PRCDUniNG VIRU3-FREF STRAV»'3ERRY rUNTS i:.' ENGLAriD 



5^traT;berry growers in England have some of the same troubles as grovrers in Lhic 

 country. Anong the more serious cf these are virus infections. Four strains of 

 viz'us have been recogni::ed, each of which can be identified by inoculation into 

 the Alpine stravfberry, Fragaria vesca , which grows wild in England. The virus 

 situation becane serious enough and the denand from grovrers insistent enough so 

 that a very interesting method has been developed for suppljdng virus-free plants. 



A single virus-free plant was found and taken to the Experiment Station at 

 East I.ialling. From this single plant virus-free runner plants are produced. These 

 are sold to strawberry plant propagators who dc nothing but produce strawberry 

 plants. They never produce any fruit. These propagators increase the plant supply 

 by what is called the isolated block method. The plants are set in a double row 

 and the runners from four plants trained to the center of the square formed by 

 these plants. Thus, the field becomes a checkerboard of these squares or blocks 

 with two foot paths between them. If one of these blocks becomes infected, it can 

 be removed at once without infecting ether blocks. These stock nurseries must be 

 at least a mile from any commercial stravfberry planting. The beds are lumigated 

 7vith nicotine to keep their, free of aphids vrhich transmit the virus. Tv^'ice during 

 the s'jmraer the stock nursery is inspected 'oy a representative from the ministry cf 

 Agriculture. If it passes inspection, a special stock certificate is used. As a 

 further precaution these stock nurseries must renexi their stock from the original 

 source at East Mailing every three or four years. 



naturally the plants produced by the plant propagators are high priced; too 

 high priced to be sold to the grower. They are sold to nurserj'Taen with an ordinary 

 license v^ho produce plants for the stravfberrj' grov/er. This may seem like a costly 

 and time consuming way to produce strawberry' plants, but it gets results. 



— J. S. Bailey 



irjFECTiGN A:ra incubation periods k-r apple scab 



Infection Period ; In the case of primary infection of apple scab, an infection 

 period is an overall period of sufficient vretness to allow discharge of ascospores 

 from the overv,rintered leaves, their disseminati'^n to green leaves and fruits, their 

 gennination, and penetration far enough to establish infection. Length of such 

 a wetting period varies with the temperature. A v/et period Vi'ith insufficient water 

 or insufficient length to permit ascospore discharge, dissemination, germination 

 and penetration vrould not be an infection period. Intennittent rain periods may 

 constitute an infection period provided not more than 3 hours of drying occurs 

 between the wet periods. 



For secondary infections by the summer spores (conidia) of apple scab, an 

 infection period implies a vretting of sufficient duration for dissemination 



(dripping and wind-blovm in rain) , germination and penetration by the suimaer spores. 



It may be only about tv;c- thirds the length of the earlier primary infection periods. 



Table 1 indicatec the relationship between time and temperature requii-ements 

 for primary infection in orchards vfith medium to heavy scab carryover. 



