460 



Eradicating Gall Mite (Big Bud). 



[Aug., 



ERADICATING GALL MITE (BIG BUD) 

 FROM BLACK CURRANT STOCKS. 



H. GouDE, N.D.Hort., 

 HoHicultural Adviser to the Norfolk County Council. 



The question of raising clean stocks of black currant bushes 

 has been a problem in horticultural circles for a generation. 

 The failure to do so is undoubtedly the cause of the annual 

 propagation of the disease and its distribution to all districts 

 where black currants are cultivated. The assurance that bushes 

 for planting are free from " big bud " is of little practical 

 value; the important point is whether they are free from 

 " mite." None of the stocks that I have examined during 

 the past seventeen years have been entirely free from " mite." 

 The infestation was seldom so severe as to cause " big bud " 

 in one- or two-year old bushes, but "big bud " would develop 

 as soon as the bushes were subjected to the strain of faulty 

 cultivation, adverse weather, or fruit bearing. The plantation 

 then becomes unprofitable and is usually grubbed up. 



Where a clean start can be made and the plantation estab- 

 lished as far as possible away from all source of infection, the 

 stock would remain free from " mite." Where it is not 

 possible to secure this condition, clean planted bushes have 

 remained free from " big bud " for seven years, even though 

 planted side by side with infected bushes, and have at least 

 six or seven years of profitable hfe before them, proving 

 the value of an absolutely clean start. At the present time it 

 is the exception to see profitable plantations twelve years old. 

 Most cultivators have adopted the method of close planting and 

 grubbing up the bushes as soon as they develop " mite " or 

 " reversion." In this way the establishing cost is a frequently 

 recurring charge on the cultivation of the crop, and what 

 should be the heaviest fruiting years — the fifth, sixth and 

 seventh — in the life of a plantation are lost. 



The unfruitful condition know^n as " reversion " is preva- 

 lent in most plantations. jNIany observant cultivators associate 

 this disease with an attack of " mite." True " reversion " 

 has been observed in seedlings, proving that " mite " is not 

 the sole cause. The toxic effect of the parasite on the sap 

 is a probable contributory factor. The black currant is. like the 

 asparagus plant, very much influenced by checks to growth, 

 and any serious check, or, more particularly, combination of 



