There are various types of nematodes in nature, and only a few of them are actually harmful to plants. The most commonly known harmful types are the root knot nematode (Meloidogyne), the root lesion nematode (Pratylenchus) and the root necrosis nematode (Radopholus). These nematodes can be found everywhere, in all types of soil and in all crops (even in substrate crops).
Nematodes are therefore a stubborn pest and are difficult to combat. It is however possible to curb the growth of the population in order to limit the damage.
Thrips are the smallest winged insects in the world. They form a frequent pest in greenhouse crops. The most common types of thrips in greenhouses are:
- Thrips tabaci (tobacco thrips)
- Frankliniella occidentalis (Californian thrips)
- Echinothrips americanus
Thrips passes through six stages in its life: an egg stage, two larva stages, a pre-pupa stage, a pupa stage and an adult stage.
The duration of development strongly depends on the temperature. At 25°C, it takes about 14 days from one egg to another. The female lays eggs in the leaf and/or leaf buds. Such places can sometimes be recognised by wartlike deformities on the leaf. The larvae emerging from the eggs will start eating right away at the underside of the leaf. They are extremely agile and can eat all parts of the plant above ground. After an initial sloughing, the larva will remain in the plant for a while, but then drops to the ground to pupate, sometimes down to a depth of 15 mm. During these pre-pupa and pupa stages, the wings and antennas will develop. Subsequently, the adult insect will fly out.
- Thrips feed on the leaf through sucking zones. The tissue around these sucking zones will die. Silvery grey spots will develop, showing black specks (the excreta of thrips).
- Cucumber and sweet peppers suffer a lot of damage to the fruit. Cucumber will show deformities of the young fruit. In sweet peppers, the calyx will become detached from the fruit.
- The places where eggs have been laid are very well distinguishable, in particular on sweet peppers. They are wartlike deformities of the leaf.
- In ornamental plant cultivation, damage is usually done to the flower and/or the plant.
- Another frequent problem is the transfer of viruses due to thrips.
How to encounter
For effective extermination of thrips, it is essential to break their short life cycle (10 to 14 days in summer) by affecting as many thrips as possible with an adequate chemical product, or with natural enemies.
Leaf miner fly
It is the female leaf miner fly that does the most damage. She uses her ovipositor to make feeding dots and egg dots on the upper side of the leaf. Feeding dots are round while egg dots are oval.
Males have no ovipositor and are therefore dependent on the feeding dots of the females.
The feeding dots and egg dots of the leaf miner fly cause damage to the crop. The light-coloured, dried dots may present a serious problem for ornamental plants. In addition, there is a risk that bacteria or moulds enter the feeding dots.
But the leaf miner larvae cause serious damage to the crop, too. Once the larva has emerged from the egg, it eats itself a winding tunnel through the leaf (a mine shaft as it were). These mines cause the leaf to dehydrate and fall off prematurely.
The family is Liriomyza. Common types are:
- Tomato leaf miner fly Liriomyza bryoniae
- Florida leaf miner fly Liriomyza trifolii
- Chrysanthemum leaf miner fly Chromatomyia syngenesiae (Gerbera and Chrysanthemum)
The life cycle of the leaf miner fly comprises the egg stage, three larva stages, a pupa stage and an adult stage. As soon as the larva emerges from the egg, it starts eating and makes a mine in the leaf, between its outer layers. With its mouth hooks, the grown larva cuts a hole in the leaf. It subsequently creeps out of the leaf and falls down to the ground. The larva burrows into the ground or seeks other hiding-places to pupate. From the pupae, leaf miner flies emerge which, in their adult stage, lay eggs in the leaf again. The leaf miner fly measures a few millimetres and is black in colour, usually with a yellow spot on its back.
If chemical agents are used, natural enemies are killed too, as a result of which the leaf miner fly can develop rapidly.
The root system of a plant forms the basis for its existence. No wonder the plant invests 50% of its energy in this system.
