This time of year we have problems dealing with rain and heat stress. The rains brought on the toadstools.
Toadstools are the reproductive phase of certain soil fungi, comparable to the flowers of plants.
Consider all toadstools poisonous, unless you know toxic toadstools from edible mushrooms. This most likely is a disease called bud rot. It becomes infectious during the rainy season. Birds fussing on the infected fronds take the fungus to other palms, and it washes down to the vital bud tissue. Early symptoms are yellowing then browning of the new foliage shoots, usually accompanied by an odorous rot.