Armyworm Risk Calculator

Protect your garden with a smarter armyworm risk check. Enter field conditions and scouting counts. See risk levels and next steps in minutes today.

Enter conditions and scouting observations

Use your best estimates. For accuracy, base numbers on recent scouting within the last 2–3 days.
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Select the closest match for your area and season.
Use the last 24–48 hour average if possible.
Higher humidity often supports survival and feeding.
Moderate rain can improve host growth and risk.
Very windy conditions can reduce moth activity.
Moist soils often create greener, more attractive hosts.
Frequent watering may keep growth tender and attractive.
Crop selection sets a baseline host attractiveness.
Young plants are generally most at risk.
Dense canopy can shelter larvae and reduce detection.
Weeds provide shelter and alternative hosts.
Residue can hide larvae and pupae near soil level.
Nearby grasses or corn can act as sources of moths.
History raises the baseline likelihood of recurrence.
Less scouting increases uncertainty in the estimate.
Count small and medium larvae across several plants.
Estimate percent leaf area removed in the worst spots.
If you don’t use traps, leave at 0.
Lower numbers mean a more active, recent flight.
Lady beetles, lacewings, parasitic wasps, birds.
Used only to adjust near‑term risk; follow labels.
Notes are included in exports.
Reminder: This tool estimates risk for garden planning. It is not a pesticide recommendation. If you choose any control product, always follow the label for your crop.

Example data table

Sample entries show how conditions and scouting can change risk.
Scenario Weather Scouting Habitat Estimated output
Cool & low evidence
early spring bed		 18°C, 55% RH, 4 mm rain 0.2 larvae/plant, 1% defoliation Low weeds, sparse canopy Low ~ 20–35
Warm & building flight
mid-season vegetables		 27°C, 75% RH, 18 mm rain 1 larvae/plant, 5% defoliation, 15 moths/week Some weeds, medium canopy Moderate ~ 40–60
Hot spot outbreak
young plants near grasses		 29°C, 82% RH, 22 mm rain 6 larvae/plant, 30% defoliation Dense edges, many hosts nearby High ~ 70–95

Formula used

The calculator computes a 0–100 risk score using a weighted index:

Core equation
Raw = 0.28·WeatherIndex + 0.22·HabitatIndex + 0.10·CropIndex + 0.40·ScoutIndex
Adjusted = clamp(Raw + ScoutingUncertainty − NaturalEnemyReduction − TreatmentReduction, 0, 1)
Score = round( max(Adjusted, EvidenceFloor) · 100 )

EvidenceFloor is applied when larvae and defoliation are both high, to prevent underestimating an active outbreak.

How to use this calculator

  1. Choose the armyworm type that best matches your season and region.
  2. Enter recent weather: temperature, humidity, rainfall, and wind.
  3. Describe your garden habitat: soil moisture, irrigation, canopy, weeds, residue, and nearby host plants.
  4. Add scouting evidence: larvae per plant, defoliation, moth trap counts, and days since first moth capture.
  5. Click Calculate risk. Review actions and index breakdown.
  6. Use Download CSV or Download PDF to save your results for records.
Tip: If you have multiple beds, run one calculation per bed and add bed names in the notes field.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.

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