North of England Orchid Society -

 Pests & Problems - or one or two common ones in the U.K. at least...

North of England Orchid Society -

Identifying and treating pests and problems...

Orchid Pests and Problems.

Orchids generally do not suffer from the usual plethora of ailments which affect many of our favorite garden plants.

This is for two reasons, firstly many of the species and hybrids we grow are alien to our local atmosphere, and consequently also alien to many pests and diseases we find outdoors, and the second one is that because of the fact that we grow them mainly indoors they are not exposed to the problem in the first place.

UUnfortunately, when a problem occurs it can be difficult to eradicate once is gains a foothold.

First step.

Identify what your orchid Problem is.

The most common orchid pests in the UK

  • aphids

    Aphids
    their poo leaves
    a sticky deposit

  • boiduval scale a real horror

    Boisduval Scale
    attacks cattleya etc.,
    hard to control

  • mealybug

    Mealybug
    hides in compost
    as well as leaves

  • brown scale attacks phalaenopsis

    Brown Scale
    hides under leaves
    of orchids

  • hslugs and snails

    Slugs & Snails
    eats anything
    leaves silver trail

  • thripadult

    adult thrip
    the nymphs
    do most damage

  • spider mite causes real damage to leaves

    spider mite invisible to
    naked eye thrive
    in dry conditions

  • orchid perfectly repotted

    weevils nibble
    the edges of leaves
    and flowers

Here are a few, in no particular order:- ....

Slugs.
Even if you think you haven't got any problem with these night-time assassins, you should always be vigilant for their silvery trails, sprinkle at regular intervals with a good slug liquid, and if you feel adventurous, take a torch-light trip into the growing area after dark, a good well aimed boot is something they have not grown immune to.

Weevils.
When you wonder why there is suddenly a ragged  in one of your best grown leaves, or chunks missing out of its margin, or the flowers then most likely you have weevils; arm yourself with a bottle of something suitable from the garden centre and follow the instructions. Its no use spraying the once, you must have strict regime of spraying every 5 days or so over a period of three weeks to eradicate most pests and their eggs as they hatch.

Common Scale.
There are two types of scale which you are likely to encounter when growing orchids;- The first one attacks Phalaenopsis in particular, and can migrate to most other soft leaved plants, look on the underside of the leaves for these hard brown limpet like creatures, if you have only one or two, wipe them off with a cloth soaked in methylated spirits, or resort to a systemic insecticide regime as mentioned in the above paragraph, systemic insecticides act by being absorbed into the plant tissue, effectively making the plant poisonous to its attacker, but they should be used with care, do not exceed the stated dosage to avoid damaging the plant.
The other can be very nasty, and primarily has a taste for Cattleyas and their cousins, but can adapt to devouring other orchids such as Vanda's, this is:- Boisduval scale. A very fancy name for a real horror, you may notice flat round scales on the underside of the leaves, which if left unattended will produce a whole shipment of what appears at first to be a white fungus or mealybug, these are the nymphs by the thousand, and they are setting off to desiccate the rest of you collection.
The trouble we have in the UK is that it is a tropical insect, and many of our pesticides do not treat the problem, one we have found to be of use recently is Doff, you may have to search around to find it, it is very effective against this type of scale, and several other pests as well, you will probably have to give the plant a good cleaning after a couple of weeks or so for aesthetics. Prior to treatment, take an old toothbrush, dipped in methylated spirits, and having removed any old sheaths ( papery coverings from around the pseudobulbs), scrub gently to remove the majority of the adults.

Mealybug
Usually appears as a cotton wool ball around leaf axils, or inside the sheaths of new shoots, the above fungicide pesticide soon sees them off, but again if its very localized, then methylated spirits on a cotton bud sees them off wonderfully.

Thrips, greenfly, blackfly, spider mite.
They all find a niche somewhere, the latter is another difficult customer to deal with, and in addition to spraying, it is a good idea to wipe the leaves and stems of infected plants with a methylated spirit soaked cloth, every few days if necessary to kill the eggs.

SPOTS AND DISEASES.
Orchids can fall foul of leaf rot, mildew, botrytis and many other pathogens, by and large, providing there is a good air movement around the plant, and that by nightfall the leaves are fairly dry, then fungal infections should not be a problem, and correction of the bad condition, along with a fungal spray (check with the garden centre that it is safe for orchids) should do the trick, a fast fix for a localized leaf infection is to dust a little cinnamon onto the infected area !

