Cause The fungus Puccinia sorghi (alternate host is corn) has been found on oxalis in Washington while Puccinia oxalidis (alternate host is creeping barberry) was found by the OSU Plant Clinic.
Symptoms Yellow to yellow-orange pustules (aecia) cover the leaves for P. sorghi.
P. oxalidis - Light-green spots occur on the upper leaf surface with pustules in the middle. The lower leaf surface is covered with powdery golden-yellow to orange-yellow pustules (0.2 to 0.5 mm in diameter) often arranged in circles. Heavily infected leaves die.
Cultural control
- Space plants to allow for good air circulation.
- Remove and destroy infected leaves on the plant and fallen leaves.
Chemical control
- Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker may be helpful before symptoms develop. 24-hr reentry.
Reference Šafránková, I. 2014. Occurrence of rust disease caused by Puccinia oxalidis on Oxalis triangularis in the Czech Republic-short communication. Plant Protection Science 50:17-18.