CALL TO THE SMALL FRUIT COMMUNITY:
Developing effective management of Prionus species in blueberries requires a comprehensive understanding of their biology, regular monitoring, and integrated tactics. Thus, community-wide coordination is crucial for effectively diagnosing infestations and collecting information about these pests. If you have seen these beetles on or near your blueberries, please contact the small fruit entomologist, Lorena Lopez, at llopezq@ncsu.edu.Identification and Biology
Prionus laticollis (Broad-necked Root Borer): These beetles can grow up to 2 inches in length (adults). They have a blackish to reddish-brown coloration and are commonly found in the eastern U.S., where they primarily affect fruit trees like apple and cherry.
Prionus imbricornis (Tilehorned Prionus): Similar in size to P. laticollis, they are distinguished by their antenna, which is segmented and appears saw-like. This species is found across the eastern and central U.S. Adult beetles of eastern species of Prionus (P. laticollis and P. imbricornis) typically become active and are visible from late June through the first week of August, with a peak in mid-July. Warmer temperatures in the southeast can cause faster development and adult emergence as early as April or May.
Prionus californicus (California Root Borer): The largest, growing up to 3 inches (adults), found predominantly in the western U.S., affecting crops such as hops and stone fruits like peaches. Adults generally emerge from late June through August.
All three species have similar lifecycles, beginning as eggs laid in the soil near host trees. The larvae (up to 3.5 inches before pupating) cause the most damage by feeding on the roots for several years (3-5 years) before pupating in the soil and emerging as adults. Adults are typically nocturnal and are active from late spring to late summer, depending on the species and environmental conditions.Host Plants and Damage
These beetles target a variety of crops and woody plants across different regions. These beetles' larval stage is primarily responsible for the damage, as they bore into the roots and sometimes the lower trunk portions of the trees, causing structural weaknesses and increased susceptibility to diseases and environmental stresses. The larvae impair the plant's ability to absorb water and nutrients, leading to reduced vigor and, eventually, death. Adults may or may not feed during their lifespan (1-2 months). Affected plants often exhibit canopy dieback and may be easily uprooted due to weakened root systems. Early detection is crucial to mitigate the impact on these economically important crops and trees.Fruit Trees:- Apple trees are commonly targeted, showing signs of gradual thinning and yellowing of foliage and eventual limb-by-limb mortality.
- Cherry trees, along with other stone fruits such as peach and plum, are also affected. These beetles tend to hollow out, girdle, or sever the wood of roots and crowns.
- Pecan trees suffer particularly when old orchards begin to decline, showing weakening limbs over the years.
Ornamental and Forest Trees:
- Cottonwood and native ornamental trees and shrubs are listed as hosts, experiencing damage similar to that seen in fruit trees.
- Oak, hickory, and other hardwood trees are also vulnerable to Prionus beetle infestations, especially in settings where these trees are prevalent.
Other Plants:
- Hops, an essential crop in brewing, and hazelnuts (fruit tree), face challenges from Prionus californicus, particularly in the western U.S.
Prionus Beetles in North Carolina Blueberries
In October 2010 and again in January 2013 growers reported 'Duke' highbush blueberry fields with severe damage to roots and crowns caused by grubs feeding on the underground parts of the plants. To our knowledge, this is the only report of Prionus beetles feeding on commercial blueberries. The infestation was reported in a commercial farm in the blueberry-producing area of North Carolina in the south coastal area, where most of the commercial blueberries are grown.In early summer 2024, a severe infestation with Prionus larvae was again reported in the same area in 'Duke', O'Neal', 'Star', and 'Legacy' highbush blueberry cultivars. After confirming the presence of advanced instar grubs in multiple plants in one of the locations, pheromone traps were placed in three locations in the state to monitor adult emergence.
