Orchid Disease

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.