Eurasian Hemp Borer

Grapholita delineana

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eurasian hemp borer in hemp stem Eurasian hemp borer larva in hemp stem.

mature eurasian hemp borer larva in hemp stem
Late-stage Eurasian hemp borer larva in hemp stem.

Eurasian hemp borer adult moth Eurasian hemp borer adult moth.

eurasian hemp borer damage on hemp flowers
Eurasian hemp borer damage near hemp flowers.

eurasian hemp borer damage on hemp leaves
Eurasian hemp borer damage symptoms.

Hosts

  • Field-grown hemp
  • Hops
  • Knotweed
  • Various weeds in the family Polygonaceae (buckwheat family)

Description

Larvae range in color from creamy-white with a dark head when young to reddish-orange when mature. Adult moths hold their wings tent-like over their back. They are dull, brownish-gray with white lines on the wings. 

Life Cycle

Egg | Larva | Pupa | Adult

  • 2 to 3 generations per growing season.
  • Overwinter as caterpillars within the stems and folds of leaves and pupate in spring.
  • Adults emerge in mid-spring, mate, and lay eggs on the host plant.
  • Larvae feed on the leaf surface and then bore into the stem where they will remain until they pupate and emerge as adults.

Damaging Lifestage(s): Larva

Damage Symptoms

Larvae bore into the stems and buds of hemp. Stem damage includes wilting or dieback and slight stalk swelling. Primary damage is most noticeable in mid-to-late summer when larvae tunnel into developing flower buds and stems. Affected plants will have stunted growth, split stems, dieback, and may die. Developing seeds can also be damaged.

Time for Concern

Spring through harvest.

When and Where to Scout

  • Look for larvae on leaves in midspring, mid-summer, and late summer.
  • Inspect stems for areas of swelling and frass (excrement) where larvae have entered the stem.
  • At harvest, inspect buds and stems for larvae.

Threat Level

Medium if established

Occurrence in Utah

This pest has only been identified east of the Rocky Mountains and is not known to occur in Utah. 

Management

  • Reduce overwintering larvae by removing crop debris, including stems and stalks.
  • Keep the field weed-free, especially weeds in the buckwheat family.

When to Consider Treatment

If needed, an approved insecticide application must coincide with egg hatch to kill larvae before they bore into the stem.

Look-alikes

European corn borer, corn earworm.

Caterpillar Insecticides

Utah-Registered Product Active Ingredient(s) Notes
Agree WG Bacillus thuringiensis ssp. aizawa  
Aza-Direct Biological Insecticide azadirachtin  
AzaGuard  azadirachtin  
AzaSol azadirachtin  
Azatin O Biological Insecticide azadirachtin  
Azatrol EC Insecticide azadirachtin  
Azera Insecticide azadirachtin  
BT Now Bacillus thuringiensis ssp. kurstaki Greenhouse use only.
Bug Buster-O Extinguish Ant Bait pyrethrins Greenhouse use only.
Deadzone diatomaceous earth  
Deliver Biological Insecticide Bacillus thuringiensis ssp. kurstaki  
DiPel DF Biological Insecticide Bacillus thuringiensis ssp. kurstaki  
DiPel DF Biological Insecticide Dry
Flowable		 Bacillus thuringiensis ssp. kurstaki  
DiPel PRO DF Biological Insecticide Bacillus thuringiensis ssp. kurstaki  
Evergreen Crop Protection EC 60-6 pyrethrins  
Ferti-Lome Dipel Dust Biological Insecticide (RTU) Bacillus thuringiensis ssp. kurstaki  
Ferti-lome Fruit Tree Spray pyrethrins  
Grandevo CG;WDG Chromobacterium sub strain PRAA4-1 cells  
Javelin WG Biological Insecticide Bacillus thuringiensis ssp. kurstaki  
Leprotec Bacillus thuringiensis ssp. kurstaki  
Molt-X azadirachtin  
Neemix 4.5 Insect Growth Regulator azadirachtin  
Prizefighter ammonium nonanoate  
Pycana  pyrethrins Greenhouse use only.
Pyganic Crop Protection EC 1.4 II; 5.0 II pyrethrins  
SPEAR-LEP gs-omega/kappahxtx-hv1a Supression only; combine with a Bt product for greater efficacy.
Tersus Insecticide pyrethrins  
Thuricide N/G Bacillus thuringiensis ssp. kurstaki  
Valent Professional Products DiPel Pro DF Biological Insecticide Dry
Flowable		 Bacillus thuringiensis ssp. kurstaki  
Venerate CG Burkholderia sp. strain A396  
XenTari Biological Insecticide Dry Flowable Bacillus thuringiensis ssp. aizawai  

Photo Credits

  • Whitney Cranshaw, Colorado State University, Bugwood.org
Precautionary Statement: Utah State University and its employees are not responsible for the use, misuse, or damage caused by application or misapplication of products or information mentioned in this document. All pesticides are labeled with ingredients, instructions, and risks, and not all are registered for edible crops. “Restricted use” pesticides may only be applied by a licensed applicator. The pesticide applicator is legally responsible for proper use. USU makes no endorsement of the products listed in this publication.