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Pest, Disease & Weed Timing CalendarsPest Scouting Calendar for Field Crops
Field crop scouting pays off when it follows growth stages from emergence to harvest. This guide lays out a calendar built on stages, weather and a repeatable walking pattern.
Key points
- Tie every scouting observation to a crop growth stage.
- Use a repeatable field pattern with the same number of stops each visit.
- Use thresholds from your own state extension service, not numbers from another region.
- Keep field records so a crop adviser can see the full history.
When does field crop scouting start?
Scouting begins at planting, not when the crop looks stressed. Stand establishment problems such as seedling feeding, poor emergence and early weed pressure show up in the first weeks, and a stand check at emergence tells you whether to look closer. State scouting calendars, like the one Iowa State publishes for corn and soybean insect pests, are organized by crop stage because that is what drives the risk.
Start with a stand count or a walk through a few spots in each field about the time seedlings emerge, then repeat as the crop moves through its vegetative and reproductive stages.
Which growth stages need the most attention?
Each crop has windows when particular pests do the most harm. In corn, early season seedling pests, whorl-stage leaf feeders, silking and grain fill each have their own concerns. In soybeans, the vegetative stages, flowering, pod set and seed fill matter. Check your extension crop guide for the stage-by-stage list for your state.
Note that a pest present in a field is not the same as a pest that is hurting yield. The same insect can be harmless at one stage and costly at another, so tie every observation to a stage.
- Emergence: stand, seedling feeders, early weeds
- Vegetative: leaf feeding, early aphid colonies
- Reproductive: pod and ear feeders, aphid buildup
- Seed fill to maturity: late season insects and lodging
How should you walk a field?
Use a pattern that covers the field rather than a single spot. A common approach is a zigzag or a W across the field, stopping at several points, with a fixed number of plants checked at each. Avoid sampling only near the road or the edge, though a few edge checks help you catch early arrivals.
Take the same number of stops each visit, mark them on a map if you can, and check the same plant parts each time. Consistency makes counts comparable from week to week.
How do thresholds and weather fit in?
University of Nebraska-Lincoln soybean aphid guidance, for example, ties decisions to a threshold based on the percentage of plants infested and whether populations are rising. Thresholds exist for many field pests, and they differ by crop, stage and state, so use the numbers from your own extension service.
Weather shapes everything. Warm weather speeds insect development, wet conditions favor many diseases, and drought stress changes how a crop tolerates feeding. Watch the forecast and local pest alerts, then adjust your visit frequency.
What should you record and share?
Record field, crop stage, planting date, date scouted, weeds and insects seen and how many plants were checked. If you work with a certified crop adviser or a scout, shared records speed up decisions.
Field history matters too. Note previous crop, tillage and any earlier pest problems, since those often predict where to look first the next season.
When should you call for help?
Send a photo or a sample to your county extension office when you cannot identify a pest or when damage does not match what you expect. Do this early, since identification determines everything that follows.
For control decisions, the label is the law, pre-harvest intervals apply, and pollinator protection matters during bloom. Applicator licensing varies by state, so confirm what is required before you act.
What does a worked scouting week look like for field crops?
For example, if you farm corn and soybeans and plant corn first, your early visits focus on the corn stand, seedling feeding and weeds, while the soybean fields get a quick emergence check once they are up. By the time corn reaches its leafy stages, soybeans are emerging and need their own stand count. Each field sits at a different stage, so each visit has a different checklist.
Write the checklist for each stage on one page and carry it with you. A short list keeps you from fixating on the pest you know best and missing a quieter problem such as a disease starting under a wet canopy or a weed patch that escaped early control.
Late in the season, shift attention to what will affect harvest and next year. Note lodged plants, stalk problems, late pod feeding and weed escapes by field, since those notes shape next year's rotation and early season plan.
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.