Red Spider Mites


Red Spider Mite

This advice on the dreaded Red Spider Mite was sent to me by a Bonsai Garden Forum friend, John McDonald (Sanjomc). I have found it to be the best article written on this subject, especially the included humour, thank you very much John, - Kath.

I can think of nothing more soul destroying than getting Red Spider mites on your plants. Horror of horrors… how could anyone who has been growing plants for a couple of years not know of this terrible affliction? Easy, Very Easy!

Mea culpa, Mea culpa. I brought a plant to a show that had evidence of these mites on the leaves. How could you do such a thing you may well ask? The answer is simple… I had never seen them, didn’t know what they looked like, was unaware that my insecticide was little or no use against them, and despite asking more expert growers than me, was still as ignorant of the pest as when I started. I have become an outcast in my own Club. Previously friendly folk now dip their eyes or look away, when I pass. Suddenly, Red Spider has become a topic of hushed conversation, in corners, as heads turn and shiftily raised fingers point in my direction. Speakers bring it up, and all those knowing heads nod, and I can feel the eyes glancing across at me as my neck tries to draw my head down below the level of my collar. Oh, the shame! I just want to die… Then I wake up. Does anyone else know about this pest? So I ask a question… and lo and behold there doesn’t appear to be anyone who knows the answers, or who are prepared to admit to knowing about it. Perhaps they are afraid of the stigma that I now feel, lest others will think they must have the pest in their greenhouse. Maybe they are just like me - ignorant of the problem.

I have, therefore, done some research, which members may find of interest. I hope so. It may help to get people talking to me again.

What are Red Spider mites?
They are tiny, crawling, wingless, insects (well actually they are arachnids for those who like to be pedantic about semantics) that have 6 or 8 legs depending on the stage of the development. Juvenile mites have 6 legs and the adult 8. They are so small that they are invisible to the naked eye, and a magnifying glass is needed to see them. If you imagine the full stop that I have just used they are more difficult to see than that.

The BIG question… what colour are they?
Most people would say RED of course. Some say they are black, some say green. Therefore if you are checking your plants you will know what you are looking for… or will you? This has got to be one of the biggest misnomers guaranteed to mislead the unwary. A RED SPIDER MITE is only RED at a certain stage of the year, after hibernation and in the springtime. The newly hatched mite is almost white (off white/buff coloured); the adult can be almost white (but in varying degrees through to green) with two spots on its back, looking like a saddle. These spots are said to be very dark green or very dark red, so dark that it could be taken for black. But these are only spots and not the whole insect. It is also known as the Two Spotted Spider Mite. There is also another mite who is sometimes found on plants indoors and that is the Carmine Spider mite, but I haven’t seen that one yet, so I don’t know how it develops.

What is the Breeding Cycle?
Adults can lay eggs from only 36 hours old!!! The eggs are more easily seen with the glass as they are laid in small clusters, usually close to the veins of the underside of the leaf. You may also see the Adult two-spotted female close by, as she will lay about 5/6 eggs every day. However, as I mentioned it speeds up dependent upon temperature. One account that I have read suggests that at 60 degrees she produces 20 offspring, at 70 degrees she and her offspring number 13,000 and at 80 degrees she represents a potential 13,000,000 individuals, and all within one month! This is clearly a major problem in the making, as the short breeding cycle (as little as 8 days from an egg to an adult breeding pest) combined with the early ability for the young to procreate, means that a massive infestation can arrive in a very small space of time. Hence the reason for the paranoia surrounding this pest!

How does the hot dry dusty atmosphere increase the likelihood of infestation?
Simply speaking, the heat of the greenhouse speeds up the life cycle. It can be as short as three days in hot places, and as long as a month in cool weather. So clearly temperature is key to the proliferation, along with a dry dusty atmosphere. As Greenhouses tend to be warming up considerably from April it is about this time that the breeding really gets going. It will go on until autumn given the conditions when is tends to slow down as plants begin to take on dormancy. The remaining females will now turn RED (described by some of being more Orange than red) and find places to hibernate. This is likely to be in the soil or compost of the host plant, or in the bark of mature plants, or in the wood or brickwork of the building itself. Bear in mind they are extremely tiny so no crevice is too small for a winter home for them. They will re-emerge in the spring and will be bright red (or Orangey red). A cooler temperature and moist atmosphere is thought to slow down their metabolism and slow the reproductive rate so misting and capillary matting may help in control.

Where should you look for them?
As with most pests they will be found on the underneath of the leaves so they have to really be looked for regularly. But you can’t see them can you? On close inspection you will see the effects of the eggs from above. The hatching young will eat away at the underside of the leaf, sucking the life out of the plant and this sometimes leaves a visible mark through and onto the top of the leaf. This may be yellowish or silvery and will be a small cluster of spots, each about the size of a full stop, and only by the fact that they are clustered does the mite give itself away. Most of us don’t notice mites until the infestation is established and the plant has been damaged. Leaves of affected plants seem to be drying out very quickly, which they are, as the mites suck the very life giving sap from them. Dead and dried out leaves fall and the plant begins to fade away. As the adults colonise the plant they may also spin a very fine web over the leaf and from branch to branch, and alas from plant to plant. At this stage you must take drastic action. This also enables them to walk down the host plant across the compost, over the bench or floor and up onto the next victim. Real serial killers these are. The webbing also tends to act as a shelter for the young underneath the leaf so that the effectiveness of sprays is considerably reduced.

