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yard weed with black seeds

Black Medic

Black Medic, also known as Medicago lupulina or Yellow Trefoil, is a Summer annual weed. This means that it germinates sometime in the late Spring, grows well during the heat of Summer, then dies off with the cold weather. Black Medic is sometimes referred to as Yellow Clover because it looks like Clover with teardrop-shaped leaves, but has a yellow flower. The seed pods of Black Medic are also unique. They turn black when they’re ready to drop. If you can remove the Black Medic before this happens, it will help eradicate the plant, as the seeds are its only way of reproducing and they can stay viable for years and throughout Winter.

What Causes Black Medic?

It’s important to understand the conditions needed for Black Medic to thrive. A little Black Medic is normal. It will fill in the bare areas during the heat of Summer. A lot of Black Medic however, typically indicates that your lawn is being mowed too short in the Spring and Summer, your grass types are not strong or healthy enough to compete with the weed or your soil is compacted. If you notice the Black Medic growing by the roadside or next to a sidewalk, this is a sign that your soil quality is compromised due to foot traffic and compaction is the underlying problem.

How To Get Rid Of Black Medic?

Since Black Medic has a short lifespan, the bulk of your effort should go towards improving your lawn to prevent this weed from populating the following year. But there are a few things you can do to eliminate the weed right away.

  1. Pick the Black Medic. If you’re able to do this when the soil is wet, that would be ideal, as the roots will more easily and cleanly pull out of the ground. Black Medic grows out of a central location, so hand weeding can be very effective for removing the weed from large areas.
  2. Another option for elimination is to use a natural weed suppressant, such as Weed Beater Fe, which will be successful in killing the weed, however it also causes stress on the surrounding grasses, so use it sparingly.

How To Prevent Black Medic?

Black Medic and other annual weeds will emerge where your lawn is not competing. It could be that you’re mowing your lawn too short, which is keeping your grasses from growing stronger than your weeds. It could also be that the grasses you have are too weak and old and just don’t fight that well. Another option is that you have dry, compacted soil. Luckily, there are several ways to address the issues that could be resulting in the Black Medic in your lawn.

Mowing Problems

  1. One of the worst things you can do for your lawn is remove too much of the grass blade in a single mowing. Removing more than 1/3 of the grass blade length in a single mowing will turn the grass brown, stop root growth, and invite in weeds. So set your mower blades high.
  2. Dull mower blades are another common mowing issue because they rip the grass, instead of cutting it. This leaves your lawn vulnerable to disease and weeds and also dehydrates the grass blades, causing them to turn brown. A hardware store should be able to sharpen your blades for you. Try to do this every 20 hours worth of cutting or at least once per season

Grass Problems

  1. If you have older poor grasses, a total Lawn Renovation might be the best choice.
  2. If you don’t want to go that far, simply Slice Seeding your current lawn should make a big difference.

Soil Problems

  1. Given that compacted soil is an ideal environment for Black Medic to grow, we recommend aerating your soil. You can do Core Aeration or Liquid Aeration. If you’d like a DIY solution for aeration, try Liquid Aerator on the areas where you’re noticing the problem.
  2. Lastly you can try our Organic Soil Builder application, which will add valuable organic matter and nutrients to your soil, serving as an organic fertilizer that will promote healthy and balanced grass growth.

Contact us to learn more or to get our opinion on what would be best for your specific situation.

Middle Tennessee Weed Gallery

Type: Grass
Life Cycle: Annual, perennial
Growth Habit: Clump, dense patches
Leaf Color: Light green
Reproduces by: Seed
Appearance: Typically grows in clumps or bunches. The stem can grow up to 8 inches high. It has slightly flattened. This is not to be confused with perennial bluegrass which is more desirable.

Barnyardgrass

Type: Grass
Life Cycle: Summer Annual
Growth Habit: Bunch-Type to Slightly Spreading
Leaf Color: Medium Green
Reproduces by: Seed
Appearance: This sparse, spread out grass, has a flat leaf that has a bluish-purplish tint to it. It can grow up to 4 feet tall if not mowed! It is also a “nutrient drain” in your yard, pulling the nutrients away from the good grass.

Bermudagrass

Type: Grass
Life Cycle: Perennial
Growth Habit: Low spreading
Leaf Color: Medium to dark green
Reproduces by: Seed, rhizomes, stolons
Appearance: This is a low, dense spreading grass. It is often used in sports fields where it is very hardy and can quickly recover from damage. It can be a difficult weed to remove because even though the tops of the plants only grow a few inches high, the roots can go down over 6 feet!

Black Medic

Type: Grass
Life Cycle: Summer Annual
Growth Habit: Bunch-Type to Slightly Spreading
Leaf Color: Medium Green
Reproduces by: Seed
Appearance: Looks very similar to and is often confused with clover, however the flowers are yellow rather than pink or purple. It is considered a noxious weed.

