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Bacteria are microscopic, single-celled organisms that have a cell wall. Their genetic material, a circular strand of DNA, floats inside the cell and is not surrounded by a nuclear membrane. Therefore, bacteria do not have a true nucleus as do plants, animals, and fungi.

Bacteria called Ralstonia solanacearum attack almost 200 plant species in 33 different plant families. This constitutes one of the largest known host ranges for any plant pathogenic bacterium.

Bedding plant production has become a specialized, energy-efficient, and highly-profitable business. The short period of time between seeding and selling the crop leaves no room for mistakes. Plant diseases cannot be allowed to reduce the quantity of plants for sale or to reduce plant quality by stunting plants or spotting the flowers and foliage.

When one living organism is used to inhibit the activity of a living plant pathogen, it is said to be a biological control agent (BCA).

The fungus Thielaviopsis basicola (Berk. & Br.) Ferraris is a soil inhabiting fungus that can cause root rot and branch dieback on a number of woody and herbaceous plants including holly, begonia, geranium, poinsettia, cyclamen, gerbera, and pansy.

The plant pathogenic fungus Botrytis is found virtually everywhere plants are grown. It is fast growing, can grow on many different sources of nutrients, survives well in the greenhouse, and can attack many different types of plants. The disease caused by Botrytis is commonly called Botrytis blight or gray mold.

Cucumber mosaic virus (CMV) was named for one of the first plants in which it was found. However, it can infect a very large number of different woody and herbaceous plant species.

Fungi belonging to the genus Cylindrocladium attack over 100 woody ornamentals including azaleas, rhododendrons, camellias, junipers, white pine, and holly. Many foliage plants including asparagus ferns, palms, and spathiphyllum are susceptible as well.

Damping-off is the rotting of seeds in the soil and destruction of newly emerged seedlings by fungi.

Many things make plants unwell. Diseases are only one cause of poor plant growth. In diagnosing problems of plants from the production area, the retail area, the landscape, or home all the possible causes of poor or abnormal growth must be considered.

Prewash tools, benches, and equipment to remove soil and plant debris because disinfestants do not penetrate these well.

Downy mildew is the common name for a group of highly specialized obligate parasites of vascular plants. These organisms are distinctly different from the powdery mildews.

Root rots of floricultural and woody ornamental crops are one of the most important causes of crop loss.

A fungicide disrupts either energy producing reactions or a chemical building (synthesis) reaction within the target fungus. The way it kills the fungus is termed the fungicide's 'mode of action.'

The following is a guide to assessing the threat of disease in a nursery operation.

The following is a guide to assessing the various procedures and equipment used in a greenhouse, keeping in mind the threat of pathogen, mite, and insect population development in the crops being grown in a particular greenhouse.

The objective of heat treatment of soil is to reduce the numbers of weeds, insects, and disease-causing organisms in the soil and thereby promote plant vigor, increase yield and quality and decrease the need to use pesticides later in the production cycle.

Selecting plants for placement in the interiorscape as well as monitoring them for diseases and planning appropriate disease management strategies can be simplified if the key plants used in the interior are known and if the key pathogens on those plants can be identified.

Selecting plants for placement in the landscape as well as monitoring them for diseases and planning appropriate disease management strategies can be simplified if the key plants in the landscape are known and if the key diseases on those plants can be identified.

‘Organic’ methods involve growing and maintaining healthy plants without using synthetic (man-made) fertilizers, pesticides, hormones, and other materials. In organic disease control, natural materials (things found in nature or that exist in the environment) can be used to inhibit or prevent the activity of plant pathogens.

Over-fertilization of commercial pot or container-grown crops results in high concentrations of soluble salts in the potting medium.

Plant injury (phytotoxicity) may occur when chemicals are employed to protect plants from pests, fertilize plants, regulate plant growth, etc.

A few of the common powdery mildews and the plants that each can infect are listed below.

Powdery mildew occurs on many different flowers, woody ornamentals and trees including roses, snapdragons, African violets, kalanchöe, English ivy, zinnias, photinia, oak, lilac, and begonias.

While root rot can be caused by several different species of the fungus-like organism Pythium, the most commonly encountered species in the northeastern U. S. are Pythium irregulare, Pythium aphanidermatum, Pythium cryptoirregulare and Pythium ultimum.

It is very helpful to know where information can be obtained to diagnose and learn more about plant diseases.

