Dish mustard, stinkweed, treaclewort
Thlaspi arvense L.
Annual Broad-leaved Weeds
An annual or overwintering weed of arable land, roadsides and waste places. Field penny-cress is scattered throughout most of the UK but is commoner in the south and east of England. It is not recorded above 1,000 ft. It succeeds in both dry and moist habitats and adapts readily to environmental conditions. Field penny-cress thrives in nutrient-rich loams.
There is evidence that field penny-cress was a weed of crops in the Bronze Age. It is a frequent birdseed alien.
Genetically distinct, early and late flowering forms have been reported. The two forms are distinguishable by leaf shape.
The plant smells strongly when crushed and is sometimes called stinkweed. Milk is tainted when cows eat the plant. The seeds contain a glucoside that breaks down to a form of mustard oil and can cause poisoning in livestock. Nevertheless, field penny-cress is cultivated as a food plant in some countries. Oil can be extracted from the seeds but is of variable composition. The seeds are a diuretic and were formerly taken against rheumatism.
Field penny-cress flowers from March to October. The flowering of early flowering forms is hastened by increasing temperatures but that of late-flowering forms is delayed. Plants are self-compatible and are generally self-pollinated but 10-20% outcrossing can occur. The first seeds are produced in early July but the seed may be shed over several weeks.
Persistence and Spread
Field penny-cress seeds buried in undisturbed soil have given 87% germination after 10 years. A small number of seeds remained viable after 30 years burial in soil. Seeds mixed with soil in the field and left undisturbed declined by 52% after 6 years but in cultivated soil the loss was 92%. Dry-stored seeds gave 80% germination after 1 year but none after 5 years.
Viable seeds have been found in pigeon droppings and seedlings have been raised from the excreta of various birds. Apparently-viable seeds have been found in samples of cow manure. With rumen digestion there is a gradual loss of viability with time and after 24 hours the reduction may be up to 70%. However the diet can have an effect on digestion time and hence seed survival. Ensilage for 8 weeks appears to kill field penny-cress seed. The seeds are also killed by windrow composting for 2 weeks at 50-65°C. In dry heat, seed was killed when heated at 85°C for 15 minutes.
Seeds will float in water for 24 hrs and dispersal during irrigation is possible.
The presence of nitrate encourages seed germination and it has been suggested that to reduce weed emergence fertiliser applications should be delayed until after crop emergence has occurred. However, this may not apply to organic systems where fertility building will have taken place earlier.
Field penny-cress increases markedly following a series of spring cereals. Studies in oats have shown that more seeds are left on the ground after combining than if the oats are cut with a binder and threshed elsewhere. In many cereals, field penny-cress seeds mature and are shed before crop harvest. Seed germination should be encouraged by surface cultivations and the seedlings can then be controlled by further cultivations and hoeing. Field penny-cress can be hoed off readily in row crops. Seed bearing plants should not be ploughed-in.
Laying land down to a 3 to 4 year grass ley will choke out the weed.
Updated November 2007.