Soybean rust
Tiny tan to reddish brown spots with raised pustules on the underside of the lower leaves, which yellow and drop early.
Crops it strikes
What you see
When to act
From flowering, check the underside of the lower and middle leaves every week with a hand lens for tiny tan pustules. Start sprays at the first pustules, since rust spreads fast in humid weather and the loss comes from early leaf drop.
What to spray
- ChlorothalonilFRAC M05ShopeeLazada
- MancozebFRAC M03ShopeeLazada
- PropinebFRAC M03ShopeeLazada
- TriforineFRAC 3ShopeeLazada
- Copper hydroxideFRAC M01ShopeeLazada
- Bordeaux mixtureFRAC M01ShopeeLazada
- CaptanFRAC M04ShopeeLazada
- Potassium bicarbonateFRAC NCShopeeLazada
- Cuprous oxideFRAC M01ShopeeLazada
Active ingredients only, never brands. The FRAC group tells how it works: switch to a different group next time, so the disease does not learn to survive it. Spray only when the damage is worth the cost, and only with products registered with the Fertilizer and Pesticide Authority for your crop. Follow the label. The Shopee and Lazada links only show who sells something with that active ingredient, not a recommendation of any seller or product.
Resistance: Soybean rust has grown resistant to triazoles (FRAC 3), strobilurins (FRAC 11) and SDHIs (FRAC 7) in South America and elsewhere. Use those groups only in mixes with mancozeb or chlorothalonil, and never the same group twice in a row.
How to prevent it
- Plant early in the season and avoid late plantings that fill pods in the wettest months.
- Grow a tolerant or early maturing variety where one suits your area.
- Pull volunteer soybean and clear wild legume vines such as kudzu near the field. They keep the rust alive between crops.
- Plant at the same time as your neighbors, and do not plant beside an older rusty field.
- Space the rows so the canopy dries quickly after rain.
Where this comes from
Not sure it is this one?
Many diseases look alike. Send a photo to Anee, the smart farm technician in anee.io. She reads it with your crop, its age and the weather, and tells you what it most likely is and what to do first. In Tagalog or English.