To continue from the last entry I wanted to add a bit more information about the sticky excretions found below plants on paving, cars, patio furniture etc..... This sticky residue is honeydew that actually is excreted from tiny insects i.e. spider mites, scale, aphids and thrips. This honeydew is often collected by ants and you may see a trail of ants going up tree or shrub trunks looking for honeydew and also for the insects that produce it. The ants are known to "farm" the insects protecting them and bringing them into sheltered areas.
These insects are piercing-sucking insects (yuk) and literally suck the life out of plants. They are most often found on the backs of the leaves and look like specs of dust. If you want to be horrified get out a magnifier and look at them up close. They reproduce rapidly in the warm season on stressed plants (many of which have been planted in the wrong location). When not given enough light, water or air circulation plants become stressed and the bugs move in.
It helps to give your plants a bath regularly to discourage colonies from forming and to wash dust from the leaves allowing the pores or stomata to breathe. For more serious infestations use a mild soapy solution in a hose end sprayer to wash the plant or tree then apply the appropriate pesticide (take sample to nursery and check with nurseryperson for products). Some of these pesticides are fairly non-toxic i.e. 'Safer Insecticidal Soap'. I try to avoid using pesticides in our garden but will use insecticidal soap from time to time to avoid longterm damage from these posts.
Aphids usually show up in spring on tender shoots and can be treated with soapy solution alone. They are very easy to control normally. Of all the above pests, scale, is the hardest to control because it has a little shell over the actual bug. With scale the plant must be sprayed when the insects are in their crawling stage so the help of a good nursery person is important or a tree spraying company for large trees. Scale is severly affecting Liriodendron and the Deciduous Magnolias (Saucer Magnolia), so keep an eye out if you have these trees.
Signs to look for in the garden are wilting, silvered leaves, specs on the backs of the leaves, that sticky stuff we spoke of, black residue on the trunks and loss of leaves (more than usual). Inspect your plants occasionally in order to get ahead of any pest problems and the garden will thrive.