Orchid Disease

[fred]

When it comes to disease orchid pest, any form of extermination should be repeated at intervals, for, although the first application kills flying pests, the dormant stages are rarely touched and must be killed at maturity.

One of the most deadly orchid pests, but fortunately not very common, is the Cattleya fly (Eurytoma orchidearum).

This insect lays its eggs in the tender new leads of the Cattleya. The lead, when the eggs have hatched and the nymphs begin to feed, swells grotesquely and becomes soft to the touch.

The nymph finally eats its way out of the lead, emerging as a fly about a quarter of an inch long with a coal-black body and light transparent wings.

A plant that has been attacked by this orchid pest, should be isolated and the injured growth cut off and burned. Careful observation of the new growths should lead to discovery of the condition before the nymph emerges as a fly to cause more damage.

When it comes to disease orchid pests, another vicious pest much dreaded by growers is the Cattleya or Dendrobium beetle (Diorymellus laevimargo), which does not, incidentally, limit its operations to the species for which it is named.

This hard-shelled, shiny black beetle, about a sixteenth of an inch long, has a curving beak with which it attacks flowers, buds, and leaves.

It lays its eggs in the new green tips of the roots, where the larvae then hatch and, by feeding, destroy the root growth. The mature beetle is quick and agile, and when disturbed will usually drop to the potting material, where it is almost invisible.

These beetles are less active in the early morning and late at night, and hand picking may get rid of many of them at these times.

Cockroaches are voracious orchid pests, and seem fond of orchids, but they are not apt to be prevalent. When damage caused by such a pest is apparent—chewed leaves and bulbs—the grower will patrol his house in the dark with a flashlight and hand pick the pests.

Other unfriendly foes may be detected in a similar way; snails and slugs feed in the dark, and do much damage to the blooms.

Growers wax eloquent on their sad part in providing luscious orchid salad for these hungry pests. Benches set in cups, filled with oil, and provided with covers to keep the water from overflowing them are used by some growers.

Clean ground, gravel or cement floors, free of vegetative growth, help to keep them out. It seems, however, that the most careful precautions against their entrance fail and a control is needed.

Any of the snail baits on the market may be used—preferably in pellet form. Pellets of Snarol or Buggetta may be scattered on benches and floor, with varying results, frequently disappointing.

Cory's Bait and Sander's Sui-slug apparently give a good control, although the pests at times still prefer the orchids.

A tempting bait may be formed by mixing any of the bait meals with rotten lettuce leaves. Placed in a fresh leaf on top of the potting material, these tid-bits will lure the pest from other spots.

However, they must be removed before watering, an item of labor in a large house. Earwigs, also destructive, may be controlled by the same methods, using earwig bait. They will also crawl into a rolled-up newspaper at night, which can be burned in the morning.

Fungi, bacterial diseases, and virus diseases are all menaces. The conditions conducive to orchid growth are those under which fungi thrive. There is a friendly fungus, Rhizoctonia, that is found in association with orchid roots.

Unfortunately, however, unfriendly fungi are present just as frequently, especially on a weak or sick plant. Too high humidity in the house, coupled with chilling from a sudden temperature drop or draft, will encourage fungus growth.

The damp heat used for seedling growth is particularly attractive to certain damping-off fungi. Once the fungus has attacked the seedling it becomes a race as to which will grow the faster.

When it comes to disease orchid pests, there are too many kinds of fungi to mention any but the major types. Gleasporium forms on the leaves yellow spots that eventually run together to form a large brown spot. Spread of this fungus can be prevented by airing and drying.

Bacterial disease in the orchid house is a little-understood subject. Again air and drying out before chilling do much to avert damage. A brown rot is caused by Phytomonas cypripedii, which frequently appears in the growing points of Vandaceous plants or often in wounds. Erwinia carotovera will enter a wounded leaf and infected parts turn dark green.

Spread of the infection is rapid and results in complete collapse of the leaf and bulb. As this disease may be spread by contaminated hands or tools, cleanliness and care will prevent damage.

It is wise to cut off the injured part, burning it, and then sterilizing the knife or shears before touching another plant. Badly infected plants should be burned, infected plants of any kind isolated.

Phalaenopsis seem to be peculiarly susceptible to the disease of bacterial black spot. This appears as a tiny pearly spot in the crown and goes unnoticed frequently. The spot gradually turns black, spreads, and the leaves drop off, leaving an apparently dead crown.

In some cases such a plant may be nursed back to health and blooming, by repotting in new medium, injuring the roots as little as possible, and spraying lightly until new leaves form.

Water allowed to stand in the crown of the Cypripedium plants frequently results in a wet rot that destroys the flower buds. Overhead spray, particularly when the sky is overcast and plants do not have an opportunity to dry out, allows water to drip down into the tissue surrounding the new growths.

Should this tissue turn black and soft with rot, it must be removed from the pseudo-bulb with tweezers. Care should be taken to avoid injury to dormant eyes or roots at the base of the growth. If rotted tissue is not promptly removed, the entire lead may be destroyed.

There has been much discussion of virus disease in orchids, but all too little is known for any certainty. A virus is apparently responsible for the mottled or marbled appearance occasionally noticed in blooms.

It seems to be a disturbance of the pigment and is in no way related to the 'watermarks' made by thrips. Plants suspected of virus infection should be isolated.

Considering the prevailing ignorance about virus, it is a good idea to isolate and watch any plant in poor condition for an unknown reason. There is a theory that a virus may be responsible for the blackening of tissue around the newly formed bulb.

