1 - Mid-winter cold caused damage to roses and other plants, now late spring freezes and drying winds have caused additional damage.
Q. I have a fair number of roses that have always bloomed magnificently for me, but I am afraid this year it is going to be different. Many of the hybrid teas and one regular tea rose have large amounts of dead wood, and have required extensive pruning just to remove the dead wood. More worrisome is the fact that after pruning to live wood, the branches are often then dying further back, with leaves shriveling up. Many of the roses have large sections with extremely yellow leaves, and misshapen, curled leaves, especially in the yellowed areas, or where branches are dying back after being pruned. Even my Peace rose, usually very vigorous, looks bad, and The Queen Mother, a Kordes rose, is very badly affected. The species roses seem to have been spared, but the Alba and the Centifolia, are affected, although to a lesser degree. The Bourbons are a little better off. We sprayed with Ironite™ last weekend, hoping that would fix things, but it does not seem to be helping too much yet. In late February we applied a dry rose food on the ground in each bed. Do you think my roses have a disease, or is this just a combination of an extremely cold winter and some soil deficiency that I need to remedy? The affected roses are in several separate beds. I am attaching a couple of pictures. Any advice you can give will be appreciated.
A. This has been the rare winter and spring that gardeners are often warned about, but do not often experience. They will be spoken about in gardeners' stories for many years. The weather systems have thrown many of their worst conditions at New Mexico this year.
The dieback in your roses is to be expected after a winter such as we have experienced. The continued dieback of new growth may be due to damaged "wood" restricting the movement of water up the stem to the new buds, to late frosts, or to the extremely dry spring. The species and bourbon roses are hardier, so it is expected that they will show less damage.
It is possible that as you trimmed the dead wood from your roses, you did not cut back into undamaged wood. If the cambium and associated vascular tissues were damaged in the winter, they may have been able to support some growth by the buds. However, as the weather warmed and the buds needed more water, the damaged vasculature was not able to supply the needed water. As a result, the buds may die back.
We have had continuing late frosts that can cause the leaves on the new growth to become crispy, and sometimes kill the whole new stem. In the first case, the new stem will produce new leaves after the cold weather passes. In the second case, if the wood below the bud was not injured excessively, buds from the base of the frozen growth can develop and replace the frozen new growth.
The dry winds and warm spells (between the frosts) can also attribute to the drying of the new growth. If the vasculature of the stems has been damaged, then water stress can result in dying of the new growths, especially after windy days. Most of New Mexico has experienced strong, drying winds this spring.
As cold as it was, and as unsettled as the spring has been, many of our insect pests overwintered well and may be causing problems. I have seen thrips, aphids, and some spider mites on plants already. They can also contribute to discoloration, curling, and drying of leaves on new growth.
Gardening in New Mexico is always challenging, but this year is one to remember!
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: email@example.com, office: 505-865-7340, ext. 113.
For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!