dog-binder, dog daisy, hog
Anthemis cotula L.
Stinking chamomile is a native annual or biennial weed that was troublesome in arable fields particularly in cereals. It does not thrive well on undisturbed soils. It is locally common especially in central and southern England on heavier soils. Stinking chamomile prefers the relatively dry climate and warmer summers in these areas of the UK, however, it is only moderately drought resistant. Although it is more frequent on heavy clay and clay-loam soils it also occurs on calcareous and neutral soils but is usually rare or absent from light soils.
Stinking chamomile is very variable and plants of different sizes and habits can be found growing in farmland. It will hybridise with scentless mayweed (Tripleurospermum inodorum) and corn chamomile (A. arvensis) but the hybrids are sterile. Stinking chamomile was a weed of crops in the Iron Age but is now described as vulnerable in the BSBI species status list 2005.
The plant has a distinct smell when bruised and the crushed foliage may cause blistering on the hands. The ripe seeds are also said to cause blistering. The smell has resulted in it being used as an insect repellent in the past. It is also a mouse repellent. Stinking chamomile, either fresh or dried in hay, can taint milk if eaten by dairy cows.
The first flowers open in mid-June and flowering reaches a peak in July. Spring-germinated seedlings flower from July to August. A further flush of flowering may occur from September to October if new shoots develop on the cut down stumps left in cereal stubble. The flowers on individual plants are self-incompatible and rely on insect pollinators. A single flower head may contain 50-75 seeds. The average plant will produce from 600 to 12,000 seeds but plants with 27,000 seeds have been recorded.
In the laboratory, light and alternating temperatures give the best seed germination. Smaller seeds appear to germinate more readily than large ones. Seeds without the outer coat or pericarp germinate better than intact achenes. Scarification also encourages germination. In the field, emergence takes place mainly in autumn and spring but odd seedlings can emerge at anytime. Stinking chamomile is frost hardy at the rosette stage and can grow as a winter annual in Britain. Growth recommences in March and flowering stems begin to elongate in early May.
Seeds have remained viable for 25 years buried in damp sand. In soil, 6% of seeds were still viable after 11 years. Some seeds were still able to germinate after 25 years burial in undisturbed soil but only a small number of viable seeds remained after 5 years in a cultivated soil.
Stinking chamomile seed has occurred as a contaminant of cereal and cultivated grass seed.
Conservation tillage that reduces moisture loss and keeps seeds near the soil surface appears to favour the weed. Control is by preventing seeding through the use of surface cultivations in spring and summer. The inclusion of root crops in the rotation also helps.
The fungal pathogen, Botrytis cinerea Fr. sometimes damages stinking chamomile severely in a wet autumn. The larvae of Apion sorbi F. (Coleoptera) attack the flower head. The larvae of Cucillia chamomillae (Sciff.) (Lepidoptera) also feed on stinking chamomile.
Updated October 2007.