Camellias, aphids and mouldy soot
Hello, I've done quite a bit of research on the appearance of thick black spotches on my camellia leaves and now know that it is called mouldy soot and is caused by aphids. So far I don't seem to have the "cattle herder" ants but I'm sure it's just a matter of time! The problem is that it won't stop raining! Can I apply Neem oil in the rain? It seems counter-intuitive. A second question is how to attract beneficials. I've read that fennel, dill, mint and yarrow will attract ladybugs and lacewings. I already have a mint invasion in another part of my garden so am strongly disinclined to grow it near my camellias. However, the rest require strong sun while the camellia requires shade. Is there any other herb that attracts beneficial bugs, or deters aphids that I can grow in the shade? By the way, my otherwise excellent nursery recommended a neonicotinoid but I don't want to harm bees so will not use. I'm a little confused on the logic, anyway, as the pesticide was to be applied to the roots of the camellias. How does that stop aphids? Thank you,
Montgomery County Maryland
If trees or shrubs are stressed by poor site conditions such as drought, poor drainage, poor planting techniques, over mulching, etc. it is not uncommon for them to be susceptible to possible insect and disease problems such as sucking insects like aphids and scale insects (there are several types). As they feed, they exude a honeydew which fosters the growth of a black sooty mold. Make sure you identify the pest before you spray. Look for this. See our website for aphids http://extension.umd.edu/hgic/aphids-trees-and-shrubs and scale insects. http://extension.umd.edu/hgic/armored-and-soft-scales-trees-and-shrubs If you need to control, Insecticidal soap can help clean the mold on the leaves. Follow label directions and do not spray in the rain. Contact must be made with the target pest for control. Some predators and parasites may help control naturally. It is important to follow good cultural practices regarding camellia. See the link from Clemson http://www.clemson.edu/extension/hgic/plants/landscape/shrubs/hgic1062.html Also, do not over fertilize as this can make the shrub attractive to sucking insects.
Look at our publication for plants that attract beneficial insects. If you have flowering plants in your landscape, the beneficials should find the pest insects. http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG62%20IPM%20A%20Com...
In general neonics are systemic insecticides. They are taken up by the root system and into the plants. We do not recommend for aphids and not effective for some scale insects.