PLANT PROTECTION UNIT
NEMATODES
Nematodes are probably the most numerous Multi-cellular animals in the world and are found in nearly every biological niche that will support life. Nevertheless, they escape notice because most kinds are too small to be seen without the acid of a microscope. The majority of the 1500 describe species are non – parasitic and live freely in fresh or salt waters or in soil where they feed on microorganism such as bacteria, fungi, and algae. However, nematodes have been found to be parasites of virtually all animal and plant life. The can cause great physical discomfort and debilitation to man and his domestic animals as well as a variety of plant diseases that take their toll of crop production.
APPEARANCE, SIZE, NAME, AND TYPES OF PARASITISM
NEMATODES: Is a small multi-cellular member of the animal kingdom possessing all major physiological system except the respiration and circulatory system.
In general, nematodes are worm like in appearance with slender, cylindrical, unregimented bodies tapering toward the head and tail. However, the female of some species become smolten at maturity with their bodies forming shapes characteristics of the genus and/or species to which they belong.
Nematodes can also been known as; eel worms, nemas roundworm, threadworms, todes or worms.
HOW NEMATODES DISTRIBUTED IN SOIL
The vertical distribution of nematode in a cultivated field is usually irregular but is closely related to the distribution of plant roots and the area adjacent to the root feet of soil and as many as six billion have been estimated in the top inch of an acre of soil. Information on the distribution of nematodes have been received from a depth of 17 feet in a grape vineyard and citrus nematode are form to a depth of 6 to 8 feet.
MOVEMENT OF NEMATODE IN THE SOIL
The importance of active nematode movement in soil is related entirely to localize activities near the host plant rather than to their spread over the large areas. Nematodes spread through the soil very slowly under their own power. Most being incapable of traveling more than a few inches in their life. It is important to realize that nematodes cannot move into adjacent field under their own power. All species of nematodes haves a life stage they can move through the soil. This may involve the soil or from one feeding site to another or for reproduction.
HOW NEMATODES SPREAD
Nematodes can easily be spread by anything that moves and can carry particles of soil or plant material.
HOW NEMATODES SURVIVE UNFAVORABLE CONDITIONS.
Many plant parasite nematodes can survive in soil for at least one year in absence of a suitable host. During this period they probably in a quiescent of inactive state that is often associated with a lowered metabolic rate.
Nematodes may also survive without a host in or on piece of root that remain way in the especially important in replacing field having a history of perennial crop, as roots that are left may remain alive for as long 4 or 5 years
FACTOR DETERMINE THE AMOUNT OF INJURY CAUSED BY NEMATODES
The injury caused by nematodes is related to many variables including the nematodes species and its feeding; the susceptibility of the host plant various factors including soil type, soil moisture and temperature, host of nutrition, duration of the grow.
SIGNIFICANCE OF NEMATODES TO CROP PRODUCTION UNDERESTIMATES SO MANY YEARS.
Their several reasons
1. The soil – borne character of nematodes.
2. Their microscopic size
3. Their hidden mode of life either in the soil or inside tissues
4. Their study is technically very difficult
5. The tendency on agriculturalists to judge the health and growth conditions of plants mainly on the basis of the above – ground parts.
DISEASE COMPLEXES
The mechanical and chemical injury caused by nematodes provides for entrance and establishment of pathogenic bacteria and fungi.
Mechanical injury caused by nematode feeding decreases the ability of plants to take up water and nutrients from soil.
TYPES OF SYMPTOMS CAUSED BY NEMATODES
The symptoms that are commonly found on underground parts of plants are abnormal growth in nematode.
1. ROOT KNOTS OR ROOTS GALLS:
These are abnormal enlargements of the root caused by feeding of nematodes that may or may not be enclosed within them.
2. ROOT LESIONS:
These are discolored and often collapsed of the root consisting of cells on which nematodes have fed. They vary in size from a few cells to.
3. ROOT ROTS
When nematode infections are accompanied by plant pathogenic bacteria or fungi, large portions of the root may rot.
4. EXCESSIVE ROOT BRANCHING (SPANGLING)
Numerous short lateral roots may form in the vicinity of nematode injury causing a spangled rap root or a hairy root condition.
These root symptoms are usually accompanied by non characteristic symptoms in the above – ground parts of plants appearing primarily as reduced growth, symptoms of nutrient deficiencies such as yellowing of foliage, excessive wilting in hot or dry weather, reduced yields and poor quality or products.
VIRUSES THAT ARE TRANSMITTED BY NEMATODES
There are several plant viruses such as grapevine fan leaf virus, Arabic mosaic virus, tomato ring spot virus, tomato black ring virus, raspberry ring spot virus and tobacco rattle virus are transmitted by nematodes when they feed on an infected plant and subsequently feed on a healthy plant.
