How To Kill Spidermites

Indoor gardening is a large diverse hobby where you will find lots of conflicting opinions but there is one thing that growers can universally agree on: Spidermites are a horrorible plant pest. One of the biggest problems with spidermites is how quickly they can breed and get out of control, what starts as a mild infestation can evolve into a crop devestating one in a very short period of time. At the first signs of infestation you need to go to war on your mites and employ all weapons at your disposal to eliminate them. The earlier you can identify and start treating a spidermite infestation the more successful you will be.

There are two forms of spidermites that you will come up against, the two spotted spidermite and the red spidermite. Both are equally destructive and can be considered as the same pest. 

spidermites-types

Left : The two spotted spidermite. Right : The red spidermite. Gross!!!

Spraying

The most straightforward way to take on spidermites is with a spray of some sort, sprays are effective at getting spidermites under control and can eradicate them if you are thorough enough with your spraying and repeat it at suitable intervals over a period of time. There are many sprays available, each have there own merits but are essentially doing the same thing, suffocating spidermites by contact.

How effective spraying will be depends on the level of the infestation. If you look at the pictures below and further down the page you can see the various stages of spidermite infeststion. If you only have a light to mild problem as shown by the first two pictures then spraying will be quite effective. If you have a more severe infestation as shown by the second set of pictures then you will struggle. We would also not recomend spraying in the later stages of flowering when you have big flower formations as you will risk causing rot.

spidermite-infestation

Left : The initial stages of a spidermite infestation, small numbers of mites which appear as little more than small black dots to the naked eye can be seen on the undersides of leaves. The small white globules in this picture are spidermite eggs. Right : As the mites take hold you will start to notice some light webbing on or around the leaves and some signs of damage where the mites have been feeding.

Before spraying prepare your plants by removing as many leaves that are damaged and showing signs of infestation as possible. The more spider mites you can remove manually the better and by tidying your plants up a bit spraying will be much more effective. The best time to spray is just before your lights come on.

Because most sprays work by covering mites and suffocating them it is important to get complete coverage of your plant so you kill as many mites as possible with each spraying session. We would recomend getting a pressure sprayer as these will work much better upside down, some models even come with a handy spray lance which makes things easier still. The technique you want to employ is to cover both the tops and primarily the bottoms of the leaves where the majority of the spider mites are hiding out.

With your spray bottle angled upwards move it up the plant while spraying and then with your spray bottle angled down spray down the plant while spraying. work your way around the plant until both the tops and bottoms of leaves are thoroughly covered. This first spray will deal your spidermite population a defeat but will not win the war, to eradicate the mite menace you need to continue your campaign.

Wait for 5-7 days after your first spray to give your plants time to recover as some sprays can cause mild plant stress especially the first time you use them. You are also waiting for the eggs which will probably have survived your first spray to hatch out. The name of the game with this second spray is to kill these newly hatched spider mites before they can reproduce themselves as well as catching any adult mites you missed with the first pass. Tidy your plants up again if necessary by removing mite damaged leaves and thinning the plant out a little, then using the same technique as before apply a second spray to your plants.

You should continue spraying in 5-7 day intervals until the problem is under control or eliminated.

Blasting Method

If you grow in pots or a system that you can move, a good technique when spidermites are quite rampant (see pictures below) is to take your plants into the shower and use your shower head to blast the mites off your plants. This approach is a little risky if your shower is very powerful, in this case put a little distance between the shower head and your plants, you want to remove spidermites not leaves and stems. Work your plants over with the showerhead, pointing it slightly up and working from the base of the plants upwards.

This technique is only recomended  when your plants are well developed with strong stems. On its own this will not eradicate spidermites, what it will do is significantly reduce their numbers and destroy their webs so that standard spraying will be more effective.

spidermite-infestation-2

Left : The spidermite problem begins to get out of control, large numbers of mites are mooching around your plants at will and webbing is becoming joined up over leaves and stems . Right : A totally out of control spidermite problem, webs cover whole areas of plants and the mites are present in such large numbers that they are destroying the leaves and stems.

Spidermite Predators

One of the most effective ways of eradicating spidermites is to stop trying to fight nature and have it work for you instead by employing biological pest control and getting in some predator bugs to eat your spidermites. 

The most effective predator for spidermites is strangely enough a mite itself called Phytoseiulus Persimilis. Phytoseiulus is capable of eating large numbers of red or two spotted spider mites and is a very active, quick moving predator which will actively hunt out spidermites wherever they are hiding. Once all spidermites have been brutally consumed the predators will disperse and starve to death. 

Predators are more effective during the early stages of plant growth when spidermite populations and the amount of plant matter are small. Also remember that any sprays that kill spidermites will also kill spidermite predators so don't spray once you have introduced predators.

spidermite-predators

Left : The phytoseiulus persimilis predator mite is the scourge of spidermites everywhere. Ugly little devil. Right : Phytoseiulus in action tucking into a two spotted spidermite, they are equally effective on red spidermites. 

Sterilization

The easiest way to completely eliminate a spidermite problem is to sterilize your room once your crop is done and introduce new plants from a trusted source or begin again yourself from seeds.

Spidermites can hibernate in the corners and recesses of your room, biding their time until you introduce some nice new plants for them. Once your room is completely cleaned down leave your lights on 24 hours a day for 3-4 days. This will hatch out any eggs and awaken any sleeping mites who will then starve to death. Follow this up by sterilizing your room with a bleach based cleaning spray to get into all the hard to reach areas.

If you want to go really 'gung ho' you could at this point smoke bomb the room with a fortefog fumer.