Question
My dwarf yaupon holly have spider webs all over them. The leaves turn brown near the webs and fall off until the whole bush is leafless.   When you shake the bush, white flies fly out.  This has been happenning for the last few autumns. What do you think it is and what can I do to get rid of it?

Answer
Sounds like spider mites and whiteflies.
Spider mites have tiny mouthparts modified for piercing individual plant cells and removing the contents. This results in tiny yellow or white speckles. When many of these feeding spots occur near each other, the foliage takes on a yellow or bronzed cast. Once the foliage of a plant becomes bronzed, it often drops prematurely.

Heavily infested plants may be discolored, stunted or even killed. Web producing spider mites may coat the foliage with the fine silk which collects dust and looks dirty.

Spray the foliage with a miticide making sure you wet both sides of the leaves. Miticides Spider mites are usually not killed by regular insecticides, so be sure to check the pesticide label to see if "miticide" is present. Pesticides claiming "for mite suppression" are usually weak miticides and will not perform well. There are few products available to the homeowner. Dicofol (=Kelthane) is registered for over-the-counter use but is difficult to find. Acephate (=Orthene), dimethoate (=Cygon), chlorpyrifos (=Dursban), diazinon, disulfoton (=Di-syston), and malathion have over-the-counter product labels but are considered weak miticides.


Whiteflies

Whiteflies damage plants by sucking out plant juices. Because large amounts of sap can be removed, primarily by the developing nymphs, heavily infested plants can be seriously weakened and grow poorly. Leaves often turn yellow, appear dry and drop prematurely.

Also, because whiteflies suck out more plant juice than they can digest, the excess is excreted as a sweet, sticky substance called honeydew. The honeydew covers leaf surfaces and acts as a growth medium for a black, sooty mold. Both the removal of plant juices and the presence of the black, sooty mold growing on the honeydew can interfere with photosynthesis.


Insecticides will work but they will need to be sprayed at least three times about a week apart. Make sure both sides of the leaves are covered with the spray. Recommended insecticides are:
acephate--Ortho Isotox Insect Killer, or Ortho Orthene Systemic Insect Control

malathion--Ortho Malathion 50 Plus Insect Spray, Dragon 50 percent Malathion Spray, K-Gro Malathion 50 Insect Spray.

permethrin--Spectracide Lawn and Garden Insect Control.

bifenthrin--Talstar 10 WP

imidacloprid--Merit 75 WSP.

These are contact insecticides and will kill the adults present.

Since these insects are sucking insects the systemic insecticides will get into the plant juices and as the whiteflies suck the juices they will get the insecticide.  


Some insecticides can be applied to the soil and taken up by the roots of the plants. These are called systemic insecticides. The most recent, Imidacloprid, is sold under the trade name Bayer Advanced Garden Tree & Shrub Killer Concentrate. (Merit is the trade name of imidacloprid used by professional tree care companies.) It is applied as a drench over the root zone. An older梐nd much more toxic梥oil systemic insecticide that is still available for some ornamental plant uses is DiSyston (disulfoton). DiSyston is sold as granules or in plant food mixtures for soil application.