Yellowing Infected Potato Plant (image) University of California - Riverside Caption A yellowing infected potato plant. The white sugary-looking substance is psyllid excreta. The clear whitish substance is psyllid exoskeleton. Credit A. Hansen, UC Riverside. Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.