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Orchid Society
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Chemicals in the Garden
by Dr. Bert Pressman

Most hobbyists feel uneasy about the hazards of garden chemicals. I have heard experts advocate cumbersome protective garb when spraying, seemingly more appropriate for warding off evil spirits than chemical hazards. Others dogmatically admonish, "Never mix chemicals." Why not? What is needed for protection is informed advice and a little common sense. Perhaps the following comments will help put you more at ease when spraying orchids with various chemicals, such as insecticides, fungicides and fertilizers. As a general rule, fungicides are less toxic than insecticides, and fertilizers not toxic at all.

Physan [same as RD-20], at 1½ - 2 Tsp./gal, is a mild, general purpose agent for controlling bacterial, fungal and viral diseases. RD-20Since it is used extensively to control algae in our swimming pools, to wash down milk cow barns, and to disinfect the hands of surgeons, it is obviously not extremely hazardous. Physan is a "quaternary amine," which is chemically inert, but acts as a strong detergent, capable of disrupting microorganisms, but not solid tissue such as plants and skin [caution: keep it out of eyes]. It can be mixed with most other garden chemicals without chemical interaction, and also acts as a "spreader" to promote even wetting of foliage by the spray. When Physan is added to concentrated fertilizer solutions, however, an oil gunks out which can eventually accumulate and foul up the sprayer.

Cleary's 3336 [in smaller quantities sold as "THIOMYL, systemic"], is a replacement for BENYLATE, no longer available. I recommend it at 2 Tsp/gal, although some sheets specify ½ Tsp/gal. Orchids are attacked by several different types of fungus. To broaden the spectrum of fungi protected against, I add 1 Tsp/gal of another fungicide, TRUBAN. You can buy Cleary's-Truban, premixed, as "BANROT." Some growers prefer the fungicide DITHANE, but I find that the concentrated suspensions, required by the Gilmore sprayer, tend to clog up the orifice. To mix a batch of fungicide, first decide what volume of spray you need for the job [for me this varies from two gallons for a hand pump sprayer, to six gallons from a hose-end sprayer, see below]. For each gallon of spray desired, put 2 Tsp. Cleary's, and 1 Tsp. Truban [or 1 Tbsp. Banrot] in a cup, add a little water, and macerate to a thick, smooth paste. Add more water and macerate to a progressively thinner paste that will mix with water easily; transfer to the sprayer reservoir, add 1 ½ Tsp./gal Physan and bring to mark with water. DithaneShake to mix uniformly. You are now ready to spray. Common sense dictates not spraying into the wind or during a very windy day. Try to keep the spray out of your eyes and lungs. If I am conscious of some spray having gotten on myself, I do shower and change my clothes afterwards. If you have a troublesome fungus problem, you can spray every week or two; for prophylaxis, every month or so. Every couple of months you can broaden the antifungal spectrum by adding 1/8 Tsp./gal of the very potent SUBDUE to the mix. [Note: Subdue is very potent but very expensive. You may want to divide a commercial sized bottle with other growers.] Copper in the form of KOCIDE, [1 Tbsp./gal] is particularly useful on Phalaenopsis in the fall, but be careful as it is injurious to thin-leaved orchids and Dendrobiums.

I prefer ORTHENE as my general purpose insecticide, since it is water soluble, an advantage over the old standby, MALATHION. Besides, it smells more, which makes one think it is doing more. I use it at 1 Tbsp./gal, along with about a Tbsp./gal or so of Palmolive liquid soap, which not only acts as a spreader, but is also toxic to some insects [e.g. Scale] in its own right. Orthene may not be as effective against mites, which are not truly insects, and if that's your problem, you might want to use a specific miticide such as PENTAC, along with the Palmolive.

The trick to using the Gilmore, variable spray ratio, hose-end sprayer is knowing that, at a dial setting of 10, it takes 3 ½ gallons of spray to empty the 16 Oz reservoir. Accordingly, 3 ½ Tsp. of a chemical in a full reservoir gives 1 Tsp./gal spray. For other settings the following table may prove useful:

[Lower settings are less accurate, hence I don't use them.]

If smaller spray volumes than 3 ½ gallons are desired, reduce the initial volume added to the reservoir. For example, at a dial setting of 10, it requires 1 ¾ gallons of spray to empty a half filled reservoir, i.e. one containing 8 Oz liquid. If 3½ Tsp. chemical is diluted or suspended in the 8 Oz liquid, this will produce 1 ¾ gallons of spray containing a concentration of 2 Tsp./gal..

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