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General Plant Diseases

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

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.

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.

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.

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.

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.

Selecting annuals and perennials 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 are known and if the key pathogens on those plants can be identified.

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.

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.

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.

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

The bacterium Pseudomonas syringae, is an opportunistic pathogen that can attack a wide variety of woody plants especially when they are damaged by frost or injured in some way.

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.

Most plant diseases cause a loss of yield or damage the aesthetic qualities of the infected plant. Certain diseases of trees, however, weaken their structure and create a hazardous situation where property damage or serious bodily injury could result from falling limbs or the toppling of the entire tree.

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.

There are several fungi in the northeast that are responsible for loss of needles and mortality of spruce trees. In this video, you will learn how to identify the types of spruce trees that are affected, the symptoms of the two most common needlecast diseases, and what if any treatments are available.