WSU Extension

Hortsense

Caption: Rose bullhead
Photo by: R.S. Byther
  
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Rose : Bullheading (cold damage)
(revision date: 4/23/2014)


Biology
Bullheads are the most prevalent when temperatures dip to 53-59 degrees Fahrenheit during early flower development. Low temperatures appear to alter metabolic activity, which results in the abnormal appearance of buds and resulting flowers. Flower buds exhibit a flat-topped appearance and weigh more than normal buds with a pointed tip. The number of short petals and petaloids increases, as well as the amount of secondary florets near the bases of flowers. Baccara, Talisman, and cultivars belonging to the Columbia family are especially susceptible.
Management Options

Non-Chemical Management
  • In spring, prune bullheads and allow new flowers to develop in warmer weather.
  • Do not plant in cold areas, and protect roses from frost.
  • Do not fertilize, prune, or water heavily late into the season. This can encourage growth that cannot acclimate well in autumn.
Select non-chemical management options as your first choice!

Chemical Management


None recommended

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Caption: Rose bullhead
Photo by: R.S. Byther