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.-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.


When should I harvest my garlic? 

Harvest garlic when the foliage begins to dry. In Iowa, garlic is usually harvested in August or September. Carefully dig the bulbs with a garden fork or shovel. Dry the garlic in a warm, dry, well-ventilated location. Place the garlic on an elevated wire screen or slotted tray to promote drying. When the tops have dried, cut off the dry foliage 1 inch above the bulbs. Also, trim off the roots and brush off any loose soil. Place the bulbs in a mesh bag or open crate and store in a cool (32 to 40 degrees F), dry (65 to 70% relative humidity) area. Garlic can be stored for 3 to 6 months if properly dried and stored. An alternate way to store garlic is to braid the foliage together immediately after harvest, dry, and then hang the braided garlic in a cool, dry location. 

How can I control black spot on my roses? 

Black spot is a common fungal disease of roses. Symptoms of black spot are circular black spots on the leaves. Infected leaves turn yellow and drop prematurely. Initially, symptoms develop on the lower leaves and gradually move upward. By late summer, severely infected plants may be nearly defoliated. 

The black spot fungus overwinters on fallen leaves and infected canes. Spores are splashed on to newly emerging foliage in spring.  Black spot development is favored by warm (75 degrees F), wet weather.    

A combination of cultural practices and fungicide treatments are often necessary to control black spot. The first step in controlling black spot is to select a suitable planting site for roses. Sites that receive full sun and provide good air movement are best for roses. Full sun and good air movement promote drying of the rose foliage and discourage black spot infections. Reduce the amount of overwintering fungi by carefully cleaning up leaf debris in fall. When watering roses, apply water directly to the ground around the plants. Do not wet the foliage. Fungicide applications must begin at the first sign of disease symptoms. 

There are yellow-green bugs eating the flowers on my roses.  What are they and how can they be controlled? 

The yellow-green bugs are probably the adults of the northern corn rootworm. The larvae of the northern corn rootworm feed on the roots of corn plants. The adults (yellow-green beetles) appear in mid-summer and are present until frost. Corn rootworm beetles feed on corn silks and tassels. When the tassels and silks dry up, the beetles migrate to nearby gardens and feed on the flowers of many annuals, perennials and roses. They are especially fond of plants with yellow flowers. 

Control of northern corn rootworm beetles in gardens is difficult. While the insecticide Sevin is effective, northern corn rootworm beetles will continue to migrate from corn fields to gardens until a hard frost. As a result, repeated insecticide applications are necessary. Another option is to protect plants with cheesecloth or fine mesh netting. 


Contacts :

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


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