TYPES OF BACTERIAL DISEASES THAT ARE ASSOCIATED WITH NEMATODES
Nematode and bacterial interactions are thought to be largely confined to a wound and/or vector relationship. However, more may be involved in the various wilts and rots caused by bacteria. The nematode is actually serve to increase the pathogen city of the bacteria by decreasing the Vigo of the plant.
FACTORS THAT AFFECT THE GROWTH AND REPRODUCTION OF NEMATODES
1. TEMPERATURE OF THE SOIL
Temperature effects nematode activities such as hatching, reproduction movement, development and survival and also affects the host plant. Most nematodes become inactive at a low temperature range of 40o to 60oF; have an optimum range of 60o to 85oF and become inactive at a high temperature range of 85o to105oF.
2. MOISTURE OR SOIL WATER
Nematodes need free water films around soil particles for all of their activities. Dry soil conditions will depress nematode activity and may result populations of many nematodes being killed. Saturated soils are not favourable for most nematodes because such soils lack oxygen probably; optimum moisture conditions are between 40 and 80 percent of field capacity.
3. SOIL TYPE
The activity of nematodes is related to soil pore diameters, soil particle size thickness of soil – water films, and soil aeration, the soil texture determines, for a large part, which nematodes are likely to cause a problem in a particular area.
4. HOST PLANT
In addition to serving as a source of food for nematodes, plant roots may also modify tine soil environment by depleting moisture, increasing carbon dioxide, reducing oxygen and contributing a variety of organic substances to the soil solution.
5. CULTURAL PRACTICES
The grower can either build up the populations of nematodes to tremendous numbers reduce them to low levels. Continuous planting of crops susceptible to certain species of nematodes, or allowing host weeds to grow, may lead to yield reduction by increasing nematode populations.
THE BENEFITS OF NEMATODE CONTROL
1. Increased size, quantity and quality of produce which increases profits.
2. Healthy plants that are less susceptible to other plant pathogens and able to withstand wolvers growing condition.
METHOD FOR CONTROLLING NEMATODES SELECTED
The method is usually depends on the biology of the nematode species in the crop and its value per acre, the methods of spread, the cultural and the relative cost of available control methods.
THERE ARE FOUR GENERAL TYPES OF CONTROL THAT CAN BE USED
1. Cultural practices including crop rotation, resistant varieties, and early planting.
2. Biological methods
3. Mechanical or physical methods
4. Chemical
3. Less replanting is required because the plant are vigorous.
4. Better utilization of the nutrients and moisture by the plants.
METHOD FOR CONTROLLING NEMATODES SELECTED
The method is usually depends on the nematode species in the crop and its value per acre, the methods of spread, the cultural practices already used, the ecological relationships and the relative cost of available control methods.
THERE ARE FOUR GENERAL TYPES OF CONTROL THE CAN BE USED
1. Cultural practices including crop rotation resistant varieties, end early planting.
2. Biological methods
3. Mechanical or physical methods
4. Chemical control for the most effective control it is best not to rely on any one method.
The chemicals used for control of nematodes are called nematicides are known as soil fumigants.
THE ADVANTAGES OF USING NEMATODES
The primary advantage of chemical control over that of other methods is the nematode populations in the treated areas are reduced to low densities. Within a matter of days after the chemical is applied.
This enables the grower to plant a cash crop soon after treatment or in some case, at the time of treatment. Another important benefit is that several of the nematicdes in use today are multiple purposes.
Nematodes are not very often recognized as a major cause of damage to the crop. Practically impossible to be seen with the naked eyes, these animals are nevertheless present in most of the soils and, feeding on cultivated crops, they can bring about poor crop growth and low yields which are economically intolerable by the farmers.
Nematodes are tiny, long – shaped, worm – like animals, usually 0.5 to 2mm long. There size and the transparency of their body make them invisible to the naked eye. They have digestive, nervous and reproductive systems but unlike earthworms. Nematodes can either live free in a soil or in a water medium or as parasites in living hosts such as man, animals and plants. While the species living free in particularly dangerous and have to be controlled for they may cause weaknesses, deficiencies or convey virus diseases.
HOW TO IDENTIFY THE CHARACTERISTIC SIGNS OF NEMATODE INFESTATION
1. Unthrifty aspect and late growth of plants
2. Stunted branches and stems
3. Root distortions, emergence of galls and cysts, development of a root system with shorter finer and weaker root.
4. More or less severe root decay,
5. Leaf dryness.