Where do they come from, you may well ask?
I trust most people know about the Birds and the Bees, so I won’t go into that except to say that insects bring in more disease and infestation than any other method, and big bees can do considerable damage to your carefully tended show plants in a very short space of time. You may be aware that the wild honeybee is itself under threat of extinction by a “mite” which is attacking them. Therefore as the bees fly from plant to plant they are well capable of spreading other mites or viruses from infected to clean plants. Personally, I believe that white fly and aphids are the biggest cause of the spread of rust among plants, along with bees and wasps.

What can you do about the problem?
1) It is about his time that a pair of kneeling pads becomes useful, as you may have to refer to praying before the problem is solved! Just kidding…

2) Most importantly prevention is better than cure, as I have found to my cost. If you can cut off the source of supply then you are on your way to preventing and outbreak of whatever sort in your greenhouse. Place “bug screen” over open windows and doors to stop ingress of pests, whilst still allowing air to circulate. You will almost certainly become aware very quickly of how effective this is in keeping down the number of insects getting at your plants in the first place. I replace whole sections of glass with this screen and this helps to keep the temperature down and the airflow up! Replace the glass in the greenhouse door with screen and you can ignore the advice of “leave the greenhouse door open on hot days”. This will only let the blighters in. Keep the bees out and there is less chance of getting a Red Spider infestation.


3) Remove any infected plants immediately… and if you can afford to lose the plant then burn it or get rid of it… don’t throw it into your compost bin as this may lead to re-infestation. You may be fortunate enough to get a “clean “cutting or two” before disposing of the plant, but let that be a lesson to you, and think of it as part of the learning curve.

4) Check your plants regularly for any tell tale signs… Pick the plant up and look underneath the leaves using your magnifying lens and you may see the Mites moving about, or eggs clustered. You will be on the lookout for other insects anyway so now use the magnifying glass and check for Red Spider as well. It may seem obvious but don’t buy infected plants. And DON’T bring infected plants to the plant sale. Do not be afraid to get out your magnifying glass and really check out any plants you are about to buy! It will save you a lot of time, effort, and expense in the long run. I, for one, will always carry my glass to plant sales in future.

5) Keep a generous space between plants to prevent mites dropping from one plant to the next… This is true for most crawling pests too… This is probably the biggest fault that us “space restricted” amateurs have. We always cram too many plants into our small greenhouse, or growing space, and thereby bring most of our problems upon ourselves. So how many plants is it possible to have in a 12 x 8 greenhouse? Good question. How does about 30 or 40 sound? One “Expert” I know tells me that you shouldn’t have more than a dozen, and perhaps that is too many. As a broad rule of thumb, one 5” pot will contain a plant 15” in diameter. If you leave a 3” gap between plants you will need about 18” square for each fully-grown specimen. Hence a 12 ft Greenhouse will take about 8 x 5” pots along the length. A 6” pot therefore requires 21” square, and a 7” pot will need 2ft square, and so on… Easy to see how the space is quickly used up…

6) If you are lucky you will find the problem early and have a good chance of eradicating the problem… by simply squashing the mites and the eggs between finger and thumb, but I find that this always tends to damage the leaf.

7) You could try washing them off with a strong water sprayer. Some people use soapy water for this…but you should cover the surrounding area under the plant to catch any mites that fall from the plant as they could infect other plants.

8) Improve the conditions in the greenhouse with more misting and cooler temperatures… this may be a bonus for Fuchsia growers as the harder you can grow the plants the better they seem to like it. If you can afford it, install a watering and misting system. Together with capillary matting & increasing humidity by hosing down the hot greenhouse floor you will almost certainly keep mites at bay. Be careful about increased humidity as this can lead to botrytis if allowed to cool down too much, particularly at night. A cold humid atmosphere will certainly lead to increased botrytis problems. You need to strike a balance with regard to heat and humidity.

9) Introduce Biological controls – predatory mites. These can eradicate red spider mites PDQ provided they are introduced early i.e. before the infestation is out of control. Other predatory mites feed directly on the Red Spider mites and will devour them at a rapid rate. The predators should gain control in about 4 weeks by which time they will have eaten all the Spider mites and then they become cannibals and eat each other until they too have all gone. A bit expensive I understand, but worth it if it puts you back in control. The secret here appears to be to introduce the predators before the problem gets out of hand. If you do use predators you will almost certainly have to stop using insecticides, as they will kill your precious beneficial insects as well. There is also a period to wait between your last spray and your first introduction of predators.

10) Some people regard chemical sprays as less effective, but Polysect is reputed to be a good control against mites and other pests. Read the label carefully as you will see that differing strength mixes are required for the various pests.

