| Q I
would like to know the best way to combat spider mites in a collection of
phalaenopsis. I have sprayed the plants (top and underside of the leaves)
with Kelthane (2 tsp./gal.). I followed the initial spraying with a second
application one week later. I’m concerned about the mites’ developing
a resistance to this miticide. Is there a systemic miticide available that
does not require a follow-up spraying (i.e., kills adults and eggs and
does not require spraying the underside of leaves, which was very time
consuming)? Unfortunately, Kelthane is the only miticide available here,
but I could bring something back when I travel to the United States if it
is more effective. I grow in a lath house, so an aerosol bomb is not an
option. The humidity here is naturally quite high, and, as a result, I did
not suspect the damage was from spider mites, as I understood they
preferred dry conditions.
The infestation was quite serious so I sprayed a third time (one week later) with Safer Insecticidal Soap. It says on the label that it is effective against mites but I would like to know if you have any knowledge about its use against mites. A I presume you are having problems with two-spotted rather than false spider mites. Kelthane is not used so much for mite control any more and you are wise to be apprehensive about resistance problems developing. One of the best long-term miticide programs was a combined spray of Pentac (flowable) and Mavrik, but the Pentac now seems to be unavailable in the United States. Insecticidal soaps are derived from fatty acids and potassium salts, and, when applied as a dilute spray, they will damage cell membranes of spider mites. You have to make sure you achieve complete plant coverage or they will be ineffective. Horticultural oils, derived usually from the petroleum refining process, can be sprayed on plants to smother mites~ The newer formulations, often termed light or summer oils, can be applied to growing rather than dormant plants with two provisos. Again, you must achieve a complete foliage cover to get mite control and always spray early in the day so that the plants are completely dry before the heat of the day when oils will often cause flower and foliar damage. When next in the United States, look also for one of the newer miticides, such as Akari. It has low dermal and oral toxicity, and is vastly more effective as a miticide than Kelthane. One of its great advantages is that it causes prompt knockdown of adult mites so foliar damage is halted immediately with almost a month’s residual control as well. I do not think it is registered for use on orchids at this time, but you will not have to worry about this in your country. You can always keep some on hand to use when a major infestation is noted. As with all insecticides, spray a small test block of phalaenopsis first and make sure there are no phytotoxic effects. I would look into your cultural program also, as the buildup of such a mite problem would suggest to me that your humidity is too low for the best results and the light may be too bright. Optimal phalaenopsis conditions do not favor mites. -- Andy Easton, Director of Education, American Orchid Society, 16700 AOS Lane, Deiray Beach, Florida 33446 (e-mail aeaston@ aos. org). |
Reprinted, with permission, from "Orchids" - The Magazine of the American Orchid Society, Dec., 2001.