and arrangement. those belonging to the other families of dicots and monocots leaf blades are broad and fully expanded Ipomea triloba (Kamote-kamotehan) 4. According to growth habit a) Creeping – weeds with parts are creeping on the ground. Example: Cynadon dactylon b) Vines- weeds that are usually common among plantation crops like in banana, pineapple, etc. c) Shrubs- these are weeds that are common in cattle ranches in the Philippines examples are the Chromolaena odorata and Lantana camara d) Trees –there several trees that are considered as they are grown out of place. 5. According to body texture a) Herbaceous – most weeds are herbaceous in body texture and can be easily controlled chemically. Example: Portulaca spp. d) Woody- weeds with woody body texture are harder to control. Example: Lantana camara  Ten World’s Worst Weeds Pictures adopted from Holm et al. retrieved on November 13, 2018 available at hannahtomlisson.webly.com show the world’s worst weeds. V. EXPLORE (TASKS/ACTIVITIES) Form a group of 5 members. Explore at least 5 weed species (each country) native to ASIA, AFRICA and EUROPE. Make an infographic showing its characteristics, classification and contribution or influence on each country's agriculture industry. VI. DISCUSSION BOARD 1. Form a group composed of 3 members. Look for at least two persons (not from your classmates) to share/discussed with them about 3 most important learnings you gain from this topic. Record your activity. VII. POST – COMPETENCY CHECKLIST Answer the following questions accordingly. Encircle the letter which you think is the correct answer. 1. Which of the following weed species is an example of a broadleaf? a. Cyperus rotundus b. Imperata cylindrical c. Monochoria vaginalis d. Cynadon dactylon 2. The measure of the adoptive potential of a weed that enables it to survive in an environment, which continuously disturbed by man, is referred to as: a. Adaptability b. Persistence c. Phenology d. Sociability 3. The following species reproduce asexually EXCEPT: a. Cyperus rotundus b. Fimbristylis littoralis c. Cynadon dactylon d. Tridax prucumbens 4. A weed, which germinates that grows vegetative produces seeds and is able to live for more than two years is: a. Annual weed b. Dicot weed c. Biennial weed d. Perennial weed 5. Cyperus rotundus is able to persist because: a. It produces asexually b. It is a broadleaf c. Its seeds have long viability period d. It has cylindrical stem 6. Which of the following weeds could be found in the lowland rice a. Euporbia hirta b. Amaranthus viridis c. Lantana camara d. Monochoria vaginalis 7. Identification of weeds at the seedling stage is quite difficult because: a. Weeds belong to the same family are very similar in appearance in this stage. b. Weeds cannot be easily seen due to their small size c. Weeds tend to grow taller than crops d. Weeds do not grow at this time 8. The relationship of weed in relation to crop production is best described as: a. A product of natural selection b. A pest at a particular situation c. A plant without use. d. A plant grown out of place 9. A weed that is totally submerged in water is known as: a. emergent b. floating c. submergent d. terrestrial 10. An example of a woody plant is: a. Euphorbia hirta b. Cyperus rutundos c. Lantana camara d. Eleusine indica “Weeds are flowers too once you get to know them” -A.A Milne