Now would be a good time to inspect mugo pines for what appears to be stray straw near the shoot tip. Close examination of the shoot could reveal the black heads of European pine sawflies. These grow to an inch in length and will defoliate mugo and other pines. Fortunately these sawflies are easily killed by an application of spinosad (Fertilome borer and bagworm killer), or 2% horticultural oil.
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