Raspberries: Flower buds turn brown prior to opening

Browning of flower buds prior to opening may occur due to diseases:

Botrytis
Fire blight.

Flower buds may also turn brown after a hard freeze:

Frost damage.

Botrytis, the same fungus that causes gray mold on fruit, can infect flowers and buds before they open, causing them to turn brown. It can also infect canes. These infections are problematic only under very wet conditions. If these tissues are placed in a plastic bag and kept warm and moist, the fungus will sporulate.

Raspberry cane with brown, dry fruit buds. Some of the buds appear to have had fruit, which has shriveled and turned brown.

More raspberry Botrytis fruit rot information

Fire blight can affect raspberries as well as other fruit crops. This bacterium causes the growing points (primocane tips and fruiting laterals) to quickly turn black and die. This is relatively rare in raspberries, but is observed occasionally.

Raspberry cane tip that is entirely brown and dry. Fully-formed fruit are the same brown color as the leaves. Lower down the cane, healthy green leaves are growing. — Fire blight on raspberry.

(Photo: A. Schilder, MSU)

Raspberry cane tip that is bent over and shaped like an upside-down letter U. All of the affected cane tissue is uniformly beige-brown and appears crispy and dry. Infected cane is growing above healthy, green leaves.
(Photo: A. Schilder, MSU)

More raspberry fire blight information

Frost damage is of greatest risk when flower buds are about to open, as floral tissue loses its winter hardiness after buds swell and break. Because floral tissue is more tender than other vegetative tissues, the only sign of frost damage may be necrotic tissue at the center of the flowers. Initial yields will be reduced, but subsequent yields will not be affected.

Blackberry branch on blue background. There are multiple flower buds along the branch, and each flower has a black center. The branch is otherwise healthy and green. — Frost damaged flowers in blackberry. Note the black, necrotic tissue. Photo courtesy of Kathleen Demchak, PSU.