A new shade for ’22: Very Peri

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common groundsel, Senecio vulgaris, is a widespread annual winter weed (although it is also considered a summer annual since it can germinate in the spring, summer or fall). It adapts to wet and dry sites and reproduces rapidly from seed and has several generations per year.

Overwintering seeds germinate from late fall to early spring. New plants mature throughout spring and early summer, usually fading with the summer heat. Flowers develop within six weeks of seedling emergence. The seeds are dispersed mainly by the wind. Each plant produces up to 1 million (1700 on average) viable seeds, depending on growing conditions. Plants that grow under stress can produce seeds when they are only a few inches tall. Seeds buried for six months in the soil germinate when exposed to light.

Management issues

Groundsel can be found year round, but it is most active during the cooler growing seasons of spring and fall. The 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 cannot survive on shaded, trampled or mowed sites.

The seeds are easily spread with wind, irrigation water, mulch, and on clothing and vehicles. Flowering weeds that are pulled up and not removed from the site may still produce seeds.

Cultural / mechanical control

Cultivation: Remove ragwort plants when they are small by hand, hoeing or shallow plowing. Fall management of groundsel is important to prevent dormant seed production.

Mulch: A 3 inch layer of medium / coarse (fine pitch) mulch can effectively prevent ragwort seedlings from growing through as long as the mulch surface can dry out. Windblown seeds do not establish well in mulch that dries out between rains.

Fertilizer placement:

Research at container nurseries in Oregon has shown that ragwort control is significantly improved by planting instead of spreading fertilizer over the container stock.

Win: A thick cover crop between the nursery rows can supplant the groundsel.

Ground vapor: Steaming the soil or potting soil can kill both dormant and non-dormant weed seeds (180 ° F for 30 minutes).

Fallow fields: The number of seeds in the soil was reduced by 70% after one year of fallow of fields and by> 90% if this method was extended for a second year.

Chemical control: Watch for seedlings from early spring, especially after the first hot rain, and until early summer. Watch for new seedlings again in late summer / early fall and remove as soon as possible. Don’t wait until spring to control weeds that germinate in the fall. Control is best when applied to the foliage of actively growing young plants. Rotating the mode of action of herbicides is important in reducing herbicide resistance.

For nurseries grown in the open field, two to four herbicide treatments are required per year. Treatments should be timed because one season ends and another begins. Timely applications of non-selective herbicides can control weeds in field crops.

In container nursery production, only selective preemergence herbicides can be used safely. Apply pre-emergence herbicides in late fall. In a containerized nursery production cycle, the timing of herbicide application is important: 1) during coating propagation, 2) site preparation before placing containers on the ground, 3) when planting ‘potting and 4) about a month after potting.

* Disclaimer: Complete reliance on a single herbicide may result in resistance and population displacement. The chemicals listed show activity against this weed; however, chemicals showing activity will not always provide complete control. Tank mixing more than one chemical often improves efficiency, as do sequential applications of a single chemical. Always use pesticides according to label directions.

The information provided in this document is provided with the understanding that no discrimination is intended and no endorsement of the University of Maryland Extension is implied. Read labels carefully before applying pesticides.

Deborah Smith-Fiola and Stanton Gill, University of Maryland Extension To read this extension publication in its entirety, including references, visit https://bit.ly/groundsel_UMD.

Dora W. Clawson