raspberry CROWN borer
Beginner
Scientific Name: Pennisetia marginata (Order Lepidoptera; Family Sesiidae)
Identification
- Adult is a clear-winged moth with a black body with yellow bands, similar to yellowjackets.
- Measures approximately 25 mm in length and has a wingspan of about 30 mm.
- Adults are active during the day.
- Larvae are usually found in the crown of the plant.
- Larvae are white with a light brown head, three pairs of very small true legs and four pairs of prolegs.
- Affected canes become weak and spindley, fruiting canes often collapse while fruit is still immature, and foliage may wilt and die.
- In late fall and early spring, canes will usually break at the base when tugged.
- Closely examine raspberry crowns for frass, tunnelling damage, and the crown borer larva itself if the crown is cut open.
Often Confused With
Phytophthora Crown and Root Rot
Winter Injury
Nutrient Deficiency
Yellowjackets
Period of Activity
Adult crown borers are active during the day and present in brambles from late July to September to lay their eggs. The crown borer larvae hatch in September and October and begin their move to the base of the plant. At this point, pesticide use may still affect them. Larvae are most easily detected in the crown in the fall, spring and early summer. Pupation occurs in July of the second year.
Scouting Notes
Researchers are working on the development of a pheromone lure to attract adult insects but these are not yet available. Scout the field for the adult insects on calm sunny days from July to September. Turn over young leaves to check for eggs. Look for weak growth, wilting leaves and bent canes and try tugging and pulling the plant to expose the root. Use a spade to dig up damaged plants, carefully shake the soil off the roots and inspect the crown. Sawdust-like frass, galls and tunnelling are indicative of crown borer larvae. Carefully cut through the crown with clippers or shears to look for larvae.
Thresholds
None established.
Advanced
Scientific Name: Pennisetia marginata (Order Lepidoptera; Family Sesiidae)
Identification
The raspberry crown borer is a clearwing moth. The adult has a black body with yellow bands, similar to yellowjackets. It measures approximately 25 mm in length and has a wingspan of about 30 mm. The adult is active during the day.
Crown borer larvae are white with a light brown head. They possess three pairs of very small true legs and four pairs of prolegs. They bore down to the crown where they spend their time feeding on the crown tissue and consequently creating tunnels. Their burrowing severely damages the crown and eventually affects above-ground tissue. The canes become weak and spindly and fruiting canes often collapse while the fruit is still immature. Foliage may wilt and die on affected canes. Eventually, primocanes become so few in number that the planting dies out.
In late fall and early spring, tugging the affected cane will usually cause it to break at the base. Close examination of the crown will reveal frass, tunnelling damage, and often the crown borer larva itself if the crown is cut open.
Often Confused With
Phytophthora Crown and Root Rot
This is a disease caused by a fungus that causes primocanes to be weak and die out. Phytophthora can be diagnosed by scraping the epidermis of the crown at ground level to reveal the underlying tissue. Reddish brown tissue in the affected area is a typical symptom of phytophthora.
Winter Injury
Both crown borer and winter damage can cause weakened fruiting canes with low vigour, but if the damage is due to winter injury the new primocane growth is strong and vigorous. In contrast, crown borer injury results in weak primocane growth in the spring following winter injury.
Nutrient Deficiency
Although symptoms of nutrient deficiency may be evident, this could be caused by the damage to roots from crown borer. Examine crowns for crown borer larvae before jumping to conclusions about nutrients.
Yellowjackets
Crown borer adults may look similar to yellowjackets due their size and the black and yellow bands on their bodies. However, yellowjackets, which belong to the wasp family have a very narrow, pinched waist that separates their lower abdomen from their thorax.
Biology
The raspberry crown borer has a two-year life cycle. Females lay single, reddish-brown eggs on the underside of young leaves. The adult is active for about one week. Females can lay around 140 eggs in this time.
The larvae emerge about one to two months after egg-laying and migrate down to the base of the cane. They overwinter in a hibernaculum below the soil surface. In the spring, they begin boring tunnels and cavities into the crown tissue. The larvae also create girdling and feeding damage on roots and other canes belonging to the same crown. They spend their second winter within the roots of the plant and by this point they measure between 13 and 20 mm. Fully matured larvae measure between 25 and 30 mm. During July of the second summer, pupation occurs inside the crown and mature adult crown borers emerge between late July and September. The pupae measure about 20 mm in length and are of a reddish-brown colour.
Period of Activity
Adult crown borers are active during the day and present in brambles from late July to September to lay their eggs. The crown borer larvae hatch in September and October and begin their move to the base of the plant. At this point, pesticide use may still affect them. Larvae are most easily detected in the crown in the fall, spring and early summer. Pupation occurs in July of the second year.
Scouting Notes
Researchers are working on the development of a pheromone lure to attract adult insects but these are not yet available. Scout the field for the adult insects on calm sunny days from July to September. Turn over young leaves to check for eggs. Look for weak growth, wilting leaves and bent canes and try tugging and pulling the plant to expose the root. Use a spade to dig up damaged plants, carefully shake the soil off the roots and inspect the crown. Sawdust-like frass, galls and tunnelling are indicative of crown borer larvae. Carefully cut through the crown with clippers or shears to look for larvae.
Thresholds
None established.
Management Notes
- Apply a registered insecticide in a high volume of water directed at the base of the cane in fall or early spring before the larvae tunnel in. Treatment is required for two years to break the cycle of this pest. See OMAFRA Publication 360: Fruit Crop Protection Guide (Chapter 3: Berry Crops) for a complete list of insecticides and timing.
- Cut out, remove and destroy infested plant matter to kill the larvae.
- Remove nearby wild brambles to reduce the likelihood of infestations.
