Field pennycress

Field pennycress

The enemy: Field pennycress (Thlaspi arvense L.)

Strategy: This is an annual invasive plant that invades grain crops, development properties and other disturbed sites. This mustard from Europe grows to a height of 18 inches and produces very white four-petal flowers that resemble whitetop (Lepidium draba). The flowers form a columnar raceme that produces numerous seed pods. The difference is that field pennycress will have a bright white taproot and whitetop will have skinny, black roots that break off of the mother root. The leaves are somewhat serrated and wavy and alternate on stems. The strongly scented plant was originally brought here to be grown for its oil. Seeds are quite unique in that the pair are generally surrounded by a membrane to resemble a flat, oval fan.

Attack: As with most annual mustards, this plant invades areas quite quickly. It flowers early in the spring and can make a dense monoculture quickly. The plant is forgeable by livestock but can taint the taste of milk in dairy cattle. Once established, it covers other plants and does not allow them to receive daylight or moisture.

The defense: With most annuals, mechanical control is very effective. Waiting until the plant is mature is best as many of the seeds will have germinated. Herbicides such as 2,4-D and Banvel are effective when the plants are young, but once mature stronger more effective herbicides such as Telar XP and Escort XP (and other SU class herbicides) are most effective. With these last two products, grazing animals can remain in the area and are not affected by the spray. Fall is also a great time to treat any fall of these germinated weeds. Get this plant early as to reduce the amount of seed produced.

To learn more, call Bonneville County Weed Superintendent Jeffrey Pettingill at 208-529-1397 or email