What the most recent research shows about these two pests in Florida blueberry crops

FLATHEADED BORERS INFESTING FLORIDA BLUEBERRY PLANTINGS

THE FIRST REPORT of borers infesting blueberry plantings was in November 2014. During 2015 and 2016, blueberry growers in Florida reported the presence of galleries (tunnels) packed with insect frass in the canes of their blueberry plants. Samples were brought to the University of Florida, Fruit and Vegetable IPM Laboratory and larvae were recovered from galleries found on the stem of blueberry bushes. Specimens collected from samples were identified as flatheaded borers (Coleoptera: Buprestidae) at the Division of Plant Industry in Gainesville. This pest is believed to be in the genus Chrysobothris spp. There were no adult beetles recovered from any samples taken from the field.

It appears that older blueberry bushes with developing bark are the most susceptible to attack by these flatheaded borers. Buprestid beetles are often metallic in appearance and larvae are cream to white and have a distinctive flattened head, thus the name “flatheaded” borer. Adults lay their eggs on or within crevices of tree bark. After the egg hatches the larva bore into the bark of trees and begin feeding, creating galleries filled with sawdust-like frass. These galleries affect the growth and production of plants by interrupting the flow of nutrients taken up by the roots causing it to wilt. In addition, the damage caused by flatheaded borers often weakens the plant, making it susceptible to secondary infection by other bacteria or fungal agents.

Many buprestids are recognized as important economic pests of deciduous trees and shrubs including apple, pear, cherry, persimmon, walnut, white and black oaks, elm, beech, hickory, chestnut, hawthorn, and willow. Chrysobothris species prefer stressed or injured trees. Blueberries can become stressed from diseases, nutrient deficiencies, or age, which may make them more susceptible to attack by the unknown borer. For instance, the Pacific flatheaded borer (Chrysobothris mali) is common in the western U.S. and attacks pome, stone fruits, and occasionally blueberry. Chrysobothris mali is known to attack apple trees that are water stressed.

To effectively manage flatheaded borers in blueberries, we recommend pruning of older canes after harvest. Special care should be taken to remove infested canes from the field. Since the larvae are usually hidden deep in the bark, growers should use pesticides with systemic activity. It is believed that the adults are active in the spring and when this information is confirmed, pesticide applications could be made to target adults during that time. As for now, applications can be made against the larvae after harvest shortly after the first sign of infestation.

INCIDENCE OF CHILLI THRIPS IN FLORIDA BLUEBERRIES

Chilli thrips were first detected in southern highbush blueberries in Orange, Sumter, and Hernando counties during the summer of 2008. Chilli thrips, Scirtothrips dorsalis Hood, is a major polyphagous pest of many crops. It has been reported to attack over 100 known ornamental and fruit crops in more than 40 families. In blueberry, Chilli thrips feed on young leaves, causing leaf bronzing and shoot dieback in late spring to early summer, shortly after the bushes are pruned During heavy infestation, the edges around younger leaves and stems are eaten and leaf curling develops. The Chilli thrips are smaller than the flower thrips and are approximately 0.04 inches long with dark fringed wings and dark spots across the back of the abdomen.

High infestations of Chilli thrips could reduce yield during the following season. In addition, plants become more susceptible to secondary infection and disease pathogens. The life cycle of Chilli thrips are similar to the Florida flower thrips that are present in early spring. Female S. dorsalis insert their eggs into blueberry tissues, and the eggs hatch in about six to eight days. Females are capable of laying between 60-200 eggs. Newly hatched larvae then pass through two larval stages (first and second instars). These larval instars last for about six to eight days, during which time they feed on blueberry tissues. They then pass through a prepupal and a pupal stage, during which time they do not feed. Chilli thrips complete their life cycle in 17 to 21 days under ideal conditions. In Florida, most of the outbreaks in blueberries were recorded in July, August, and September on new growth.

Management for Chilli thrips includes eliminating host plants, including weeds that support their growth and development. The application of systemic insecticides Assail® (Acetamiprid) and other Neonicotinoid insecticides can be used particularly on young plants where the leaf often tends to curl during heavy infestation. Spinetoram Delegate® is also an effective tool and it has the added benefit of conserving natural enemies that regulate the thrips population. Conventional products that can be used to manage Chilli thrips include Malathion, Diazinon, and Sevin® (Carbaryl). Natural enemies, such as Orius insidiosus and Geocoris spp., are good natural predators of thrips.

For more information, contact Dr. Oscar Liburd at oeliburd@ufl.edu.

CREDIT

story by OSCAR LIBURD

Oscar Liburd is professor of Fruit and Vegetable Entomology, UF/IFAS.