This weed germinates anytime between spring and fall when conditions are suitable. Annual sow-thistle thrives where moisture is available, especially disturbed areas resulting from overgrazing, natural processes or cultivation. This weed may compete with other desirable plant species. The seeds are easily disseminated by the wind due to the pappus of white hair at one end. The overwinter rosette phase may also serve as a reservoir for both vectors and viruses.
Many distinguishing characteristics exist when determining annual sow-thistle from perennial.
Although hard to compare when the two are not aligned, these characteristics may help distinguish one from the other. Annual sow-thistle reproduces only by seed and has deeper lobed leaves. Perennial sow-thistle has a larger hairy flower head and is more spiny. Scouting Techniques Take a minimum of 20 weed counts across the field. Frequently scout low lying areas for patches of this weed.