Common groundsel, Senecio vulgaris, is a prevalent winter annual weed (although also considered a summer annual since it can germinate in spring, summer, or fall). It adapts to both moist and dry sites and reproduces rapidly from seed and has multiple generations per year.
Overwintering seeds germinate from late fall through early spring. New plants mature throughout spring and early summer, usually fading in the summer heat. Flowers develop within six weeks after seedling emergence. Seeds are spread primarily by wind. Each plant produces up to 1 million (avg.1,700) viable seeds, depending upon growing conditions. Plants growing under stress can produce seed when they are only a few inches tall. Seeds buried for six months in soil germinate when exposed to light.
Groundsel can be found all year long but are more active during the cooler growing seasons of spring and fall. Seeds germinate over a wide range of temperatures. Seedlings are frost tolerant and germinate very early in the spring and even earlier under row covers/greenhouses. Groundsel can’t survive on shaded, trampled or mowed sites.
Seed is easily spread with wind, irrigation water, mulch, and on clothing and vehicles. Flowering weeds that are pulled and not removed from the site can still set seed.
Cultivation: Remove groundsel plants when small by hand removal, hoeing, or shallow tilling. Fall management of groundsel is important to prevent dormant seed production.
Mulch: A 3-inch medium/coarse (not fine) mulch layer can effectively prevent groundsel seedlings from pushing through as long as the mulch surface can dry out. Wind-blown seeds do not establish well in mulch that dries out between rains.Fertilizer placement:
Research in container nurseries in Oregon demonstrated that groundsel control was greatly improved by dibbling instead of broadcasting fertilizer on top of container stock.
Outcompete: A thick cover crop between nursery rows can outcompete groundsel.
Soil steaming: Steam heating of soil or potting mix can kill dormant and non-dormant weed seed (180 °F for 30 minutes).
Fallow fields: Seed numbers in soil were reduced by 70% following one year of allowing fields to go fallow and by >90% if this method was extended for a second year.
Chemical control: Monitor for seedlings beginning in early spring particularly after the first warm rain, and through early summer. Monitor for new seedlings again in late summer/early fall and control as soon as possible. Do not wait until spring to control fall germinating weeds. Control is best achieved when applied to foliage of young and actively growing plants. Rotating herbicide mode of action is important to reduce herbicide resistance.
For field grown nurseries, two to four herbicide treatments are needed per year. Treatments should be timed as one season is ending and another is beginning. Timely applications of non-selective herbicides can manage weeds in field grown culture.
In nursery container production, only selective, pre-emergent herbicides can be used safely. Apply pre-emergent herbicides in late fall. In a container nursery production cycle, herbicide application timing is important: 1) during liner propagation, 2) site preparation before setting containers on ground, 3) at potting, and 4) approximately one month after potting.