The herbivorous nematodes are not large (up to 2 mm in length) representatives of roundworms, which prefer moist soil and are endo- and exoparasites of various plants. Different types of nematodes settle in various plant organs: in roots and stems, buds and buds of flowers, on leaves. This leads to disruption of the functioning of damaged organs and, in consequence, the death of the plant. Affected plants lag behind in growth and development, curvature of stems, shortening of internodes, thickening of petioles, drying up of buds and falling of leaves can be observed. Parasites are able to tolerate various bacterial and viral diseases, for example the tomato ring spotted virus, the leaf curl virus and many others. Affected by nematodes, plants die in the absence of treatment.
Leaf nematodes of the genus Aphelenchoides affect mainly the aerial organs of strawberries and chrysanthemums, penetrating through the stomata and minor damage to the plants. These nematodes can parasitize internally or from the outside on leaves, kidneys, or rudiments of reproductive organs. Most ornamental plants live endoparasitically, multiplying in the mesophyll.
Stem nematodes, which belong to the genus Ditylenchus, severely harm flower crops, such as: begonias, carnations, tulips, phloxes, hyacinths; As well as vegetables and green: onions, garlic, tomato, cucumber, parsley. Parasites damage the organs above the ground, rhizomes and bulbs. Especially dangerous are they for bulbs of lily flowers during storage. On the cross section of the affected bulbs, you can see areas of grayish-brown color. When stored in conditions of high humidity and temperature, the nematodes cause rotting of the bulbs. In narcissus, they are the cause of ring bulb disease. On tulips nematodes can cause the appearance of yellowish or brownish stripes and spots on the outer scales.
Meloydoginosis of vegetable crops (damaged by root nematodes) in greenhouses is the most common and very dangerous disease, which is hard to eradicate. As hosts of root-knot nematodes, which belong to the genus Meloidogyne, more than 400 plant species are known. Among them - all the main vegetable and most of the ornamental crops, cultivated in a closed ground. Control requires special knowledge, extensive practical experience and significant financial costs. The activity of root nematodes causes the formation of so-called galls, on the roots of plants - these are round or elongated thickenings, which are formed under the action of enzymes of the parasite, within which the pest feeds and multiplies. Galls prevent the normal passage of water through the roots, because of what the plant fades in hot weather.
Root nematodes not only directly deplete plants, but also contribute to the development of fungal, bacterial and viral diseases that penetrate through the damaged root pests. With a continuous infestation of nematodes with cucumber roots, after three, at most four months, up to 80% of the plants die.
With a similar infection of tomato and aubergine over the same period, yield losses reach 25-30%. At the same time, numerous accompanying infections of the root system and above-ground organs are intensively developing. No less harmful are nematodes and on ornamentals, where they significantly reduce the quality of products and also contribute to the spread of concomitant bacterial and fungal diseases.
Leaf nematodes are colorless, very mobile worms-parasites long up to 1 mm. Deciduous nematodes cause pale yellow spots, which eventually become brown and dry out. Infected with nematodes, leaves can thin out. Sometimes necrotic shapeless spots may appear, deformed shoots and reproductive organs.
Stem nematodes colonize stalks, leaves and flowers, causing thickening of affected organs and tissues. These representatives of roundworms do not exceed a length of 1.7 mm. Stem nematodes cause blanching of affected parts of the plant and bloating on the stem. Damaged organs eventually become brown and die.
The aerial parts of plants affected by root nematodes have external signs, which can be attributed to the symptoms of deficiency of certain mineral elements. Sometimes the plants do not manifest such symptoms at all. In a closed ground with a strong infection, wilting leaves is observed. However, it is easy enough to diagnose nematode infection by the root system of the plant: on the roots, more often at the branching points, it is possible to detect galls - thickening, which in some susceptible species can reach several centimeters in diameter.
Galls on the roots can form not only under the influence of root nematodes, but also as a result of the development of bacterial infections, therefore, in order to correctly diagnose it is necessary to confirm the presence in the roots of female nematodes. With meloydoginosis, a female binocular lens can easily detect females and egg sacs on the affected roots.
An important issue of the diagnosis is the presence of egg sacs with eggs on the surface of the galls. Moreover, the largest egg sacs are formed on small galls and practically do not occur on the surface of the sinhalese, in which the entire cycle proceeds inside the root. Young egg bags 0.5-1.5 mm in size, yellowish in color, eventually turn brown.
Deciduous nematodes fully develop on one plant. The soil serves only as a temporary habitat. The presence of droplet moisture on plants, which does not dry out for a long time, can cause nematodes to spread. Through damage and stomata on the leaves, the pest enters the plant. The female lays up to 250 eggs. The development time of one generation is from 15 to 45 days.
The development of one generation of stem nematodes takes from 3 to 5 weeks. The whole cycle of the parasite flows into the tissue of the host plant. All larval stages and adults are invasive. Cryptobiological, that is capable of experiencing unfavorable conditions, is the fourth larval stage, which in the external environment can persist from six months to a year.
Gall nematodes can give from 1 to 13 generations per year. Larvae of nematodes, leaving the egg, look for host plants and penetrate into its roots, where they begin to feed. Optimal conditions for pest development are moderate soil moisture (40-60%) and temperature in the range of 20-30°C. Over time, young nematodes are transformed into immobile females and males capable of moving. The development of root nematodes in a greenhouse is in most cases a classical parthenogenetic cycle. Males are rare and do not take part in breeding. Their life expectancy is 3-5 weeks. The reproductive period of the female lasts 2-3 months, during which time it is able to postpone up to 2500 eggs. It forms on the surface of the root an egg sac from a gelatinous secreted substance. For the development of one generation, 24-28 days is needed.
The second larval instar is resistant to unfavorable environmental conditions (cryptobiological instar) and can remain virulent up to 6-12 months. The temperature interval at which the invasive larva of gall nematode is able to show activity is in the range of 5-40°C.
In conditions of greenhouses, the root nematodes can develop in one of two types of life cycles. The first type is observed in the initial period of plant population and is characterized by the mandatory migration of the invasive larva from the egg sac to the soil followed by the defeat of a new root or new host plant. The second type of life cycle involves a short migration along the rooting system and the transformation of larvae into egg-laying females without entering the soil.
1) Sterilize the soil before use.
2) Warming of the planting material before planting.
3) Plants where leaf or stem nematodes develop should be immediately removed and burned.
4) Plants affected by root nematodes are immersed in hot water (50-55 °C) by roots in 5-15 minutes. Bulbs affected by stem nematodes are heated in water at 43 °C for 5-9 minutes, sometimes with the addition of formalin at a concentration of 0.06%.
5) Growth of plant varieties more resistant to nematodes.
Nematofagin BT based on the fungus Arthrobotris oligospora can be used to protect plants from root nematodes. The product is applied 2 weeks before planting or at the time of planting. Treatments are repeated every 2 weeks.
To control nematodes, plants are treated with organophosphorus pesticides (phosphamide, mercaptopos, lindane) every 3-5 days, making 2-4 treatments. Against the root nematodes, products based on Abamectin - Akarin and Phytoverm are also used. The modern contact nematocide is Nematorein, which is characterized by low ecotoxicity and high selectivity of action.