Half of this goes to absorption of nutrients while the other half is used for root maintenance and growth.
The roots serve to anchor the plant in the soil but also play an important role in absorption of elements, which is only really possible via the root hairs. These root hairs need to be re-grown continually, as they only live for a few days.
Biopak and Modicell by Deruned are effective solutions for problems with your crop's root system.
Biopak ensures a healthy root environment thanks to it containing active micro-organisms.
Modicell is particularly suitable for speeding up the breakdown of root residues in an artificial substrate, while also stimulating the growth of new root hairs.
Botrytis is a common problem in all crops which are regularly moist. The spores of this mould are very easily spread through the air. Botrytis can then penetrate plants, particularly through open wounds.
The spores require moisture in order to germinate,and can absorb sufficient moisture from the air once the relative humidity is more than 93%.
The speed at which they germinate depends on the temperature. A Botrytis infection can be latently present in a plant for weeks on end, before becoming active again.
The Biopak natural crop protection preparation by Deruned contains bacteria which protect the plant against moulds such as Botrytis.
Biopak is therefore effective in the fight against Botrytis.
Other useful measures in combating Botrytis are to lower the humidity and to avoid lengthy wetness of a crop above ground.
The taxus weevil is a serious problem in many ornamental plants. Especially the damage caused by the grub, feeding on the roots, may cause wilting and death of the plant. This pest belongs to the snout beetle family. Fruit plants, but also Azalea, Taxus, Camelia etc. are very sensitive to the taxus weevil, as are pot plants, such as Cyclamen, Kalanchoe, Fuchsia and Primula. Damage occurs in particular in slowly growing plants, which are unable to compensate for their roots being eaten away.
The life cycle of the taxus weevil consists of:
- an egg stage
- 6 or 7 larva stages
- a pupa stage
- the adult stage
The first adult taxus weevils emerge in May. They measure about 8 mm and are brown-black in colour. The beetle cannot fly, the shields on its back are grown together with its body. The taxus weevil is an excellent runner, however. It can move lots of metres in only a few hours. A nocturnal insect, it hides in the ground during daytime, under balls of earth, plant remnants etc. It is hard to notice the taxus weevil therefore.
The white eggs are laid from July to September. They produce the larvae, which are transparent white in colour. The larvae measure about 1 mm and will grow to about 10 mm. In winter, the larvae remain in the 3rd or 4th stage, to become active again in spring when temperature rises. In spring, the larva pupates in the ground. The pupae measure about 8 mm and will produce the adult beetles.
The adult beetle eats the leaves especially at night, which can be detected by round punctures at the edge of the leaf, which may be a problem for the ornamental value of a plant. The larva does the most damage, however. The young larva will first feed on plant remnants but also on root-hairs. When the larva grows larger, it will also feed on larger roots. Further, the stem of the plant will be eaten bare near the base, and thick roots will be peeled as it were. As a result, the plant will go limp or die altogether.
How to combat
The taxus weevil is hard to combat. The adult has a tough shield and only moves at night, which makes it hardly accessible to pesticides.
The larvae can also hardly be controlled due to their hiding-places in the ground. Besides, the larvae are extremely resistant to a lot of chemicals.
Fusarium is a mould which cannot be combated once it has become established in the plant. Affected plants are less productive and are generally doomed.
Fusarium spores are very easy to tackle however, especially when they begin to germinate. The spore is very vulnerable at that stage and can be killed by its natural enemies (bacteria), while also preventing further spread of fusarium.
The Biopak natural crop protection preparation by Deruned contains various bacteria which protect the plant against moulds such as fusarium. These bacteria compete for space and food with the moulds and in doing so lower the infection pressure.
Also check out Biopak
Pythium is a stubborn mould which is one of the first to re-appear in the crop after steaming. Infection pressure by Pythium is therefore virtually impossible to avoid. Pythium lives off dead organic material found in the soil (or in substrate) but can only actually infect a plant once it is already weakened.
