When should spider mites be treated? - briefly
Intervention is required once mite numbers exceed a few per leaf or when stippling, yellowing, or webbing becomes noticeable, typically early in the growing season before plants flower. Prompt treatment prevents rapid colony expansion and severe foliage loss.
When should spider mites be treated? - in detail
Spider mite infestations develop rapidly under warm, dry conditions, so intervention should begin before populations reach damaging levels.
Inspect plants weekly during the growing season. If the average of five leaves per plant shows more than three adult mites, or if webs appear on the undersides, treatment is warranted. In greenhouse or indoor environments, commence control when temperatures exceed 75 °F (24 °C) and humidity falls below 50 %, because these parameters accelerate reproduction.
For outdoor crops, initiate measures when the forecast predicts a stretch of at least five consecutive days with temperatures above 80 °F (27 °C) and low rainfall, as these conditions favor exponential growth.
When using chemical or horticultural oil sprays, apply at the first sign of egg laying—typically when females are observed laying on leaf surfaces. Follow with a second application 5–7 days later to target emerging nymphs, and a third treatment 10–14 days after the first to ensure complete eradication of the life cycle.
Biological controls, such as predatory mites, should be released early, before the pest population exceeds the economic threshold. A release rate of 1–2 predatory mites per square foot is effective when applied at the onset of the first infestation.
Summary of timing guidelines:
- Weekly scouting throughout the season.
- Initiate treatment when mite density > 3 per leaf or webs present.
- Start control at temperatures > 75 °F (24 °C) with humidity < 50 %.
- For outdoor crops, act before a 5‑day heat spell above 80 °F (27 °C).
- Apply chemical/oil sprays at first egg‑laying, repeat 5–7 days later, and again 10–14 days after initial application.
- Release predatory mites early, maintaining 1–2 individuals per ft².
Adhering to these thresholds prevents population explosions and minimizes damage to foliage.