Citrus Collar Rot June UpdatePublished June 25, 2019 at dimensions 1024 × 1024 in Experiment: Control of Citrus Gall Wasp. ← Previous Next → One of the trees (4A) was showing signs of collar rot. This is usually caused by poor airflow around the trunk. It indicates that it is time for us to give our depot a tidy up and make some more room for the trees to be spread out further.