- - AGRICULTURE CORE CURRICULUM - - (CLF7000) Advanced Core Area: PLANT AND SOIL SCIENCE (CLF7350) Unit Title: PLANT PATHOGENS AND PESTS ____________________________________________________________________________ (CLF7354) Topic: WEED CONTROL Time Taught in Year(s) 5 hours 3 AND 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson the student will be able to: Learning Outcome #: (F-15) - List and discuss five ways weeds cause damage and production loss. (F-16) - Collect, press, and mount fifteen weeds common to your area. (Use flower and/or seed stage.) (F-18) - Identify the difference between a contact and a systemic pesticide. (F-19) - Compare the effects of selective and nonselective herbicide. (F-20) - List the three plant growth periods when herbicides can be applied and advantages of each, namely preplant, preemergent, and post-emergent. (F-21) - Demonstrate four types of chemical application including band, spot, broadcast, and direct spray. Special Materials and Equipment: Materials to collect insects (description at the end of this topic). References: Hartman, H. (1988). PLANT SCIENCE. pg 238-242. Marer, P. (1988). THE SAFE AND EFFECTIVE USE OF PESTICIDES. pg 12-29. Wood, Powell, and Anderson. WEED SCIENCE. pg 1-51. Evaluation: Quiz by instructor TOPIC PRESENTATION: WEED CONTROL INTRODUCTION A. A weed may be defined simply as "any plant growing where it is not wanted". B. Weeds can be annuals, biennials, or perennials. C. Whether a plant is a weed depends entirely on how the plants affect the interests of an individual or community. WEED CONTROL A. Weeds are a problem because they cause production loss. 1. They reduce crop yields. 2. They increase cost of production. 3. Weeds reduce quality of crop and livestock products. 4. Some cause irritation and hayfever. 5. Some are poisonous to man, livestock and wildlife. 6. They spoil the beauty of turf and landscape plants. 7. They compete with crop plants: Shade them, take up water and nutrients, and a few are parasitic. B. Many of the most troublesome weeds now present here were introduced into this country from Europe during colonization and early settlement of our country. 1. Examples of these imports include Johnson grass, Russian thistle, Field Bindweed (Morning Glory), Canada thistle, and Klamath weed. 2. These are all perennials and proven to be persistent and difficult to control. C. Various methods are used to control weeds. 1. Historically primitive tools were used to cut out weeds. 2. Mechanical control is still being used, equipment like tractor-drawn disks, harrows, and various other implements are used. (Hoes are used widely.) 3. Mowing is helpful for some types of weeds. 4. Mulching is an effective way to physically control weeds in small areas. 5. Fire is used to control vegetation along roadsides, ditchbanks and other work areas. D. Modern weed control techniques have brought more scientific methods into use: 1. Preventive measures, such as reducing weeds in irrigation canals and use of clean seed are used to reduce sources of weed seeds. 2. In crop competition techniques, the crop plants are induced to grow so vigorously that they overcome the weeds. 3. Biological control works when a natural enemy of a weed can be introduced to a weed problem area. 4. Chemical weed control continues to be improved - giving us new materials that destroy weeds through many varied modes of action. (The way that the chemical destroys the target weed.) E. Weed control chemicals (herbicides) can be classified as either selective or nonselective. 1. Selective weed chemicals have a mode of action selective to only a single or small number of weed species. (e.g., 2,4-D is a selective herbicide for broad-leaved plants.) 2. Nonselective weed chemicals are effective against all vegetation to which they are applied. F. Herbicides can further be classified according to the timing of their application in relation to the growth cycle of the weeds or crops. 1. A preplant treatment is one that is incorporated into the soil before the crop is planted. a. The crop plant must be highly tolerant of the herbicide. b. It is safer on the crop and uses less herbicide than post emergence application. 2. A preemergent application is applied to the soil surface after the crop is planted but before emergence of the weed seedlings, the crop seedlings, or both. a. This method is also safer on the crop, and b. cheaper because of less herbicide needed than postemergent applications. 3. A Postemergent application is one that follows the emergence of the crop plants, or both. a. Costs are higher than preplant and preemergent treatments. b. It may not be as safe. G. Another classification of herbicides is by the method used for application. 1. In a broadcast treatment the whole area is covered uniformly usually by a liquid or granular herbicide. 2. Band treatment is when a relatively narrow band just covering the crop row is treated with herbicide. 3. Spot treatment indicates that herbicide sprays are directed to a clump of weeds (as in an orchard) or to a small area where a clump of perennial weeds has become established. 4. A direct spray is one that is in direct contact with the target weed. (The weed is present when you spray.) H. Herbicides can be classified as to whether they are contact or systemic. 1. A contact herbicide is a chemical that will kill a plant on contact. 2. A systemic herbicide is one that is taken up into the plant tissues and transported to other locations where it will affect pests. __________________________________________________________________ ACTIVITY: Have students collect, press, and mount fifteen weeds common to your area. Use flower and or seed stage. Suggestions and hints for collecting, pressing, and mounting plant specimens. 1. Select a representative sample of the weed specie. a. Include stems, leaves, flowers, seeds and roots. b. Dig up weeds to prevent damaging the roots. c. Shake plants to remove excess soil. 2. Record information (you will need this information later when you label your specimen). a. Location (where sample was taken) b. Description of site (characteristic of soil, terrain). c. Is weed an annual or a perennial? d. Date. e. Your name. 3. Carefully place weed on absorbent paper a. Take time to straighten plant parts and keep leaves from folding. b. Neatness will pay dividends later. 4. Place specimen in a plant press or in a stack of absorbent paper with a board with a weight on top. 5. Remove from press when adequately dry. a. Each type of weed will have characteristics that will require somewhat different treatment (fleshy leaves, thick stems, large flowers or seeds). b. Thick stems and some inflorescences can be cut in half (with the length of the stem) on the back side to reduce thickness. 6. Place on a permanent paper (Biology or Botany paper works well) and scotch tape or glue specimen in place. 7. Label properly. 8. A technique that works well and will give you a more permanent specimen is to: a. Cover the weed sample with clear contact paper (usually available in 6'x18" rolls). b. Some practice is required so that you avoid wrinkles forming in the contact paper. c. Suggest that you practice first with weed samples that can be easily replaced. d. Be sure to put your label in place before covering with contact paper. 9. Punch holes in your papers and place in a permanent binder. __________________________________________________________________ 7/24/90 sg #%&C