Ken Ostlie

1
Weather Effects on Corn Rootworm Population
Dynamics and Management

• Ken Ostlie
• Department of Entomology - University of
  Minnesota
• ostli001_at_umn.edu
• [phone] office [phone] cell

2
Why Talk about Weather Effects on Corn Rootworm
Population Dynamics?

• Direct Effects on Corn Rootworms
• Eggs
• Larvae
• Pupae
• Adults

• Indirect Effects
• Corn Weedy Grass Hosts
• Soil Environment

3
Direct Effects of Weather on Corn Rootworms
Overwintering

• Overwintering of corn rootworm eggs
• Northerns more winter hardy than westerns!
• WCR egg mortality begins ca. 19oF and increases
  dramatically with freeze units (Gustin 1981,
  Godfrey et al. 1995, Lawson 1986). Mortality
  exceeded 95 after 4 weeks at 14oF.
• NCR egg hatching success actually increased
  during the first 8-10 weeks at temps of 23oF and
  only declined with prolonged exposure (4 to 6
  weeks or more) at temps below 14oF. Mortality
  was only 42 after 4 weeks at 14oF.
• Depends on egg distribution in soils, tillage /
  residue cover, snow depth and harshness of winter
  temps. Fluctuating temps are more detrimental.

4
Corn Rootworm Development is based on Temperature

• Egg development begins at ca. 52oF (similar to
  corn) and requires ca. 680 760 DD for 50
  hatch.
• Degree-days calculated from air temps and
  adjusted for minimum (52oF) and maximum (64oF)
  thresholds provided the best predictors of
  northern and western emergence Davis et al.
  1996. Evidence of adaptation to local
  conditions.
• Male WCR emerge 1-3 days earlier than female and
  develop faster at all stages.
• NCR emergence relative to WCR varies, peaking
  earlier in northern sites and later in southern
  locations. NCR emergence is generally longer
  than WCR.
• Predicted peak emergence for WCR for Minnesota
  has varied by 8-12 days over the last 4 years.

5
Weather can Alter the Synchrony Between Rootworms
and Root Development
Strnad et al. 1987
Delays in root development or accelerated hatch
reduced food availability increased larval
competition
6
Newly Hatched Larvae and Pupae can Drown in
Saturated Soils

• Impact depends on
• Timing of rainfall
• Amount and intensity
• Soil texture and drainage

7
Adult Longevity and Reproductive Success Reduced
by Heat Drought
Drought and heat reduce the availability of
silks and pollen.
8

• Whats Changed with Corn Production?
• Earlier planting dates
• Higher plant populations
• Narrower row spacing
• Higher yielding hybrids
• Reduced tillage
• These Changes Increase Corn Rootworm Survival or
  Damage!
• Higher yields with smaller root systems gt
  Pushing the envelope on roots!

9
Weather Effects on Corn Rootworm Management

• Wind during application can displace insecticide
  bands
• Rainfall is required to activate soil
  insecticides and move them into root zone.
• Eroding rains before hatch may displace
  insecticides
• Excessive leaching moves insecticides out of root
  zone
• Soil moisture and temperature affect insecticide
  half-life

10
Factors Affecting Performance of Corn Rootworm
Management Options

• Corn rootworm pressure
• Site conditions (soil charcteristics)
• Field history and cultural practices
• crop rotation
• tillage
• planting date
• fertility
• hybrid
• weed control
• Insecticide application
• Application (placement, equipment, weather)
• Weather
• Soil moisture
• Soil temperatures

11
Soil Insecticide Degradation and Corn Rootworm
Phenology
12

• Weather and Interpretation of
• Management Trials
• Application conditions
• Rainfall (planting to hatch)
• Temperatures (planting to hatch)
• Occurrence, severity and timing of lodging
  events
• Timing / severity of weather- related stresses on
  yield

13
Weather and Yield Loss from Corn Rootworms

• Impaired uptake of water and nutrients (worse
  during drought)
• Increased incidence of stalk / root rots (worse
  under stress)
• Reduced light interception by lodged canopy
• Interference with pollination from lodging or
  silk feeding

14
Lodging Affects Grower Perception of Management
Success