By Dr Kerry C Harrington
In the last issue of Golf and Sports Turf Australia, we discussed the biology and control of the plantains. There is another group of weeds that grow in much the same way as plantains, forming rosettes in turf with seed-heads that are often pushed up above the mowing height, to be chopped off each time the mower passes by. However, dandelion and many of its close relatives differ from the plantains in that they have bright yellow flowers that make them very conspicuous. They also belong to a different family, namely the Asteraceae family (formerly the Compositae family), to which many other troublesome turf weeds also belong.
The true dandelion has the botanical name of Taraxacum officinale. However, there are several other weed species which look just like dandelion and often get confused with it. In this article we will also look at three of the main "look-alike" species, namely catsear (Hypochaeris radicata), hawkbit (Leontodon taraxacoides) and hawksbeard (Crepis capillaris). Note that some of these weeds have other common names associated with them at times. For example, catsear is sometimes also called flatweed or rooted catsear, and hawkbit can be known as hairy hawkbit, common hawkbit and lesser hawkbit.
The rosette growth form of all these species can be seen in Fig 1. They can appear as single rosettes (as shown with the dandelion plant), but often develop into multiple rosettes (as shown with the hawkbit plant). It is fairly easy to differentiate between the four species when they are flowering (Fig 2). Both dandelion and hawkbit have unbranched flower stems with one flower per stem. The dandelion flower stem is hollow and rather fleshy whereas the stems of hawkbit flowers tend to be more fibrous, solid and much thinner in diameter. The flower stems of both catsear and hawksbeard are branched. There are no leaves on the flower stems of catsear whereas with hawksbeard there is almost always at least one leaf on the stem, though these leaves are usually much smaller than the rosette leaves.
In the vegetative stage, as with most weeds, identification can be a bit more difficult. The leaves of dandelion and hawksbeard usually have almost no hairs and are quite smooth, whereas the leaves of catsear and hawkbit are covered in bristly hairs and tend to feel rougher and also thicker than the other two species. Differences in leaf shape are shown in Fig 3. Of the smooth, hairless leaves, the lobes of a dandelion leaf tend to point backwards towards the base of the leaf much more than those of hawksbeard, which usually point straight out. With the thicker bristly leaves, a comparison of leaves that are similar in length will show that hawkbit leaves are usually much narrower than catsear leaves. To be certain, you can check using a magnifying glass because many of the hairs on a hawkbit leaf divide into two at the end (i.e. they have "split ends") whereas this does not occur with catsear.
Note that there is another weed species in Australia called smooth catsear (Hypochaeris glabra) which looks very much like catsear except it has almost no hairs on its leaves. It appears that catsear and smooth catsear often interbreed, giving plants with intermediate amounts of hairiness.
All four of these species are found commonly throughout Australia. It is normal to find several of them growing with each other in the same area of turf, though the species which is the most dominant of the four varies depending on a number of factors including the locality within Australia.
Dandelion, hawksbeard, hawkbit and catsear are all perennial weeds, but they can also act as annuals or biennials under adverse environmental conditions, escaping the effects of severe drought as seeds. However, their deep tap-roots will allow them to thrive under mild drought conditions, making use of water deeper in the soil profile than shallower rooted turf grasses. The large food reserves stored in these tap-roots also help the species regrow rapidly following disturbance or ineffective control attempts. The rosette growth form ensures that growing points, located at ground level, are left untouched by the mower, and leaves radiating out from this growing point are often below the mower's blades as well. As a result, they grow very successfully as turf weeds throughout the world, especially in temperate areas. These species are also tolerant of many growing conditions, especially low soil fertility.
As you may have gathered from my address at the start of the article, my experience with turf weeds and their control is mainly based on the New Zealand situation. The weed species and their susceptibility to herbicides is much the same in Australia as in New Zealand, but the registration of herbicides to control these weeds differs substantially between the two countries. Below I shall outline what we do in New Zealand to control these weeds, but you must bear in mind that these herbicides are not necessarily registered for this use in Australia, so check the label first.
The seedlings of these species are fairly susceptible to most herbicides commonly used in turf. However, because of the large tap-root systems that develop once these weeds get established, older plants are more difficult to control. As a general rule, dandelion tends to be the most difficult of these weeds to control, while hawksbeard and hawkbit tend to be more susceptible than catsear. Under good growing conditions in spring and autumn when the soil is moist, 2,4-D or MCPA can give reasonable control of hawkbit, hawksbeard and perhaps catsear, though repeat applications may be required, especially with older plants. For dandelion and catsear plants, it is usually necessary to use triclopyr/picloram (Grazon DS) or MCPA/dicamba mixtures (e.g. Banvel M, Fairway) to obtain adequate control. Other commercial products such as clopyralid (Lontrel) and triclopyr (Garlon 600) can be effective against these weeds, though once again it is the hawksbeard and hawkbit plants that are easier to control.
Kerry Harrington is a Senior Lecturer in Weed Science at Massey University, Palmerston North, New Zealand