THE THISTLE MENACE

Te Awamutu Courier, Volume 75, Issue 6443, 7 November 1947, Page 7

THE THISTLE MENACE

RECENT ARRIVALS IN WAIKATO STATEMENT BY RESEARCH OFFICER Recent arrivals in the Waikato area, are winged thistle, variegated or milk thistle and nodding or musk thistle. Winged thistle has been known to occur locally for several years, and is widespread through the Raglan, Waikato and Waipa counties, according to Mr R. K. Ward, officer in charge of weed control research, at the Hamilton Soil Fertility Research Station. Winged thistle has also been reported in Otorohanga, Matamata and Piako counties and doubtless it extends beyond these boundaries. : Variegated thistle fortunately, is more restricted in its occurrence, as also is nodding thistle. The latter is better known in the South Island in cultivated areas, while variegated thistle is a major weed in the pastor- • al areas of Wanganui and Hawke’s I Bay. There, it has assumed alarming , proportions and the expenditure of ! labour and money in its control is considerable. It cannot be foretold how these thistles will behave under Waikato conditions, but there is reason to sup- | pose that in our lighter soils and with our better distributed rainfall, they will succeed as well, if not better, than the heavier soils further south. Probably also they will mature and seed much earlier in the season. To give farmers the opportunity of inspecting these thistles, thus eni abling them to be recognised when | encountered, the Soil Fertility Rei search Station will exhibit living specimens at the forthcoming Waikato A. and P. Show, and an officer will be present to answer enquiries on this and related weed control matters. ! Several methods for the control of winged thistle have been attempted by farmers with different results. • Grubbing: This is only partially i successful, and as regrowth of shoots 1 : from the crown commonly occur, regular attention is necessary to see that ; these are grubbed before flowering occuijs. Grubbing is liable to cause considerable damage to the sward. Regrowth is probably worse when grubbing is commenced too early, when the soil is very moist and the, plants have considerable food reserves in their tap-roots. It must be i remembered that winged thistle ; matures earlier than other thistles, : and attention must be given it so ? much earlier than is required for ■ Scotch thistle, for example. I Slashing or Mowing’: When this is done while the plants are soft and luscious, stock will readily devour the wilted foliage, but whpn carried out at this stage there js generally strong regrowth of shoots from the crowns. If delayed too long, and the plants are commencing to flower, there is every possibility that the seed will ripen and spread the weed. When flowers are showing colour they should be nipped off from the stems before the plant is stashed or grubbed. This will cut .off the supply of sap and the setting of seed will then be impossible. The -later that i slashing is carried out the better is | the kill likely to be, but the danger i of seeding is so great under these i conditions that it cannot be recommended. Sodium Chlorate: This has proved successful when applied either as a spray or in the form of a dust consisting of 5 parts of chlorate to 95 parts of agricultural lime. A teaspoonful applied to the crown of I young plants is effective, while a ! handful sprinkled on tall plants is i required. Spraying with a 5% solui tion of chlorate is also effective, but j is inclined to cause excessive damage ! to the sward. One virtue of chlorate J. is that it rapidly brings growth to a i full stop if adequately applied. The • fire hazard associated with chlorate is j to be remembered. I Hormones: Most thistles are quite j susceptible to spraying with hormone ' weedkillers and tests carried out in | Hawkes Bay gave favourable indicai lions in the case of winged thistle, j while local trials proved variegated ■ thistle to be susceptible also. Horj mones are not poisonous to stock, i Thistles treated with these materials I become palatable to sheep and cattle ; which will readily attack hormone j treated plants. Whether this will decrease the effect of the weedkiller or • not is yet to be -proved. i One thing always to be remembered ! with hormones is the slowness of their action. If applied when the plants are in flower, the hormone does not work quickly enough to put a stop to seeding while the older the plant is the more woody and resistant it becomes. Consequently the best I time to use hormones appears to be ! when the plant first commences to ! “bolt.” i The Research Station staff laid ; down a large trial in the Kairangi ! area on the 15th October. The , materials used were Agroxone and ■ Weedone diluted at the rate of 1 gal- ; lon of concentrate to 100 gallons of j water and the spray solutions were j applied by means of small power ’ spray outfit. Approximately 150 gal- ! lons of solution per acre were applied ; to an almost continuous infestation of I plants growing up to two’ feet in ■ height. Small plots were pegged oft I and treated with weaker solutions to ! discover if less material would be j equally effective. An inspection of the experimental I area was carried out a week after | treatment and it was found that all j sprayed plants were responding well •to the application of hormones, i Although it is too early to be certain, experience in the use of hormones with other plants suggests that strengths of spray even weaker than I 1-100 should be effective, although slower in action. It would appear to be almost too late now to consider • hormone spraying for winged thistle control because flowering has commenced. The identification of a mature winged thistle plant is simple but effective control depends upon its reci ognition at early stages of growth. The young plants are often rather , pale coloured with their leaves presed flat against the soil, making it difficult to see plants from any distance. The leaves are not so closely dissected as in Scotch thistle, nor are they so spiny. Although all parts of . the plant are hairy this fact is not so ■ j striking as in the case of Scotch I I thistle. As they grow larger winged

thistle plants appear more bunchy and less open than do Scotch thistle plants and they bolt to the flowering stage earlier in the spring. The stems are ribbed with tiny fringes and the plant gets its name from this characteristic. The plant may grow as tall as six feet. It is usually very erect with few lateral branches which also tend to become erect and not spreading. The flowers are small, tinted lilac pink and as in Californian thistle they are borne in clusters. Variegated thistle is unmistakable because of its rank habit of growth and the presence of pale milk coloured tracks on the upper surface of the smooth shiny leaves. The plant may grow to six feet, is spreading in habit and will bear large spiny mauve coloured flowers placed singly at the ends of the branches. Nodding thistle is somewhat like ’ Scotch thistle, though smaller, with large red flower heads held inverted at the ends of long stalks, each bearing one head.