Brown lesions in the leaves is caused by Botrytis.

Bulbs that look greenish or are soft to mushy have a bulb rot.

If solid colored petal tulips are planted but develop, white to green streaks in the petals, the tulip is infected with a virus.

Fungicides and sanitation are helpful for Botrytis.

Discard rotting or moldy bulbs.

Eradicate virus infected plants.