# Corn earworm

> Helicoverpa zea, a moth caterpillar that bores into developing cannabis flowers outdoors, leaving frass that triggers bud rot; growers call it budworm.

- Canonical: https://genetixbay.com/knowledge/glossary/corn-earworm.html
- Also written: budworm, budworms, bud worm, Helicoverpa zea, cotton bollworm, tomato fruitworm, CEW
- Glossary category: Pests and diseases · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

The corn earworm (*Helicoverpa zea*), also called cotton bollworm or tomato fruitworm, is a noctuid moth whose larvae feed in flowers and [fruits](https://genetixbay.com/knowledge/glossary/achene.md). On outdoor [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) and cannabis it is the main "budworm": larvae tunnel into [colas](https://genetixbay.com/knowledge/glossary/cola.md) during flowering. Mature larvae are up to about 4 cm long and vary from green to brown or pink, with light and dark stripes along the body.

## In practice

Moths migrate and lay eggs singly on flowers from mid to late summer, so damage peaks just as buds are bulking. Look for small holes, browning patches inside colas and pellets of [frass](https://genetixbay.com/knowledge/glossary/frass.md); pull apart any bud with a brown spot. The bigger loss is often secondary *[Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md)* that starts in the frass. *[Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md)* sprays aimed at newly hatched larvae, before they bore in, are the usual biological option. [Pheromone traps](https://genetixbay.com/knowledge/glossary/pheromone-trap.md) show when moth flights begin. Check what is registered for cannabis locally, including the [pre-harvest interval](https://genetixbay.com/knowledge/glossary/pre-harvest-interval.md).

## Don't confuse with

- **European corn borer**: bores into stems and branches rather than buds.
- **Bud rot alone**: grey fuzz and brown tissue with no frass or tunnels.
- **Tobacco budworm**: *Chloridea virescens*, a close relative with similar habits.

## Related terms

[Caterpillar](https://genetixbay.com/knowledge/glossary/caterpillar.md), [Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md), [Botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md), [Scouting](https://genetixbay.com/knowledge/glossary/scouting.md), [Action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md)

## Read more

- [Caterpillars on cannabis: species, degree-days and control](https://genetixbay.com/knowledge/pests/caterpillars.md)

## Sources

1. Oregon State University Extension. Corn earworm management in hemp (EM 9626). https://extension.oregonstate.edu/catalog/em-9626-corn-earworm-management-hemp
2. Utah State University Extension. Corn Earworm (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-corn-earworm