Prionus root borer: biology, behavior and management. Angelita L. Acebes-Doria Tree Nut Entomology University of Georgia - Tifton

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1 Prionus root borer: biology, behavior and management Angelita L. Acebes-Doria Tree Nut Entomology University of Georgia - Tifton

2 Foliage Feeders Aphids, Mites, Phylloxera, Leaffeeding caterpillars Nut feeders Nut casebearer, Pecan weevil, Shuckworm, Stink bugs Trunk & root feeders Ambrosia beetles, Prionus root borers

3 Root feeder Prionus rootborers

4 Prionus Beetles: 2 Species associated with Pecans Tilehorned Prionus beetle Male Broadnecked Prionus beetle Male Female Female

5 Prionus Root Borer Descriptions Root borer Adult Root borer Larva Root borer larva June Beetle Larva

6 Prionus Root Borer Life Cycle Spend 3-5 Years Feeding!!! Mated females lay eggs in the soil near the roots. Young larva feed on root barks and will tunnel into and feed in the roots soon after. Adults emerge and reproduce. Non-feeding pupa in the soil before emerging as an adult.

7 Prionus Root Borer Behavior During the day, adults remain hidden beneath loose bark or debris at the base of the tree. Males begin flight starting at sunset and are attracted to lights; females most likely do not fly. Females can live 1-2 weeks but are capable of producing hundreds of eggs ( ). Females lay eggs at a depth of 1-4 cmm near the base of the host trees. After hatching, the larva bores and digs down to the roots and begin feeding. They can move through the soil from one root to another starting on the surfaces of small roots and eventually entering the woody root tissues. Life Cycle is 5-7 years.

8 Impacts of Root feeding on Pecan Trees Root borers feed on the tap and lateral roots. Pecan Roots 1. Tap Root 2. Lateral Roots 3. Fibrous Roots 4. Mycorhizzal Roots

9 Impacts of Root feeding on Pecan Trees Root damage from Prionus infestation

10 Prionus Root Borer Damage Larvae can chew on underground irrigation pipes.

11 Signs & Symptoms of Root borer Infestation Tree infested with Root borers Older trees in gradual decline Limbs look weaker and weaker each year Foliage on dying trees is irregular and thinner and lighter in color than that on healthy trees Root system can be reduced by 75-90% over several seasons (Sparks, 1974)

12 Signs & Symptoms of Infestation Infested trees easily topple over due to compromised root system Crown galls

13 Why are root borers hard to manage? - Numerous alternate hosts growing in unmanaged woodlots next to orchards (oaks, hickories, grapes, poplars, chestnuts, etc.) - Removal of infested trees does not eliminate infestation. - Immature larvae are hard to control due to being underground and/or protected by root tissues. - Long life cycle (impacts of management cannot be immediately measured). - Limited studies on management options. Silver lining: Advances on Monitoring Beetle Populations

14 Monitoring Options Light Traps Pros: Effective in catching male beetles Cons: Also attractive to other insects

15 Monitoring Options Pitfall Trap Pros: Effective in catching females Cons: Also catches other insects

16 Monitoring Options: Pheromone-Baited Traps Males are attracted to prionic acid Females are attracted to alphapinene Light Traps with Pheromone Lures Pitfall Traps with Alpha-Pinene Pheromone Lure for Female Attraction

17 Monitoring Options Lure Pheromone-baited Panel Traps Effective in capturing males Provides a good indicator of when beetles are present and the changes in populations throughout the season Collection jar with killing agent Note: Can capture Prionus from the wooded areas

18 When are beetles present? Pheromone-baited Trap Georgia: Peak activity is mid-may to early/mid June Beetles emerged earlier in southern sites than in northern sites

19 Weekly Beetle Captures Across 4 Years of Trapping in Georgia 85 traps deployed in ~800-acre orchard from late April to early September. Traps checked early Capture trends vary each year. Peak activity: mid-may to early June

20 Which beetle species are present? Tilehorned Prionus beetle Prionus pocularis beetle

21 Relative Beetle Abundance (2018) /26/2018 5/26/2018 6/26/2018 7/26/2018 8/26/2018 Tilehorned Prionus Prionus pocularis Recorded to attack roots and stumps of pine trees. Does this attack pecan?

22 Management Options - Maintain healthy trees. Trees that are attacked most likely are already stressed due to disease, drought, mechanical damage or soil fertility issues. - Trees in decline: cut back/prune to make the canopy comparable to the root system - Trees with crown gall: remove infected trees - Re-planting of new trees: treating area with chlorpyrifos may help reduce existing beetle populations

23 Chemical Control Chlorpyrifos treatment of the soil around the base of the tree trunk at 250 ml per 200 L of spray effectively controls the adult beetles (Dutcher and Bactawar, 2014) Counted beetles trapped in treated and untreated arenas Untreated: 17 captured, 0 died Treated: 24 captured, 22 died ~92 % Mortality Recommendation: Application of chlorpyrifos (8 oz/50 gallons of water) along the herbicide strip

24 Mating Disruption Disrupt the mating behavior of the adults by inundating an area with sex pheromone lures Mating Disruption Lure Three orchard sites were selected (Dutcher and Bactawar, 2014) At each site, two blocks were chosen: Block 1: Deployed 240 lures/ha along herbicide strip Block 2: No lures were deployed Pheromone-baited traps were placed in each block to monitor mating success Result: Tilehorned male beetle captures in mating disruption block were significantly less than in control site.

25 Control Options against Prionus in Similar Systems Prionus californicus (pest of hops, peach, cherry in the western states). Soil fumigation as a pre-planting option Systemic materials: effective only in younger larvae on roots and not against older larvae in crown or lower trunk Imidacloprid may suppress local populations if used over several years. Trunk applied materials may kill adults and inhibit egg-laying but will not suppress larval populations.

26 Control Options in Similar Systems Prionus laticollis (pest of tree fruit in the northeast and mid-atlantic states). Trunk spraying of chlorpyrifos

27 Potential Areas of Research for Management of Prionus root borers in Pecans Soil fumigation prior to planting of new trees in previously infested areas Systemic insecticides for larval control Use of pheromone lure (behaviorally-based management): Mating Disruption Attract-&-Kill Measuring impacts of management strategies

28 Monitoring - Scout for infestation - Monitor beetle populations Cultural Management - Maintain healthy trees - Prune infested trees - Remove heavily infested trees Integrated Pest Management of Prionus root borer Chemical Control - Herbicidal strip spraying - Trunk spraying? - Systemic insecticides? Behaviorally-based Tactics - Mating disruption? - Attract-&-Kill?

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