Broadleaf Plantain

Type: Broadleaf
Life Cycle: Perennial
Growth Habit: Bunch-Type
Leaf Color: Light Green
Reproduces by: Seed

Buckhorn

Type of Plant: Broadleaf
Life Cycle: Perennial
Growth Habit: Bunch-Type
Leaf Color: Dark Green
Reproduces by: Seed, Rootstock

Chickweed

Type of Plant: Broadleaf
Life Cycle: Winter Annual
Growth Habit: Spreading
Leaf Color: Light Green
Reproduces by: Seed

Cinquefoil

Type: Broadleaf
Life Cycle: Summer perennial
Growth Habit: Low growing, spreading
Leaf Color: Medium green
Reproduces by: Seed

Clover

Type: Broadleaf
Life Cycle: Perennial
Growth Habit: Erect, dense patches
Leaf Color: Dark Green
Reproduces by: Stolons, above ground

Crabgrass

Type of Plant: Grass
Life Cycle: Summer Annual
Growth Habit: Flat, Spreading
Leaf Color: Light Green
Reproduces by: Seed

Dallisgrass

Type: Grass
Life Cycle: Perennial
Growth Habit: Flat fan, clump
Leaf Color: Medium green
Reproduces by: Rhizomes, seed

Dandelion

Type of Plant: Broadleaf
Life Cycle: Perennial
Growth Habit: Bunch-Type
Leaf Color: Dark Green
Reproduces by: Seed, Rootstock

Foxtail

Type of Plant: Grass
Life Cycle: Summer Annual
Growth Habit: Erect, Clump
Leaf Color: Light Green
Reproduces by: Seed

Goosegrass

Type: Grass
Life Cycle: Summer Annual
Growth Habit: Flat, Clump
Leaf Color: Medium Green (Silver Center)
Reproduces by: Seed

Ground Ivy

Type: Broadleaf
Life Cycle: Perennial
Growth Habit: Spreading
Leaf Color: Dark Green
Reproduces by: Seed, Rhizomes, Above Ground Runners

Henbit

Type: Broadleaf
Life Cycle: Winter Annual
Growth Habit: Slightly Spreading
Leaf Color: Dark Green
Reproduces by: Seed

Johnson Grass

Type: Grass
Life Cycle: Perennial
Growth Habit: Erect
Leaf Color: Light Green
Reproduces by: Seed, Roots

Knotweed

Type: Broadleaf
Life Cycle: Summer Annual
Growth Habit: Spreading
Leaf Color: Dark Green
Reproduces by: Seed

Nimblewill

Type: Grass
Life Cycle: Perennial
Growth Habit: Low growing patches
Leaf Color: White-green
Reproduces by: Stolons

Nutsedge

Type: Sedge
Life Cycle: Perennial
Growth Habit: Erect
Leaf Color: Yellow-green
Reproduces by: Rhizomes, Tubers

Orchard Grass

Type: Grass
Life Cycle: Perennial
Growth Habit: Erect, clump
Leaf Color: Blue-green
Reproduces by: Seed

Oxalis

Type: Broadleaf
Life Cycle: Summer Annual
Growth Habit: Erect
Leaf Color: Light Green
Reproduces by: Seed

Purslane

Type: Broadleaf
Life Cycle: Annual
Growth Habit: Slightly Spreading
Leaf Color: Medium Green, Leaves THick and Very Fleshy
Reproduces by: Seed

Quackgrass

Type: Grass
Life Cycle: Perennial
Growth Habit: Flat fan, clump
Leaf Color: Blue-green
Reproduces by: Seed, rhizomes

Sheep Sorrel

Type: Broadleaf
Life Cycle: Summer perennial
Growth Habit: Low spreading
Leaf Color: Medium green
Reproduces by: Seed, rhizomes

Shepherd’s Purse

Type: Broadleaf
Life Cycle: Winter Annual
Growth Habit: Flat fan
Leaf Color: Grey-green
Reproduces by: Seed

Speedwell

Type: Broadleaf
Life Cycle: Winter Annual
Growth Habit: Slightly Spreading
Leaf Color: Dark Green
Reproduces by: Seed

Spurge

Type: Broadleaf
Life Cycle: Summer Annual
Growth Habit: Spreading
Leaf Color: Bluish Green
Reproduces by: Seed

Thistle

Type: Broadleaf
Life Cycle: Biennial
Growth Habit: Erect
Leaf Color: Glossy dark green
Reproduces by: Seed

Wild Carrot

Type: Broadleaf
Life Cycle: Biennial
Growth Habit: Erect
Leaf Color: Medium Green
Reproduces by: Seed

Wild Violet

Type: Broadleaf
Life Cycle: Winter
Growth Habit: Low growing, spreading
Leaf Color: Dark Green
Reproduces by: Stolons, rhizomes

Black-grass

Black-grass is a native annual grass weed that occurs throughout the UK but is found mainly in the cereal growing areas of southern and eastern England. It rarely occurs outside of cultivated land and is most abundant in winter crops. Black-grass is often found spreading into arable fields from the field margins. It is chiefly confined to heavy land, occurring only occasionally on sandy or gravely soil but has begun to appear on chalk.

