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I have a healthy raspberry plant in its second year of living on my balcony. It's been producing a decent amount of fruit and has grown new canes, ready for next year. However, in the last week or two some of the leaves have started to turn yellow then brown in the middle. It doesn't seem to be leaf curl, or lack of watering (from my limited knowledge of raspberries).

Does anyone know: a) what is the problem, and b) how do I solve it? Should I cut the browning leaves away?

Extra info:

  • The plant gets sun from morning to mid-afternoon (balcony is south-east-facing).
  • I live in south Germany where the summers are hot (average 25-30 deg C).
  • Last year it lived in a slightly shadier area, and I didn't have this problem.
  • Its pot is about 40 cm deep, but I water it often and the roots look fine.
  • There appear to be a few weevil-type bugs on the plants; Google suggests they might be vine weevils.

Leaves turning yellow and brown in centre Another example of the yellow/browning effect

Tempest16
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  • It does a little bit look like sun burn to me, is it possible that this year it has been getting more direct light for longer hours? You could try moving it to a more shady area. – Persistent Plants Jul 16 '20 at 02:16
  • It has been getting more direct light for longer hours, yes. Thanks for the suggestion; I"ll give it a go. – Tempest16 Jul 19 '20 at 15:11

2 Answers2

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I agree that spider mites could be the culprit. Hot and dry conditions encourage spider mites and so it may sometimes seem that the hot weather is the cause of the burns. You can find some information on "mite burn" here:

https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2769&context=extension_curall#:~:text=Spider%20mites%20typically%20feed%20on,protect%20the%20eggs%20and%20nymphs.&text=Mites%20cause%20damage%20to%20raspberry,are%20predisposed%20to%20winter%20injury.

Included are two photos (from my own garden) showing similar symptoms on the leaves and the spider mites hiding underneath.

To get rid of them you could try spraying them with water and dish soap. I use one teaspoon of dish soap per 0.5 litres of water. The spray also helps to dislodge their little protective webs.

Mite burn damage on raspberry leaves

Spider mites and webbing under raspberry leaves

t13878
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Let me add my answer to your question. Yes, indeed, the sun is the culprit for these burns. The sun and heat increase transpiration (evaporation of water). As a result, the synthesized substances from the leaves do not have time to be transferred to the roots and other organs. Their concentration in the leaves increases and they "poison" the leaf cells. This is probably due to the lack of certain enzymes. I also faced such leaf burns last year and I got the impression that this is directly related to a slight (latent) magnesium deficiency, or a predominance of potassium over magnesium FOR CURRENT TEMPERATURE. It is nevertheless necessary to shade your plant and this is obvious. As a second tip, you should increase the strength of the root system by increasing the volume of the container. 2. Spider Mites (Tetranychus urticae Koch) cause similar symptoms in the initial stage (when there is no cobweb yet).

Artem Kolesnikov
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