Best weather to spray cotton
The weather window for spraying cotton — Delta T, humidity, wind, inversion and rain — plus drift sensitivity, defoliation timing and the preset values.
Cotton receives many applications over a long season — herbicides, repeated insecticides, plant growth regulators, and defoliants or desiccants at the end. It is also one of the crops most sensitive to off-target herbicide drift, which is why its window is set more conservatively than most.
The weather window
- Delta T: 3–8 °C in the app's preset — a slightly higher lower limit than the usual 2, which keeps you further from the calm, near-saturated conditions that go with inversions. See Delta T.
- Humidity: avoid very dry afternoons, and wet foliage where the label advises against it. See humidity and dew point.
- Wind: a light, steady breeze within the label's range, blowing away from sensitive areas. See wind speed for spraying.
- Inversion: do not spray under one. See thermal inversion.
- Rain: leave the product's rainfast period clear. See rain and spraying.
Crop-specific considerations
Drift sensitivity. Cotton that is not tolerant to them is highly sensitive to some growth-regulator herbicides used in neighbouring crops. When you spray cotton, the reverse also applies: products used in cotton may harm crops, gardens or water nearby. Coarser droplets, the right wind direction and label buffers are the main tools. See spray drift.
Coverage for insect control. Many cotton pests feed inside the canopy or on the underside of leaves, and insecticide coverage in a dense canopy is demanding. Balance coverage against drift with the droplet class and water volume the label recommends.
Defoliation and desiccation. Timing is usually decided by crop maturity — for example the proportion of open bolls, or other maturity measures used locally — and the label. Weather matters too: defoliant activity generally depends on temperature, and cool conditions can slow it, so check the label's temperature guidance. Uniform coverage of the whole plant is important, and rain soon after application can reduce the effect.
Pollinators. Follow the label's pollinator statements during flowering.
Typical applications
Herbicides, insecticides, fungicides where needed, plant growth regulators, and defoliants or desiccants before harvest.
Setting it up in PulveCast
Choose the Cotton preset. It sets Delta T to 3–8 °C, humidity to 50–90 % and Coarse as the ideal droplet class; in automatic mode the app suggests an even coarser class when the wind requires it. Crop presets are part of Pro; the free Custom preset lets you enter the same values.
Other crops
- Best weather to spray soybeans
- Best weather to spray corn (maize)
- Best weather to spray sugarcane
- Best weather to spray wheat
- Best weather to spray coffee
- Best weather to spray rice
- Best weather to spray citrus
- Best weather to spray vineyards
- Best weather to spray potatoes
- Best weather to spray pastures
Frequently asked questions
Why is the cotton preset different from the others?
Cotton is very sensitive to drift, so the preset uses a Coarse droplet class and a Delta T of 3 to 8 °C, keeping further away from the calm, near-saturated conditions linked to inversions. Humidity is set to 50 to 90 %.
What weather is best for cotton defoliation?
Warm conditions generally favour defoliant activity, while cool weather can slow it. Check the label for temperature guidance, avoid rain within the rainfast period and apply with the usual drift precautions.