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What's bugging you? July 5, 2017

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Black medic

This week's weed is the last of my series on "The Ten Most Unwanted Weeds in the Garden." At least these were my top 10 weeds for my yard. There are many more weed candidates left and I will probably cover some of them over the next several months.

This week's weed is black medic, Medicago lupulina. It is a member of the pea family and while many people think it is a clover, it is not. It is in the same genus as alfalfa and can be a nasty weed if one has the right conditions to foster its presence. It goes by other names such as black nonesuch, hop clover, black weed, yellow trefoil and many more.

As an annual, it relies mainly on seed production to reproduce. But it can be a short-lived perennial in warmer areas. It grows as a low trailing plant with stems mainly radiating out from a central and substantial tap root. It has a compound leaf, much like a clover, with three slightly oval leaflets each with finely toothed margins.

There are tiny yellow flowers produced in clusters much like a pom-pom. It flowers between May and September. A single mature plant can produce thousands of seed. Therefore my sage advice as always with annuals is to eliminate this weed before it flowers and produces seed.

A native of Eastern Europe and Asia, this weed can be found all across the United States. It infests lawns, gardens and roadsides. Black medic is an excellent soil problem indicator, growing in areas of compacted soil and soils low in nitrogen. As a member of the pea family, black medic roots have nitrogen-producing nodules and hence grows well where the soil is nitrogen poor. Fertilizing and aeration are two cultural management techniques to discourage this weed. Adding organic soil amendments to compacted soils also helps with the compaction issue.

And this weed is highly adaptable, growing in dry or moist soils and alkaline, neutral or slightly acidic soils. It is often a pioneer weed in recently disturbed areas. It requires sunny locations, not doing well in deep shade.

Hand digging works well in controlling this weed if it is addressed when small. Larger plants have very substantial tap roots and are more difficult to remove enough root to prevent regrowth. Pre-emerge herbicides such as Preen®, Prevent®, Gallery®, Treflan® or Snapshot® will prevent seeds from successfully germinating and emerging. Make sure the label allows their use in your particular garden site. Post emergence sprays containing 2,4-D or glysophate work well as does Confront®.

Summer is upon us with a vengeance. I am still playing catchup in my garden and paying dearly for my sweaty efforts. Butterflies are appearing in greater numbers and kinds. I think I'll discuss butterflies in my next column. Until then, happy gardening.



Jim Leser retired to Cedaredge in 2007 after a career with Texas A&M University Extension in entomology. He is a member of the Cedaredge Tree Board and a Colorado Master Gardener.

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