How to treat strawberries for the corn earworm and spider mite? - briefly
Apply a spinosad‑based insecticide at early larval stages to control corn earworm, and follow with a horticultural oil or sulfur spray to suppress spider mite populations, respecting label intervals and pre‑harvest restrictions. Rotate products with different modes of action to prevent resistance and monitor pests regularly for timely intervention.
How to treat strawberries for the corn earworm and spider mite? - in detail
Strawberry growers must address two distinct pests: the corn earworm, a nocturnal moth larva that feeds on fruit, foliage, and flowers, and spider mites, tiny arachnids that cause stippling, bronzing, and leaf drop. Effective management combines cultural, biological, and chemical tactics, applied according to scouting data and economic thresholds.
Scouting and thresholds
- Inspect plants weekly during the growing season. Look for earworm larvae on fruit and flowers; a single larva per plant can cause market‑rejectable damage.
- Examine undersides of leaves for spider mite webs and stippled tissue; a population exceeding 5 mites per leaf segment warrants action.
Cultural controls
- Rotate strawberries with non‑host crops (e.g., legumes, brassicas) for at least two years to reduce overwintering earworm pupae in the soil.
- Remove plant debris, fallen fruit, and weeds that shelter adult moths or mite colonies.
- Maintain adequate irrigation and mulching to keep plants healthy; stressed foliage is more attractive to both pests.
- Space rows to improve air circulation, lowering leaf humidity and making the environment less favorable for mite reproduction.
Biological agents
- Apply Bacillus thuringiensis (Bt) var. kurstaki when earworm larvae are early instars; repeat applications 5–7 days apart if larvae persist.
- Use entomopathogenic nematodes (e.g., Steinernema carpocapsae) in the soil to target earworm pupae.
- Introduce predatory mites such as Phytoseiulus persimilis or Neoseiulus californicus when spider mite counts exceed the threshold; release rates of 20–30 predators per m² are effective.
- Deploy neem oil or horticultural oil sprays early in the season to suppress mite egg hatch; repeat every 10–14 days, avoiding intervals shorter than the oil’s residual activity.
Chemical options
- For earworm, select insecticides with proven efficacy and short pre‑harvest intervals, such as spinosad (1 mg a.i./L) or chlorantraniliprole (0.05 mg a.i./L). Apply at the first sign of feeding and rotate modes of action to delay resistance.
- For spider mites, use miticides that belong to different IRAC groups, for example, abamectin (0.5 mg a.i./L) followed by a pyrethroid‑based product (e.g., bifenthrin 0.1 mg a.i./L) after a 7‑day wash‑out period.
- Observe label restrictions for residue limits and re‑entry intervals, especially close to harvest.
Resistance management
- Alternate between biological and chemical controls weekly to minimize selection pressure.
- Record product names, active ingredients, and application dates; avoid using the same IRAC group more than two consecutive times.
Integrated schedule
- Early season (planting to first fruit set): implement sanitation, mulch, and row spacing; begin weekly scouting.
- First detection of earworm larvae: apply Bt; follow with a soil nematode treatment if pupae are suspected.
- First detection of spider mite colonies: release predatory mites; supplement with neem oil if populations rise rapidly.
- Mid‑season peak (fruit development): rotate to a chemical insecticide for earworm if damage exceeds threshold; use a miticide from a new IRAC group for mites if biological control is insufficient.
- Late season (pre‑harvest): discontinue broad‑spectrum chemicals; rely on biological agents and cultural sanitation to protect fruit quality.
By adhering to this structured approach—regular monitoring, targeted cultural practices, timely biological introductions, and judicious chemical use—strawberry production can maintain low pest pressure from both corn earworm and spider mite while preserving yield and fruit marketability.