The irregular verb spread is unchanged in the past tense (e.g., “she spread the butter”) and as a past participle (e.g., “the butter is spread). Spreaded appears occasionally in informal contexts, but it is not a standard form, and most dictionaries don’t recognize it (for what that’s worth).
The Oxford English Dictionary does record a few historical instances of the word—one from the 16th century and two from John Keats’s 1818 poem Endymion—but it has never been widely used. It is more common today than it has ever been, and even now it is rare.
Though spreaded is rare in edited publications, it is not hard to find a few scattered examples:
This pigment production plant is spreaded over 89 acres and includes a warehouse, R&D and application laboratory. [Business Standard]
The overall response to the incident inspired many kudos from Chief Ray, who spreaded credit around. [Sooke News Mirror]
Locals said the fire originated from electric short circuit at a house which soon spreaded to adjacent houses. [Financial Express]
But spread is usually uninflected, as in these cases:
Crude oil spread its foul sheen over the Gulf. [Miami Herald]
Recently, especially near the coast, the most common tomato disease has been tomato late blight, which is spread by spores that are carried in the air, not the soil. [San Francisco Chronicle]
An army mutiny which erupted last week in the West African state of Burkina Faso has spread to a fourth city. [BBC]