Cotton Square Borer
Immature cotton square borer larva.
Cotton square borer larva and
associated damage on cotton.
Mature cotton square borer larva.
The adult cotton square borer caterpillar is also known as the gray hairstreak.
Gray hairstreak butterfly.
Strymon melinus
Hosts
- Many flowers, fruits, seeds and buds of apples, blackberries, corn, cotton, lantana, legumes, and strawberries
Description
Larvae are white to pale green or pale yellow with dense, short hairs on each body segment, giving a velvety appearance. Adults are blue-gray butterflies with small hair-like “tails” extending from the hindwings and an orange patch surrounding a black spot on each wing.
Life Cycle
Egg | Larva | Pupa | Adult
- 2-3 generations produced annually.
- Overwinter as pupa and emerge late in the spring as adults.
- Adults lay single, flat eggs on host foliage.
- Larvae pupate on the host plant by attaching themselves with silk strands.
Damaging Lifestage(s): Larva
Damage Symptoms
Young larvae feed on leaf surfaces, later boring into stems, leaf midribs, and buds.
Time for Concern
Early spring through late fall.
When and Where to Scout
Look for single eggs on leaf surfaces during early spring. Watch for butterflies during the day. Look for larvae on leaf surfaces and towards the center of the plant or near the midribs of leaves.
Threat Level
Low. This is an uncommon pest in hemp and feeding injury does not typically affect overall plant health.
Occurrence in Utah
Not yet detected on hemp in Utah.
Management
- Keep crop area weed-free.
- Hand-pick and destroy larvae
When to Consider Treatment
The need for treatment is rare.
Look-alikes
Budworms and other caterpillars.
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
- Mature larva - Whitney Cranshaw, Colorado State University, Bugwood.org
- Adult on flower - Kevin D. Arvin, Bugwood.org
- Immature larva - Ronald Smith, Auburn University, Bugwood.org
- Mature close-up - Charles Olsen, USDA APHIS PPQ, USDA APHIS PPQ, Bugwood.org
- Larva with damage - John Ruberson, Kansas State University, Bugwood.org
- Gray hairstreak butterfly - Jerry A. Payne, USDA Agricultural Research Service, Bugwood.org