Pests
Orchids, like most plants, can suffer from a number of pests and diseases. Pests can arrive in your collection by various means and summer, when they are breeding rapidly, is the most dangerous time. Some are fairly easy to deal with but many can cause severe damage or introduce viruses, either of which could result in the loss of your plants. Placing newly purchased plants into a quarantine area for the first couple of weeks is a good idea as any problems should show up in that time so you can prevent them spreading to the rest of your plants. Pests can reproduce at an alarming rate, but good culture and handling and checking your plants regularly will help you identify any problems quickly and prevent them escalating. Most people who grow orchids will suffer an attack at some point. Don’t be disheartened and blame your cultural methods if you suddenly find bugs on your favourite orchids – you probably just bought a bunch of flowers or opened a window!
Photos will be added to this section when we have them but, as that might mean we, or one of our friends, is suffering an infestation of something, we have to regard the current lack of illustration as a good thing! If anyone has a good, clear, photo of an orchid bug or the effect of a viral attack, please use the Contact Us form to get in touch with us. We would be happy to use it to illustrate the problem. We would also like to hear what methods you used to tackle it.
Aphids
These little horrors must be familiar to most people. Certainly anyone who gardens in the UK will have had to tackle them on all kinds of plants, indoors and outdoors. Blackfly are black; greenfly are, well, green (although they sometimes have a reddish-brown colour) and are small, approx. 1/8 inches (3 mm) long. Adults and juveniles are similar in shape, being narrow and pointy at the head end, broader and pointy at the other end, and wider in the middle (from your orchids’ sap!) Apart from the size and the adults’ wings, there is little difference between the adults and their young.
Aphids breed very rapidly, producing several generations within a couple of days. They attack leaves and flowers, and are particularly fond of young, juicy, new leaves and buds. Your soft-leaved orchids are most at risk, as their tissues are easier to penetrate. They leave a sticky residue, called honeydew, in their wake. This can encourage ants, which “farm” the young aphids for this sweet treat. Aphids can carry viruses, which they pass from plant as they suck the sap from the leaves. If numbers build up they may severely weaken a plant.
Control of aphids is not difficult, in theory, although because of the speed of their breeding we have sometimes found them harder to deal with than some of the traditionally more difficult pests. Treatments need to be repeated regularly in warm weather and constant vigilance is needed. They are soft-bodied and can be squashed by hand, if only a few are present. Ladybirds (ladybugs) and their larvae eat large quantities and are a good method of control in greenhouses or outdoors. There are plenty of organic, pet and people-safe, sprays available if you prefer, or need, to use them. After all, while ladybirds may be quite nice in the garden, you probably don’t want to have them roaming all over your living room! Do read the labels though as some sprays may not be suitable for use on orchids.
Caterpillers
In the last couple of years I have been plagued by something that lays eggs on the undersides of leaves. The hatchling, at some point, glues a folded-over leaf to itself, or sometimes if two leaves are crossing it will glue them together, and it pupates in there. The resulting caterpillers are exactly the same colour as the undersides of the leaves it feeds on – in my greenhouse, mostly masdevallias – and are incredibly difficult to spot. If I find the webs I squash them, but only once have I seen a caterpillar (and my partner spotted it, I didn’t, even when he was pointing at it). I have no idea what it eventually turns into, but it is currently a worse problem for me than all these others put together!
Red Spider Mite (Two Spotted Mite) and False Spider Mite (Flat Mite)
These tiny pests are probably the ones that strike terror into the hearts of orchid growers (and other indoor gardeners) more than any other. They suck the sap from the leaves, killing the plant cells and eventually the leaf. If left unchecked they will kill the plant and spread to others. (Red spider mite should not be confused with the larger – approx 0.25 inch – red, velvety coloured spider-like insect you sometimes see in the garden. That is a velvet mite and is easy to see. The young of velmet mite are often the ones that cause the itchy red swellings on your legs after you’ve been gardening. They bite, but you’re unlikely to feel them at the time.)
Idenfication in the early stages can be difficult as they are so small. You may notice tiny white dots on the underside of the leaves, usually in the creases along the mid or side ribs. There may be small rust-coloured patches on the underside of the leaf and sometimes similar ones, and/or tiny white dots on the top of the leaf. These are usually dead plant cells rather than the mites themselves. There may be very fine webs across the leaves, as in the picture (right) of an unfortunate Dendrobium Genting Fragrance, but not always.
Spider mites normally live on the undersides of leaves and are extremely difficult to see with the naked eye. They’re not easy to see with a camera either, even one that focuses as close as does mine (2 cms). This photo is the best I could do without a microscope, and even magnified you can only just about make out the mites. They are the rusty-red coloured dots with legs, and can be seen towards the bottom and the left side of the picture.
