An Alien Weed Host of Heterodera rostochiensis in England

Extract

Many crops of carrots grown in gardens and on a field scale, during the War, have been infested with a weed which bears a resemblance to Solanum nigrum. It has been identified as Solanum sarachoides Sendtner. The plant is a native of Temperate and Sub-temperate South America. The carrot seeds containing this impurity are said to be of Californian origin.

The plant possesses oval leaves, slightly more wavy than those of British specimens of S. nigrum. They are smooth and dark green in colour, but the stems are covered with short hairs. The habit is procumbent to prostrate and the weed creeps extensively through the dense foliage of the carrot crop. The inflorescences are borne laterally and display minute white flowers. Dark green berries are produced in great profusion each containing about 25 seeds. There is evidence that the plant is becoming established on light soils, in the market gardening districts of Staffordshire, and it is doubtless localised elsewhere.

It was noted that where the weed was growing adjacent to plots of potatoes affected with blight (Phytophthora infestans), that its leaves were also attacked. The lesions resembled those of potato blight and the identity of the fungus was confirmed by Mr. N. C. Preston, of Harper Adams Agricultural College.