Protocol for Controlling |Insects on Roses

Q. We bought this house about two years ago. There was this rose already planted.  I noticed last summer the leaves get a shiny look on them and a sticky feel. We had roses at other house never saw this before. Do you have any idea what it is and what to do?

Horticultural oil for the winter months

A. This usually means it is one of the sap-sucking insects feeding on leaves, soft stems, and flower buds. Sometimes flower petals. These insects suck on plant juices by piercing the plant and causing physical damage and/or transmitting diseases. 

They use the plant juices for their sugar content but can't use it all so they poop it out the backend as a sticky, shiny excrement. This sugary excrement attracts ants. The answer learned that if they protect these plant juice-sucking insects from other insects that might hurt them they can group them together and treat them like we would treat dairy cattle. 

They have also learned that they can move the immature of these insects to new locations and spread them out and get an even greater benefit from them. We would call it expansion to improve their "economy of scale".

The list of insects include aphids, whiteflies, mealybugs, and the scale insects. Perhaps even thrips. The number one insect on roses during cool weather is aphids. In hot weather it is usually whiteflies because aphids do not like hot weather like whiteflies do and aphid numbers dwindle while whitefly numbers are on the rise. 

Besides giving off the sticky shiny excrement, aphids cause immature leaves to begin to curl as they grow giving them even more protection since the curled leaf also protects the "herd". Adult whiteflies are pretty good flyers and when the plant leaves are disturbed they usually take flight looking like a bunch of flying white dandruff. Least common are mealybugs and scale insects.

Here is the protocol I would use for growing roses here and controlling their insect pests.

•           During the winter months and early spring months spray roses with horticultural oil twice, about a month apart, covering the entire plant.

•           During February, March and possibly April spray the bottom sides of expanding leaves with insecticidal soap and control ants. I would spray 2 to 4 weeks apart depending on whether I saw a problem developing.

•           As a flower buds are developing, spray with Spinosad for thrips control if thrips are causing damage to flower buds.

Pyrethrum-based insecticide

•           As warm weather is developing, inspect the plant for whiteflies and damage from whiteflies. Control ants. Spray with pyrethrum based insecticides or use insecticidal soap until they are

controlled.

An alternative is to use a conventional insecticide that contains imidacloprid and apply it to the soil as a liquid drench at the beginning of the season. I am not a big fan of this insecticide for flowering plants. It has been implicated in colony collapse disorder for honeybees.

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