Light brown dusty residue on houseplant leaves - please help identify (photos attached)

[JimBob123]

Hi everybody,

Hope someone can help as I am at my wit's end!

I have been fighting a bad infestation of mealybugs and scale insects on my houseplants in my conservatory for a couple of years.

I have tirelessly attempted various organic treatments (soap, neem oil, rubbing alcohol) but alas no use, so eventually resorted to a systemic insecticide (imidacloprid) mixed into the soil surface.

Following two rounds of treatment, it seems to have worked on my citrus plants as the white cotton wooly mealybugs are gone and the scale insects have discoloured and I think are dead. It hasn't worked on my succulent Jade plants though as they still have the white telltale cotton wool on them :-(

However, my main issue now is a new light brown dusting (almost looks like fine sand) covering many leaves of most of my houseplants including the treated and untreated ones. When i rub the residue it, it forms a wet slightly sticky mess. I have no idea what it is, so have attached some photos of some affected plants. This has only appeared in the last month (since treating with the systemic insecticide.

Does anyone know what this might be? Is it mould? Or is is a new infestation of insect I can't identify? Is it anything to do with the existing infestation?

It's very frustrating, I seem to fighting a losing battle! Any help would be greatly appreciated from anyone who might be able to help identify the problem and offer a suitable solution.

Many thanks,
Jim

 

[cpp gardener]

Some of it looks like sooty black mold which is growing on the honeydew secreted by the scale and mealybug. It should rinse off with warmish water and a wet paper towel. You may have spider mites as well. Try giving the plants a shower the next time they need to be watered to rinse the leaves and wash off mites. Mites HATE showers, so that would help a lot.

 

[JimBob123]

Some of it looks like sooty black mold which is growing on the honeydew secreted by the scale and mealybug. It should rinse off with warmish water and a wet paper towel. You may have spider mites as well. Try giving the plants a shower the next time they need to be watered to rinse the leaves and wash off mites. Mites HATE showers, so that would help a lot.

OK great thanks for the advice, will definitely try giving them all a good shower! I was hoping the honeydew production would decrease since treating with the systemic insecticide, but it looks like it may actually have gotten worse!

 

[cpp gardener]

It may be leftover that is now growing mold and not new stuff.

 

[Oliver Buckle]

Good one, cpp, it's easy to forget plants naturally get rained on. A good shower makes me feel better, why not a plant?