Hi Marie-

I found this article for you. I just recently sprayed my nandina (heavenly bamboo)with anti-wilt since it completely defoliated in last winters cold and dry conditions. Hopefully it will help.

Winter Protection

Most bamboo remain evergreen throughout the winter. The foliage of some will "beige" to a degree depending upon the severity of the weather, exposure, and degree of winter protection. Bamboo planted in marginally hardy areas, or where exposed to a high wind-chill factor, will often die back to the ground, but will remain root-hardy and send out culms in May or June. Adequate Mulching is most important for winter protection of your plants - a 6 to 8 inch layer of well-composted manure, oak leaf humus or pine bark mulch is recommended. Anti-Desiccant Spray applied to the foliage is a good way to prevent damage from the drying winter winds. In Extreme Winter Conditions, bamboos may be bent over and covered with burlap or pine boughs to prevent desiccation.