Reddish brown pustules on bean leaves from rust fungus, identification and control.
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Bean rust shows as small reddish brown raised pustules mostly on the underside of leaves, which release rusty spores when rubbed, and heavy attack causes leaves to yellow and drop early, cutting pod yield. It spreads in humid, moderate temperature weather and over wet leaf surfaces. Use tolerant varieties where available, give wider spacing and trellising for air flow, avoid overhead evening irrigation, and remove crop debris after harvest. Fungicides are used at early pustule stage and rotated by mode of action, but follow the label dose, the pre harvest interval and local KVK advice since pods are eaten. Do not rely on a single fungicide repeatedly.
In Kullu my French beans got the rusty brown pustules under the leaves in the humid spell. Wider spacing and trellising for air flow, plus avoiding evening overhead watering, cut it down.
One caution: do not lean on a single fungicide. I sprayed the same one repeatedly and it stopped helping, rotating modes of action per the label and clearing crop debris after harvest worked better.
A tip from my Kullu field: I pick tolerant varieties where I can and clear the crop debris after harvest. The leftover stubble from last year was where my rust started again.
I watch the underside of the leaves for those small rusty brown pustules and act at the first few rather than waiting. Once they spread and the leaves start yellowing and dropping the yield is already cut.
Rust hit me worst in the humid moderate weather with wet leaves overnight. Shifting watering off the evening so the foliage dried before night slowed it noticeably on my plot.