All rot should be cut away from the affected leaf or bulb and the injury cauterized with flowers of sulphur or corrosive sublimate, neither of which should be allowed to touch the roots. The tool used in removing rot should be sterilized before being used again.

[fred]

The damage that can be done by pests and orchid diseases in an orchid greenhouse is so appalling that no effort should be spared to prevent their initial entrance.

The first line of defence is a roomy, airy greenhouse, in which balance is scrupulously kept.

The grower who inspects plants frequently should be able to halt an invasion of pests before it gets under way, while the preservation of plants and the immediate segregation of sickly ones prevent pests and orchid diseases from gaining an easy foothold.

The successful grower is a good housekeeper—picking up dead leaves, removing dead plants, and isolating sick ones. Adequate bench room for each plant is also an advisable precaution. The greenhouse can be kept clear of pests and diseases only if the grower recognizes signs of trouble and is acquainted with effective means of control.

There are a few merely bothersome pests whose appearance need occasion no alarm, although the grower may wish to be rid of them. Ants and fruit flies are the most common members of this category.

Many growers dislike ants. In the jungle ants have friendly relations with orchids—stinging ants often preventing human desecration of the plants—but in the greenhouse ants are unsightly and unnecessary.

They have never been proved guilty of damaging orchids, but as sometimes they live in cooperation with the mealy bug and may assist aphis, it is just as well to prevent their entrance into the greenhouse.

Ant-proofing outside the house is the safest and simplest method of dealing with them. Fruit flies are often found in the greenhouse.

When it comes to orchid disease, they feed on decomposing Osmunda and, although at times difficult to distinguish from the scale fly, they do no harm. Routine spray will dispose of them.

Thousand-legged insects, mites, and sow-bugs are occasionally found in the greenhouse but apparently do no harm.

The tiny plant lice that thrive in decomposing potting materials are harmless though disturbing to a grower's sense of neatness and order, and almost impossible to eradicate.

Where possible, garden snakes, toads, frogs, and salamanders should be encouraged, as they feed on pests.

The coming of spring and warm days brings thrips, red spiders, and aphis. The maintenance of humidity in the greenhouse during this period will not only keep plants from being burned, but will also control these pests as they are susceptible to pneumonia.

Such control is especially important because these pests are extremely small and may do damage before they are seen.

Nearly all flower-lovers have seen thrips-marked gladiolas; the petals and leaves of orchids attacked by thrips are disfigured in much the same manner. Red spiders leave ugly rust marks, particularly apparent on leaves of the Cymbidiums, and they can kill Miltonias.

In the past, systematic spraying with rotenone, pyrethrum, or nicotine provided a fair control for thrips, red spider, and aphis. Some growers even burned nicofume (a poisonous gas, difficult to handle) two or three times a year. In spite of all precautions the pests seemed to persist.

Any form of extermination should be repeated at intervals, for, although the first application kills flying pests, the dormant stages are rarely touched and must be killed at maturity

[Cynthia, Prescott, AZ]

On the subject of virus mentioned by Fred near the end of his post, I do not think the idea of tossing doubtful plants, unless of course they have color break, which leaves the diagnosis fairly certain, is a good one. It is likely more non-virused plants will be thrown out than virused ones, and it will make very little change in the number of virused plants in a collection. I suspect, based on my experience of the number of plants purchased from reputable dealers that turned out to be virused, that about 5 to 10% of any collection is virused, and tossing a few plants, most of which are not virused will make too little a dent to help much. My recommendation is to toss any badly growing plant, which is likely caused by virus in its late stages, but who really needs a very poor performer any way, toss any with color break, then always use sterile tools, new or sterilized pots, disposable gloves for repotting, and avoid stabbing your plants with a finger nail or other dirty object. And if you do accidentally poke a plant, heat the spot with a soldering iron or hot glue gun. Beyond that, just enjoy your orchids, virused or not.

[Mr Speciosum]

For the last six years I have had a LARGE problem with slugs with the occasional snail thrown in and every year was the target of aphids. I used Supracide to 'burn' the little pests that lived in the bark medium and Rogor in combination with White Oil for the aphids. That was until I discovered FROGS! Or more to the point, they discovered me, or at least, my tunnel house. In the last year, I have found 1 snail, 1 small slug and Zero aphids on 700 plants. I still inspect my plants at least once a week, sometimes as much as 4 times weekly due to the paranoia of six years of conditioned pest eradication but it's exciting to see the changes occuring to the plants even in a 24 hour period. No longer do I rely on pesticides, except for the religous spraying with white oil of any new orchid which enters the house, even though I have an arsenal Monsanto would go green with envy over. My little froggies are now the first line in the defence of pests. Have had only one negative with the frogs which was that they laid eggs in the top leaf axis' of a large Den., which in turn rotted the flower caps off....small price for peace of mind and the joy of seeing these beautiful amphibians hopping from plant to plant.

[fred]

very interesting way to treat your plants.

with Frogs.

I think we would like to know more about this way of treatment.

may be you could enlighten us.

[Mr Speciosum]

Hi fred,
I'll try to expand on frogs, but really not too much to say. They eat anything they can get their tongues onto, which includes earthworms, slugs, not too sure about snails, as I can't remember seeing any empty shells, and I think they go any other flying insect they can get.



the 'Froghouse'. Placed in the middle of a paddock on a disused concrete slab.





YooHoo, I'm hiding in here.





or am I hiding here??? Just two of the 'obvious' exterminators that have made 'the Froghouse' their home.

[manfred]

I thinks that is fantastic.Take my hat off to you guys growing orchids in Tassie.I think I am doing it tuff in Sydney.
cheers Manfred