Sticky plants often require treatment for sucking bugs

My 11-year-old poinsettia is sticky on both the leaves and branches. What is wrong with it, and how do I fix it?

­— Irene

When a plant gets sticky leaves and stems (at least when it’s not supposed to be sticky), that’s a pretty good indication that you have some sort of piercing-sucking insect on the plant. These are things such as aphids, scale and mealybug.

Actually, all three of these insects can occur on poinsettias. Aphids are small pear-shaped insects that often congregate at the tips of stems.

Scales really don’t look like insects at all. They’re usually small brown (sometimes black, gray, or white) hard-shelled “bumps” on the leaves and stems of the plant. Since they don’t really look much like a bug, they can be hard to spot for most people.

Mealybugs look like small little tufts of white cottony fluff stuck in nooks and crannies on the plant.

These insects suck the sap of the plant, weakening it as well as causing other problems such as distorted growth, decreased flowering or reduced growth and vigor.

This group of insects also secretes a clear syrupy liquid called honeydew. This is the sticky stuff you’re seeing. Honeydew is partially digested plant sap.

There are a number of different treatment options to choose from and many spray insecticides that will control these insects. Of the three, aphids are generally the easiest to control. Sprays with insecticidal soap, malathion, or imidacloprid will do a good job. The soap and malathion are both contact insecticides, so you have to spray the plant completely to get good control. The imidacloprid works as a contact insecticide as well as a systemic so while good complete coverage is helpful, it’s not a must with it. One or two sprays should do the trick.

The scales and mealybug are tougher problems to solve. You can use the same insecticides as with the aphids, but I’d probably lean more toward the systemic. The hard shell of the scale and the waxy, cottony fluff of the mealybug repel the spray and tend to protect the insect from it. A systemic is absorbed into the plant and these guys will get a dose of it when they suck the sap.

The common systemic insecticide for houseplants is imidacloprid. Imidacloprid will do a pretty good job on the mealybug but not on most scale. For that you’ll have to rely on the contact insecticides I mentioned before and just keep applying them for several months, rotating to a different spray occasionally.

I have an older yucca that didn’t bloom this year. It bloomed last year, but not the year before. Prior to that, it bloomed every year. What’s wrong, and can I fix it?

— Karen

It sounds like you’ve had your yucca for a few years. With an older plant like that, it usually helps to divide it up and replant it. You can treat it like an overgrown perennial.

Dig it up in March sometime, clean off a good part of the dirt and then divide it into smaller parts.

This invigorates the plants and promotes healthy new growth. To ensure the best results, be sure to amend the soil and work it well before you replant your divided yucca.

Dennis Hill is the nursery manager at Bookcliff Gardens, Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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