Главная - Энциклопедия вредителей и болезней - Nematodes (Chromadorea, Enoplea)

Nematodes (Chromadorea, Enoplea)

“… if all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes. The location of towns would be decipherable since, for every massing of human beings, there would be a corresponding massing of certain nematodes. Trees would still stand in ghostly rows representing our streets and highways. The location of the various plants and animals would still be decipherable, and, had we sufficient knowledge, in many cases even their species could be determined by an examination of their erstwhile nematode parasites.”

N. Cobb, 1914.

Morphology

Nematodes are simple multicellular animals, usually containing 1,000 cells or fewer. They are similar to worms in appearance, but taxonomically different from earthworms, wireworms or flatworms. These are bilaterally symmetrical, soft-bodied (without a skeleton), non-segmented roundworms. Most species of nematodes attacking plants are microscopic. Basically, the body of nematodes looks like a “tube in a tube”. Nematodes feed on microorganisms and plants, such as bacteriovorus, fungi, omnivores, predators, and plant parasites. However, some of them are serious pathogens for humans, animals, and plants. Those who attack animals or people do not attack plants, and vice versa. Cardiac helminth in dogs and cats is an example of nematode diseases of animals and humans.

A number of genera and species of nematodes cause serious damage to a wide range of hosts, including deciduous plants, agronomic and vegetable crops, fruit and nut trees, lawn and forest trees. Some of the most harmful types of nematodes: affect the root node (Meloidogyne spp.); cause a cyst (Heterodera and Globodera spp.); affect the root system (Pratylenchus spp.); cause twisting (Helicotylenchus spp.); burrowing species (Radopholus similis); affect the bulb and stem (Ditylenchus dipsaci); reniform nematode (Rotylenchulus reniformis); dagger nematodes (Xiphinema spp.); affecting bud and leaf (Aphelenchoides spp.); causing pine wilt disease (Bursaphelenchus xylophilus).

Nematodes that parasitize plants can infect the roots, stems, foliage and flowers of plants. All nematodes that parasitize plants have a piercing oral apparatus called a stiletto. The presence of a stiletto is a key diagnostic feature that distinguishes nematodes that parasitize plants from all other types of nematodes. The nematode that feeds on bacteria, Caenorhabditis elegans, is one of the most studied animals on the Earth. It was the first animal to have its entire genome completely sequenced. Learning C. elegans has provided a new perspective on the development, neurobiology, and behaviour of animals.

Signs and Symptoms

Typical root symptoms indicating a nematode attack are root nodes or galls, root lesions, excessive root branching, damage to root tips, and root system growth retardation. Symptoms on the aboveground parts of the plant, indicating a root infection, are slow wilting of the entire plant, wilting even with abundant soil moisture, yellowing of foliage and a decrease in the number and size of leaves. In fact, these are symptoms that can appear in plants that lack a properly functioning root system. Bulbous and stem nematodes form a swelling of the stem and shortened internodes. Reniform and leaf nematodes deform and kill kidney and leaf tissue. In some cases, crop loss may occur even without visible symptoms.

Distribution

Parasitic nematodes are easily spread by any physical means that can move soil particles — equipment, tools, shoes, birds, insects, dust, wind, and water. In addition, the movement of plants or parts of plants infected with nematodes will lead to the spread of parasites.

Control

There are various methods to reduce crop losses from nematodes:

1. Plants with genetic resistance

Plants of resistant species and varieties. For example, in an area with soil heavily infected with a root-knot nematode, plant apricots, cherries, apples, pears, or plums that are resistant, and not very susceptible peaches or nectarines. (There is a peach rootstock resistant to root nematodes called “Nemaguard”, developed by breeders in the USA, which allows you to grow a peach even on infected soils.) Some vegetable crops — sweet corn, asparagus, and cabbage — are resistant to root nematodes, while radishes are susceptible. Among ornamental plants, African marigolds, azaleas, camellias, and oleanders show good resistance.

2. Agronomic method

Carry out crop rotation to fight nematodes. Turnover is useful for controlling species with a narrow range of hosts, such as sugar beet affected by sugarbeet nematode. Where the value of the crop is too low to justify large-scale fumigation of the soil, crop rotation is the only practical method of controlling nematodes.

Use cover cultures that reduce damage from nematodes. Cover crops can also improve soil structure and fertility, reduce soil erosion, be used as animal feed and suppress weeds, insects, and pathogens. Examples of cover crops that have been proven to suppress nematodes include cowpea, rapeseed, velvet beans, and Sudan grass.

3. Chemical method

Before planting, treat the soil area with fumigant. Soil mixtures for plants grown in containers can be treated with fumigant or pasteurized with steam at +82C for about 30 minutes. But this method is usually too expensive for field crops. Also, methyl bromide can seriously impact the crops in which it is used.

In certain cases, use nematocides. All nematocides are poisonous, and they should be used carefully, following the instructions on the containers exactly. Most of these materials can damage or kill plants if applied too close to root zones. As the number of commercially available nematocides decreases, more and more attention is being paid to the development of alternative IPM methods (Integrated Pest Management). It is a system for managing the phytosanitary state of ecosystems through the integrated use of various plant protection tools and methods to ensure the phytosanitary well-being of the territory, as well as a section of plant protection science.

4. Biological control