# Best weather to spray potatoes

> The weather window for spraying potatoes — Delta T, humidity, wind, inversion and rain — plus blight programmes, coverage, desiccation and Custom settings.

- Canonical URL: https://pulvecast.com/crops/potatoes
- Language: en
- Last updated: 2026-09-19
- Path: Home › Spraying weather by crop › Best weather to spray potatoes
- Site guide for agents: https://pulvecast.com/llms.txt

Potatoes are often on a regular fungicide programme through the season, especially against late blight, which thrives in warm, humid weather. That creates a tension: the conditions that increase disease pressure — humidity, leaf wetness and rain — are the same ones that make a good spraying window hard to find.

## The weather window

- **Delta T:** 2–8 °C. See [Delta T](https://pulvecast.com/guides/delta-t).
- **Humidity:** high humidity is common in blight weather; the concern is wet foliage and calm, near-saturated air. See [humidity and dew point](https://pulvecast.com/guides/humidity-and-dew-point).
- **Wind:** a light, steady breeze within the label's range. See [wind speed for spraying](https://pulvecast.com/guides/wind-speed-for-spraying).
- **Inversion:** calm, humid mornings and evenings are prone to inversions. See [thermal inversion](https://pulvecast.com/guides/thermal-inversion).
- **Rain:** the rainfast period is critical in a protective programme. See [rain and spraying](https://pulvecast.com/guides/rain-and-spraying).

## Crop-specific considerations

**Blight programmes.** Protective fungicides need to be on the leaves before infection. Many growers use disease-risk forecasts to time sprays, then look for the best weather window within the interval set by the programme and the label. A dry window long enough for the product to become rainfast is often the deciding factor.

**Canopy coverage.** Once the canopy closes, the lower and middle leaves are harder to reach. Water volume, droplet class and a Delta T in range all affect coverage.

**Aphids and virus.** Where aphids spread viruses, insecticide timing is driven by pest activity and the label.

**Haulm desiccation.** Before harvest, the foliage is often killed off chemically or mechanically. Uniform coverage matters, and neighbouring crops that are still green need the usual drift precautions.

**Tramlines and wet soil.** Heavy, wet soils limit when ground sprayers can enter, which can push applications into marginal weather. Plan ahead using the forecast.

## Typical applications

Fungicides (often on a regular programme), herbicides before emergence, insecticides where needed, and desiccants before harvest.

## Setting it up in PulveCast

There is no potato preset, so use **Custom**. It starts from Delta T 2–8 °C, humidity 55–95 % and a Medium droplet class. Conservative starting points:

- Keep Delta T at 2–8 °C.
- Set the droplet class to what your nozzles produce, or leave it on automatic.
- Lower the maximum wind from the 25 km/h default towards 15 km/h (about 9 mph), or to the label's limit.
- Lower the precipitation probability limit from 50 % if your fungicide needs a long rain-free period.

## Other crops

- [Best weather to spray soybeans](https://pulvecast.com/crops/soybean)
- [Best weather to spray corn (maize)](https://pulvecast.com/crops/corn)
- [Best weather to spray sugarcane](https://pulvecast.com/crops/sugarcane)
- [Best weather to spray cotton](https://pulvecast.com/crops/cotton)
- [Best weather to spray wheat](https://pulvecast.com/crops/wheat)
- [Best weather to spray coffee](https://pulvecast.com/crops/coffee)
- [Best weather to spray rice](https://pulvecast.com/crops/rice)
- [Best weather to spray citrus](https://pulvecast.com/crops/citrus)
- [Best weather to spray vineyards](https://pulvecast.com/crops/vineyards)
- [Best weather to spray pastures](https://pulvecast.com/crops/pastures)

## Frequently asked questions

### Can I spray potatoes in humid weather?

Often yes — blight programmes regularly have to. High humidity itself is not the problem; wet foliage, calm near-saturated air and inversions are. Check Delta T, wind and inversion, and leave the product's rainfast period clear.

### How long before rain should I spray potato fungicide?

Follow the label's rainfast period or rain-free interval. Many growers plan the spray around the forecast so the product has dried and become rainfast before rain arrives.

## Check the spray window before you go to the field

PulveCast gives a green, yellow or red verdict for every hour from Delta T, humidity, wind, gusts, drift risk and thermal inversion. Free on Android and iOS, no account needed.

- Google Play: https://play.google.com/store/apps/details?id=com.pulvecast.app
- App Store: https://apps.apple.com/app/pulvecast/id6779816829