The issue: Black medic
Black medic (Medicago lupulina) is a summer annual from Eurasia that grows low to the ground. It is most commonly found in poorly maintained lawns, but is also found in waste and disturbed areas and field crops that are flood irrigated. It is nitrogen fixing and does well in low fertility situations when surrounding plants are weak.
A deep taproot helps black medic tolerate droughty conditions. The first true leaf is simple and almost round; all subsequent leaves are trifoliate and typically dark green. The clover-like flowers are small and yellow. The stems thread through the turf, forming a low mat that may be up to 2 feet across.
Black medic spreads only by seed, which will develop below mower height. It continues to germinate and flower all summer long.
Integrated pest management options:
· Prevention: Keep ditch banks, roadsides, driveways, and walking paths free of seed-producing plants.
· Mechanical: Hand pull plants and destroy any that have seed heads on them. Must be done continually throughout the summer. Mowing is not effective, but tillage is.
· Cultural: Maintain healthy, desirable plants.
· Biological: Grazing can reduce, but not eliminate seed production.
· Chemical: Early spring, pre-emergent herbicides containing dithiopyr (Dimension), or oxyfluorfen and oryzalin (Rout); post-emergent herbicides containing 2,4-D, dicamba and mecoprop-p applied in mid-spring. Be cautious of using herbicides near non-target plants or when temperatures are above 85 F. Be sure the target weed and crop, or landscape situations are listed on the product label. Always read and follow herbicide label directions.
Because of summer-long seed production, black medic control efforts must be continual throughout the growing season. Combine different IPM techniques as much as possible for several years. A continual monitoring program is essential.