 Weeds are plants that you don't want in your school landscape. They invade empty spots and lawns, cover bare soil, or creep in unplanted areas. They tend to grow in areas that are wet or over-watered. Even desirable plants that you want in your landscape can invade areas where you don't want them and become weeds. Weeds may be unsightly, cause health problems, or have other undesirable impacts. Weed populations vary from season to season. You don't have to let weeds take over your school. You can reduce most weed populations to tolerable levels and prevent large invasions with an integrated pest management program. This presentation will show you how to carry out an IPM program for weeds. We'll explain what an IPM program is, give you tips for identifying weeds and understanding their biology, discuss weeds that are particularly troublesome, and various strategies for managing them. We will stress the importance of prevention, including practices such as hand-weeding and cultivation, using mulches, and planting with competitive plants. We will discuss how and when to use herbicides as part of an IPM program. At the end of the presentation, there will be an interactive component that will give you a chance to review and discuss the concepts you've just seen. So let's get started and learn how to manage those weeds. Weeds are managed for a variety of reasons. Weeds can crowd out desirable plants and look untidy, provide hiding places for pests such as insects, rats, and mice, and interfere with other types of pest control operations around structures. Another reason is that some weeds may pose some sort of hazard. Clover in lawns where children play is a concern since it attracts bees, especially if there are any reports of bee allergies. Other weeds, if left unmanaged in sidewalk cracks or unplanted dry areas, can become tripping or fire hazards. Prickly weeds such as burr clover can also be problems. Integrated pest management or IPM uses environmentally sound yet effective science-based ways to keep pests from annoying you or damaging plants. IPM programs usually combine several pest management practices for long-term prevention and management of pest problems without harming you, the students, or the environment. Pesticides are applied as a last resort, and least toxic methods are used. In an IPM program, the goal is not to completely eliminate all weeds, but to keep them at a level that you can live with. The landscape maintenance supervisor generally decides when management is required, although administrators and others may have a say in the standards. Do you want nice-looking school grounds, but don't have a large staff to keep it tidy? Do you want to save money while protecting the environment? You can do all of this using an IPM approach. Create an IPM-friendly landscape using a combination of preventive methods such as mulches and competitive plantings, and you can stay on top of your weed problems. If you don't plan ahead and prevent weeds from establishing weeds, can get the upper hand. It is important to monitor the school regularly for weeds to see where, when, and which weeds are invading. Knowing what type of weed you have is necessary to determine the best management strategy. There are three general categories of weeds, broad leaves, grasses, and sedges. Broad leaves, such as oxalis, have wide leaves of various shapes with veins branching out in various directions. Grasses, such as Dallas grass and large crab grass, have narrow leaves with parallel veins arranged in sets of two with round or flattened stems. Sedges, such as yellow nut sedge, have leaves arranged in sets of three with stems triangular in cross-section. Remember, sedges have edges. It is really important to identify your weed to species so that you can choose the most effective management practice for that weed. Many weeds are similar in appearance, but may require a different approach to management. For more information on identifying and managing your weeds, check out the UC IPM website. You'll find several resources available on weed identification, including a pest note series, a weed photo gallery, and a key to weeds in lawns. For even more help in weed identification, take your weed to your local Cooperative Extension office. The plants that become weeds are successful because they are very competitive and invasive. In addition to common weeds, watch out for invasions of lawn grasses and vigorously growing ground covers into areas of your landscape where you don't want them. Weeds reproduce quickly and spread by seed or plant parts such as fleshy roots, tubers, or stolons, which are stems that creep along the ground, or rhizomes, which are underground stems. Weeds or other undesirable plants often invade landscapes, gardens, or lawns that are either poorly maintained or not cared for properly. Often identifying the weed present can give you an idea of an underlying