A commercial product called T.A.T. has been used, as a spray, at intervals of three to six months, with harmless but efficient results. Other solutions of D.D.T. with oil should be avoided by the amateur because of the penetrating quality of such solutions. A suspension of 50% wettable D.D.T. in water, one tablespoon to a gallon, is a safe and easy control, but it will settle if not agi­tated. In fact the result seems to be elimination rather than con­trol of flies and ants as well as the scale. Unfortunately it does not seem to have the same effect on snails and slugs.

Cockroaches are voracious 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 since they are composed of arsenic or methaldehyde, which on direct contact will burn the bulbs. 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.

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. The affected parts of the plant should be wiped with a dilution of o.i per cent bichloride of mercury. Cladosporium causes brownish spots on the leaves, which eventually turn black, and the leaves col­lapse. Bordeaux 4-4-50 or ammoniacal copper (Solcap or Bordelo may be used) will check this fungus. Wiping with corrosive sub­limate will control Diplodia, which forms brownish pin specks on the leaves, and Cercospora, which causes roughened olive-green spots to appear. Oncidiums are the usual victims of Phylosticta, which shows in dark spots on upper and lower leaf surfaces and yields to copper sprays. Excess humidity encourages leaf mold, Botrytis cinerea, on Cattleyas, but it can be controlled by simply drying the air and providing more ventilation. Ventilation is per­haps the best defense against many of the fungi, hence the re­peated warning against allowing the greenhouse to become over­crowded. Soap in insecticide spray and oil in commercial sprays help control fungus, but oil sprays must be used with caution, as oil in any but minute quantities is injurious to orchids. About 20 minutes after oil is used the plant must be washed with a fine water mist. However, the simple formula of 50% wettable D.D.T., suspended in water, 1-800, is so efficient for pests that it is foolish for the amateur to use oil at all.

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. Corrosive sublimate (0.1%) applied to injured parts should check the spread of this disease. 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. However, if the tiny beginning of the disease is noted, immedi­ately treated with 1-1000 bichloride of mercury or Bioquin 700, the advance of the disease may often be checked completely.

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. As so little is known about the cause or cure of virus infection, it may be wise to destroy doubtful plants—the loss of one or two specimens is certainly preferable to infestation of the entire house. 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.

Some growers attribute the frequent appearance of dry or blackened flower sheaths, and the consequent loss of blooms, to a virus but there is no conclusive proof of this. The consensus of opinion is that the condition is a result of a lack of air, or sudden chilling while damp. The dry sheath may be removed by slitting both side 'seams' and pulling each half toward the leaf with a quick jerk. This procedure may save the buds. Infrequently it will be found that buds have succumbed to wet rot inside an appar­ently healthy sheath. It is likely that this condition results from steaming caused by the 'sweating' of an excessively heavy sheath that has been subjected to too much heat. Many growers make a practice of cutting off the tops of such very heavy sheaths as soon as the buds show at the base. Cattleya Mossiae has a habit of forming the sheath months before the bud appears. This sheath very frequently dries up and turns black, but the buds usually survive.

D.D.T. has been mentioned several times in this chapter. The discussion of pests and diseases cannot be closed without more detailed consideration of this boon to pest control. D.D.T. has been available for just the years since the war, but experimenta­tion has taken place rapidly with excellent results. We reiterate that the amateur must use caution in handling D.D.T. mixed with oil; spraying every three to six months with a suspension of 50% wettable D.D.T. in water, one tablespoon to the gallon, is a safe, easy, and effective control. Many commercial growers have been using D.D.T. over a period of years with success, but they keep their formula secret.

Ernest N. Cory, writing in the American Orchid Society Bul­letin, says that, correctly used and compounded, D.D.T. emulsions have been proved specific for thrips, Dendrobium beetle, and many types of scale, and that the treatment need not be more frequent than once in six months. At the U. S. Botanical Gardens an emulsion of Xylol-Triton has been used on certain species of orchids for a period of two years without harm. An emulsion of 20% D.D.T., zo% Triton B 1956, and 60% Xylol in a concentration of 80 cc. to a gallon of water is the formula recommended by Mr. Cory. He advises controlled experimenta­tion with a  few plants  before adoption  for general  use.

D.D.T. may be used safely in a duster in powder form. It is harmless to plants when suspended in water, but is difficult to use this way, because constant agitation is required to prevent precipi­tation. Some type of spreader makes the use of D.D.T. easier and more effective, but also more dangerous. Oil gives D.D.T. a pene­trating quality that powder alone does not have. Oil is harmful to Miltonias, perhaps less so to Cattleyas, and apparently not at all to Phalaenopsis. If the use of oil as a spreader is necessary, wash­ing the plant with a fine mist of water about 20 or 30 minutes after spraying will counteract the harm in some measure. The spray should not be allowed to roll back into the crowns or axils of the plant. Sometimes, while harmless in themselves, D.D.T. and a spreader in combination may be injurious to plants. Camel­lias and hibiscus have been damaged by a combination of Volck and D.D.T. This is reason enough for the grower to experiment, if he must, on a small scale.

In brief the rules for control of pests and diseases are: (1) abso­lute cleanliness; (2) plenty of air and bench space, with no crowd­ing of plants; (3) immediate isolation of infected or suspected plants; (4) proper control of humidity with no chilling while the house is wet; (5) a routine system of spray with a noninjurious insecticide, perhaps alternated with fumigation by burning nico-fume; (6) removal of armored scale by brush or fine mist spray under pressure; and (7) sponging fungus-infected spots with cor­rosive sublimate or copper sprays and dusting injured parts with sulphur to check the spread of rot.

The grower who keeps his plants in good health, providing the most favorable environment for vigorous growth and repotting at the proper time with fresh potting material, will cut to a mini­mum his troubles with pests and diseases. Plants with healthy bulbs, leaves, and roots are remarkably pest- and disease-resistant.

We again emphasize the necessity of handling all insecticides with extreme care. Exact attention should be paid to the precau­tions advised by the manufacturers, such as wearing a mask and rubber gloves when using the insecticide. The definite toxic effect of many of the new discoveries is still a mystery.

Are You Ready To Move Onto The Next Lesson? Click Here...