Rose (Rosa spp.) and hybrids-Bullhead

Cause A physiologic problem when temperatures drop into the 50s during early flower development. During this time there are major changes in the balance of different growth regulators present within the flowers. Prevalent in the cultivars Baccara and Talisman and those in the Columbia family of roses. The plant is not permanently affected.

Symptoms Buds have a flat-topped appearance instead of the pointed tip normally preferred. Flower buds are larger in size and weight, have many short petals and petaloids, and have a profusion of secondary florets bearing carpels near the base of the flower.

Cultural control Cut off damaged flowers to promote new canes with normal flowers.

Reference Horst, R.K. and Cloyd, R.A. 2007. Compendium of Rose Diseases and Pests. Second Edition. APS Press. St. Paul, MN.