What's wrong with my roses? (Hint: Weird weather)

Unusual spring conditions prompt problems for Sacramento-area roses

Botrytis freckles and browns the edges of a Pink Promise rose. (Photos: Debbie Arrington)

May usually is the rosiest month in Sacramento. Warm, dry days coupled with raging growth hormones make for bountiful blooms and healthy plants.

But not this month. Sacramento area rose lovers report problems usually not seen in mid-spring: Botrytis, powdery mildew and blind shoots. All these issues can ruin rose blooms (or eliminate them all together).

Powdery mildew coats foliage on a Dorothy Perkins rambling rose.

The reason? Our yo-yo weather. Instead of consistently warmer weather, Sacramento temperatures have bounced up and down this spring. In early May, cool weather with just enough moisture to dampen foliage and blooms prompted outbreaks of two fungal diseases, botrytis (also known as gray mold) and powdery mildew.

Common in late fall, botrytis attacks buds as they open, turning them to mush. It starts out looking like freckles, then quickly turns petals brown and soft. Roses quite often refuse to fully open.

Powdery mildew is primarily a foliage fungus, covering leaves and stems with what looks like an explosion of powdered sugar. (It can coat buds, too.) Its activated by temperature; days in the 60s or 70s are its sweet spot.

The good news? When days turn 90s degrees, these fungi disappear. They can’t stand high heat. The forecast for this weekend: 92 degrees.

Infected foliage and blooms will fall off and be replaced by healthy growth. Pick up these discards and dispose of them in trash (not compost). That will help cut down on reinfection.

Instead of a bud, there's only a stub on this Marilyn Monroe rose.

Meanwhile, blind shoots are a reflection of weather conditions. When days go from cold to hot to cold again, roses get confused and push out stems with no terminal bud – a flower at the end. Instead, a blind shoot has an odd little stub at its bloom end and nothing but leaves. No matter how long the stem grows, it will never bloom.

The solution is easy: Cut the blind shoot off. Prune the stem back to just above the first five-leaf leaflet. The bush will soon sprout a new stem, most likely with a bud at the end.