In oral allergy syndrome, the reaction is limited to the mouth, lips, tongue and throat. Any person who has seasonal rhinitis or hay fever to pollen is susceptible to this syndrome. It has been found out that pollens from trees (birch, alder or hazel), grasses and weeds (ragweed or mugwort) contain proteins that have a structure similar to those present in some fruits, vegetables, and nuts. So when these kinds of food items are consumed by a susceptible person, an allergic reaction is triggered.

http://en.wikipedia.org/wiki/Oral_allergy_syndrome

For example, people allergic to latex rubber may react to "bananas, avocados, kiwi, chestnut, and papaya.

Ragweed Allergy: “Ragweed, in theory, cross-reacts with bananas and melons, so people with ragweed allergies may react to honeydew, cantaloupe, and watermelons, or tomatoes.
Zucchini, sunflower seeds, dandelions, chamomile tea, and echinacea also go on that list.

Birch Pollen Allergy: People with birch pollen allergies may react to kiwi, apples, pears, peaches, kiwi, plums, coriander, fennel, parsley, celery, cherries, carrots, hazelnuts, and almonds.

Grass Allergy: People with grass allergy may react to "peaches, celery, tomatoes, melons, and oranges.

Oral allergy syndrome is diagnosed when there remains an accurate history of symptoms in people with seasonal allergic rhinitis. The Skin Prick Test is not much reliable because the commercial extracts available will give a negative result most of the time. The most reliable diagnosis method would be the prick-prick testing with fresh fruits and vegetables. In this method, the testing needle is first inserted into the fresh food and then used to prick the individual’s skin.

I never had an allergist do the PRICK-PRICK testing on me. I do not know which allergists do this.