Answer: Several things can cause browning needles on a spruce. But if you suspect mites, you may want to inspect your plant thoroughly. An easy way to check for mites is to hold a white piece of paper under a branch and tap the foliage: tiny specks should fall to the paper and then move. You can also see them with a hand lens (they are barely visible to the naked eye). Spruce spider mites are most active in the cooler weather of spring and fall. To understand how to control them, you need to understand their life cycle. The mites lay eggs in the fall. The eggs overwinter under bud scales or at the base of needles and hatch in spring. The larvae, nymphs and adults feed on the needles and sometimes twigs. Successive generations are produced every two or three weeks until autumn -- hence the fast and drastic build-up. The infestations tend to reoccur from year to year. Often, damage inflicted in fall and spring goes unnoticed until the following summer. The first indication of a problem is stippling and distortion, increasing to browning and dropping needles, next you might see a silky webbing on the underside of the branches; the webbing eventually becomes quite noticeable when it catches up dead needles, dirt and debris.
A bad infestation can kill branches or the entire plant. It is very diffficult to control spruce spider mites. Horticultural oil and dormant oil can be effective in suppressing the mites if applied properly. You must apply any spray to thoroughly wet the foliage and try to contact as many mites as possible and be especially sure to cover the undersides. In other words, thorough spray coverage is absolutely critical. In addition, you must be careful to follow the label instructions. Horticultural oil is used when the mites are active, and dormant oil is used to kill the overwintering mite eggs. It would be applied when the weather turns cold -- in late fall after there have been several light frosts or in late winter or early spring (before bud break).
If you do not find evidence of spider mites on your spruce, you may want to consider damage from dog urine, a fungal disease, or poor soil drainage. Stress roots can cause the tops of the plants to die out. Hope this sheds some light on the possible problems your Bird's Nest Spruce is undergoing.
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