VIRUS.
It is very difficult if you have a plant suffering from a virus disease to identify which particular type it is, and most likely a useless exercise anyway, as viruses are almost impossible to cure, thankfully, providing you are hygienic around the growing area, and that any tools used on the plants are thoroughly sterilized after use between different plants, you should not encounter this type of problem.

Viruses are the most widespread disease problems affecting orchids and fortunately most of them are rare and in many cases hardly cause symptoms.

Only a few orchid viruses are common and can cause problems, the two most important of these are Cymbidium mosaic virus (CymMV) and Odontoglossum ringspot virus (ORSV). These viruses are found throughout the world and have a wide host range, affecting many orchid genera.
CymMV virus infection causes leaves to show a mosaic pattern of light and dark green areas, or black/brown necrotic spots often appearing as a line with sunken areas on both sides, Petals may develop lines of necrotic spots, however floral symptoms may be delayed up to 10 days after opening, so healthy appearing flowers may be sold on
 ORSV virus infection causes necrotic spots, sunken areas, chlorotic streaks, line patterns and ring spots on leaves and stems. Cattleyas and their hybrids display colour breaks with irregular streaks of pigmentation.
Floral symptoms render the plant valueless, while the leaf symptoms make it unattractive as a house plant.
Both viruses are easily transmitted from plant to plant by contaminated cutting tools, work surfaces, used pots and hands. Therefore, if an infected plant is added to a collection, the virus can easily be spread to healthy plants through propagation and other normal day-to-day plant care practices. Both these viruses which affect orchids are very stable and lose their infectivity very slowly, so sap from an infected plant that has dried onto tools, pots or benching provides an excellent source of infection. They can remain infectious for weeks or longer under the right conditions. The greatest risk of spread is via vegetative propagation from an infected mother plant and is the easiest way to find yourself with more virus infected plants.

If plants to be meristemmed are displaying suspicious symptoms, they should always be tested for viral infection first, before introduction to a greenhouse.




TREATMENTS
Should be carried out giving due consideration to the instructions for use and safety provided by the manufacturers of the control substances we list below; solutions which we have used and found to be satisfactory for ourselves, the decision to try one or more of these in your environment must be yours and made under your own responsibility.It is always a good idea to try and remove as many of the pests and their eggs a possible before applying insecticides.
Pure methylated spirits (not surgical spirit) is excellent for this purpose, apply a little on a cloth and wipe both sides of the leaves, for the less aggressive pests this alone can be a cure in itself.

Don't expect a one off cure, several applications given over a period of three weeks at five day intervals may be needed. do not use more  than one insecticide at a course of treatment or you may build up resistance to it.

One home made cure can be produced in the kitchen if you want a non toxic insecticide, here is the recipe for you to try at your own risk :- Six heaped teaspoons of ascorbic acid (vitamin C.) three teaspoon of plant friendly detergent (non ionic) and a pint of water, spray onto aphids and suchlike, the mixture will kill any insects which absorb oxygen through their skin, but not their eggs. As prevention is always better than a cure, treat new plants with respect, quarantine them if possible, try not to let intake fans suck air in from anywhere near a flower border or hedge, and always be prepared to sacrifice a "well infected" plant for the sake of the rest. It will not work on all pests

One or two of our members resort to a more agressive treatment which they swear by - try it at your own risk.
Fill a bucket with fresh water, and add household bleach ( Domestos) add enough to give a frothy appearance when mixed in. remove the plant from the pot, shake off all the compost, and immerse the roots and plant fully in the bucket for about 5 minutes, after which rinse the pant in clean water and re pot.

SYMPTOMS AND CAUSES.

Irregular markings on leaves, discolored or uneven patches on flowers possible viral infection.
Uneven pieces removed from leaf border weevils.
Un-natural silvery underside to leaves spider mite.
Silvery trails on plants and benches slugs or snails.
Holes in leaves or flower stems or flowers slugs or snails.
Dark mildew on leaves, hard limpet creatures underside of leaves common scale.
Cotton wool type of stuff ( brownish creature inside of mass) mealybug.
Flat scales on mainly underside of leaves and or tiny white fluffy masses boisduval scale.
Depressed dark spots possibly with lighter ring round them fungal infection.
Limp flaccid leaves on Phalaenopsis etc. root problems.
Dark brown or whitened patches on leaf sunburn.
Yellow or very light green leaves but plant flowers too much light.
Dark green leaves but plant does not flower too little light.
Flower buds develop then turn yellow and drop off shock.
Leaf tips turn brown over feeding.
Honey dew on leaves greenfly.
Plant falls out of pot earthquake.



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