On Crops: Spinach
Eastern US, Canada, Iran, Greece, and other areas where spinach is commercially grown
In cool autumn weather, yellowish to white blisters form on leaf undersides of established spinach plants. The white blisters often form rings, and turn into patches of chalky white powder. There also may be blisters present on stems. Older leaves that grow close the ground are the most likely ones to show infections. White rust requires cool, wet weather around 15C (60F) to spread to new leaves.
Spinach leaves that are infected with white rust are inedible.
Choose resistant varieties when they are available. Make sure plants get good air circulation and plenty of sun, and keep weeds controlled to promote prompt drying after rains. Use mulch to keep soil from splashing onto plants during heavy rains. Avoid using sprinklers or other overhead irrigation methods after lettuce heads or hearts have formed. Always rotate spinach to a fresh planting site.
Clip off and compost affected leaves as soon as you see them. With the return of dry weather, spinach plants will usually produce a new crop of sound leaves from the plants' centres. If the damage is so extensive that the planting is not worth saving, pull up and compost the plants so the tissues will be completely rotted by the following growing season.