Horticulture Science Lesson 37 Identifying and Managing Plant Pests in the Greenhouse Interest Approach Bring one or more plants that are suffering from disease or insect problems into the classroom. Also bring in one healthy plant. Ask the students to explain why the infected plants could cause a problem. Ask them if the infected plants should be put in the greenhouse with the healthy plants. Ask them to explain their answer. Student Learning Objectives Identify the major pests found in the greenhouse. Discuss the management of greenhouse pests. Student Learning Objectives Describe the different practices of integrated pest management used in the greenhouse. Terms aerosols aphids aster yellows biological control botanical insecticides Botrytis blight caterpillars chemical control Terms cultural/physical control dampingoff dip drench Erwinia fumigants fungus gnats granular horticultural oils Terms insect growth regulators insecticidal soaps leaf miners mealybugs microbial organisms mites parasitic organisms Phytophthora plant health powdery mildew Terms predatory organisms Pythium Rhizoctonia sanitation scale spray Thielaviopsis tobacco mosaic Western flower thrips whiteflies What are the major pests found in the greenhouse? The health of crops grown in a greenhouse is challenged by a variety of pests and diseases. The ability to identify major greenhouse pests and diseases is the first step in a pest management program. Insect pests can severely damage or ruin a crop if their populations are not managed. What are the major pests found in the greenhouse? Aphids are pear-shaped, soft-bodied, usually wingless insects. They are often green or yellowish in color. Aphids have the ability to reproduce very rapidly. Astonishingly, they give birth to live young that are pregnant! Aphids use their mouthparts to pierce the plant and suck out juices. Aphids attack a wide variety of greenhouse plants. What are the major pests found in the greenhouse? Caterpillars are the larvae of various moth species. They damage greenhouse crops by eating the plants. Fungus gnats are long-legged, winged, gray-black insects less than 1/8 inch long. The larvae of fungus gnats feed on root hairs and tunnel into plant stems. They prefer a growing medium that is constantly moist. What are the major pests found in the greenhouse? Leaf miners are small, stocky flies. The adult deposits eggs inside a leaf. The eggs hatch, and the larvae feed on the interior of the leaf, making tunnels as they move along. Chrysanthemums are subject to leaf miner damage. What are the major pests found in the greenhouse? Mealybugs are slow-moving, oval-shaped, whitish insects. They have a waxy finish and produce small cottony masses. Mealybugs pierce plant leaves and suck the plant juices. As with aphids, they give birth to living nymphs. What are the major pests found in the greenhouse? Mites have eight legs and are related to spiders. Mites pierce leaf tissues and suck juices. Symptoms of damage include a yellow speckled appearance to the leaves, and, in severe cases, yellowing of the leaves and defoliation. Two spotted spider mites and red spider mites are among the most serious greenhouse pests. They appear as tiny specks on the plants and are often found on the undersides of leaves and near the apical meristems. What are the major pests found in the greenhouse? A two-spotted mite has two dark spots on its back. Spider mites create a complex network of webbing as they move about a plant. Cyclamen mites infest a broad range of plants and are not visible to the naked eye. Bulb mites damage lily bulbs and the developing shoots. What are the major pests found in the greenhouse? Many types of scale insects infest greenhouse plants. Typically, they have flat, oval, often brown bodies. They may or may not be covered with armored shells. Scale insects pierce plant leaves and stems and suck juices. Western flower thrips are small dark brown insects with two pairs of fringed wings. They have rasping mouthparts that scrape plant tissue. The damage they cause to many kinds of plants often appears as whitish discoloration. What are the major pests found in the greenhouse? Whiteflies are small white insects. They generally camp out on the undersides of leaves, where they pierce the tissues and suck juices. Their flat, scale-like larvae feed on the undersides of the leaves. Whiteflies are major pests of poinsettias and fuchsias. What are the major pests found in the greenhouse? Diseases affect roots, leaves, stems, and flowers of floriculture crops. 1. Botrytis blight is a fungal disease that can attack nearly all greenhouse crops and is a common problem with cut flower storage. It causes a brown rotting and develops fuzzy, gray mold as it produces spores. Botrytis blight is most common when temperatures are between 60 and 70F, air circulation is poor, and humidity is high. What are the major pests found in the greenhouse? 2. Erwinia is a bacterial disease that causes rotting of plant tissues. The bacterium enters the plant through wounds. It is a common problem on Dieffenbachia, Philodendron, chrysanthemum, and Cyclamen. What are the major pests found in the greenhouse? 3. Powdery mildew is a fungal disease. Characteristic symptoms include a white dusty coating to leaves and flowers. Infected plants can become stunted. High humidity contributes to powdery mildew problems. What are the major pests found in the greenhouse? 