Answer: Is it possible your shrubs dried out while you were away? Lack of water could cause leaves and branches to turn brown. If the webbing on the shrubs is fairly fine, you may have spider mites. Mites are so tiny, they're hard to see, but hold a piece of white paper under suspected leaves/stems and tap sharply. If mites are there, they will drop off and you can see them moving on the paper. They're usually a rusty brownish/orangish color. Mites like dusty plants and dry conditions, and a severe infestation can cause the symptoms you describe. They are best controlled with a daily blast of water from the hose. If possible, spray early in the morning, before the sun gets too hot. If that doesn't work, try an insecticidal soap.
Note that pests often attack plants that are under stress, whether it be caused by over- or underwatering, inappropriate sun exposure, or lack of nutrients. Maintaining healthy plants is the best way to prevent pest problems.
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