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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.

8/14/2008

The foliage at the ends of the branches on my honey locust is turning brown.  Why? 

The browning of the honey locust foliage is probably due to the mimosa webworm.  Damage occurs when the caterpillars tie honey locust leaflets together and feed on the foliage inside the tightly compressed, protective webs.  Affected foliage gradually turns brown.  There are two generations of caterpillars per year.  Extensive damage is most obvious following the second generation in August.

Damage from the mimosa webworm is seldom serious to otherwise healthy, well-established trees.  The webs and browned foliage are unsightly.  The damage is more aesthetic than serious.

Chemical control for mimosa webworm is rarely warranted.  A treatment after foliage has turned brown is ineffective and a waste of time.  Such late treatments may do more harm than good by destroying the natural enemies of the pest rather than the pest itself.  Sprays must be applied at the start of the caterpillar period and before webbing is apparent to be effective (mid-June and again in early August in Iowa).  Insecticides available to homeowners include Bacillus thuringiensis (e.g., Dipel), Sevin, permethrin, bifenthrin, cyfluthrin, deltamethrin, fluvalinate, lambda-cyhalothrin and spinosad.  Read and follow directions on the insecticide label. 

How do I control nimblewill in my lawn? 

Nimblewill (Muhlenbergia schreberi) is a warm-season perennial grass. Nimblewill is a thin, wiry grass that is pale green or gray-green. It spreads by aboveground shoots or stolons, often forming circular spots in the lawn. Nimblewill is easy to spot in the lawn because it greens up late in the spring and turns brown in early fall.

At the present time, there is no way to selectively control nimblewill growing in Kentucky bluegrass or other cool-season lawns.  The nimblewill infested areas will have to be completely destroyed with an application of glyphosate (Roundup) or dug up. 

However, a new selective herbicide will likely become available in 2009.  Tenacity (mesotrione) will destroy the nimblewill, but will not harm Kentucky bluegrass or other cool-season grasses. 

What would be a good planting site for the magic lily? 

The magic lily (Lycoris squamigera) is a rather intriguing plant.  Other common names include resurrection lily, surprise lily, hardy amaryllis and naked lady.  The life cycle of Lycoris squamigera is different from most other plants.  Its long, strap-shaped leaves emerge in the spring, but die back to the ground by early summer.  Pink, lily-like flowers are borne on 18- to 24-inch-tall, leafless, flower stalks in mid to late summer.  Each flower stalk produces 4 to 12 flowers. 

The magic lily performs best in partial shade to full sun in well-drained soils.  Plant bulbs 4 to 5 inches deep and 6 to 8 inches apart.  Since the dying foliage is rather unsightly, interplant the magic lily with other perennials. 

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Contacts :

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

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