Pythium is often found after another infection or following infection with nematodes. A Pythium infection is easily recognisable at the root, where the outermost layer is easily peeled off. In order to suppress Pythium, it is important to give the soil or substrate plenty of capacity, and a well developed micro-ecology is essential.
From practice, we hear more and more about problems with Garden symphylans. Since the use of Parathion was forbidden, the problem of Garden symphylans has been playing an increasingly important role. There is still a lot of vagueness about this pest, however.
Garden symphylans is a small, bright creamy-white centipede of about 5 to 7 mm long. It has 2 extremely agile antennas and, in the adult stage, 12 pairs of legs. The larvae have fewer legs. Their forward movement is characterised by a quick, winding gait. Adults can survive in the ground for quite a few years. Most eggs are laid in spring, but sometimes also in autumn. Eggs are only laid if the temperature exceeds 10°C. The development from egg to adult stage takes 2 to 4 months, depending on the temperature.
The garden symphylans feeds on algae, fungi, mosses and, in certain periods, on cuttings and young roots. It can therefore do much damage to a young crop. It is basically found on every type of soil, but prefers comparatively heavy soils having an excellent structure.
It is found at depths of more than 50 cm and can move quickly through the ground. Steaming proves to have little effect on the garden symphylans therefore.
The presence of garden symphylans is easy to detect by immersing a scoop of ground in a bucket of water. After a short while, they will float up to the surface. But take care: springtail will also float up to the surface and they are often mistaken for garden symphylans!!
DeruNed can provide you with an analysis of any presence of garden symphylans and if so, how many. Just ask our research department.
Soil is a very complex system. Despite so much research already having taken place into the composition of soil and soil types, many processes are as yet unknown, as well as the many organisms living in the soil.
Thanks to hydroponic cultivation, we have become much more knowledgeable and can therefore react more effectively to the soil problems of crops. After all, organic fertilisation, bacteria and enzymes can be applied to positively influence a number of processes in the soil.
Disease pressure is decreased, the soil is less readily compacted, etc.
DeruNed offers a number of crop protection preparations which contribute to a healthy soil environment. Biopak restores a disturbed soil environment while Modicell activates the micro-ecology.
Also check out Biopak of Modicell
Snails consist for 98% of water, and it is this moisture which determines their level of activity.
A snail exudes water through the skin and around its base, in the form of mucus. The base must be slimy underneath to enable the snail to move forward. On dry surfaces, the snail therefore loses a lot of moisture while on the move. As soon as the snail finds itself on moist ground again, it will re-absorb moisture through its base. This explains why a snail's weight may vary enormously.
High atmospheric humidity will not cause snails to move however: At 100% R.H., a snail can no longer cool itself and will try to stay put. This is due to the great heat produced by motion, which can only be given off by evaporation.
Below 75% R.H., it is too dry for the snail to move.
And so the ideal conditions are: R.H. between 75 and 100% and a decreasing temperature (for cooling without evaporation). This situation mostly occurs at night, which is why snails are often detected then.
A snail's favourite temperature is around 17 degrees. At higher temperatures, above 20 degrees, the snail has great problems avoiding overheating. It will evaporate more. At lower temperatures, the snail will move to become warm again. Under 5 degrees however, the snail can hardly move any longer and below zero it will easily freeze to death. Wintering is only possible by hiding well and laying eggs. Snails do not hibernate. Instead, they live on fallen leaves and suchlike.
The snail is a hermaphrodite, but cannot fertilise itself. Two snails can fertilise one another however. A snail is sexually mature after about 3 months. Eggs are laid throughout the year, but autumn is the most active period. A snail may live to be 1 to 2 years and lay some thousand eggs in that period. The eggs can only develop if the temperature is higher than 5 degrees. At lower temperatures, the development stagnates, but the egg will not die.