Some black-grass populations have developed resistance to some widely used graminicides and this has contributed to an increase of the weed on conventional farms.

In addition to its effect on cereal yield, black-grass suffers from ergot (Claviceps purpurea) and this can result in contamination of the grain at harvest. The fungus is the same strain that infects wheat.

Black-grass flowers from May to August, sometimes into October. The flower heads appear above the cereal crop in May and June. Additional flower heads may develop on side branches. The flowers are wind pollinated but are self-fertile. Seed production ranges from just 50 up to 6,000 seeds per plant. Seeds ripen quickly and many are shed before cereal harvest. Those that remain on the plant are likely to contaminate the harvested grain.

Some seeds are able to germinate soon after shedding, others remain dormant for a few months. Light and fluctuating temperatures appear to increase seed germination. If conditions are favourable most seeds germinate in the autumn, mainly in late October and early November. There is a smaller flush of seedlings in spring, which is greater if autumn germination has been prevented by weather or soil conditions. Dormancy is induced when seeds are present in waterlogged soil. Around 60-70% of the seedlings in a flush are derived from seeds less than a year old. Seedlings that emerge from depths of 2 to 5 cm in a ploughed soil are unlikely to be from freshly shed seeds. Black-grass seeds normally germinate near the soil surface, even shallow burial will result in some degree of dormancy. Emergence of black-grass seedlings decreases with increasing depth of burial in soil.

The decline of seed in soil is greatest in the first year but appreciable numbers can remain after 4 years in both cultivated and undisturbed soil. If seeds are ploughed down deeply they may retain viability for 11 years. Black-grass seed does not persist for long in peat soils. Seed sown in the field and followed over a 5-year period in winter or spring cereals had an annual decline rate of 80%. Emerged seedlings represented 15% of the seedbank. Seeds in dry storage will still germinate after 13 years but viability begins to decline after 8 years. Seeds stored under granary conditions gave 34% germination after 1 year and 7% after 4 years.

The position of black-grass patches remains relatively stable in arable fields. The grass exhibits little ability to spread rapidly into other areas but persists where it has become established unless control measures are taken.

Black-grass seed has been found as a contaminant in cereal, grass and clover seed samples. Contamination was greater in home-saved seed.

Seed is not considered to survive passage through the digestive systems of birds or animals but it has been found in cattle droppings.

In the past, straw and stubble burning after cereal harvest killed a significant proportion of the freshly shed black-grass seeds but this is no longer an option.

Early drilling of winter cereals leads to severe infestations because it coincides with peak black-grass emergence and the weed has time to tiller before winter. Sowing cereals before 25 October has been shown to increase black-grass infestations, sowing after 5 November has led to a decrease. However, there may be a substantial loss in yield if winter wheat is drilled after mid-November. Infestations are often worse on badly drained, heavy soils where there is a high proportion of winter cropping. In cereals, narrow crop rows (18 cm) suppress black-grass growth more than rows wider apart (35 or 53 cm).

Where black-grass seed has been shed in the previous crop, 80-90% of black-grass plants in a direct-drilled winter wheat crop will be from the fresh seeds. Where there is only a small reserve of seeds in the soil, ploughing generally reduces the level of infestation from fresh seeds while tine cultivations leave most seeds ready to germinate in the surface layers of soil. However, on a field that has suffered black-grass infestations for many years viable seeds will be present throughout the soil profile and ploughing will unearth the buried seeds ready to germinate in large numbers. A population model used to determine the effect of soil tillage on the level of black-grass infestations in winter cereals suggests that to prevent a likely build-up of black-grass under minimum tillage systems the land should be ploughed every 5 years.

Weather conditions during the maturation of black-grass seed can affect the level of seed dormancy. Seed can be more dormant following a cool damp summer and ploughing may be more appropriate to avoid a prolonged period of seedling emergence. After a hot summer, the seed is less dormant and will germinate readily if conditions are favourable after shedding, negating the need for ploughing.

In spring cereals, early sowings suffer worse black-grass problems but delaying drilling can reduce the potential yield of the crop. Black-grass is less competitive in a spring crop but it can be a significant source of fresh seed.

Black-grass seedlings are very susceptible to mechanical injury and do not tolerate trampling or soil disturbance. Shallow ploughing and surface tillage will encourage seeds to germinate freely. The seedlings can then be destroyed by further cultivations or ploughing. In root crops, thorough cultivations will destroy the young plants. In cereals, harrowing when the soil is dry kills small seedlings. In grass seed crops, mowing or grazing in the first year may be required to prevent the black-grass seeding and reduce infestations in year 2.

Fallowing can reduce seed numbers in soil dramatically and an autumn fallow is ideal for this autumn germinating weed. However, seed numbers will build up again rapidly if seed shedding occurs in subsequent crops.

Strategies developed to deal with herbicide resistant black-grass may also be relevant in organic systems. They consist of ploughing at least once every 4-5 years, including a higher proportion of spring crops in the rotation and delaying the sowing of autumn cereals.