Preventative controls focus on limiting the spread and establishment of weed seeds. These methods can be grouped into five main categories: preventative, cultural, mechanical, biological, and chemical weed control. Farmers and ranchers use a variety of methods to control weeds. Agricultural ecosystems are regularly disturbed by actions such as tilling and grazing. Weeds are of particular concern in agriculture. When a change in the physical or biological components of an ecosystem damages existing plant populations, space opens up for weeds to move in. Often weeds become a problem in disturbed environments. However, some native species are also considered weeds. Many weeds are invasive species, meaning they have been introduced (they are not native) to an environment in which they have a tendency to spread rapidly, causing damage to the environment, human economy, or human health. Most weeds grow and spread aggressively, outcompeting more desirable plants. However, in Italian cuisine, dandelions are considered a desirable vegetable and in other cultures, dandelions are an important medicinal herb. For example, many homeowners consider dandelions growing in their lawns to be weeds. A weed is simply a plant that is undesirable to people in the location it is growing. The same plant can be a weed in one location and a desirable crop in another. Every species of plant has its own, individual characteristics these unique traits are the basis for creating and using a dichotomous key. To make a positive identification, farmers may rely on a dichotomous key, observing characteristics like the presence or absence of a defined stem the type and texture of the leaves the kinds of flowers and the type of fruit, pod, or other seed casing that the plant produces. Knowing the identity of the plants in a field, both wanted and unwanted, is important in helping a farmer target and eliminate any weeds that might interfere with his or her harvest. For example, farmers who grow row crops want to eliminate as many weeds as possible in order to ensure that they can harvest only the plant that they intend to sell. Taxonomy or taxanomic classification is a practice used by scientists to classify living and nonliving items for the purpose of identification. Though classification may seem like a complicated scientific process, it is actually intuitive and useful in both scientific and real-world settings. Whether the reader is on a different continent or even generations into the future, they should be able to identify the same item using the same classification scheme. Scientists use a detailed language to communicate with precision to others who read their work. The goal of a single-access or dichotomous key is to take an object or organism that is unknown and, following the key, make a positive identification of the item. *These items are included in the Seed ID Kit, which is available for purchase from. Note: While any seeds will do for this activity, some of the best to work with include seeds from the legume family (soybeans, alfalfa, peas, etc.) as well as seeds that students may be familiar with from the food that they eat that will be available at your local grocery store, including a wide variety of beans, popcorn kernels, pumpkin seeds, and sunflower seeds.Samples of up to nine different types of seeds*.Small "Mystery" envelopes, 1 per group*.Folders or manila envelopes labeled “Classified,” 1 per group*.Seed Classification Dichotomous Key activity sheet.Seed Classification Bracket activity sheet.Example of How to Create a Dichotomous Key handout. Weed Ecology and Control PowerPoint slides.America's Tumbleweeds Are Actually Russian Invaders article and associated video.
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