1912.J Summary of Agricultural Experiments. 1037 



Weeds, Insect and Fungus Pests. 



Tall Oat Grass and Onion Couch (Jour. Agric. Sci., January, 1912). — 

 One of the commonest grasses in this country is Tall Oat Grass 

 (Arrhenatherum avenaceum, Beauvais), and it is occasionally included in 

 the "seeds" mixture for temporary or permanent pasture. In some 

 localities a form of this grass, known as Onion Couch [or Knot Grass 

 or Pearl Grass], becomes an extremely objectionable weed on arable 

 land. This plant is identical in appearance with Tall Oat Grass, except 

 that at the base of the stems a chain of bulbs is formed. Each bulb 

 is capable of giving rise to a new plant, and as cultivation merely 

 breaks up the chain of bulbs, the weed is extremely difficult to eradicate, 

 while a liberal supply of seed is formed in June and July. 



Botanists differ as to whether the Tall Oat Grass and the Onion 

 Couch are distinct species, or whether the bulbous form is assumed 

 as a result of variation in conditions of habitat. 



To test this point, seeds of Onion Couch were gathered from various 

 localities and sown by Miss L. M. Underwood at Rothamsted in various 

 soils with different amounts of moisture, shade, and at different rates. 

 The two kinds of seed, which were indistinguishable, were sown in 

 September and were well up before winter set in. Bulbs began to appear 

 in the following March, and by May all the pots sown with seed from 

 the Onion Couch were producing chains of bulbs, while the plants 

 from Tall Oat Grass Seed remained normal. 



It is concluded that the habit of forming bulbs is hereditary, and 

 does not depend on the conditions of the habitat. Except for the bulbs, 

 no difference could be noted between the two plants. 



Investigations on Potato Diseases (Jour. Dept. of Agric. and Tech. 

 Inst, for Ireland, January, 1912). — The Third Report, by Mr. G. H. 

 Pethybridge, gives an account of the work done in 191 1 at the tem- 

 porary research station at Clifden, Co. Galway. Owing to the excep- 

 tionally dry summer, comparatively little damage was done to the potato 

 crop by the various diseases, and the investigations were therefore 

 carried out under unfavourable conditions. Various experiments were 

 made with regard to the prevention of ordinary "blight" or potato 

 disease (Phytophthora infestans, de Bary), and the results may be 

 summarised as follows : — 



(1) Bordeaux mixture made with lime was slightly more effective 

 than when soda was used, though it is pointed out that the mixture 

 with soda is more easily prepared. 



(2) The plots sprayed twice, starting late (July 17th), were least 

 attacked by disease. This was owing to the dry July and August, in 

 which disease made little headway, but it did develop in the wetter 

 September, and the latest sprayed plants were better fitted to resist it. 

 The conclusion previously arrived at — that spraying prevents disease best 

 when done before a period of wet weather — is thus confirmed. 



(3) Even in a dry summer like 191 1 spraying was effective and profit- 

 able, not only in the West of Ireland, but also in the drier climate of Co. 

 Dublin, where it resulted in an increase in total crop of about two tons 

 per acre, and reduced the proportion of diseased tubers. 



(4) Lime-sulphur spray was found to be utterly useless in warding off 

 the disease. 



(5) Soaking " seed " in copper sulphate solution and in Bordeaux 



