SPANISH HEATH

New Zealand Journal of Agriculture, Volume 99, Issue 5, 16 November 1959, Page 417

SPANISH HEATH

Can be

Controlled and Land Free of It Protected

Against Infestation

By

W. F. LEONARD,

Scientific Officer, Department

of Agriculture, Christchurch, and J. P. BEGGS, Farm Advisory Officer, Department of Agriculture, Blenheim

RESEARCH by the Farm Advisory Division of the Department of Agriculture in Marlborough during the past 10 years has been directed to retaining or restoring for grazing land either in danger of infestation with Spanish heath or already infested. The approach has been to seek an effective and practicable method of dealing with existing stands of heath and a way of keeping land free of the weed once it has been destroyed or where infestation has not yet occurred. The spraying of chemicals seemed to offer the greatest prospect of killing heath and the key to protection from re-infestation was believed to lie in the raising of soil fertility.

'T'HOUGH there are details of soil fertility which call for further research, trials have shown that heath can be controlled and, more important, that land free of the weed can be protected against infestation. The provision of competitive pasture cover is the long-term solution. If the soil fertility can be improved to do this, not only will the heath be permanently suppressed, but large areas of marginal land will be improved in productive capacity.

Distribution

The plant is often associated with tree heath (Erica arborea) and the extent to which each species occurs is not well known. Spanish heath (E. lusitanica) is, however, known to exist from Wellington to the central area of the North Island, probably extending further north, while in the South Island infestations are known in Marlborough, Nelson, North Canterbury, and about Reefton.

It is likely that the plant is present in other localities, though not recorded. Spanish heath is unpalatable to stock and concern has been felt at its threat to grazing land. Until recently, however, little was done to control it, probably because of two causes: firstly, no satisfactory means of killing existing hill country infestations was known, and secondly, the fact that heath is a weed of low-fertility soils only was not appreciated.

Control Methods Where land can be cultivated no great problem exists. Not only can the plants themselves be destroyed but, more important, on such land the soil fertility can normally be raised readily to prevent re-infestation. Afforestation through tree planting or natural reversion is a possible alternative use for land infested with Spanish heath. However, if grazing of stock is the aim, some positive action is required to maintain these areas in production. Chemical Control Trials for killing existing heath were begun in earnest about the time that hormone-type weedkillers became available and in November 1947 and March 1948 trials with the ethyl ester of 2,4-D and the sodium salt of MCPA were laid down. The 2,4-D was applied as a spray at 1 lb acid equivalent per acre, and the MCPA at 1 lb and 3 lb per acre as a 1 per cent dust. Though a kill to ground level was secured, regrowth soon appeared at the bases of all plants. A second similar application to one trial gave equally poor results. Subsequent trials illustrated that a complete foliage kill could be secured by the application of any one of a number of herbicides, but great variation occurred in the amount of regrowth which followed their use. In March 1952 a trial with the butyl and butoxy-ethanol esters of 2,4,5-T and mixed esters of 2,4-D and 2,4,5-T was laid down. The rates of application were 1,2, and 3 lb acid equivalent per acre applied in 120 gallons of water. These rates as applied to the mixed esters refer to the total of the two ingredients which were present, in the proportion of 2 parts of 2,4-D to 1 part of 2,4,5-T. The usual foliage kill followed application, but next spring a disappointingly large amount of regrowth appeared from the bases of plants on all 2,4,5-T plots. The regrowth was sprayed in autumn, but even this second application failed to kill all plants, though the number surviving on the 2 lb and 3 lb plots was considerably reduced. On the other hand plots treated with the mixture of 2,4-D and 2,4,5-T gave much better results. A good deal of regrowth appeared on the 1 lb plot, and little on the 3lb one. A single re-treatment cleared the 2 lb and 3 lb plots of Spanish heath, this being in marked contrast to the pure 2,4,5-T treatments. An identical trial established a year later gave similar results.

Weedkillers Used The superiority of the mixture over the straight 2,4,5-T suggested that further investigation into, the use of 2,4-D might be worth while. Trials were accordingly laid down to test 2,4-D and a number of other materials which had become available since the original 2,4-D trials were established. Included were materials derived from the parent acids 4-CPA, MCPA, 2,4-D, 2,4,5-T, and 2,4,5-TP, among them being the mixture of 2,4-D and 2,4,5-T esters already mentioned. Each material was applied at 2 lb and 4 lb acid equivalent per acre, one series being applied with water at 125 gallons per acre, and a second series with a similar amount of water plus diesel oil at 10 gallons per acre. Some regrowth appeared on all plots, and a year after the first application each was treated with its original material at 2 lb acid equivalent per acre, diesel oil only at 10 gallons being used as the diluting agent. In all cases the addition of diesel oil gave a greater kill than that obtained on the corresponding plots where water alone was used as the spreader. The ethyl ester of 2,4-D emerged as the material to be recommended for killing Spanish heath, and diesel oil as a diluent to increase effectiveness. This ester is readily available, relatively low in cost, and gave a kill of heath equal to the best obtained in the trial.

