Burclover is a commonly used name for two prickly invasive clovers, Black Medic Medicago lupulina and California Burclover Medicago polymorpha. Since the beginning of the last drought we had, probably around 2007, my neighborhood has slowly been overtaken by burclover. It is the tiny clover looking plant with yellow flowers and then prickly spiral shaped seed pods that stick to beach towels, picnic blankets, and dog fur. I have been hand pulling it from the beginning, not wanting to resort to chemicals for control. Each week, prior to mowing, I spend a few minutes or so, going over the front lawn looking for any new signs of it to pull. This time of year, it is slightly darker than my Bermuda grass so it is easy to spot. At the neighbor’s house, I spot it even easier with all the tiny yellow flowers on larger established patches.
My efforts to eliminate it have been futile, so much so it makes me want to cry. I feel bad for George because he gets the burs stuck in his fur and it probably hurts when we comb or pull them out. The whole neighborhood has it, with a few lawns on the block that look like all they have now is burclover. It seems to be easily spread by the pets, the yard men, and the kids. With the water restrictions, thin bare patches began to make the lawns on the block ideal for the burclover to take over. After discussing it with the next door neighbors last month, we have decided to team up to each make a concerted effort to get rid of it over the next few seasons. I compiled a page of control methods suggested by U.C. Davis ANR and Cooperative Extension to share with the neighbors. It is at the bottom of the post.
Wednesday, I spread a giant bag of corn gluten all over the front lawn and parkway. Although I spread compost on the lawn at least once a year, Corn Gluten is a natural fertilizer that is also reported to have allelopathic properties to inhibit the growth of broadleaf weeds, like clover. It wasn’t necessary to spread it out back since the burclover has never managed to get a foot hold. The chickens like to munch on any patches that manage to germinate.
U.C. Davis ANR and Cooperative Extension offer some “best practices for control,” for both organic gardeners like me that want to avoid synthetic chemicals and folks like my neighbors that just want to kill it by the easiest means possible, as long as it doesn’t pose a risk to the kids or pets, and be done with it for half a year. The following is an excerpt from the page I shared with the neighbors:
MANAGEMENT OF BURCLOVER
Clovers are relatively easy to control in the home garden by hand-pulling, cultivation, and the application of mulch. In large, landscaped areas herbicides may also be necessary. Because clover seed has a hard seed coat that is very heat tolerant, composting and solarization are not as effective in reducing clover’s seed viability as they are with other weed species. The hard seed coat also allows the seeds to survive longer in the soil than many other weed seeds; clover seeds can germinate over many years, making the control of these plants an ongoing effort.
Once clovers are controlled, change cultural practices in the landscape and turfgrass to reduce the chance of reinfestation. Insuring a thick stand of grass can help exclude clovers in the lawn. Lack of nitrogen fertilization can also influence clover growth. Adjust the fertilizer program to include more nitrogen and less phosphorus in turfgrass. Mulches can be effective in excluding clovers and other weeds in landscapes.
Annual clovers can be easily controlled by hand-pulling, hoeing, or cultivation. Mulching, depending on the size and depth of the mulch, can prevent seedling establishment. Before seeds germinate, a 4-inch thick organic mulch (e.g., compost, wood chips, etc.) can prevent establishment of clovers. Organic mulch can also be applied after the seedlings have germinated but must be applied in a thicker layer (4 to 6 inches) and must cover the plants completely to block out all light. Organic mulches need to be reapplied each year to maintain the 4-inch-thick layer because they decompose and the thickness of the mulch declines over time. Woven black landscape fabric can exclude weeds over a number of years. Larger plants are more difficult to control with mulching, but they can be hand-pulled or hoed.
Both established annual and perennial clovers can be controlled with postemergent herbicides. The best herbicide to use depends upon the species of turfgrass. Warm-season turfgrasses such as bermudagrass, zoysiagrass, and kikuyugrass will tolerate products containing mecoprop and dicamba but not triclopyr. Cool-season turfgrasses will tolerate all of the herbicides that control clover. The herbicide 2,4-D is not effective for clover control; it will injure the plant but does not control it.
Preemergent herbicides available for landscape use are effective but generally unnecessary in the home landscape where annual clovers are easily controlled by the methods mentioned. For landscape professionals, herbicide formulations that contain isoxaben are effective for controlling annual clovers and can be used around many woody shrubs and trees. Most established annual flowers tolerate this herbicide. Herbicide formulations containing oryzalin, trifluralin, or pendimethalin will control most grass species and some broadleaf weeds but will miss many other broadleaf species, including legumes like burclover.