problem. Once you know the cause of the problem, you can take measures to fix it. Keeping a record of what weeds you find around your yard can be helpful to determine if certain weeds are increasing or decreasing in response to your management actions. Here are some maintenance problems and weeds that commonly result from them. Areas that are over-watered or waterlogged can become infested with weeds such as annual bluegrass, crabgrass, or nut sedge. Compacted soils or bare areas are often infested with knotweed or spotted spurge. Lawns low in nitrogen fertilizer are susceptible to weeds such as clover, burclovers, and black medic. Thin areas in lawns are susceptible to dandelion invasions. Lawns mowed too short are susceptible to Bermuda grass invasions. Understanding the life cycle of weeds is key to managing them. Weeds are generally grouped as annual weeds or perennial weeds. Annual weeds complete their life cycle in one season. Annual weeds sprout from seeds, grow and develop flowers, and produce more seeds before dying. Some common annuals include spotted spurge, crabgrass, annual bluegrass, and south thistle. You want to control annual weeds before they flower and produce seeds because they can produce another population for next season. Perennial weeds are much harder to manage than annual weeds. Perennial weeds, such as Bermuda grass or Oxalis, live for more than one season. Plants grow from seeds or vegetative plant parts during part of the year. They mature and then die back when the weather changes. The underground plant parts can overwinter and form new plants the following season. It is easier to manage perennial plants before they can become established. Perennial weeds are hard to control because they can produce seeds and also spread by tubers, underground roots, or other vegetative parts such as stolons and rhizomes. Control perennials before these vegetative parts or seeds form. Manage weeds before you plant, before the weeds emerge, and before weeds mature. Plan and design your landscape and properly prepare your site to prevent weed problems before you plant. Plant competitive species, develop dense plantings, and apply mulches to discourage weeds from emerging. Once weeds have emerged, regular cultivation and mowing are your key tools. The smaller the weed, the easier it is to control it. Do not let weeds go to seed or develop tubers or other vegetative or reproductive parts because your management problems will be multiplied many times over. In areas not yet planted, manage weeds before you plant. Dig out existing vegetation, including buried vegetative parts of weeds. Cultivate the soil, irrigate to let weeds germinate, and then cultivate the area again to remove newly germinated seedlings. Soil solarization can control most weed seeds after vegetation is removed. However, it requires that a clear plastic tart be placed on the soil surface for about four to six weeks during the hottest part of summer. If you have serious weed problems with perennials or for very large areas, an application of a non-selective herbicide may be warranted. Switching from sprinkler irrigation to drip or other low output irrigation systems in landscape beds can reduce water use and extensive weed growth. Your soil type and plant selection are key components in preventing weeds. Soils must be able to hold enough water and nutrients so that your desired plant can establish a healthy root system, yet they must also have good drainage so that they do not become waterlogged. You can amend your soil before planting, but be sure to get soil from a reputable site. Confirm with your supplier that it does not contain herbicide residues, weed seeds, nutsedge tubers, or other propagules. Try to establish new plantings as quickly as possible so that weeds will not have a chance to take over. In landscapes, plant vigorous plants that are adapted to local conditions. Plant ground covers or other plants that will cover bare area so that they can shade out weeds. For lawns, plant a grass species that grows well in your area. Mulches are very effective at preventing weed germination and growth. A mulch is a layer of material that is put on the soil surface around plants to prevent weeds from growing. Seedlings need light to grow, and mulches block the light and suppress the growth of many weeds. Many mulches also help to hold moisture in and reduce soil compaction and erosion. Some mulches even improve the soil by adding nutrients. Many materials are available as mulches. There are organic mulches that include wood chips, bark chips, sawdust, leaves, or compost, rock mulches, and synthetic mulches such as plastics or fabrics. Any mulch that can be thrown, such as a rock or large pieces of wood or bark, may be unsuitable to use around a school. Avoid mulches such as hay that may contain weed seeds. Proper application of mulches can really help to reduce weed populations. Before