How to fight spider mites on hydrangeas? - briefly
Treat infestations with a thorough spray of neem oil or insecticidal soap, covering the undersides of leaves and reapplying weekly until mites are gone. Remove heavily damaged foliage and maintain consistent moisture to lessen plant stress and deter future outbreaks.
How to fight spider mites on hydrangeas? - in detail
Spider mites are tiny arachnids that feed on the undersides of hydrangea leaves, causing stippling, yellowing, and leaf drop. Early detection is essential; inspect foliage weekly, especially after dry, warm periods. Look for fine webbing and moving specks when shaking a branch over white paper.
Control measures fall into three categories: cultural, biological, and chemical.
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Cultural practices
- Water plants deeply in the morning to increase leaf humidity, making the environment less favorable for mite development.
- Prune dense growth to improve air circulation and reduce leaf temperature.
- Remove fallen leaves and debris that can harbor mites and their eggs.
- Apply a strong jet of water to the undersides of leaves once a week; this dislodges mites and reduces their population.
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Biological agents
- Introduce predatory mites such as Phytoseiulus persimilis or Neoseiulus californicus; release rates of 10–20 predators per square foot are effective for moderate infestations.
- Use entomopathogenic fungi (e.g., Beauveria bassiana) as a foliar spray; follow label rates and apply during cool, humid conditions for optimal infection.
- Encourage natural enemies by planting companion species that attract lady beetles and lacewings.
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Chemical options
- For severe outbreaks, apply a miticide containing abamectin, spirodiclofen, or bifenthrin; rotate active ingredients to prevent resistance.
- Follow label instructions regarding concentration, spray interval (typically 7–10 days), and pre‑harvest intervals.
- Prefer systemic products only when foliage coverage is insufficient, but be aware of potential impact on beneficial insects.
Monitoring after each treatment is critical. Count mites per leaf using a magnifying lens; a threshold of fewer than five mites per leaf generally indicates acceptable control. Adjust tactics based on population trends, favoring non‑chemical methods whenever possible to preserve pollinator health and prevent resistance buildup.