Whitefly on cabbage and kale
Whiteflies on brassicas are a different situation from whiteflies on tomatoes. The cabbage whitefly (Aleyrodes proletella) and related species that colonize kale, cabbage, and other brassicas in the eastern US are cool-season pests that build on fall crops and overwinter on host plant debris. They.
—- title: "Whitefly on cabbage and kale" slug: whitefly-on-brassicas hub: problems category: "Disease-by-host" description: "Cabbage whitefly coats brassica leaves with waxy nymphs and honeydew. Identify the brassica-specific species, understand why cool fall weather suppresses populations, and apply targeted controls." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 8 —-
Whiteflies on brassicas are a different situation from whiteflies on tomatoes. The cabbage whitefly (Aleyrodes proletella) and related species that colonize kale, cabbage, and other brassicas in the eastern US are cool-season pests that build on fall crops and overwinter on host plant debris. They are primarily a problem on fall-harvested kale and collards, not the hot-summer crops. Unlike tomato whiteflies, the brassica-infesting species are not major virus vectors in North America.
I don't grow brassicas at my Long Island property, so this guide draws on NC State Extension, Cornell Cooperative Extension, and Clemson HGIC research.
The pest
The primary whitefly species on brassicas in North America is the cabbage whitefly (Aleyrodes proletella), with some contribution from the greenhouse whitefly (Trialeurodes vaporariorum). Per Cornell Cooperative Extension, these species prefer cool conditions (60–75°F, 15–24°C), which is why they peak in fall on cool-season crops.
Per NC State Extension, unlike the silverleaf whitefly (Bemisia argentifolii) on tomatoes, brassica whiteflies are not confirmed vectors of economically significant viruses in North American vegetable production.
Identification
Adults
Per Clemson HGIC:
- White, 1–2mm, with wings held flat and horizontal over the body (similar to greenhouse whitefly)
- Found on the undersides of leaves in the inner canopy
- Rise in clouds when plant is disturbed
Nymphs
Per Cornell Cooperative Extension, nymphs on brassica leaves:
- Flat, oval, pale greenish-white scales on leaf undersides; barely visible without magnification
- First instars (crawlers) are mobile; subsequent instars are sedentary
- Whitefly nymphs on kale appear as pale oval spots thickly coating leaf undersides
Plant symptoms
Per NC State Extension:
- Pale yellow patches on leaves where nymphs are densely clustered
- Waxy, whitish deposits on leaf undersides where nymphs have fed (the waxy secretions from nymph feeding)
- Sooty mold on honeydew deposits
- Distorted inner leaves on cabbage heads when populations are high early in head formation
Heavy infestations on kale and collards can make the crop aesthetically unmarketable with extensive sooty mold, but direct plant death is uncommon in garden-scale plantings.
Seasonal pattern on brassicas
Per Cornell Cooperative Extension, whitefly populations on brassicas in the mid-Atlantic and Northeast follow a seasonal pattern:
- Low populations on spring crops (cool weather, fewer generations)
- Populations build on summer-planted fall crops as plants establish and temperatures moderate
- Peak populations on kale and collards in October–November before hard freezes kill the insects
- Hard freeze (-5°F persistent) kills active stages; eggs and some nymphs may overwinter on plant debris
This pattern means fall crops planted in late July–August are most at risk; spring crops harvested by June face lower pressure.
Management
Early planting and harvest scheduling
Per NC State Extension, harvesting fall crops (kale, collards) before heavy frost reduces the period of maximum population exposure. Spring crops planted as early as possible and harvested before July avoid the worst fall pressure.
Row cover exclusion
Per Cornell Cooperative Extension, lightweight row cover (Agribon row cover AG-15 or equivalent) applied from planting through harvest physically excludes adult whiteflies from colonizing young plants. This is effective on fall crops and small plantings. Remove covers for harvest access.
Yellow sticky traps
Per Clemson HGIC, yellow sticky traps at canopy height monitor adult populations and intercept some adults. Place traps at first transplant and replace as they fill.
insecticidal soap and horticultural oil
Per NC State Extension, insecticidal soap (2%) and horticultural oil (1%) kill nymphs and adults on contact when applied to leaf undersides. Apply every 5–7 days during active population buildups. Both products have no residual activity; coverage of leaf undersides is critical.
Natural enemies
Per Cornell Cooperative Extension, parasitic wasps (Encarsia formosa and related species) are the primary natural enemies of brassica whiteflies. These small wasps lay eggs inside whitefly nymphs; parasitized nymphs turn black. In gardens where broad-spectrum insecticides are not used, natural enemy activity often limits whitefly populations before they reach damaging levels.
Manage plant debris
Per NC State Extension, remove brassica crop debris promptly after harvest. Whiteflies overwinter on plant debris; thorough cleanup reduces the overwintering population for the following season.
Common problems table
| Symptom | Likely cause | Action |
|---|---|---|
| White clouds rising from brassica leaves | Adult whitefly | Confirm with leaf underside inspection; apply soap |
| Pale oval scale-like insects on leaf underside | Whitefly nymphs | Apply soap or oil; thorough underside coverage |
| Sooty mold on kale or collard leaves | Whitefly honeydew | Control whitefly; mold resolves when source gone |
| Yellow patches on leaves, dark nymph scales | Heavy nymph infestation | Multiple soap applications; consider row cover |
| Population persists through fall | Cool-season species — does not need heat | Will collapse with hard freeze; manage or wait |
Frequently Asked Questions
Are whiteflies on my kale the same species as on my tomatoes?
Per NC State Extension, likely no. Tomato whitefly infestations in the eastern US are typically greenhouse whitefly (Trialeurodes vaporariorum) or silverleaf whitefly (Bemisia). Brassica infestations are typically cabbage whitefly (Aleyrodes proletella). These species have overlapping host ranges but different preferred hosts and seasonal patterns.
Do kale whiteflies spread disease like tomato whiteflies?
Per Cornell Cooperative Extension, brassica-infesting whitefly species are not confirmed vectors of economically significant diseases in North American brassica production. The primary damage is sap feeding, honeydew, and sooty mold — significant but different from the TYLCV risk with tomato whiteflies.
Will hard frost kill whiteflies on my kale?
Per NC State Extension, yes — hard frost below 28°F (-2°C) kills active whitefly stages. Kale plants that survive frost can be harvested post-frost with improved flavor, and whitefly populations on those plants will have collapsed. Light frost does not kill all stages.
Can I use the same soap spray on brassicas as on tomatoes?
Per Clemson HGIC, insecticidal soap labeled for vegetable use is safe on brassicas at labeled rates. Some brassica cultivars are more sensitive to soap phytotoxicity — test on a small area first and do not apply in full sun or to drought-stressed plants.
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Recommended gear: Best Floating Row Covers for Pest Exclusion (2026) — our buyer's guide covering picks for every budget, ranked by Extension publication consensus and personal use.
Sources
- NC State Extension — Brassica Pest Management
- Cornell Cooperative Extension — Vegetable Pest Management
- Clemson HGIC — Brassica Pest Management