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PestNet is a network that helps people worldwide obtain rapid advice and information on crop protection, including the identification and management of plant pests. It started in 1999. Anyone with an interest in plant protection is welcome to join. PestNet is free and is moderated, ensuring that messages are confined to plant protection.
Crops > Fruits & nuts > Guava > Guava ring necrosis, possibly mite, India
June 2014. From Odisha, India, rings of necrosis around the circumference of guava fruit.
There were several suggestions:
Look for eriphyid mites using a x15 hand lens or better a low power microscope (Australia).
Guava style-end ring rot (Phomopsis rot). (Ed., probably not likely as this is an ‘end’ rot, whereas the symptoms above are more equatorial, and the russetting is very convincing for mite damage (country not given).
Pestalotiopsis (El Salvador).
The suggestion that the cause was mites was further supported by a member who said that he had seen similar disease in grapefruit and orange. Here is his response:
Although this example shows damage to guava, the symptoms resemble the damage seen on grapefruit and orange when heavily infested with citrus rust mite. Note that with citrus rust mite the population on fruits is found mainly on the healthy tissue, not on the necrotic brown/black parts of the fruit. In citrus rust mite, populations on foliage are found mainly on the underside of the leaves, often two to three times the numbers found on the upperside. Eryophyid mites are usually VERY small (much smaller than red spidermite), have only two pairs of legs (!) are elongate and often almost colourless. Good luck in finding them (if present…)
Species of Eryophyidae are often restricted to one or few hostplants, many cause plantgalls but some only cause russeting of fruits and/or foliage, for instance Phyllocoptruta oleivora, the citrus rustmite. Unfortunately, I do not have copy of books on this remarkable family of mites where hostplant-associations are listed (I have seen such a book long ago, but cannot remember title or author). If anyone on PestNet has access to hostplant information of eryophyids, please check whether there is one known from guava and report back to us.