Biology and Management of the Pecan Weevil

Biology and Management of the Pecan Weevil Phil Mulder
Professor and Head
Department of Entomology and
Plant Pathology
Introducing •  Dr. Jacquelyn (Jackie) Lee –  B.S. Arkansas Tech, Biology –  M.S. University of Arkansas, Entomology major –  Ph.D. University of Arkansas, Entomology major –  GeneFcs minor •  Senior Biologist R&D -­‐ DowAgroSciences 2008-­‐2013 •  OSU PesFcide Coordinator and Extension Entomologist 2013. Pecan Weevil • 
Associated with North American hickory for millions of years. –  Reflected in the synchrony between the weevil and its hosts today. –  Confirmed hosts in United States Carya species (11-­‐12 species) and Persian Walnut, Juglans regia •  Management confounded by: –  Rainfall variaMon –  Onset of crop maturity –  CulMvar selecMon –  Surrounding topography –  Soil type –  Crop load –  Etc. Pecan Weevil Life Cycle and Biology Pecan Weevil OviposiMon •  Weevils begin emergence after heavy rain (late July early August).
•  Feed on nuts in water stage causing nuts to abort and fall
(~ .25 nuts/day/weevil).
•  Nuts in gel stage are suitable for egg laying? Most suitable are those
in the dough stage. Mid to late August.
•  Female oviposits eggs in 15-30 nuts (2-4 eggs/nut in about 2 hours).
Up to nearly 80 eggs/female.
Larval DescripMon and Development 1st - Avg. 3.9 days
3rd - Avg. 6.5 days
2nd - Avg. 3.7 days
4th - Avg. 5-9 days feeding
Pecan Weevil Emergence Avg. 20.3 days after feeding
Pecan Weevil Diapause 1-2 years
Avg. – 18 to19 days
•  Weevils in diapause: well protected, don’t feed, “sip” oxygen.
•  rely on stores of fat body and exhibit an 8-fold decrease in
• 
oxygen consumption compared to active stages.
4-13 inches below surface with little to no lateral movement (so
in the drip line of host tree).
Pecan Weevil Adult • 
Adults emerge from soil (3-4 days)
after a heavy rainfall (1-2 inch)
event starting as early as mid-July.
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Majority emerge in August to
September, but may continue to
emerge into mid-October.
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10% will not emerge until the
following year.
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When the water stage is being
converted to kernel.
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Avg. longevity is 15-30 days, but
may live for up to 56 days.
Male pecan weevil
Female pecan weevil
Pecan Weevil Adults XXX • 
Initially, enter the tree to
search for food (about .25
nuts/day) and oviposition
sites (avg. about 45 eggs).
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If no pecans are found or if
many nuts are already
infested, in the tree where
they emerged, then they may
fly to adjacent trees.
• 
Newly emerged weevils
predominantly crawl up the
bole of the tree, but some fly
into the canopy and some
never make it to a tree.
Pecan Weevil Adults and Fruit Damage • 
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Feeding damage causes nut
abortion in the water stage.
After shell hardening can
cause black spots on kernel.
Introduce molds that degrade
the gel causing “sticktights”.
Destroy the entire kernel (2-4
larvae) and proliferate the
population.
Monitoring and Managing Pecan Weevil •  Limb jarring - Swingle (1935) , Bissell (1939).
Impractical, inconvenient, strenuous particularly in
large orchards.
•  Tree bands - Beckham and Dupree (1954) Hinrichs and
Thomson (1955). Messy, applications must be repeated,
weathering, destroys specimens. Cloth and burlap
bands (Tedders, 1974; West and Shepard, 1975), did not
indicate seasonal emergence patterns as well as cone
emergence traps, also captured other critters (spiders
and snakes). Tygon tubing (West and Shepard, 1975)
Construction time long.
•  Pyrethrum Sprays - Pyrenone® (Raney and Eikenbary
(1971), Polles and Payne (1973). High cost, frequency,
time limitations.
Monitoring and Managing Pecan Weevil •  Pheromone traps – Harp and Van Cleave (1970), used
caged weevils with some effectiveness. Gray (1974),
used grandlure but ineffective.