It is very helpful to know where information can be obtained to diagnose and learn more about plant diseases.

The pathogenic fungus, Rhizoctonia, is known to cause root rots, stem rots, damping-off and, in some cases, a blight of leaves. It is a soil-borne fungus favored by warm, moderately moist soil conditions.

Where do diseases begin? The greenhouse manager who can answer this question is in an excellent position to prevent losses due to plant pathogens by reducing or eliminating the numbers of pathogens at their source.

Where do diseases begin? The nursery manager who can answer this question is in an excellent position to minimize losses caused by plant pathogens by reducing or eliminating the numbers of pathogens at their source. The major sources of living things that commonly plague nursery crops are noted here.

Tobacco mosaic virus (TMV) is named for one of the first plants in which it was found in the 1800s. However, it can infect well over 350 different species of plants.

Viruses are submicroscopic entities capable of causing disease. They are a piece of nucleic acid (genetic material) surrounded by a protein coat. Once inside the plant cell, the nucleic acid portion directs the plant cell to produce more virus nucleic acid and virus protein, disrupting the normal activity of the cell.

Wettable powder pesticide labels list the amount to use in terms of pounds per 100 gallons. When lesser amounts are to be mixed, growers, homeowners, and even university personnel frequently follow the old rule of thumb that 1 lb/100 gal = 1 tablespoon/gal.

Informational table showing disease name, symptoms, pathogen/cause, and management of African Violet diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Aglaonema diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Aster diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Baptisia diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of begonia diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Calceolaria diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Carnation (Dianthus) diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Catharanthus (annual vinca) diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Christmas cactus diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Chrysanthemum diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Cineraria diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Cordyline (Ti Plant) diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Crassula (Jade Plant) diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Cyclamen diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Dahlia diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Delphinium diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Dieffenbachia diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Dracaena diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Easter Lily diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Echinacea diseases.

Edema is a disease that affects geraniums, causing leaves to yellow and die. It is thought to be due to adverse environmental conditions. Therefore, it does not spread from plant to plant.

Informational table showing disease name, symptoms, pathogen/cause, and management of Exacum diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Fern diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Ficus diseases.

While most nematodes are soil-dwelling, the foliar nematode Aphelenchoides lives only briefly in soil. More importantly, it lives on the above-ground portions of plants, often without causing any obvious symptoms.

Informational table showing disease name, symptoms, pathogen/cause, and management of Fuchsia diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Gaillardia diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Gazania diseases.

Bacterial blight of geranium is the single most important disease of geraniums.

Informational table showing disease name, symptoms, pathogen/cause, and management of Geranium diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Gerbera diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Gladiolus diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Gloxinia diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Goldenrod (Solidago) diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Gypsophila diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Hemerocallis (Daylily) diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Impatiens diseases.

Two closely related viruses, Impatiens Necrotic Spot (INSV), and Tomato Spotted Wilt Virus (TSWV), once called the I-strain and L-strain of tomato spotted wilt, have been widespread and devastating in the greenhouse industry.

Informational table showing disease name, symptoms, pathogen/cause, and management of Iris diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of English Ivy (Hedera) diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Grape Ivy (Cissus) diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Kalenchoe diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Lily Of The Valley (Convallaria) diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Maranta diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Marigold diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Narcissus diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Norfolk Island Pine diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Palm diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Pansy diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Petunia diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Philodendron diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Poinsettia diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Pothos diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Primula diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Rose Diseases (Greenhouse) diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Rudbeckia diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Schefflera (Brassaia) diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Snapdragon (Antirrhinum) diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Spathiphyllum diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Statice diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Syngonium diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Tulip diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Verbena diseases.

Informational table showing disease name, symptoms, pathogen/cause, and management of Zinnia diseases.

Biotic diseases involve fungi, bacteria, viruses, nematodes, etc., and abiotic diseases involve non-living things. Of the two major types of disease, abiotic diseases are by far the most important ones on landscape and nursery plants.

Informational table showing disease name, symptoms, pathogen/cause, and management of Amelanchier diseases. (Shadbush, Serviceberry)

Ash (Fraxinus), oak (Quercus), sycamore (Platanus), maple (Acer), dogwood (Cornus), and many other deciduous hardwoods are susceptible to a leaf disease called anthracnose that is caused by various species of the fungus Apiognomonia.