Spider mites are much more active during the Summer. They like dry conditions, which are often found inside the home or the conservatory, so raising the humidity can help to keep them at bay, but it won’t get rid of them once they’ve arrived. They do not feed in the Winter, but will hide in cracks and crevices ready to strike again in warm weather.
Treatment can also be difficult. Although the mites are usually found on the undersides of the leaves, they also hide in leaf creases and in the papery sheaths around canes and pseudobulbs.
There are products on the market now which will kill them effectively and, if you don’t mind using chemical sprays there are plenty to choose from. I don’t recommend any for orchids although I have used them on occasions. Spidermite Control, which is available in the UK, is an effective control. It is advertised as an organic control and appears to contain an oily substance so needs to be well shaken before and during application. It is not sold as a spidermite killer but as a control. We can’t comment on Neem Oil although we have heard that it is also effective. Unfortunately, much as we’d like to try it, it isn’t authorised for use as an insecticide in the UK. Those of you in countries where it is available will know far more about its uses and effectiveness than we do. Spraying will need to be repeated regularly as the eggs will not be affected by the spray. You can, however, buy Neem leafshine wipes…
For those who prefer a more natural form of defence, or attack, there is a predatory mite, called Phytoseiulus, which feeds on red spider mite. It is active once temperatures reach 16C and should be introduced as soon as red spider mite is spotted. There are also predatory mites called Amblyseius, which tolerate lower temperatures and humidity than Phytoseiulus. As with the ladybirds, the natural solution is more suited to use in a greenhouse than the home, where introducing even more bugs mite (sorry!) not be quite your cup of tea!
Slugs and Snails
There can be few who are unfamiliar with these everday pests. They are unlikely to be a problem in the house, although we have had them occasionally arrive in the growing medium of a newly purchased plant, so it’s not impossible. In greenhouses or outdoors they can cause far more damage. Both will eat their way through leaves and disfigure them, and they just love soft, new growth and buds.
The very large, black, slugs you often see in the garden are not the main enemy. The worst of all are ones you rarely see. They are small, less than an inch in length, and a dirty grey-pink in colour. They hide in the soil or the growing medium in pots by day, feeding at night, and can eat through the roots and kill the plant very quickly. Unfortunately I don’t yet have a picture of those.
There are various methods of controlling slugs and snails. Snails are easier to handle, literally, and can be picked up by their shells for disposal. They can be very small though, and are not always as easy to see as the common garden snail in the photo below. Slugs are not pleasant to handle. The mucous (slime) they exude clings to your fingers and takes a lot of scrubbing to remove, if you are unfortunate enough to get it on them.
Slug pellets are effective, but are harmful to other wildlife and to pets so, while we’re not going to preach organic measures, we prefer not to use them. There are non-poisonous pellets that work by drying out the mucous. These are supposed to be harmless to other animals but are not rain resistant so need to be applied when the pests are active. We have used them by direct application after rain showers, and that method is very effective, but you have to be there. We no longer use them because we can’t be sure other animals are unaffected, and thrushes and hedgehogs are scarce enough these days without taking any risks. Barrier methods include crushed eggshells or coarse grit or sand. The theory is that slugs and snails don’t like crossing rough surfaces that stick to them. We haven’t found this method to be particularly effective but others have. Copper wire has a weak electrical field that deters them, but then they’ll probably just go off and eat your prize vegetables. Both pests have a liking for beer, and small tubs half filled with flat beer can be very effective. Physical removal and disposal is the cleanest method, but it is time-consuming if you have to do it yourself, and best done with a torch after dark or after rain. Dumping them over the garden fence won’t work, they will just come back. Enlist some little helpers. Encouraging wildlife into your garden won’t stop you getting slugs and snails, but hedgehogs, blackbirds and thrushes will all help to keep numbers down outside so there’ll be less of them to sneak inside. Frogs don’t spend all their time in water so, if you can encourage frogs or toads to take up residence in your greenhouse they’ll have a comfortable home and will be happy to help you in return.
I have now found one way of deterring slugs and snails outdoors, which I have used successfully with with raised, plastic, veg planters, and that is raw sheep wool. You can buy small amounts on eBay in the Crafts section, unless you live somewhere you can gather it from fencing around sheep fields. It is wrapped around the legs in a band about 2 inches wide and secured with waterproof tape – the kind you use for securing your greenhouse bubblewrap. It is not so easy to use in a greenhouse, at least, I haven’t found a way yet, but if you can why not give it a try?
However you choose to deal with pests, the fact is you’re facing a lifelong battle and constant vigilance will be needed. The good news is that more solutions to the problem of pest are being found all the time. One of them is bound to suit you. Good luck!