Pastinaca sativa

The lepidopteran Depressaria pastinacella (parsnip webworm) is the dominant herbivore on Pastinaca (Gorder and Mertens 1984, Thompson 1978). The adult webworm lays eggs on unopened umbels from mid-May to early June. The larva then builds a web on the umbel and feeds on the flowers and developing seeds. The mature larva bores into a large stem at the base of the plant to pupate over winter, and the adults emerge the following July (Gorder and Mertens 1984).

The following life history information is from Baskin and Baskin (1979). Seedlings emerge from February through April, form rosettes and grow vegetatively for one or more years before they form an aerial shoot ("bolt") and flower. During vegetative growth the plant continuously produces and loses leaves; over winter the above ground tissues dies back leaving only one or two partially expanded leaves on each plant. Rosettes must reach a critical size before vernalization will effect flowering. Flowering occurs from mid-May to mid-June and seeds are mature by early July. The primary umbel on the main stem begins to develop and produce seed one to two weeks before the secondary umbels on lateral branches. The plant dies as the seeds mature, leaving the dead shoot standing through the winter. Seed dispersal normally occurs in autumn through late November, but many areas with P. sativa are mowed in late summer and seeds are often released as the shoots are cut. Newly mature seeds are inhibited from germination by summer temperatures. Stratification over winter increases germination ability and seeds germinate in early spring. Seedling mortality is high with less than 1% of newly emerged seedlings surviving to reproduce.