Extension News

Ask the ISU Extension Gardening Experts

Note to media editors: Got gardening questions? Contact the Iowa State University Extension Hortline at (515) 294-3108 (Monday-Friday; 10 a.m.-12 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.


Goutweed is taking over a perennial bed.  How do I control it? 

Bishop’s weed or goutweed (Aegopodium podagraria ‘Variegatum’) is an 8- to 10-inch-tall groundcover noted for its green and white variegated leaves and tolerance of poor sites. (It is also sometimes erroneously referred to as snow-on-the-mountain.) It spreads rapidly via underground stems or rhizomes. Because of its aggressive nature, some regard bishop’s weed as an invasive weed. 


Goutweed is very difficult to control. All the roots and rhizomes must be completely destroyed to effectively control bishop’s weed. Repeated efforts over several months will probably be necessary to destroy it. There are basically two ways to control goutweed. One method is to repeatedly dig up the plants and remove all the roots and rhizomes that are visible in the soil.  Another option is to apply glyphosate (Roundup) to the area. Roundup may also have to be applied periodically over several months. Regardless of the method, persistence is the key to controlling bishop’s weed. 


Little green worms are eating the leaves on my azalea.  What are they and how do I control them? 

The green “worms” are the larvae of the azalea sawfly. The larvae are green, smooth, and up to one inch long. They feed along the edges of the azalea leaves. After feeding, oftentimes only the midvein of the leaf and leaf petiole remain. The larvae of the azalea sawfly are typically present in May in Iowa. There is one generation per year. 


Small numbers of azalea sawflies can be controlled by handpicking. They can also be controlled with insecticides, such as Sevin (carbaryl). 


What would be a good planting site for butterfly weed? 

The butterfly weed (Asclepias tuberosa) is a member of the milkweed family. Plants grow 2 to 3 feet tall and produce flat-topped clusters of bright orange flowers from July through September.  Their flowers attract several butterfly species, hence the common name. 


Butterfly weed is easy to grow. It performs best in full sun. Plants should receive at least 6 hours of direct sunlight per day. Once established, the butterfly weed possesses excellent heat and drought tolerance. Because of the butterfly weed’s long taproot, transplanting is difficult.  Carefully choose a planting site and don’t disturb it. Also, the butterfly weed emerges slowly in spring. To prevent possible injury, mark the planting site and don’t cultivate in the area until the plant emerges. 


While most butterfly weeds produce bright orange flowers, a few plants in the ‘Gay Butterflies’ mixture bear yellow or red flowers. The cultivar ‘Hello Yellow’ has yellow flowers. 

Contacts :

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

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