Home / Guides / Pest, Disease & Weed Timing Calendars
Pest, Disease & Weed Timing CalendarsHigh Tunnel Disease Calendar
High tunnels trap humidity and warmth, which helps crops but also helps disease, so the calendar centers on airflow, dry foliage and clean ground.
Key points
- Humidity and poor airflow drive most tunnel diseases.
- Vent early, water in the morning and use drip irrigation.
- Scout weekly and send unusual symptoms to a lab.
- Clean thoroughly between crops and keep a log.
- Record humidity events and disease sightings together to see which conditions trigger problems.
Why are diseases different in a high tunnel?
The plastic cover keeps rain off leaves, which lowers some outdoor diseases, but the enclosed air can hold moisture for many hours. Condensation, cool nights and low airflow favor leaf molds, blights and botrytis-type problems. Soilborne diseases can also build up because tunnels are cropped intensively in the same ground. Cool nights after warm days produce the heaviest condensation, so keep an eye on the forecast and adjust venting ahead of time.
Extension specialists who work with tunnels emphasize that management is mostly environmental and cultural.
Disease timing follows the crop cycle and weather, so your calendar should list planting, bloom, fruit set and removal dates with notes on humidity events.
What should you do before planting each season?
Review last season's disease notes. Remove old crop debris, clean structure and tools, and repair vents, side walls and irrigation. Take a soil test and follow local recommendations, since salt and nutrient buildup can occur in covered soils. Small habits repeated every week do more for the farm than a big effort once a year, and the notes you keep will make the next season easier to plan.
Plan rotation within the tunnel as well as you can, and consider resistant varieties. Consider grafted plants or fresh media where extension suggests for your crops.
Mulch laid down early in the season can reduce soil splash onto lower leaves, which helps limit some diseases.
- Remove debris from last crop
- Clean and repair vents and sides
- Soil test before planting
- Choose resistant varieties
How do you manage humidity day to day?
Open sides and end walls early enough that morning moisture clears, and close later in the day only as temperature requires. Use fans to move air where available. Avoid watering late in the day so foliage dries before night. Make a habit of walking the tunnel at dawn at least once a week to see how long moisture sits on leaves before it dries.
For example, if you find heavy condensation on leaves at dawn, start venting earlier the next day and adjust irrigation timing. Keep notes on weather and what you did.
A thermometer and humidity gauge placed at plant height tell you more than readings near the door.
How should irrigation be timed?
Drip irrigation keeps leaves dry and puts water at the roots, and it is widely recommended for tunnel crops. Water in the morning when possible, and avoid overwatering, which promotes root disease and humidity.
Check soil moisture with a probe or by hand before irrigating, since tunnel soils get no rain and dry unevenly.
Dry foliage matters most overnight, so plan irrigation to finish early enough for leaves to dry before dark.
What does scouting look like?
Walk the tunnel weekly or more often when conditions are favorable for disease. Look at lower leaves, stems at soil level and the underside of leaves. Remove and bag infected leaves promptly where that is appropriate for the crop. Ask a neighbor or your extension agent what they have seen this year, since local reports often point to the next problem before it reaches your own fields.
Send unusual symptoms to your diagnostic lab. Several diseases look similar, and the right response depends on the cause.
Prune and trellis plants for airflow where your crop allows, and remove lower leaves as extension suggests.
When can fungicides or biologicals enter the plan?
If cultural steps are not enough, ask extension for options that are labeled for your crop in protected culture. Read labels for crop, interval before harvest, re-entry period and ventilation requirements. Licensing and restrictions vary by state.
Spray timing matters. Many products work as protectants and need to be in place before disease develops, so ask extension when to start in your crop.
If you use a protectant, apply it on the schedule and conditions the label states, and not after symptoms have already spread widely.
What should you do at season end?
Remove all crop residue, clean structure, and consider leaving the soil bare or planting a cover crop as advised for your area. Note disease problems, weather and what worked. Plan rotation and variety changes for next year. Include notes on rotation, variety performance and what you would change, so the next season starts with a clear plan.
Keep a simple log. It makes planning easier and helps your adviser help you.
Compare notes with other tunnel growers in your region. Conditions vary, but shared experience speeds learning.
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.