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Unit Plant Science Problem Area Managing Plant Growth Lesson Plant Responses to Herbicide Applications Student Learning Objectives 1. Describe the types of herbicides. 2. Explain the selectivity of herbicides. 3. Discuss the time of application of herbicides. 4. Explain the areas of application of herbicides. 5. Discuss the guidelines for applying herbicides. 6. Understand safety precautions when using herbicides. 7. Explain Round-up Ready plants and herbicide applications. Terms Band Application Broadcast Application Carrier Contact Herbicide Directed Application Early Preplant Herbicide Nonselective Herbicide Postemergent Herbicide Preemergent Herbicide Preplant and Incorporated Herbicide Preplant Herbicide Preplant Surface Applied Herbicide Selective Herbicide Soil Sterilant Spot Application Surfactant Translocated Herbicide What are the different types of herbicides? A. Translocated (systemic) herbicides are taken into the plant through the roots or leaves and moved to a sensitive area such as a growing point or storage organ. Translocated herbicides are important in controlling perennial weeds with underground storage organs, but timing is important. B. Contact herbicides, also called nontranslocated herbicides, are not moved within the plant but simply kill the plant tissue it contacts. Most contact herbicides are nonselective. C. Herbicides can be classified by their mode of action. The method by which an herbicide kills depends on how the plant translocates and metabolizes the chemical. D. Some herbicides inhibit lipid or amino acid synthesis, chlorophyll formation, or photosynthetic reactions. Other herbicides act as growth regulators and interfere with normal metabolism, or disrupt cell membranes. How are herbicides selected? Herbicides are classified according to the way they destroy weeds. Herbicides can be classified as selective, nonselective, or as a soil sterilant. 1. A selective herbicide is one that will kill only certain types of plants. Most herbicides used on cropland are selective because they control weeds while doing little, if any, damage to the crop. A selective herbicide is not toxic to some plants because it can be metabolized into a nontoxic substance. 2. A nonselective herbicide is one that will kill any plant it contacts. Nonselective herbicides can be used with growing crops but extreme caution must be used to prevent crop damage. Nonselective herbicides are also used in noncrop areas such as right-of-ways and around buildings where total control of vegetation is desired. Nonselective herbicides may have little or no residual activity after application. 3. Soil sterilants are herbicides that prevent any vegetation from growing for a period of months or even years. Soil sterilants are never used on cropland, but rather are used in noncrop areas where complete control of vegetation is desired for a long period of time. 4. Whether a herbicide is classified as selective, nonselective, or as a soil sterilant will depend on the rate that it is applied to the soil or plant. How does the time of application classify herbicides? A. Preplant herbicide is applied before the crop is seeded and is usually applied as part of seedbed preparation. B. Early preplant herbicide is applied 10 to 30 days before seeding and may or may not be incorporated into the soil. C. Preplant surface applied herbicide is applied up to 10 days before seeding and is not incorporated into the soil. D. Preplant and incorporated is applied up to 10 days prior to seeding and immediately incorporated because it will evaporate or be broken down by sunlight. E. Preemergent herbicide is applied before the weeds and/or crop emerges but after the crop has been seeded. F. Postemergent herbicide is applied after the crop and weeds have emerged from the soil. What are the application areas of herbicides? A. Band application is treating narrow strips with herbicides. The strip centered on the seed drill, which is usually at the top of a row. 1. A Band is usually 10 to 12 inches wide. 2. This is an efficient way to manage weeds by applying herbicides close to plants. 3. Cotton and corn plants are common crops where band application is used. B. Broadcast application is treating the entire area of a field. 1. No Bands or strips are left untreated. 2. Broadcast application is used with pastures, lawns, and grain crops that are not in rows. 3. This application is used in places where cultivation cannot be used to destroy weeds. C. Directed application is treating only selected plants or target plants. 1. Method primarily used with trees. 2. Small trees to be culled were injected with an herbicide just above the ground. 3. Directed application has been used in row crops. Newer technologies with “smart” sprayers only apply herbicides where weeds are present. These sprayers use computers and photo detectors to determine the location of each weed. 4. This approach saves money by only spraying where weeds are present. D. Spot application is treating only certain areas in a field or pasture. 1. Locations where weeds are growing are targeted. 2. Saves in the cost of herbicide and labor to apply it. 3. Used along fence rows, around barns, and in crops where weeds are in spots. What are some guidelines for applying herbicides? A. Recommendations: Herbicide recommendations vary from one year to another. Most states annually release weed control guidelines. Only herbicides approved for a particular use should be applied. The rate and timing of application should comply with the approved use. B. Soil Type: The rate of herbicide to use with preplant and preemergence applications depends on the soil. Before buying and applying herbicide, determine the type of soil. Some herbicides are more effective in sandy soils than in clay and loam soils and vice versa. C. Stage of growth: The size and age of both weed and crop plants must be considered. The best results will be achieved when the weeds are small—preferably in the seedling stage. Larger weeds are more difficult to control. D. Form of Herbicide: Herbicides are typically in a liquid form. Some are mixed with pellets of fertilizer or other materials for specific uses, such as in lawns. E. A carrier is the material in which the active ingredient of a herbicide is mixed. Most carriers are water, but some are oil. A carrier dilutes the herbicide and reduces toxicity. Carriers provide a from that allows maximum safety and effectiveness when a herbicide is used. F. A surfactant is a material added to herbicide mixes to assure that the applied material spreads over leaves and does not bounce off. Surfactants are like soap. Surface tension between the leaf and herbicide is reduced to the material spreads over the leaf surface. Surfactants are sometimes known as wetting agents. In oil-based sprays, filming agents are used to help assure good coverage. What are safety precautions when dealing with herbicides? A. All herbicides must be used only as approved. B. Do not treat food crops that are near harvest. C. Properly store herbicides. D. Keep herbicides out of the reach of children or other people who are not responsible. E. Dispose of empty containers properly. F. Flush skin and eyes with water if contact is made with herbicides. G. Know the emergency telephone number in case of an accident. H. Protect wildlife and domestic animals. I. Wear proper personal protection, including clothes, respirators, hats, gloves, and boots. What are Round-up Ready plants? Weed control practices in soybeans have evolved over the past several decades. Before the introduction of herbicides, weed control was achieved by mechanical and cultural means. Herbicides began to replace tillage and cultivation practices as the primary weed control method for soybeans in the 1960’s, at which time, soilincorporated and preemergence herbicides became the dominant chemical weed control methods. Today, roundup-ready plants emerge as a profitable and efficient means to weed control. A. Roundup Ready® soybeans set a precedent in 1996, as they were the first Roundup Ready seed product to come to market in the United States. Since then, other Roundup Ready crops such as corn, cotton and canola have been introduced. B. All are tolerant to over-the-top applications of Roundup® herbicide—providing post-emergent weed control. C. Plants, using biotechnology, are made to withstand the application of the herbicide Roundup. D. Roundup Ready herbicide works by inhibiting the production of EPSPS, an enzyme necessary for the production of amino acids essential for protein production and plant growth. As a result, protein cannot be made and the plant system collapses leading to plant death. This process is found only in plants. Roundup Ready plants have been modified using genetic engineering techniques to increase its tolerance to applications of Roundup Ready herbicide. Review/Summary What are the different types of herbicides? How are herbicides selected? How does the time of application classify herbicides? What are the application areas of herbicides? What are some guidelines for applying herbicides? What are safety precautions when dealing with herbicides? What are Round-up Ready plants?