4. Pythium is a fungal disease that attacks greenhouse plants under cool, wet conditions. It is one fungus that can cause damping-off. Damping-off is the early death of seedlings that have germinated. More mature plants can develop root and stem rots as a result of Pythium, particularly when the growing medium has poor aeration. What are the major pests found in the greenhouse? 5. Phytophthora is a fungal disease similar to Pythium. It causes crown and stem rots in cool, wet conditions. What are the major pests found in the greenhouse? 6. Rhizoctonia is a fungal disease common in wet and warm conditions. It is a widespread disease problem in the southeastern region of the country. Rhizoctonia causes damping-off, as well as root and stem rots. What are the major pests found in the greenhouse? 7. Thielaviopsis is a fungus that causes root and stem rots. It favors cool, moist conditions. What are the major pests found in the greenhouse? 8. Tobacco mosaic and aster yellows are two common viral diseases associated with greenhouse crops. Symptoms of infection include discoloration of plant tissues, stunting of growth, and deformed growth. The spread from one plant to another is primarily by feeding greenhouse insects. Tobacco mosaic virus can be spread to the plants from the hands of workers who smoke. What is involved in the management of greenhouse pests? Healthy greenhouse crops are essential to a successful greenhouse business. Plant health refers to the condition of plants. Healthy plants are free of pests and disease. They have clean foliage and flowers, along with a good rate of growth. It is important that plants be healthy while they are growing and developing. It is also important that their health be maintained after they are sold. What is involved in the management of greenhouse pests? Healthy plants have a greater capacity to defend themselves against plant pests than plants under some type of stress. Plant stress is usually associated with environmental conditions. Improper watering weakens a plants ability to fight off infectious diseases, including root rots. High humidity in greenhouses is ideal for many fungal diseases. What is involved in the management of greenhouse pests? Growers have control over many environmental factors that can keep plants healthy. 1. Care can be taken to provide a growing medium with the desired drainage, aeration, and pH. 2. Plants can be planted at the proper planting depth. 3. Optimum nutrient levels can be maintained with fertilizers. 4. One of the most important factors is to follow recommended watering practices. 5. Temperature, light intensity, and air quality can also be adjusted to meet the needs of the specific crop. What is involved in the management of greenhouse pests? No matter how well crops are grown, pests and diseases will become problems from time to time. The very nature of greenhouse crop production leads to some disease problems. In most cases, crops are of the same species, variety, or cultivar. Being of identical genetic makeup, they are vulnerable to infectious disease that can easily spread from one plant to another. Greenhouses also tend to be humid, which is ideal for many fungal diseases. What are the different practices of integrated pest management used in the greenhouse? The IPM program for greenhouse crops must be year-round. IPM control measures for a specific crop (e.g., poinsettias) should begin before the plants enter the greenhouse. Four broad areas of control include sanitation, cultural/physical control, biological control, and chemical control. What are the different practices of integrated pest management used in the greenhouse? Many pest problems can be greatly reduced or eliminated with greenhouse sanitation. Sanitation is simply the efforts made to keep a greenhouse clean. What are the different practices of integrated pest management used in the greenhouse? 1. Weeds should be removed from the interior of the greenhouse and the immediate area outside the greenhouse. Weed control is extremely important. Weeds harbor pests. Pests migrate from the weeds to the greenhouse crop to cause damage. Some greenhouse ranges have been built with concrete floors, in part to eliminate habitat for pests. A few herbicides are labeled for use inside the greenhouse. What are the different practices of integrated pest management used in the greenhouse? 2. Plant debris and other debris should be removed from the floors and benches. Debris often houses disease organisms and pests. Also, severely infested or infected plants should be removed and disposed of properly. What are the different practices of integrated pest management used in the greenhouse? Cultural/physical control consists of those methods that physically prevent activities of pests. Major advantages to cultural/physical controls are that they are safe to humans. 1. The first line of defense against plant pests is to prevent their introduction to the greenhouse. All plants should be thoroughly inspected before they are admitted into the greenhouse. Accept only clean plants purchased from reputable suppliers. What are the different practices of integrated pest management used in the greenhouse? 2. Another practice is to maintain the ideal growing environment for the crops. As mentioned, plants that are healthy are better able to fight disease organisms and pests. A good analogy is people and colds. People who eat right, exercise, get plenty of rest, and are under little stress are more resistant to colds. People who eat poor diets, are out of shape, get little sleep, and are stressed out are more susceptible to colds. What are the different practices of integrated pest management used in the greenhouse? 