Grapes have sap balls - Knowledgebase Question

Rhinelander, Wi
Question by gourmetpete
April 18, 2009
What are the small balls of sap on my grapes and what funtion do they do for the plant? They look like aphid damage, but there are no insects present.


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Answer from NGA
April 18, 2009

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What you describe is perfectly normal and even has a name. It is called guttation. Vines growing vigorously in the spring can exhibit guttation under high moisture conditions. Guttation occurs when diffusion pressure builds inside plant because of high soil moisture and a low rate of transpiration due to high humidity. Pressure is released by exuding water and minerals from specialized leaf-tip cells called hydathodes. Sap pearls will form on the end of the serrated leaf tips often leaving a dry salt mark after drying up during the day. As mentioned before, it is perfectly normal and nothing to worry about.

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