Bean rust is a fungal disease that can attack bean plants, forming orange, brown, or reddish pustules under leaves or on pods or stems. Leaves will turn yellow and fall off. It can spread rapidly, especially in humid/wet weather, by air or splashing water. The old saying is probably referring to the fact that it is best to harvest beans when the weather is dry, to help avoid spreading any rust fungus (or other diseases).
Bean rust is a fungal disease that can attack bean plants, forming orange, brown, or reddish pustules under leaves or on pods or stems. Leaves will turn yellow and fall off. It can spread rapidly, especially in humid/wet weather, by air or splashing water. The old saying is probably referring to the fact that it is best to harvest beans when the weather is dry, to help avoid spreading any rust fungus (or other diseases).