applying any mulch, make sure there are no large weeds and be sure to control perennials. Organic mulches can be very effective if applied correctly. There are various types of organic mulch, and they differ by the size of their particles. The key to applying organic mulch is to apply it to an adequate depth that keeps light from reaching the soil. Be sure to keep mulch away from the base of woody trees and shrubs. Medium to small mulches, such as wood shavings or small wood chips about three-quarter inches, should be applied three to four inches deep. There are very fine mulches such as compost or leaf mold that can be applied about two inches deep. However, these mulches may not control weeds because weed seeds can blow in and grow. Very large and throwable mulches such as bark, wood, or rock should not be used at schools. Organic mulches gradually break down and need to be replenished in order to remain effective. They are more effective and longer lasting if applied over a landscape fabric. Plastics and barrier fabrics are two types of synthetic mulches that are used under organic or rock mulches. Use landscape fabric and avoid the use of plastic mulches. Unlike plastics, landscape fabrics allow water and air to pass through them and last a long time. They should not be exposed to the sun. To install, put the fabric down with U-shaped nails. Be sure to overlap the edges. Cut an X in the fabric and dig a planting hole. Avoid leaving the soil from the planting hole on top of the fabric as this could put weed seeds above the material. Place the plant into the hole and cover the fabric with a shallow mulch layer about one inch deep. If you are applying fabric to an already planted landscape, lay the cloth close to the ground using U-shaped nails. Cut an X over the plant, pull the plant through the cloth, and cover the fabric with mulch. In order to remain effective, mulches must be maintained. Applying mulches too deep may keep the soil too moist and lead to the development of disease. Not applying mulches deep enough can allow weeds to grow through the mulch. Replenish mulch as needed and keep it at the proper depth for the type you are using. Keep in mind that even if used properly, mulches will never provide 100% control. Some perennial weeds may get through even thick layers of mulches. Some annual weeds may germinate and grow on top of them as they decompose. If weeds appear, remove them by hand when they are small and avoid disrupting the mulch. Mulching makes hand-weeding easier. You can keep your weeds down if you remove them as soon as you see them. Remove them when they are small before they have set seed. The easiest way to remove them is to just pull them out. However, hand-weeding is not practical for large areas in a school. To control perennial weeds, you must dig up and destroy all roots and underground stems and tubers. Weed knives, dandelion knives, or even screwdrivers can help dig out the weeds and their roots without much disturbance to the soil. Annual weeds can be controlled with various types of hose. Use a garden hoe to cut weeds with a chopping motion at the soil surface or slightly below the soil surface. A push-pull hoe or a hula hoe can be used for the same purpose, scraping back and forth on the surface of the dry soil to cut small weeds off at their basal stem. Portable weed trimmers or weed eaters can break older weeds or small woody weeds. In lawns, regular mowing will keep weeds down. Hot water and flaming are two alternate ways to control weeds. Hot water or steam treatments are most effective against annual or young perennial weeds and are usually applied as a spot treatment along fence lines or in pavement cracks. Apply treatment to foliage and stems. Established perennial weeds can regrow. Flaming with a propane torch can control weeds on bare soil along fence lines and in pavement cracks. Flaming is most effective against young annual weeds. Perennial weeds and grasses can regrow. Kill weeds by passing the flame over the leaves. This causes the cells in the plant to burst. There is no need to char the weed. Flaming when winds are high or on poor air quality days. Don't use flamers near wood chips, dry weeds or other flammable materials. You can start a fire. Herbicides are pesticides that are designed to control weeds. A well-designed and well-maintained landscape generally does not require herbicides. Using garden tools and mulch usually provide adequate control. Use herbicides for special problem situations such as infestations of difficult-to-control perennial weeds before establishing new plantings or in turf grass. Don't rely on them exclusively. Before doing anything, you need to figure out what your underlying problem is and work from there. For example, if you have crabgrass, you may be overwatering or have leaky sprinklers. Determine what is causing the problem and correct it. Once you have fixed the