Yesterday our Society had our annual Auction of plants. We inspect the plants before offering them for sale. Two plants had clear evidence of pest infestation. I won't post photos because I don't want the donors to see the plants. But I'll describe how I'm dealing with this issue.
The first plant was suspect from across the room. It's a monopodial orchid; the top leaves were dwarfed, twisted and distorted. I looked more closely and saw one small leaf almost folded in half, with some white fuzz in the crevice. I tried to open it and it split along the crease, revealing old mealy bug fuzz. I picked up the plant and noticed plenty of deformed leaves. As I turned over a curled leaf, I found my prey: two big, fat and living mealy bugs. I showed the members running the Auction, and we set the plant aside, far from the other plants.
The second plant is a sympodial orchid with numerous thin leaves. Almost every growth showed obvious and severe snail damage: the distal halves of leaves missing, with a ragged edge; the top of the newest growth completely chewed off; scattered holes in the leaves with ragged edges.
I brought the plants home after the auction. Nights here are in the mid 40s F / 6-8C. The snail-infested sympodial orchid easily tolerates those temperatures, so I began with that. The mealybug-infested monopodial orchid had to go into the house for the warmer temperatures, where I set it far from other plants.
This is the wrong time of year to repot the sympodial plant. It has just matured a new growth and has no active root growth. However, it is accustomed to a relatively dry winter, and the only other option was throwing it away. It is relatively uncommon in cultivation and is large enough to divide, eventually providing a few more plants for our raffle table. So I proceeded with hope.
I unpotted the snail-infested orchid over the garbage can. I removed as much old medium as I could with my fingers. This wasn't too difficult. I filled a 5-gallon / 20 liter bucket with water and added just a little liquid dish detergent. I submerged the plant and put a clay pot on top of it to hold it beneath the surface. I left it outside overnight, about 14 hours. This is long enough to drown bush snails and eggs.
This morning I removed the plant from the bucket and worked out more medium from among the roots. They look good, and most of the plant looks good. There is water damage around some of the fresher snail bites, which is expected, but experience tells me this won't be a problem. I poured the bucket out onto the street, and set the plant where it will dry, far from other plants.
My next step will be a coffee soak of the plant. Caffeine kills snails. (It probably also kills mealy bugs, but I haven't tried that - see my note below.) I've described this on OB before. I'll brew and cool strong coffee. I'll completely wet the plant's roots so it doesn't take up much coffee, which some people report damages orchid roots. I'll soak the plant for an hour in the coffee, then rinse, then dry.
Then I'll pot it up. I would normally grow this plant in S/H but it's not making roots, so I'll keep it over the winter in medium bark. Next spring, if it survives, I will divide it and move the pieces to S/H when it begins growing roots.
The monopodial plant I will treat the same, except I'll soak it in the house, where it will be warmer. I will start with lukewarm water. I will only soak it for about 6 hours because I want it completely dry before tonight, when the house will be cooler than in the daytime. Tomorrow I'll repot into S/H, because this type of plant makes roots all year, and it has a very healthy aerial root system now.
Of topic notes - Asian Cycas scale and coffee
As for caffeine killing mealy bugs - there is a cottony scale insect in continental Asia that infests species in the ancient, cone-bearing genus Cycas. There are a lot of species of Cycas; the well-known sago "palm", Cycas revoluta, is from Japan.
The scale insect reached populations of Cycas micronesica on Guam and began devastating the plants. The likely source was infested Cycas revoluta imported for landscaping of newly-built resorts. There seem to be no native predators of the scale on Guam. People were worried C. micronesica might be wiped out on Guam.
The scale reached southern Florida and began killing all species of Cycas in landscapes. It reproduced so rapidly it covers entire very large plants with white cottony insect bodies, so they looked like flocked Christmas trees. The plants died because photosynthesis was blocked. The scale would grow somewhat on other genera of cycads but did not kill them.
Pesticides were effective but the scale returned as soon as residual traces were gone.
Then a cycad hobbyist noticed that the Cycas which he habitually mulched with his coffee grounds was not infested. People began experimenting. It soon became clear mulching cycads with coffee grounds killed the scale.
So I may do some experiments with coffee next time I bring home a mealybug- or scale-infested orchid.
Suspected pests - how I did it
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