Extension News

Ask the ISU Garden Experts: Rutabagas, Ash Rust and Cabbageworms

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

6/18/2009

When is the best time to plant rutabagas in Iowa?

The rutabaga is a cool, long-season crop. It performs best when planted in summer for a fall crop. Sow seed at a depth of 1/4 to 1/2 inch from June 15 to July 15 in Iowa. Rows should be spaced 18 to 24 inches apart. Thin the planting within a few weeks of germination. After thinning, rutabaga seedlings should be spaced six inches apart.

‘American Purple Top’ and ‘Laurentian’ are suggested rutabaga varieties for home gardens. Both varieties produce globe-shaped, light yellow roots with purple tops. Their flesh is yellow.

What are the orange-colored growths on the leaves of my ash tree? Is control necessary?

Ash rust is probably responsible for the orange growths on your ash tree. Ash rust is caused by the fungus Puccinia sparganioides. The fungus produces conspicuous swellings on leaves, petioles, and twigs. Infected leaves, petioles, and twigs may become twisted and distorted. Infected areas eventually produce masses of yellow to orange, powdery spores.

Puccinia sparganioides requires two different plant hosts to complete its life cycle. Part of its life cycle is spent on ash and the remainder on cordgrass (Spartina spp.). The spores produced on ash are carried by the wind to cordgrass. The fungus then infects the cordgrass. In spring, spores from infected grasses are blown by the wind to nearby ash trees. Warm, wet weather in spring favors ash infections.

Ash rust does not seriously harm healthy, well established trees. Control measures are usually not necessary.

How do I control cabbageworms?

Cabbageworms are greenish caterpillars that eat large, irregular holes in the foliage of cabbage, broccoli, cauliflower, and Brussel sprouts. Cabbageworms can be controlled with biological or chemical insecticides. Bacillus thuringiensis (Bt) is a biological insecticide (a bacterium) that specifically targets caterpillars. Bt products include Dipel, Thuricide and others. Home gardeners can also use chemical insecticides, such as permethrin (e.g., Eight) or carbaryl (e.g., Sevin).

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Contacts :

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

Del Marks, Extension Communications and External Relations, (515) 294-9807, delmarks@iastate.edu