- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6300) Unit Title: DISEASES AND PESTS OF ORNAMENTAL PLANTS ____________________________________________________________________________ (CLF6302) Topic: WEED CONTROL Time Taught in Year(s) 3 hours 3 AND 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson the student will be able to: Learning Outcome #: (E-6) - List and discuss five ways weeds cause damage and production loss. (E-8) - Identify the difference between a contact and a systemic pesticide. (E-9) - Compare the effects of selective and nonselective herbicide. (E-10) - Demonstrate four types of chemical application band, spot, broadcast, and direct spray. (A) - Collect, press, and mount fifteen weeds common to your area (Use flower and/or seed stage) (B) - List the three plant growth periods when herbicides can be applied and advantages of each, namely preplant, preemergent, and post-emergent. Special Materials and Equipment: References: Anderson, Wood P. (1977). WEED SCIENCE. St. Paul, MN: West. Hartmann, Hudson T., Kofranek, Anton M., Rubatzky, Vincent E., & Flocker, William J. (1988). PLANT SCIENCE: GROWTH, DEVELOPMENT, AND UTILIZATION OF CULTIVATED PLANTS (2nd ed.). Englewood Cliffs, NJ: Prentice-Hall. Marer, Patrick J. (1988). THE SAFE AND EFFECTIVE USE OF PESTICIDES. University of California, Statewide Integrated Pest Management Project, Div. of Agriculture & Natural Resources, Publication #3324, 387 pages. Available from: Publications, Div. of Agriculture & Natural Resources, Univ. of California, 6701 San Pablo Avenue, Oakland, CA 94608-1239. (415) 642-2431 Evaluation: 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 or not a plant is a weed depends entirely on how the plant affects the interests of an individual or community. WEED CONTROL A. Weeds are a problem because they cause production loss to crops, rangelands, and landscaped areas. 1. They reduce crop yields by competing with the crop plant. 2. They increase cost of production. 3. Weeds reduce the quality of crop products. 4. Some cause skin irritation and hay fever. 5. Some are poisonous to people, livestock, and wildlife. 6. They can spoil the beauty of turf and landscape plants. 7 Weeds can harbor insects and diseases. B. Many of the most troublesome weeds now present in the U.S. were introduced from Europe during the years of colonization and early settlement. 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 have 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, for example, tractor-drawn disks, harrows, and various other implements. 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, providing new materials that destroy weeds through many varied modes of action. 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-leafed plants. 2. Nonselective herbicides 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 pre-plant 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. This method of treatment is safer on the crop and uses less herbicide than post-emergent application. 2. A pre-emergent 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 than post-emergent application. b. It is cheaper because less herbicide is needed than for post- emergent applications. 3. A post-emergent application is one that follows the emergence of the crop plants, the weeds, or both. a. Costs are higher than pre-plant and pre-emergent treatments. b. Post-emergent applications of herbicides are hazardous from both a safety and health standpoint. G. Another way to classify herbicides is by the method used for application. 1. Broadcast treatment is when 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 is when 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, i.e., 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 has its effect (i.e., roots). __________________________________________________________________ ACTIVITY: Have students collect, press, and mount fifteen weeds common to your area. Use flower and/or seed stage. Following are some suggestions and hints for collecting, pressing, and mounting plant specimens: 1. Select a representative sample of the plant species. a. Include stems, leaves, flowers, seeds, and roots. b. Dig up plants to prevent damaging the roots. c. Shake plant to remove excess soil. 2. Record the following information (which you will need later when you label your specimen): a. Location (where sample was taken) b. Description of site (characteristics of soil, terrain) c. Is plant an annual or a perennial? d. Date e. Your name 3. Carefully place plant 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 plant 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 plant sample with clear contact paper (usually available in 6' x 18" rolls). b. Some practice is required so that you avoid wrinkles forming in the contact paper; practice first with samples that can be easily replaced. c. 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. __________________________________________________________________ __________________________________________________________________ ACTIVITY 2: After demonstrating, have the students practice different methods of chemical applications. If you are using real chemicals, make sure that you practice good safety procedures. (Also review CLF6303.) You may want to substitute the listed items for real chemicals. 1. Use dye in water for a liquid spray. 2. Use sand for band or broadcast applications. __________________________________________________________________ 1/4/91 MT/clh #%&C