- - AGRICULTURE CORE CURRICULUM - - (CLF7000) Advanced Core Cluster: PLANT AND SOIL SCIENCE (CLF7500) Unit Title: SOIL TILLAGE, LAND PREPARATION AND CONSERVATION ____________________________________________________________________________ (CLF7502) Topic: USE OF HERBICIDES 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 #: (I-6) - Identify herbicides used for sterilization, clean up, and weed control. Special Materials and Equipment: Samples of herbicides containers; herbicides; mimeographed charts shown under activities of this topic. References: George W. Ware. THE PESTICIDE BOOK. CH 13. Hudson T. Hartman. PLANT SCIENCE. Pages 238 to 242. Evaluation: Quiz by instructor TOPIC PRESENTATION: USE OF HERBICIDES A. The introduction of 2,4-D in 1944 gave the initial impetus to chemical weed control. 1. Today the sale and use of herbicides is a multi-billion dollar industry, with sales surpassing those for insecticides and fungicides. 2. Early herbicides were generally broad-spectrum contact materials which are now being replaced by more unique chemicals that destroy weeds by varied and specific modes of action. B. Herbicides are called selective when they are used to kill weeds without harming the crop. C. A non-selective herbicide is one that's purpose is to kill all vegetation (clean up). 1. Both selective and nonselective materials can be applied to weed foliage or soil containing weed seeds and seedlings, depending on the mode of action. 2. Selectivity can be achieved by placement. A nonselective herbicide can be applied in such a way that it contacts the weeds but not the crop. 3. Each herbicide affects plants whether by contact or translocation. 4. Contact herbicides kill the plant parts to which the chemical is applied, being most effective against annuals. 5. Complete coverage is essential for contact herbicides. 6. Translocated herbicides can be effective against all weed types, but their greatest advantage is in controlling established perennials. D. Herbicides can also be classified as to the timing of application with regard to the stage of crop or weed development. 1. Preplant applications are made into the soil before the crop is planted. 2. Preemergent applications are applied to the soil surface after the crop is planted but before the emergence of the weed seedlings, the crop seedlings, or both. 3. Postemergent applications are applied following emergence of the crop seedlings, weed seedlings or both. E. Another method of classifying herbicides is by the method of application. 1. Broadcast application covers and entire area uniformly, either by spraying a liquid or spreading a granular form of herbicide. 2. Band treatment is the use of a relatively narrow band just covering the crop row (or orchard or vineyard row) with the herbicide. 3. Spot treatment is the directing of herbicide sprays to a single clump of weeds arising in a relatively clean area. This is typically used to treat small areas where a particularly difficult clump of weeds is established. F. Soil sterilizing herbicides are losing their favor. 1. Inorganic acids and salts have been used for some time as nonselective herbicides. 2. Several of these are still useful, especially for brush control. 3. The Environmental Protection Agency (E.P.A.) has placed many restrictions on these inorganic herbicides because of their persistence in soils. 4. The use of these materials should be left to experts. 5. These materials will often last for several years. A problem arises, then, when a parcel that has been treated has a change of plan for its use. It is difficult to rid the area of these chemicals once they are in the soil. G. When using herbicides or any other type of pesticide be sure to read the entire label before using the material and follow the directions exactly. __________________________________________________________ ACTIVITY: 1. Select ten herbicide containers. Have students read the directions and examine the labels. Have each student fill out a chart giving the following information on each herbicide: _____________________________________________________ Commercial | Scientific | Type of Name | Name | Formulation ______________ |__________________|__________________ | | | | | | | | | | | | | | | | | | _____________________________________________________ Restricted or | Type weeds | Toxicity Nonrestricted | Controlled | Category _______________|__________________|__________________ | | | | | | | | | | | | | | | | | | 2. Select individual weeds and treat them with different herbicides. Have students keep a daily log on changes that take place to the treated weeds. Note, especially how long it takes until the weed is controlled. ___________________________________________________________ 6/21/90 sg #%&C