[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.