1921. Babbebbi and the Black Rust of Wheat. 123 



may be practically a total loss. The statistics for the year 

 1919 give the area under wheat in the counties of Carmarthen, 

 Cardigan and Pembroke as 22.000 acres, and much of this wheat 

 land must fall within the range of influence of the barberry, so 

 that the loss directly attributable to the latter is in the aggregate 

 very considerable, even assuming that the existence of the 

 barberry is not, as many now believe, an absolutely essential 

 condition for the existence of the disease on wheat. 



Summary. 



1. It is ascertained by means of the survey that the common 

 barberry is widely and plentifully distributed in Carmarthen- 

 shire, Pembrokeshire and South Cardiganshire. The cluster- 

 cup stage of the black rust fungus is abundant on the barberry 

 in spring and early summer'. 



2. On the wheat black rust may be said to be generally 

 distributed over the same area, and causes serious losses every 

 year. In certain seasons the attacks are very severe. 



3. Wheat is regarded as a risky crop in these counties, and 

 is certainly not a paying one in barberry areas. As a result 

 there is a reduced acreage under wheat, and this is diminishing. 



4. The common barberry is the alternate host of black rust, 

 giving the fungus a good start each spring. In several con- 

 crete cases field-observations showed that the disease was 

 most intense near the bushes and had started from them. As 

 long as barberry is allowed to remain it will be a constant source 

 of infection, not only to the adjacent wheat fields, but to other 

 fields on which the summer spores from the wheat will be 

 blown. 



5. In more than one case, the removal of barberry bushes 

 resulted in slighter attacks on adjoining fields than in the 

 previous season, but until barberries are eradicated on a whole- 

 sale scale no complete elimination of the disease can be expected, 

 owing to spores blowing from other fields. Every bush destroyed 

 means so many less initial infections and the fewer the infections 

 the better will be the wheat crop. 



6. Black rust is very scarce in all other parts of the British 

 Isles and there appears no reason to doubt that if the barberry 

 w r ere exterminated in Wales the annual attack of black rust on 

 wheat would subside. This method was adopted in Denmark 

 eighteen years a<zo. and black rust in that country has now 

 practically ceased to exist. 