3. Good air circulation around the greenhouse plants reduces the incidence of fungal diseases. Fungal diseases grow and spread when moisture covers plant leaves. Air circulation helps to keep plant leaves dry. 4. Screens can be used over greenhouse openings. The fine mesh of the screens prevents pests from entering the greenhouse environment. What are the different practices of integrated pest management used in the greenhouse? 5. Yellow sticky traps used to monitor pest populations also serve as a means of physical control. Flying insect pests are attracted to sticky traps, fly onto the traps, get stuck, and die. What are the different practices of integrated pest management used in the greenhouse? Biological control involves the use of microbial, parasitic, and predatory organisms to control pests. Biological control organisms are found in nature and, therefore, are considered environmentally safe. What are the different practices of integrated pest management used in the greenhouse? 1. Microbial organisms include bacteria and fungi. A prime example is a bacterium, Bacillus thuringiensis, which effectively controls caterpillars. Some species of bacteria and fungi can be used to control aphid and whitefly populations because they are natural diseases of those insects. What are the different practices of integrated pest management used in the greenhouse? 2. Parasitic organisms help to control some pests. The parasites are natural enemies of the pests and live off the pest organisms. An example of a parasitic insect used in greenhouses is a tiny parasitic wasp. It lays its eggs on whitefly larvae. The eggs hatch with the wasp larvae inside the whitefly larvae. The wasp larvae slowly weaken and kill the developing whiteflies from within. Each female wasp lays eggs in up to 200 immature whiteflies. What are the different practices of integrated pest management used in the greenhouse? When the wasps mature, they emerge from what is left of the whiteflies, mate, and look for whitefly larvae on which to lay the next generation of eggs. a. It should be noted that chemical pesticides cannot be used in the greenhouse without killing the beneficial parasites. b. The parasites are also not effective with heavy infestations of plant pests. What are the different practices of integrated pest management used in the greenhouse? 3. Predatory organisms can be purchased and released in the greenhouse to devour certain plant pests. Ladybugs eat aphids. A mite is an effective control of thrips. A specific beetle is freed to attack whitefly larvae and adults. As with parasitic organisms, chemical pesticides should not be used when predatory organisms are introduced. What are the different practices of integrated pest management used in the greenhouse? Chemical control is the use of pesticides to control pests and diseases. Chemical control is often applied only when absolutely necessary. Pesticide application must be done safely to reduce potential injury to people and the environment. 1. Pest control has been made safer with the introduction of less toxic pesticides. This group of soft pesticides includes botanical insecticides, horticultural oils, insect growth regulators, and insecticidal soaps. What are the different practices of integrated pest management used in the greenhouse? a. Botanical insecticides are natural materials obtained from plants that are toxic to insect pests. b. Horticultural oils are sprayed on the insects to clog their breathing pores, causing suffocation. c. Insect growth regulators disrupt the growth and development of the insects. d. Insecticidal soaps dissolve the protective membranes of insects, bringing on death. What are the different practices of integrated pest management used in the greenhouse? 2. There are several methods used to apply pesticides in the greenhouse. a. Aerosols consist of atomized spray or smoke particles distributed through the air. Cans containing the pesticide can be set to release the aerosol, thus creating a fog in the greenhouse. Once the aerosol is started, the applicator can safely leave. b. A dip is a pesticide mixed with water for the purpose of submerging plants. Easter lily bulbs are commonly dipped in a miticide before planting to control bulb mites. What are the different practices of integrated pest management used in the greenhouse? c. Some materials are used as a drench, which is a solution of pesticide mixed with water that is simply poured into the pots. A common practice is to drench poinsettias with a fungicide to control soilborne disease. d. Fumigants are poisonous gases distributed through the air to all parts of the greenhouse. They are particularly effective with flying insects and pests exposed to the gases. What are the different practices of integrated pest management used in the greenhouse? e. Some pesticides are in a granular or pellet form. They are carefully measured and applied on the surface of the growing medium. These pesticides are referred to as systemic. When plants are watered, the roots absorb the pesticides into their systems. What are the different practices of integrated pest management used in the greenhouse? f. Pesticides may be applied as a spray on the plant. The small droplets of the spray cover the surface of the plant. Care must be taken with a spray to cover parts of the plant where the pest is found, such as the underside of the leaves. Review/Summary What are the major pests found in the greenhouse? What is involved in the management of greenhouse pests? Review/Summary What are the different practices of integrated pest management used in the greenhouse?