underlying problem, use preventive methods such as mulch, competitive plantings or cultivation that may make future herbicide use unnecessary. If you do use herbicides, choose one that is labeled for the type of weed that you are trying to control and that is safe for you to surround the other desirable plants in the area. When using herbicides, you must take special precautions to avoid injury to desirable plants. Herbicides are applied as pre-emergent or post-emergent and are selective or non-selective. Pre-emergent herbicides are applied before weed seedlings emerge from the soil while post-emergent herbicides are applied after weeds have emerged. Selective herbicides are designed to kill specific types of weeds such as broadleaves or grasses without damaging other plants. Non-selective herbicides kill all or most vegetation and can be the best choice when preparing planting sites. Apply post-emergent herbicides when the target weed is in the stage that is most sensitive to the product. This is usually when the weed is small and actively growing. Monitor regularly so that you know when the weeds are emerging and actively growing. If you use herbicides when weeds are small, you will need less material. In schools, herbicide use is usually limited to times of the year when school is not in session such as summer or holiday vacations. Do not apply post-emergent herbicides if rain is expected. Injury to many ornamental or garden plants may result when label instructions are not followed, but it also occurs when drift or runoff takes the herbicide to neighboring plants. Drift to damage can occur quite a distance away from the spray zone. Trees with roots growing under lawns may be affected by some herbicides applied to the lawn. Three herbicides that have been associated with plant injury are glyphosate, dicamba, and 2-4-D. Glyphosate is a non-selective herbicide and can cause injury on non-target plants. Roses are easily affected and leaves appear needle-like, yellow, or mottled with small growth. Dicamba is a selective herbicide for use on broad leaves and often used in weed and feed products in lawns. If not used according to the product label, dicamba can damage trees and plants, causing dwarfed or distorted foliage. 2-4-D is a selective herbicide that is often used in lawns to kill broad-leaf weeds. However, it can cause injury to nearby trees and shrubs if it drifts onto leaves. Be sure to use caution before, during, and after using any pesticide. Follow all directions on the product label and wear the proper protective clothing. Check the label for the active ingredient. Make sure it is labeled for the type of weed you are trying to control and that it is registered for the area where you are planning on using it. Only use the amount needed and mix it up appropriately. When using herbicides, avoid washing them into storm drains. Don't apply right before rain is expected and don't over-irrigate. As required by the Healthy Schools Act, make sure to post warning signs where pesticides are applied 24 hours in advance and 72 hours after application. Glyphosate is probably the most common herbicide used around schools. It can kill most weeds, but if not used correctly, it can also damage nearby desirable plants. Ready-to-use bottles of glyphosate are widely available, but the formulations in these premixed solutions may be too weak to control perennial weeds. Use a hand-held controlled droplet applicator or a low-pressure small pump sprayer with a flat or cone nozzle. Follow the rate listed on the label of the product using a formulation labeled for your specific use. Measure the correct amount of product. If the product label calls for it, add a few drops of a surfactant or wetting agent to allow for better spray coverage on the surface of the weeds. Some products already include a surfactant. After you add the product, rinse the measuring container and pour the rinse solution into the sprayer followed by the correct amount of water. Control perennial weeds when they are actively growing. Treatment will be more effective if weeds are not dusty or stressed for water. For small areas infested with perennial weeds, dig up the vegetative propagules, irrigate to control growth, and then treat when the new sprouts mature. For large areas, treat, irrigate, and then treat again after the new sprouts emerge. Weeds will decrease in your landscape if you have managed the area properly using competitive plantings, barriers such as mowing strips, well-maintained mulches, and drip irrigation or other low output irrigation system. Remove weeds regularly as you see them and before they set seed. For more information about integrated pest management for weeds, visit the UC IPM website or contact the UC Cooperative Extension Office in your county. For more information on school IPM, see the school IPM program website of the California Department of Pesticide Regulation.