- Author: Mark Bolda
One thing that has many times struck me about farm calls in raspberry, often in tunnels, is the appearance of yellowing starkly on one hand of the leaf in association with stress. Usually the stress comes from the tunnel being too hot, though sometimes the stress is originating from salt. It's never in my experience been associated with nutritional deficiency, with leaf nutritional analyses clearly indicating that the leaf is dying rather than being short mineral nutrition.
Checking with UC Davis scientist Dr. Neelima Sinha about this phenomenon, she suggests that the distribution of cytokinins (and perhaps other hormones), that help maintain the green of the leaf, could be uneven owing to asymmetric leaf development and therefore giving cause to the uneven yellowing of the leaf. She asks if is this handedness always occurs on the same side of the leaf? I haven't thought of it, but looking at the three photos below it does seem like this might be the case.
Any pictures of the opposite side of the raspberry leaf yellowing from what I have here (being the left hand of the leaf when looking at it from the top) from the grower, PCA and researcher community would be very interesting at this juncture.