Preventative measures: As Verbascum thapsus seedling emergence is dependent on the presence of bare ground, sowing sites with early successional native grasses or other plants may decrease seed germination and the chance of successful emergence of V. thapsus seedlings. Manual: Hand pulling of seedlings should be undertaken after they are large enough to grasp but before they produce seeds, while hand hoeing can destroy very small plants by exposing their root systems to the sun, causing them to desiccate. Small infestations of mullein can be removed by hand digging. Although this is a slow and laborious technique it is suitable for sensitive areas, such as around other desirable trees or shrubs, where other methods may not be suitable.
Mechanical Scarification, the use of ploughs and discs to uproot plants, is not recommended for the control of mullein. This is because it creates areas of bare ground that are ideal for the establishment of new mullein populations. Regular cultivation is known to be adequate for the control of mullein. Tractor-mounted mowers or scythes can be used to trim mullein, depending on the terrain. The best time to cut is when the plants begin to flower. Repeated mowing will prevent the flower stalk from bolting but if mowing is then discontinued then the plant will bolt and produce flowers.
Biological: Intentional establishment of late successional native plants among mullein infestations may result in the weeds being outcompeted and thereby eliminated.
Mullein is unpalatable to cattle and sheep due to the dense cover of trichomes on the leaves. However, goats are known to have a wide dietary range and they may be suitable for controlling or eliminating mullein through grazing. Chickens may be used to deplete the seed bank in areas where mature mullein plants have been removed, since they destroy seeds as they feed.
A curculionid weevil (Gymnaetron tetrum,), which is specific to V. thapsus, was introduced to North America from Europe. Its larvae can destroy up to 50% of the seeds. Eight other beetle species are known to attack mullein but they have not been reported in America.
Powdery mildew (Erysiphe cichoracearum) and root rot (Phymatotricum omnivorum) are two micro-organisms that cause disease in mullein, although they also affect a range of valuable crops as well. Other micro-organisms found on mullein include: Cercospora verbasciola; Phoma thapsi; Phyllosticta verbaciola; Heterodera maroni; Meloidogyne sp.; Mycosphaerella verbasciola; Ramularia veriabilis; Septoria verbasciola; and Oidium pyrinum.
Chemical: A single application of a 2,4-D/2,4,5-T mixture at 16 oz/acre at the rosette stage of development has been known to control mullein, however the epidermal hairs on the leaves can reduce the effectiveness of aqueous solutions as they hold the droplets away from the leaf itself. An initial application of the herbicide Tebuthiuron at 4-6 lbs/acre, and follow-up treatments at half this concentration, has been shown to achieve long-term control of mullein (Hoshovsky, 1986).
