Arkansas Plant Disease Management
Plant diseases arose and developed as plant life developed on earth. They have plagued man and have caused famines since the dawn of recorded history. There are over 80,000 different diseases of plants. A plant disease interferes with the normal structure and functions of our crop and non-crop plants and may affect the marketability or aesthetic value. Plant diseases can affect any part of the plant. They result from either an abiotic (non-living) agent or from a biotic (living) agent. Abiotic agents include environmental stresses that arise from temperature and moisture extremes, nutritional deficiencies and toxicities, and injuries caused by chemical or mechanical means. Biotic disease agents include the fungi, bacteria, viruses, and nematodes. The fungi cause the vast majority of biotic (infectious) diseases on all plants. Infectious plant diseases result from an interaction of a causal agent (pathogen) and a plant (host) when the time and environmental conditions are conducive for the interaction.
NOTABLE PLANT DISEASES
Ergot of Cereals
This fungus disease of cereals replaces the cereal grains with a hard fungal structure (sclerotia) that can be poisonous to humans that eat bread and animals that eat the feed made from the infected grain. Ergot is caused by Claviceps purpurea and other species. Rye is most commonly infected. Although ergotism is no longer common in humans, it was once a significant human disease during the middle ages. In 944 AD, 40,000 people died in southern France when the fungus infected grain was mixed with regular grain and milled for bread. Sometimes called "St Anthony's Fire" or "Holy Fire" because of burning sensations that consuming ergot caused in the extremities, considerable suffering among people became a major health issue. The victims' toes, arms and legs often became blackened as a result of gangrene.
Late Blight of Potato
Late blight of potato is caused by the fungus, Phytophthora infestans. It is most destructive in moist, cool weather regions. This fungus can also be destructive to tomatoes and other members of the family Solanaceae. Leaves and stems can become infected. Affected tubers and fruit develop lesions that spread rapidly. The rot continues after the crop is harvested causing a putrid odor and complete loss of the tuber. This disease was responsible for the infamous potato famines in 1845-1846 where more than a million people died of starvation and another million emigrated from Ireland. Irelands' population dropped by almost 25%.
In the early 1900s, a pathogenic fungus, Endothia parasitica, was accidentally introduced into North America. It proceeded to virtually annihilate the American chestnut. This was a popular and widespread timber tree along the eastern seaboard. The fungus produces cankers, that in turn cause splitting of the bark followed by tree death. Cankers girdle the stem, resulting in tree death. The fungus is spread by windborne and waterborne microscopic spores. Current research is focused toward using modern techniques to create resistance among the chestnut.
Sudden Oak Death
This disease was first reported in the U.S. in 1995. It is caused by the fungus-like organism Phytophthora ramorum. The organism spreads by wind and windblown rain or splashing water. Long distance spread is primarily through infected nursery stock. It is associated with the death of thousands of tanoaks in the area of California. Disease symptoms range from cankers to foliar blights. Since its discovery, the disease has been confirmed in Western forests and large ornamental nurseries in Oregon, Washington. By the end of 2004, infected plants have been identified in 171 nurseries in 20 states. This disease can also affect azaleas, camellia, myrtles, rhododendrons, and viburnum.
Plant disease management is a dynamic process that utilizes "IPM" or Integrated Pest Management as a strategy for managing pests. IPM combines biological, cultural, physical, and chemical control methods in a way that minimizes economic, health, and environmental risks. For integrated pest management (IPM) plans to be successful, they must begin with an accurate and timely diagnosis followed by the use of appropriate preventative and /or remedial strategies. Plant disease management is often based on one or more of the following methods: (1) Growing resistant varieties, (2) chemicals, (3) crop rotation, and (4) cultural practices.
The goal of IPM is to achieve long-term suppression of target pests with minimal impact on nontarget organisms and the environment.
There are five basic steps to follow when implementing an IPM Program:
Inspection / Monitoring for pest presence or damage
Establishment of an action threshold (when you should intervene to prevent intolerable damage
Employment of 2 or more control measures that are economically feasible & environmentally compatible from the following methods of control:
A. Cultural / Mechanical / Physical
B. Natural / Biological
Evaluation of effectiveness thru continued inspection / monitoring and adequate record keeping
The strategy of IPM is universal across all disciplines of pest management.