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Garlic mustard, eastern tent caterpillar and gardening calendar

By John Fulton

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[May 05, 2008]  We have reached the heat units now for garlic mustard to elongate from a rosette and begin to bloom. Garlic mustard is considered an invasive species, and some states have declared it a noxious weed. Illinois hasn't declared it such, at least not yet. The problem with garlic mustard is how quickly it spreads. It spreads so quickly it tends to choke out much of the desirable undergrowth in timber areas.

HardwareGarlic mustard is a cool-season biennial herb with stalked, triangular to heart-shaped, coarsely toothed leaves that give off an odor of garlic when crushed. First-year plants appear as a rosette of green leaves close to the ground. Rosettes remain green through the winter and develop into mature flowering plants the following spring. Flowering plants of garlic mustard reach from 2 to 3 1/2 feet in height and produce buttonlike clusters of small white flowers, each with four petals in the shape of a cross. 

Control of garlic mustard is somewhat difficult. Seeds can remain viable for at least five years in the soil. Small amounts can be pulled up (including the roots). Garlic mustard can regrow from root material. For herbicides, glyphosate (Roundup) is the most often recommended. Remember, glyphosate kills broadleaves and grasses it gets on. There has been some success with 2,4-D LV400 where there aren't concerns with other understory plants. Very large patches have been controlled with fire, but that completely destroys the understory of timbers. Remember to monitor areas for at least five years due to the seed dormancy period.


Some action at this early time may help prevent larger problems down the road. It is much easier to control small patches than large ones.

Eastern tent caterpillar

Egg hatch may be running as much as three weeks later than normal. Of course, with the crazy "spring" we've had, the insects are probably somewhat disoriented as well.

After hatching, the caterpillars create a white, silken tent in the branch crotches of crab apple, hawthorn, mountain ash, flowering cherry, and other trees and shrubs in the rose family. Eastern tent caterpillar is one of the earliest defoliators. The feeding damage does not kill the tree, but it does use some of the stored energy of the tree. To answer the eternal question "What happens if I don't do anything?" I would simply respond that forest trees are attacked every year, and they survive the onslaught.

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Control at this time can be accomplished by removing the tents, and the caterpillars inside, and taking them a long way from the tree to dispose of. When caught early, the caterpillars tend to stay in the nest. As they grow, they will not be in the nest as much. Control with sprays such as Bt, acephate, permethrin and carbaryl will also work.

Gardening calendar

The gardening calendar shows it is about time, from May 10 to May 25, to start in on our tender vegetables. This group includes green beans, sweet corn and tomato plants. It is also time for successive plantings of leaf lettuce, other greens, radishes and spinach. The way the wind has blown, it is probably a good idea to provide some protection for tender transplants for a week or two to let them get established well.

On the Web

If you haven't checked out our site on the Web, give it a look. The site address is There is an abundance of horticulture information, from local blogs to plant selectors. Most of this is available from the horticulture and environment sections. This is a good resource to answer questions you might have on many topics. Other sections are available for youth, agriculture, health, money management, "Just for Kids," "Just for Teachers," and others. There are some great online learning activities for kids, just in time for summer.

[By JOHN FULTON, University of Illinois Extension, Logan County]

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