Houseplant Aphids

(aphids come in many colors and sizes but usually you can identify them by their round or pear-shaped bodies and the two cornicles (little spikes) that emerge from the back of their abdomen. photo credit: Bob O'Neil, Purdue University)

Question:

I enjoyed the houseplants program a few weeks back. I'm still struggling with aphids, I think, on our...? Would the rubbing alcohol work on that? At what dilution would you recommend?

Answer:

If the aphid situation is really bad I would probably go to the next step of control which would be to use an insecticidal soap. If I discover a small population of aphids (i.e. a few) I usually begin by spraying the plant and its foliage with a strong stream of water. If the stream does not knock off the pests completely the hope is that the force of the water breaks their piercing, sucking mouthparts, disabling their ability to continue feeding on the plant. Then I might clean the leaves with a ½ and ½ mix of rubbing alcohol and water, physically removing as many pests as possible before placing the plants back on display. If the population is larger, but still isolated to a specific part of the plant, such as the tips of new growth, then sometimes it is best is to pinch off and remove that part of the plant to the garbage. As long as the rest of the plant is healthy and has plenty of foliage to photosynthesize pinching off a damaged shoot should not be the death of the plant. If anything pruning or pinching back your plant should promote new growth to follow. Lastly, if the plant is seriously infested, then buy yourself some insecticidal soap. As with any chemical, follow the instructions explicitly. I would place the plant somewhere safe so you can really coat the entire plant with the spray solution. I place my infected plants in the bathtub and spray them to the point of the soap running off the tips of the leaves. I let them sit and dry before putting them back into an area of direct sun, if applicable, then continuing to keep an eye on them. Because female aphids can give birth to live young in only a week’s time I would check again and potentially re-spray after a week or so. Again, follow the instructions on the bottle. Safer Soap, or some such insecticidal soap, you should be able to find at a decent florist or garden center/supplier. I usually go to either the Flower District on 28th Street or Chelsea Garden Center on 11th Avenue at 44th Street.

How to Combat Whiteflies

Question:
Can you suggest the best methods to get rid of white flies, both in a New York City garden, and then as a precaution before bringing plants indoors for the winter?

Answer:
Sure enough white flies are one frustrating little pest, aren’t they? The main problem that sets white flies apart from the other insect pests is that they can produce so many generations a year. According to reference books here in our library, most species require 20-30 days for a complete life cycle, and that length of time can be even shorter during the warmer summer months. With numerous overlapping generations in a year infestations can happen quickly and can be very overwhelming, but I am more than happy to share with you my tips for helping to control them.

First, as I like to do with all insect questions, let me describe the pest and the damage so you know more clearly what you are looking at. Whiteflies are minute sucking insects that hide and feed on the undersides of leaves. If you shake a plant with whiteflies you will see them fly up and make a little fluttering cloud. Adults lay eggs on the undersides of leaves and these eggs are gray or yellow and roughly the size of a head of a pin. The larval nymphs emerge only a few days later as translucent little scales, also on the undersides of the leaves, and begin feeding off the plant. As they suck out the plant cells to feed they continue to go through different growth stages until they become adults only a couple weeks later. As you might guess, this feeding weakens and stresses out the plant. A good tell-tale sign of whitefly damage is the sticky honeydew that they secrete and leave on the leaf surface. This sugary honeydew can lead to sooty mold, a black fungus that grows on the honeydew covering leaves and fruit. Sooty mold is not likely to kill your plant, but it sure is ugly.

If you have whiteflies on plants that you still have outside, I would go ahead and treat the plants with an insecticidal soap right away. Safer brand insecticidal soaps and other such soaps you should be able to find at your local garden center or any larger retail store (Lowe’s, Home Depot, etc.). Read the instructions and spray and coat the infested plants as best you can. Remember that spraying the undersides of the leaves is crucial since that is where whiteflies spend most of their time. I believe the bottle will recommend spraying the plant to the point of runoff. As long as the leaves of the plants are not too fragile, like certain ferns might be, you can repeat application of the insecticidal soap weekly until you see the situation getting better. In addition to spraying, any physical removal of eggs or nymphs that you can do will be a big help as well. A soapy paper towel and/or swab with rubbing alcohol will help as you attempt physical removal.

Finally, when you move the plants back inside before frost, put out whitefly traps. You can buy them prepackaged or you can make your own. Get a piece of florescent yellow paper and cut it down to 2” x 2” squares. Coat the paper with petroleum jelly. Then use a cut-down plant stake, or some such support, to place the traps in your containers. Since they are not the most aesthetically pleasing, place them in the back of the pots so they are not such an eyesore. The bright color attracts the whiteflies and they get stuck to the petroleum jelly. Throw out and replace as necessary. This way you can keep track of the pests through the winter and you can tell if there are enough of them that another application of insecticidal soap is necessary.

Red Nodules on My Maple in New York City

Question:
I have a very lovely Maple tree on my terrace. It is growing very well, beautiful leaves. However on the leaves there are tiny red nodules that are some sort of blight or insect. They don't move, but by seasons end most of the leaves have holes in them. The little red guys turn brown toward seasons end. The tree is healthy otherwise, and I would like to save it, but I cannot find out what this is or how to rid it from the maple. I have a fifty or so foot terrace, and this insect has not infested any other of the plants. If you can give me an idea of what this is and how to rid the tree of these "things" it would be greatly appreciated.

Answer:
Unsightly galls can be the work of many different kinds of flies, wasps, and mites. Because many insects only feed on specific hosts, knowing that it is a maple helps us narrow the options of what the insect is. Your description of the galls helps narrow the list down even further. The damage you are describing sounds like that of a gall mite. Eriophyd mites are microscopic mites that live and feed on many different kinds of trees and shrubs. Of the gall-forming mites, there are at least two that prefer to feed and live on maples, maple bladdergall mites (Vasates quadripedes) and maple spindlegall mites (Vasates aceriscrumena). The galls were describes to me as being more rounded than spindly, so I am going to guess that this damage is the work of the maple bladdergall mite.

As I usually do with insect queries, let me describe the life cycle and then recommended control. Adult mites over-winter on the bark of the maples. As the leaves emerge in spring the mites migrate to the fragile new leaf tissue and begin feeding. As they feed, the mites deform the plant cells and cause these galls to form. The adults burrow within these galls and lay their eggs. The larvae emerge, feed on the leaf tissue, and molt into adults in a few weeks time. The adults move on to feed and continue cycle. The galls are no longer used and usually turn brown.

The bad news is that these galls look unsightly; the good news is that this damage is not likely to kill your maple. Regarding control at this time, the only option is to remove the leaves that are heavily infested with galls. Physically removing the galls before the larvae can emerge will help control the populations. The next step is to take action the following spring. Use a dormant horticultural oil to coat the bark of the tree in spring before the leaves emerge. This oil will coat and suffocate the over-wintering mites and will help to diminish their populations before they get a chance to feed on the new leaf tissue. I would not necessarily count on complete eradication of the mites, but after two years of treatment you should find the populations to be more controllable and the damage to your maple less of an eyesore.

For this and other insect questions I refer to Garden Insects of North America by Whitney Cranshaw, available in our reference section here at the HSNY Library at 148 West 37th Street, 13th Floor.