Rob Robinson of the British Trust for Ornithology said feeder-related disease had been affecting greenfinches since 2005. Trichomoniasis, or "trike", triggers throat swelling, causing birds to starve and has killed around one-fifth of the UK's greenfinches.
In 2007 alone, around 500,000 died. A conference at the Institute of Zoology on 4 May will examine the issue.
But Jane Lawler, marketing director at the UK's leading supplier of wild bird food and products Gardman, said: "It is vital that we feed wild birds to help them survive, especially during colder months because there can be a large decline in garden bird populations.
"We encourage people to clean their feeders regularly and offer customers free advice leaflets on all aspects of wild bird care including hygiene. Our complimentary Need to Feed leaflet has a whole page dedicated to hygiene.
"It's important to keep wild bird feeders and tables clean by washing them regularly."
RSPB wildlife adviser Kirsty Peck said recent reports in New Scientist magazine and national newspapers saying that garden feeders could be a "deathtrap" for birds were "sensationalist".
She added that feeding garden birds had a beneficial effect overall but warned that gardeners needed to be careful about hygiene with their birdfeeders.
An infectious eye disease called mycoplasmal conjunctivitis, which began in poultry, has wiped out 60 per cent of house finches in the eastern USA since 1994. Undernourished and unable to see properly, they become easy prey for predators.
The British Trust for Ornithology said washing feeders regularly with clean water can reduce infection rates. It has also found that mesh or metal-frame feeders are less likely to spread disease than feeders with a single point of access.