CONTROL OF "BROWN HEART" OF TURNIPS AND SWEDES

New Zealand Journal of Agriculture, Volume 63, Issue 2, 15 August 1941, Page 109

CONTROL OF "BROWN HEART" OF TURNIPS AND SWEDES

Experiments are described in this article in the use of borax compounds to control “brown heart” of turnips and swedes without adversely affecting the germination and early growth of swedes. Broadcast applications of 40 lb. borax per acre are recommended.

By

P. B. LYNCH.

Assistant Crop Experimentalist, Wellington. IlitllHllllillllllllllllltilllllltlllllllllllllllllllttllllllllllltlllllllllt

EXTENSIVE experimental work in this country and overseas has amply demonstrated that the disease known as “brown heart” or “mottle heart” of swedes and turnips can be controlled by the application of small amounts of borax to the soil. It can be confidently stated that this disease is due to a deficiency of boron in the soils on which the crop is grown. Despite this, however, two major problems in the .use of borax (which is the most common form in which boron ’I * I 1111 * f■llllllllllllllllll■lll■ll■llll <llllll *■ltlUllltllllllllllllllll

is applied) have arisen, in New Zealand, namely: (1) The amount of borax required to control mottle. heart in some cases approaches that amount which causes severe germination injury, and (2) in some districts and in some seasons only a measure of control is obtained with borax. Severe germination injury from borax is caused by the toxic effect of

too high a concentration of soluble boron compounds around the germinating seeds and young seedlings. The sowing of soluble fertilisers, such as superphosphate, in contact with the seed will also cause germination injury, but this is of a different nature from that due to borax, and may be overcome by the use of superphosphate and lime mixtures, reverted superphosphate or serpentine superphosphate when the fertiliser is drilled in contact with the seed. It is this latter practice of drilling the. seed, manure and borax together that has made the problem of borax injury to

germination of much greater significance in New Zealand than in other countries. Typical borax injury is seen in seedlings with white or yellow cotyledons (or seed-leaves) and in stunted growth of seedlings. Seedlings in the rough leaf stage may be dwarfed, with

wrinkled leaves, and these are often variegated. Such seedlings are easily killed by dry weather or adverse growing conditions, although if they survive they will later turn green and appear normal. Trials have shown, however, that the yield may be seriously reduced due to this early

check in growth. Germination counts have also shown that many seedlings are completely killed, and further, that those surviving . take longer to come through the ground. A typical case is given in the accompanying table.

Trials at Marton

The problems outlined above were investigated in a series of experiments at the Marton Experimental Area over the past three years. The methods of approach were as follows: — (1) The search for other more slowly soluble compounds of boron than borax or the use of mixtures of borax and inert materials. (2) The effect of increasing the rate of seeding. (3) The resistance to germination injury and to mottle. heart attack shown by different swede varieties. (4) The method of placing the seed, manure, and borax in the soil. , (5) The effect of soil moisture and season. ' (6) The effect of time of sowing the seed. (7) The effect of applying borax at different times before and after sowing. , ‘ ' The results of ' a large number of trials, some hand-sown . and some drilled,, may be summarised as follows: (1) No compound of boron was discovered which was sufficiently available to the plant to control the disease - while at the same time giving no injurious effects when sown with the seed of swedes and turnips. Compounds tried were “rasorite” (a more concentrated form of borax), calcium borate (borax is a sodium borate), recrystallised borax (in large crystals), various pellets of a clay (bentonite) and borax, and various mixtures of borax with fertilisers and various rates of application of these, but none of them was significantly different from commercial borax in effect on germination. . > ’ (2) Kate of Seeding. lncreasing the seeding rate per acre when drilling

with borax in contact with the • seed gave a greater number of plants per acre. . Although in some cases lighter seedings resulted in higher percentage germination figures, these increases were not sufficiently great to compensate for the lower number of- seeds sown. Increasing the rate of seeding may, therefore, provide a means not of reducing germination injury, but of securing a sufficient number of residual plants in the field. (3) -Variety of Swede. — Vilmorin and Wilhelmsburger. appear to be slightly more resistant to mottle heart attack than Superlative and Sensation, although for some reason Vilmorin was in one trial the most severely affected by germination injury. (4) Placement of Manure and Borax. —Severity of germination injury is directly related to the amount of borax that comes in contact with the seed. The most successful treatments were broadcasting and application in bands 1 to 1-i in. to , the side of the seed in the drill. In the absence of suitable implements it is therefore recommended that borax be applied broadcast. (5) Effect of Soil Moisture and Season.— The greatest germination injury is found in a dry season, but, nevertheless, heavy rain shortly after the borax is applied appears to leach the material through the soil so that there may be little control of the disease. This was particularly marked in the trials in the 1939-40 season, when the infection of mottle heart was severe on all treatments. If very heavy rain falls shortly after applying borax it may be advisable to broadcast a second application. (6) Effect of Time of Sowing the Seed. This is directly related to the above factors of climate and soil moisture. (7) Effect of Applying Borax at Different Times.— Application of borax during or shortly after sowing may be superior to application well before sowing, but the effect of rainfall in relation to time of application may have been the deciding factor. It has been demonstrated that application may be made as late as the roughleaf stage of growth and yet give satisfactory results.

Amounts of Borax To Apply

The two graphs are taken from the results of a ' trial in the present season; and indicate that 40 lb. of borax per acre applied broadcast has given the best yields and also satisfactory

control of mottle heart.. Although the measure of control of mottle heart was by no means complete even with application of 50 to 60 lb. of borax per acre, the results • are of practical significance, for individual bulbs showed little severe infection with applications of 40 lb. of borax per acre and over. ■

Summary

The following recommendations may be made with regard to the use of borax in the control of mottle heart of swedes and turnips. '(■ ■. (1) Broadcast 40 lb. of borax per acre shortly before or after sowing. If heavy rain follows the application, it is safest to repeat the topdressing. ' - (2) Use heavy rather Than light rates of seeding. (3) i Wilhelmsburger andVilmorin swede varieties , may be used where the disease is known to be severe. However, the problems as outlined earlier are by no means completely

solved, and further intensive work is needed to supply the answer to a number of practical questions in connection with the use of borax in controlling the disease. The production of a compound of boron which can be safely drilled with the seed to con-

trol brown heart without affecting germination should be the first objective. The acreage annually devoted to turnips and swedes and the widespread and often severe losses caused by the disease undoubtedly justify the carrying out of additional research. Under

the present conditions, however, there are more urgent problems which demand immediate attention, and future intensive work on the problem has therefore been postponed in the meantime.

Treatments per acre.. Percentage germination on Dec. 30, 1938 Jan. 12, 1939 Super 3 cwt. ' . . : . 45 45 Super 3 cwt. + borax 15 lb. . . 32 40