11) It may be possible to place sticky paper traps cut into strips around the pots to prevent the mites emigrating from plant to plant.

12) Hot pepper wax - which is sprayed to prevent transpiration - is another remedy which smothers the adults on the leaves, but does not kill the eggs so be prepared to repeat applications every 4 or five days until control is established. Mites need to expire a lot of moisture from their bodies to survive. If you can affect this you are well on the way to overcoming the problem. This Hot pepper wax is also a brilliant repellent to white, black and greenfly, as they do not like the Peppery taste of Cayenne! It also makes the leaves shine which is another bonus. Again a little expensive initial outlay but it goes a very long way so you don’t need much. I love this stuff! And it is perfectly “Organic”. The cayenne powder, sprayed onto the surface of the compost in your pots, is also reputed to deter crawling insects or sciarid flies, but I have yet to try this. Sciarid is a pest that I have very little trouble with anyway. However, it may just be an organic deterrent to Vine weevil crawling onto your pots so could be worth the try. (Just as an aside, the chopped & dried stems of tobacco plants are used by cage bird breeders to keep mites at bay. The stems are incorporated in the nesting material and create an inhospitable environment for the insects. If you grow tobacco plants,( nicotiana), then you only need to hang up the plants to dry as you would with any dried plant, and you will have your own supply. And in case you want to know –yes you can smoke the tobacco, but that can be the subject of another article. Nicotine in the form of snuff is also an insect deterrent when sprinkled on top of the compost – it must make them sneeze! Remember though that tobacco is high in nitrogen so if you are one of the very fussy people who make your own potions for compost it may upset the balance of your mix. Very little is needed and this should not be a problem.

13) How many times have you ignored a mark or blemish on a leaf because there was no easily identifiable cause? I have. Sometime the culprit has gone and is now doing damage elsewhere. Or is he… Perhaps he is just too small to spot. If you have a marked or damaged leaf take it of without too much disturbance. Chances are you will be getting rid of a major headache about to unfold.

14) The Internet has some good articles if you want to go that far. Smothering the mites seems a popular method and may be worth the effort. I have taken these recipes from a website, and haven’t any reason to doubt their effectiveness.

Spray Recipe #1
Blend together the following
½ cup of starch or flour
½ cup milk
1 gallon water

When sprayed over the mites this mixture will trap them as it dries into a thin film. Repeat every 4/5 days until control established. Check plants daily to ensure effectiveness. Dead mites will turn black so are much easier to see.

Spray Recipe #2
This is also a deterrent on uninfected plants and may help to keep mites and other pest at bay. It is also good to ward off Vampires.!
½ - 1 ounce Garlic
2-3 ounces of onion
½ - 1 ounce of cloves
½ - 1 ounce of Cayenne pepper

Whiz in your blender with 1 Cup of water till very fine.

Add this mixture to one gallon of room temperature water. This spray must be repeated 3 times at 5-day intervals to kill off freshly hatched mites (the spray will not kill the eggs). If the mixture gets washed off it must be re applied.

Spray Recipe #3
This is the favourite of the person who posted it onto the website. It is a product called “Ultra Fine”. This is soap and phosphorous solution intended to specifically kill Spider mites and their eggs (as well as most other common pests) with just one spraying. Repeat after 10 days as a precaution in case you missed any the first time. I have been in touch with a guy in America to see if this is available in U.K. but am still waiting for a reply.

I will be on the lookout for this one, as it seems to be just what I/ we need!

Once control is assured I think I will try the biological methods… perhaps a few Praying Mantis, which will eat every other insect known to us gardeners, and I think I know a lad around the corner who keeps them as pets. We may be able to do a deal…hmmm.

Lessons I have learned:
Prevention is better than cure.
Don’t just pick up a plant and bring it to the show to help fill the benches. If you haven’t properly prepared the plant – leave it at home!
Take your magnifying glass with you when you are going to buy plants – no matter where from – and check them thoroughly. (As an aside, I once saw a judge use a magnifying glass to spot Rust on a plant – that is how small the problem was on that particular plant, and in no way could the exhibitor have had an inkling that there was a problem. I must admit that I thought that was a bit OTT but it did bring home the need for constant vigilance. On the other hand some plants have received awards with clearly identifiable evidence of infection/infestation, of Rust or overrun with whitefly. In those cases the exhibitors “got away with it” as far as prizes were concerned but they may have inadvertently given someone else a real headache.
Keep the Bees out of your greenhouse.
Try not to move plants in and out of the greenhouse as you could be carrying in the latest infestation. Perhaps replacing sections of glass with Bug screen will increase airflow and keep temperatures down whilst also keeping the insects out. This is a difficult one, as most of us do tend to carry plants into the greenhouse even to just work on them. Perhaps a separate area is needed.

I hope this article is of help to others like me, who know very little about the Red Spider mite and have chance to learn before the problem arises. No doubt there will be more information that can be shared from other members so keep the letters rolling in to Kath.


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