London Rocket

What is London rocket?

London rocket is a cool-season annual mustard from the Mediterranean and Middle East that has settled into the dry Southwest and West Texas. London rocket identification depends mostly on timing and shape: a ground-hugging rosette of deeply cut leaves through the winter, then branching stems topped with small pale yellow flowers and long, skinny seed pods from late winter into spring.

It causes trouble because it gets started earlier than most plants. It sprouts with the first cool weather, grows through the winter and finishes maturing before many native wildflowers have gotten going, which lets it crowd them out in wild areas and compete hard in vegetable fields, orchards and gardens. Each plant can drop thousands of seeds, and buried seed lasts about a decade, so one missed season restocks the soil for years. Like other mustards, it can also harbor pests and diseases that attack cabbage-family crops.

London Rocket identification: what to look for

Check bare or thin spots from fall through spring. Young plants are easiest to name by the leaf shape of the rosette; older plants are easiest to name by the long, thin pods that form along the branches below the flowers.

• Seedlings: Seed leaves are small hairless ovals, about 1/12 to 1/4 inch long, on stalks as long as the blade. The first true leaves are oval with smooth or slightly toothed edges; later leaves become shallowly toothed and then lobed.
• Rosette leaves: Lower leaves reach about 6 inches, are nearly hairless and deeply lobed, sometimes cut all the way into separate leaflets, with a prominent midvein.
• Stem leaves: Higher up, leaves get smaller, narrower or oblong and attach with no stalk. Many have two basal lobes that point backward, and they do not wrap around the stem.
• Stems: Upright stems branch mostly near the ground and are green, sometimes with a purple tinge.
• Flowers: Small clusters of pale yellow, four-petaled flowers, only about 1/8 inch long, sit at the tips of the branches.
• Pods: Long, slender, round pods about 1 to 1 1/2 inches long and roughly 1/25 inch wide, straight or slightly curved and angled upward. The seeds inside are tiny, oblong, glossy and tan.
• Hairs: Any hairs on the plant are simple and unbranched, a handy check against flixweed, whose hairs branch.

Where it grows in the United States

London rocket is mainly a weed of the arid and semi-arid Southwest. UC weed scientists place it chiefly in California, Nevada, Arizona, Utah, Colorado and New Mexico, and Texas A&M AgriLife Extension agents count it among the main winter weeds in West Texas lawns. In California it is most common across the southern and central parts of the state, reaching the upper Central Valley at about 2,600 feet.

It thrives where winters are mild and the ground has been disturbed: abandoned fields, roadsides, orchards, vineyards, vegetable fields, home gardens and lawns with bare spots going into winter dormancy. In wild areas it moves into deserts and streamside corridors. Because the seed sprouts as soon as cool weather arrives, bare soil in fall is its invitation.

London Rocket look-alikes

A few plants get mixed up with it:

• Tumble mustard (Sisymbrium altissimum): A taller relative, up to about 4 1/2 feet, whose upper leaves are cut into long, narrow lobes. Its flowers are about twice as large, its pods run 2 to 4 inches, and its dead stems snap off and roll like tumbleweeds, which London rocket does not do.
• Flixweed (Descurainia sophia): Its leaves are far more finely divided, with segments split again once or twice, and its hairs are branched. London rocket's leaves are simply lobed and its hairs are unbranched.
• Tansy mustard: Nearly identical in size, flower color and rosette habit, and the two often come up side by side. Extension agents treat them as a group and control them the same way, so telling them apart rarely changes your plan.

How to get rid of London rocket

Pulling, digging and mowing: Pull or hoe plants while they are still rosettes. The single taproot comes out easily, and a scuffle-type hoe makes quick work of early rosettes in beds. For larger patches, shallow cultivation before any pods form is very effective. Mowing helps only if it removes the flowering stems before the seed is mature, which gradually draws down the seed in the soil, and in lawns it pays to bag clippings once plants start flowering so you aren't spreading seed. In regions with hot summers, solarizing bare soil under clear plastic can kill both plants and seeds.

Cultural control matters most, because the right conditions keep it from coming back.

• Keep lawns thick and free of bare patches going into fall dormancy so winter mustards have nowhere to start.
• Cultivate fallow ground before plants set pods, and repeat as new flushes come up.
• On pasture or open land, grazing timed before seed set can knock it back. Sheep are the better choice, because cattle that eat a lot of it can taint their milk and meat.
• Don't count on burning. By the time there is enough dry fuel to carry a fire, the seed has usually already dropped.

Herbicides: In lawns, Texas A&M AgriLife Extension advises a preemergence herbicide put down before seeds germinate in early winter, followed by a broadleaf weed killer containing 2,4-D, dicamba or both for any plants that come up anyway. Keep the spray off nearby trees, shrubs and ornamental grasses, and skip weed-and-feed products. On non-crop ground, UC weed scientists also list triclopyr plus 2,4-D for small plants and glyphosate for rosette- to bud-stage plants; glyphosate kills any plant it touches and has no soil activity. Young, small plants are far easier to kill than flowering ones. Choose a product whose label lists your site, whether lawn, bed, pasture or non-crop area, and follow it exactly; the label is the law. If you hire someone to spray, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Keeping it from coming back

Every London rocket plant that sets pods restocks the soil for years, so the most important rule is simple: never let it go to seed. Start looking in fall, deal with rosettes before late winter, and keep at it for several seasons, since buried seed can last about 10 years.

Don't leave ground bare going into winter. A thick lawn before dormancy and prompt cleanup of disturbed soil take away the open ground this mustard depends on. If you graze livestock, run them through before seed set rather than after, and bag clippings from infested lawns while plants are flowering.

Questions we get about London rocket

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