May, 19 19 



BETTER FRUIT 



Page 9 



TABLE I 



•Applications made according to above schedule. 



TABLE III— RESULTS OF SPRAYING JONATHANS 



Lime-Sulphur Summer Spray for Apple Scab 



By C. C. Vincent, Horticulturist, University of Idaho, Moscovy 



TY/^HILE the apple scab is unknown 

 W at present in the fruit districts of 

 Southern Idaho, it is quite prevalent in 

 the fruit sections of Northern Idaho, 

 where the rainfall is from 18 to 25 

 inches per year. In fact the apple scab 

 is probably the most serious fungus 

 disease with which the fruit grower in 

 Northern Idaho has to contend. This 

 loss is far greater in these districts than 

 is generally appreciated by the ma- 

 jority of the growers. 



In many of the unsprayed orchards 

 from 10 to 75 per cent of the crop is 

 unfit for sale due to the presence of the 

 scab fungus. Financially this is a dis- 

 tinct loss to the growers, for under the 

 provisions of the State Horticultural 

 Laws of Idaho, it is a violation of the 

 law to place upon the market scab- 

 infected fruit. Aside from the losses 

 which iTiay occur in the reduction of 

 the quality of marketable fruit other 

 losses of scarcely less importance may 

 result, such as premature dropping of 

 apples, reduction in the size of the fruit, 

 dropping of scabby apples before pick- 

 ing, impairing the health and vigor of 

 the trees, etc. 



The ever-increasing difliculty of many 

 of our growers to control the apple 

 scab caused the Horticultural Depart- 

 ment of the University of Idaho to 

 carry on experiments to determine a 

 safe and effective method of control. 

 The schedule adopted was as follows: 



(1) To ascertain the value of lime- 

 sulphur as a summer spray for scab. 

 (2) To determine the number of appli- 

 cations needed to hold the scab in check 

 when applied according to the follow- 

 ing schedule: 



1. When the blossom buds show pink. 



2. WTien the petals fall. 



3. Three weeks after the petals fall. 

 To control the codling moth, arsenate 



of lead was added to the second and 

 third application. The lime-sulphur 

 used in making these tests was diluted 

 according to the following table: 



6 per cent; Jonathans from 52 per cent 

 to 7 per cent; Romes from 48 per cent 

 to 17 per cent; Grimes from 24 per cent 

 to 1 per cent. A fourth application of 

 lime-sulphur made nine weeks after 

 the petals fall for one year only gave 

 the following results: On Wageners, 

 same result as when three applications 

 were made. Grimes Golden, no reduc- 

 tion over three applications; Rome, re- 

 duced from 30 per cent to 21 per cent; 

 and Jonathan from 9 to 8 per cent. 

 The fourth application is not necessary, 

 therefore, on such varieties as Wagener, 

 Jonathan and Grimes. Should rainy 

 weather continue throughout the sum- 



A THREE-YEAR AVERAGE OF SPRAYING TESTS SHOWS THE FOLLOWING RESULTS 



TABLE II— RESULIS OF SPRAYING WAGENERS 



TABLE IV— RESULTS OF SPRAYING ROMES 



TABLE V— RESULTS OF SPRAYING GRIMES 



A study of the above data would in- 

 dicate, therefore, that with most varie- 

 ties, one and two applications of lime- 

 sulphur are not sufficient to hold the 

 fungus in check. The Grimes, how- 

 ever, seems to be quite resistant to scab 

 infections, hence one application made 

 at the time the buds are showing pink 

 should reduce the fungus to a negligible 

 quantity. I am led to this conclusion 

 by data secured during the three-year 

 period. 



Three applications of lime-sulphur 

 reduced the infection on Wageners 

 from 58 per cent in the check plot to 



mer, this application might be neces- 

 sary. To reduce the scab infection on 

 the Rome to a minimum, four applica- 

 tions are necessary under normal con- 

 ditions. 



In view of the fact that many of the 

 scab spores winter over on fallen 

 leaves, etc., I would suggest that sani- 

 tary measures be followed, as it will 

 assist materially in the spraying opera- 

 tions. To lessen, therefore, the danger 

 from primary infection, fallen leaves 

 should be plowed in the fall or early 

 spring, rotten apples and dead branches 

 Continued on page 24. 



FiGURK 1 — Showing characteristic scab spots on the fruit. 



6 per cent scabby. 94 pcr cent clean 



Figure 2 — Results with three applications of lime-sulphur. 

 Wagener variety 