•  Ground cover traps – Raney et al. (1970), Polles and
Payne (1974), Leggett and Cross (1971), West and
Shepard (1974).
•  Effectiveness of wire-cone emergence traps good for
detecting the onset of weevil emergence and
developing a prediction equation (Boethel et al. 1975).
Tarps (Nash and Thomas, 1972), tents (Raney et al.
1970), and combinations thereof (Neel et al. 1975 and
Gray 1974) have been used with great success in
capturing weevils but practical use by growers has
seen limited adoption.
Monitoring and Managing Pecan Weevil Wire-­‐cone emergence traps (Raney and Eikenbary 1969) •  Required 120 traps (12 each
under the drip line of 10
trees).
•  Had to be protected from
cattle or mowing.
•  Required exhaustive
checking, recordkeeping and
calculation.
•  Expensive, cumbersome to
store and move.
Monitoring and Managing Pecan Weevil Pyramid traps – Tedders and Wood (1994) 1) Not as costly as wire
cone emergence traps
unless you consider time
and labor for tree
whitewashing.
2) Less cumbersome to
deal with because it takes
fewer traps.
3) Not compatible with
haying and/or grazing.
4) Thresholds not well
established or confirmed.
Monitoring and Managing Pecan Weevil Circle traps – Mulder et al. (1997) 1) Least expensive trap
type.
2) Simple to build, install
and monitor.
3) Compatible with haying
and grazing.
4) Thresholds established.
Pecan Weevil PopulaMon Growth • 
Increases approximately five fold per generation and
disperses very little, unless trees in the vicinity are
devoid of fruit.
• 
Can estimate future risk based on yield, percent
infestation. Number of infested nuts per unit area 2
years ago times 5.
• 
Value of the nuts at risk is dependent on current
price at harvest then compare that to the expected
costs of management (insecticide costs and
treatment) to assess whether treatment is
warranted.
Biological Control or the Organic Challenge “Pecan Weevil” • 
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Currently, two entomopathogenic fungi species show
several levels of mixed results in both the laboratory
and the field.
Fungi
•  Beauveria bassiana – White muscardine disease
–  Botanigard, Mycotrol, Naturalis
•  Metarrhizium anisopliae – Green muscardine
disease
–  Met52, Green Muscle
Biological Control or the Organic Challenge “Pecan Weevil” • 
Trunk sprays of B. bassiana have resulted in >75%
mortality but may take more than 7 days, so the weevils
are still feeding and laying eggs for one week.
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Researchers have acknowledged keeping recovered
weevils in the laboratory under controlled conditions, so
overall efficacy would likely not parallel field conditions.
Biological Control or the Organic Challenge “Pecan Weevil” • 
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Under the right conditions entomopathogenic fungi can
result in 75% control but “recycling” of either nematodes
or fungi under “normal” field conditions would diminish
based on reduced reproduction in the host.
As weevil larvae mature they become less susceptible to
infection with entomopathogenic nematodes.
Combinations of pathogens are unlikely to improve
suppression of pecan weevil beyond what could be
expected from a single organism with a high range of
virulence.
Management Decisions
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Cultivar and Price affect the economic risk (Harris et
al. 1981).
–  End of season density of 200-1460 adults/acre.
–  So depends on nuts/lb and price.
Circle traps - 0.3 weevils/trap/day when using a
minimum of two traps per tree on ten trees (Mulder et
al. 2003).
–  Rough estimate, because even at low densities
pecan weevils cause economic damage any time
after the gel stage.
–  Market will also affect the decision – wholesale
versus retail and associated connection with
infested pecans.
Continued monitoring needed followed by 2-3
additional treatments
Treatment ApplicaMon • 
Once a treatment decision is reached apply
insecticide with an airblast sprayer calibrated to
delivery 75-100 gpa.
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Treat both sides of the tree, while traveling at the
proper speed (1.5 MPH).
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Consider pesticide compatibility for grazing.
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Consult university guidelines or
http://pecan.ipmpipe.org/ for recommendations on any
chemical treatment.
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Do NOT transport weevil infested nuts into uninfested
areas (New Mexico, Arizona and California).
Thank you for your a\enMon, Mme and friendship over the years. I have enjoyed this group of growers more than any I have ever worked alongside.