Greenfields Hydroponics UK

Pests and Diseases
Introduction
There are many approaches to pest control but it’s important to understand the reasons why infections occur so they can be properly prevented. In the natural state, no one organism will take over because of natural predators that exist to keep their numbers in control. It is also true that insects seem to attack weakened plants under stress first. In indoor gardens they normally enter through bringing infected plants into the grow space, or through the air intake vents. It is advisable to inspect carefully any new stock and preferably have a separate 'quarantine' area to grow in before introduction into the grow room. Be especially careful of plants that have been growing outdoors. You are almost inevitably going to bring insects/arachnids in with them. Part of a good prevention routine is to all treat new plants (if some time away from consumption) with an insecticide of choice, organic or not. Cleanliness is important. Remove all dead leaves and plant material. This will discourage mould and fungus knats. Also some varieties have a genetic disposition towards some diseases such as botrytis. (Leaf / bud rot). These must be monitored closely, especially in high humidity areas where fungus can flourish. Through good prevention techniques pests can be avoided but if these fail and you end up with an infestation there are still things that can be done to counter their growth. The reality is that with a short growth cycle plant if you end up with a large population of pests it need quite radical action, maybe using chemicals to eradicate them. This should at all costs be avoided because any use of chemicals has other drawbacks, such as making the plant inconsumable or be encouraging resistance in the pest to the chemicals you are using. Closely monitor your plants and learn to recognise the first signs of an imbalance in the pests/predator mix.
Growers tend to fall into two major groups. Those with good prevention techniques who use organic techniques and hardly if ever have to resort to chemicals and the less experienced and less preventative who don’t notice the initial signs and have to use nasty chemicals to counter-act a severe infestation. Crops are often lost like this.
ORGANIC APPROACH
This involves use of substances to encourage resistance to pests (eg.NEEMO spray (LINK)), yellow traps to act as a sort of flypaper, use of insecticidal soaps to de-hydrate the soft bodies of some insects and the use of specific predators (e.g. Derris). It must be noted that predators must have the environmental condition tailored for them in order to thrive, like lower temperatures or more humidity and these actions on their own also discourage the growth of some pests. Hydrogold (LINK) and PestOff (LINK) are other natural based products. Nicotine solution is also toxic to insects and has been used for many years. (Ashtray water. YUK) Pyrethrins, extracted from a plant bulb, are an effective natural insecticide and is found in many commercial preparations. All these options are great for prevention and mild attacks. The best prevention is to keep healthy plants and encourage a clean environment.
CHEMICAL APPROACH
Most chemical insecticides work by attacking the nervous system of the insects, paralysing them. It must be noted though that they can become resistant to the chemicals with over use and they hardly ever kill 100% of the population. They are nasty things to use and normally make the plant inedible for at least 2 weeks. Most are indiscriminate and go for all insect populations on the plant, including beneficials. Repeat applications are normally necessary. The readily available varieties are mostly Organophosphates and Pyrethroids (Chemical preparations of pytretrins). There are also newer more specific insecticides available but they're not always licensed for domestic use. e.g. Abamectin for spider mite.
Summary
First preventative measures.
Second environmental measures such as increasing humidity and lowering temperature. Third environmentally friendly measures.(natural predators, pyrethrins or soap) Then if all else fails synthetic chemicals.
Pests
Spider Mites
These are very small arachnids, (from the spider family) that are barely visible to the naked eye but very tenacious. They thrive in hot dry conditions and suck the sap from the leaves. Bring the humidity up or the temperature down if possible. They are visible as white spots on the leaves. If they grow unchecked they can decimate a crop. Leaves lose all green and drop off and small webs can be seen between leaves if infested. Cooler wetter conditions discourage them. Insecticidal soap can check a small infestation as can chemicals. There are natural predators available to consume them but you CANT use insecticides at the same time! Some apply beneficials a few weeks after applying insecticidal soap.
Aphids
Much more obvious! Little winged creatures that gather on the stems and suck the juices from the plant. The plant grows ill with malformed leaves and buds. They LOVE green nitrogen rich plants. Without natural predators they can quickly flourish. Because of their size its possible to wash them off if a small garden. Most insect ides are effective as are beneficials.
Thrips
They're very small, hardly visible (2mm) and look like tiny sticks with legs. They can leave nasty leaf damage, similar to spider mites. Soaps and pyrethrins can be used.
Whitefly
They look similar to aphids, but they fly off and then re-settle the plant if disturbed. They cling onto the underside of leaves and produce a black looking web substance. The plant will eventually succumb and die. Natural predators are effective. You can also use pyrethrins or yellow traps. Hoovers are also good, just disturb them and suck em up!
Fungus Gnats They are tiny black flies that live round the bottom of the plant in the dead plant material and compost. They fly about and then resettle. They are not generally a problem and many growers live with them but it has been reported that if infested heavily, root damage can occur. Sticky yellow traps are effective against them as are most insecticides. Fungus Gnat-Off is also popular.
Diseases
Botrytis (Leaf and Bud rot)
Normally a problem in high humidity areas or in damaged plants. When a plant falls or gets damaged rot can set in quite quickly. There are a few preparations to kill botrytis but most can only be applied well before crop time. Some preparations purport to discourage damage by improving their resistance to infection. Sulphur is a natural fungicide and 'sulphur bombs' exist to clear an (Empty) grow space of fungi.
Viruses
These are not at all common. Suspect everything else before considering viral infections.

Pest Control