The success of 2,4-D on Spanish heath may appear surprising, but the results of these trials agree with work in the United States and England on related species. There, too, 2,4-D was more effective than 2,4,5-T. Time of Application of Spray The tip immersion technique was used in an effort to determine the optimum time of application. Results indicated that treatment during October to March inclusive is most likely to give satisfactory results. All the Departmental trials were laid down during this period, the majority being established in autumn. Soil Fertility While the trials with herbicides were in progress it was not forgotten that low fertility is the basic cause of heath on farm land. Pilot oversown and topdressed strips were laid through existing sprayed trials, and in the autumn of 1954 a detailed topdressing and oversowing trial was established on Tuamarina silt loam, the area having been sprayed a month earlier. Fertilisers used included superphosphate, sodium molybdate, and muriate of potash, while lime at 5 cwt and 2 tons per acre was superimposed on the

fertiliser treatments. White clover seed at 3 lb per acre was broadcast over all plots.

Clover seedlings appeared in large numbers, but within a few weeks those on certain plots became yellow and died, while those on other plots thrived and soon provided a dense ground cover of vigorous white clover. These results were achieved on a soil of very low fertility and one on which only such low-fertility-demanding species as browntop, gorse, Pinus radiata, and Spanish heath manage to survive. Though marked responses to phosphate and molybdenum in the absence of lime had been recorded in parts of the Sounds area, clover establishment in this trial was nil on plots without lime. However, with lime at . 5 cwt or more per acre these fertilisers gave outstanding results. Because of the success of the light rate of lime, lower rates ranging from 4 cwt down to 1 cwt per acre were added next autumn, and 3 cwt per acre proved the minimum rate at which white clover would establish and grow vigorously. Liming and Seed Inoculation Treatments with low rates of lime and with rhizobium bacterial culture are being investigated, these treatments being superimposed on basal applications of phosphate and molybdenum. Bacterial culture has allowed white clover to establish and grow reasonably well without any applied lime, and quite vigorously with lime at 1 cwt per acre. The relationship between lime and bacterial culture in clover establishment is still not clear and research into it is being continued. Permanent Eradication Up to the present all plots on which clover establishment was successful have supported a dense cover of grasses and clover and, most important, during the five years since the first plots were laid down no Spanish heath has regenerated on the plots. Those on which clover failed to establish had in only two years become re-infested to a greater degree than before treatment. Costs If the density of Spanish heath plants is so great that spraying is essential before pasture establishment can proceed, the cost of herbicide would be about £2 10s. per acre. Application by air would cost a further £2 per acre.

Spanish heath can be killed with 2,4,5-T ester, but higher rates and more frequent applications are needed of this material, which is much more expensive per gallon than the ester of 2,4-D. Prevention Better than Cure The most effective way of minimising the cost of Spanish heath control, however, is to forestall infestation by improving soil fertility. The spraying of existing Spanish heath plants is then avoided. Where this is done heath control becomes synonymous with normal land improvement and the same techniques apply. In an area with parent Spanish heath plants the prolific seed production and the many avenues of dispersal make prevention of seed spread practically impossible. Such agencies as sheep, cattle, goats, deer, wild pigs, birds, and wind no doubt contribute to the distribution of the seed and this is one reason why land improvement is considered the best approach to the problem.

Where land is too steep for cultivation, fertiliser and seed would be distributed from the air. The cost would vary with the type and quantities of fertiliser required, the location of the property, and so on. As land infested with Spanish heath or in danger of infestation is generally of low fertility, fairly heavy initial fertiliser dressings will usually be needed. The local officers of the Farm Advisory Division can provide detailed advice for farmers and he should be consulted. The Future With the uncertain economic outlook the cost of land development may be regarded as high and this is one important reason for careful planning. If the project is developed block by block, the cost of fencing (which is vital to any land improvement programme) can be spread over several years, grazing can be satisfactorily managed, and increased stock numbers can be progressively reached.