Does Baking Soda Kill Powdery Mildew on Cannabis?

Answer

No. Baking soda does not kill powdery mildew on cannabis. It can suppress some surface growth and reduce spread in limited tests on other plants. It does not cure infected tissue. Published cannabis-specific data are limited.

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What baking soda does

Sodium bicarbonate raises pH on the leaf surface. It also leaves a salt residue. Powdery mildew spores can be affected by that shift. The effect is contact only. It does not move into plant tissue. It does not remove colonies inside leaves or stems.

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Evidence from other crops

Trials on roses and cucurbits used 0.5% to 1% sodium bicarbonate solutions, or 5 to 10 g per liter, with a surfactant in many cases. Those trials reported less powdery mildew severity. Results varied by crop, rate, timing, and weather. A spray before infection worked better than a spray after symptoms appeared. No peer-reviewed trial shows the same result on cannabis.

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Limits on cannabis

Cannabis powdery mildew is associated with Golovinomyces ambrosiae in North America. The fungus grows on leaf surfaces and sends feeding structures into plant cells. A contact spray cannot reach those structures. Baking soda also leaves white residue on buds and leaves. That residue can affect appearance and smoke quality. High rates can burn leaf edges.

Few pesticide products carry a cannabis label. Check state rules before use. Do not assume a kitchen product is exempt or safe for harvest. Potassium bicarbonate is a different salt. Do not swap one for the other without a label.

Risks

• Leaf burn at rates above 1% or under bright light.
• White residue on flowers and trim.
• pH change in the spray mix that reduces other products' activity.
• No curative action on established colonies.
• False control that lets spores spread.

What to do instead

Remove infected leaves and stems. Put them in a sealed bag. Do not compost them on site. Increase airflow. Keep relative humidity below 60% if possible. Space plants. Water at the base. Scout leaf undersides twice per week.

Use a product labeled for cannabis in your state. Rotate active ingredients. Apply at the label rate. Test any spray on a small area first. Record rates, dates, and results.

Bottom line

Baking soda is not a cure for powdery mildew on cannabis. It may slow spread in some conditions. It does not kill the fungus inside plant tissue. Use sanitation, airflow, and labeled products.