Over the past few weeks my oxalis has developed some very strange looking white spots on the tops of its leaves. In the places where the spots are it is like the chlorophyll is all gone and u can see thru the spot to the other side. There are also spots that’ll like they might possibly be burns. I put a filter on the window they are close to thinking it might have been to hot for them. However, it seems to be getting worse. U can see in the pics that all four plants now have this issue. I have been growing these plants since I was a wee girl in Ireland, and I have never had this issue. Any ideas would be greatly appreciated. Also should I cut back the damaged leaves?
Your Oxalis appears to have a scale insect infestation. Scale can be treated with a very thorough spraying with a solution of 5 parts water, 1 part alcohol and a squirt of liquid dish soap. However, because Oxalis leaves are thin and fragile they are hard to clean. Therefore, I recommend cutting back all of or most of the leaf stems – certainly all that appear to be infested – before spraying whatever remains. Pruning off all infested parts may seem radical, but it is the most effective long term treatment and if your plant is healthy, new growth will return before long.
How often should I treat the plants? Is this just a one off spraying or is there a certain regimen I should follow?
If you are really thorough in spraying all leaf and stem surfaces, one treatment should be adequate. Cutting off the infested leaves and stems will make complete coverage a lot easier. That said, you should be watchful for any signs on new scales developing and re-treat if you see any. If you catch the scale insects early, they are much easier to treat.