Extension News

Ask the ISU Experts

Note to media editors: Got gardening questions? Contact the Hortline at (515) 294-3108 (Monday-Friday; 10 a.m. -  noon and 1 - 4:30 p.m.) or send an e-mail to hortline@iastate.edu. For more gardening information visit us at Yard and Garden Online at www.yardandgarden.extension.iastate.edu


Which plants are most likely to be damaged by browsing rabbits in winter? 

During the winter months, rabbits often gnaw on the bark of many woody plants. Heavy browsing can result in the complete girdling of small trees. Rabbits may also clip off small-stemmed shrubs at ground level. Small trees with smooth, thin bark are most vulnerable to rabbit damage. Apple, pear, crabapple, redbud and serviceberry are often targets of rabbits in winter. Other frequently damaged plants include the winged euonymus or burning bush, Japanese barberry, flowering quince, fothergilla, dogwoods, roses and raspberries. 


The best way to prevent rabbit damage to young trees is to place cylinders of hardware cloth around the tree trunks. The hardware cloth cylinder should stand 1 to 2 inches out from the tree trunk and extend 10 to 12 inches above the expected snow depth. The bottom 2 or 3 inches should be buried beneath the soil. Shrubs, roses and raspberries can be protected with chicken wire fencing. 


There are some white blotches on my African violet leaves. What are they and how can the problem be controlled?

The white material on the foliage of your African violets is probably powdery mildew. Powdery mildew is a fungal disease that is common on indoor plants, such as African violets, begonias, and poinsettias. Outbreaks of powdery mildew on houseplants typically occur in winter or early spring. 


If only a few leaves have powdery mildew, pinch them off and discard them to keep the fungus from spreading. High relative humidities and poor air circulation favor powdery mildew development on houseplants. Altering the indoor environment is the best way to control powdery mildew on houseplants. Air circulation can be improved and humidity levels lowered by increasing the spacing between plants and running a small fan in the room. 


The south and west sides of several of my yews turn brown in early spring. Why does this occur and what can be done to prevent it? 

Browning of yews in late winter or early spring is usually the result of desiccation injury. Evergreen foliage continues to lose moisture during the winter months, particularly on windy or sunny days. However, once the soil freezes, the plant’s roots are no longer able to absorb moisture. Foliage exposed to the drying effects of the sun and wind may eventually dry out and die. While desiccation injury occurs during the winter months, the browning of the needles often doesn’t occur until late winter or early spring. 


To prevent desiccation injury, deeply water susceptible evergreens in the fall if the soil is dry. Continue watering on a regular basis until the ground freezes in winter. Watering is especially important to evergreens planted within the past two or three years. To help conserve soil moisture, apply a 2- to 3-inch-layer of mulch, such as wood chips or shredded bark, around each evergreen. Moisture loss can also be reduced by placing a burlap screen around susceptible evergreens in fall. Anti-desiccants may also be helpful. 



Contacts :

Richard Jauron, Horticulture, (515) 294-1871, rjauron@iastate.edu

Jean McGuire, Extension Communications and Marketing, (515) 294-7033, jmcguire@iastate.edu