476 



THE MONTHLY BULLETIN, 



COUNTY COMMISSIONERS' DEPARTMENT. 



CRACKING OF PRUNES. 



By Eakl L. Morris, County Horticultural Commissioner, San Jose, Cal. 



Until recently the cracking of prunes has been associated with irregu- 

 lar water supply. The fruit has cracked in orchards which have been 

 irrigated after they have become dry enough to check their growth. 

 During the year 1914, and, to some extent 1915, the fruit cracked from 

 some other cause which has never been explained. The damage was 

 uniform over irrigated and nonirrigated orchards, and was largely con- 

 fined to small cracks on the sides of the fruit. (See Fig. 99.) During 

 1915 the plum aphid, Hyalopterus arundinis, was more abundant than 



Fig. 99. — Showing one form of the crack- 

 ig of prunes in which the cracl<s are con- 

 ned to tlie sides of the fruit. (Original.) 



Fig. 100. — Cracking in prunes, the fruit being 

 split open across the end. (Original.) 



usual and associated with this insect was another form of cracking, 

 generally across the end opposite the stem and often deep enough to 

 expose the pit. (See Fig. 100.) 



While the loss from cracking has never been great we know now that 

 should we have a heavy infestation of the plum aphid it would be very 

 serious. We know, too, that it is exeeedinoly difficult and expensive to 

 attempt to control that insect during foliage. Its attacks are known to 

 be so spasmodic that the sudden increase this season may or may not be 

 an indication of what the condition will be next season. Some orchard- 

 ists will prefer to take a chance. Others will want to protect themselves 

 against a possible future loss. For such, the logical procedure would be 

 to spray with lime-sulphur-tobacco, just as the buds are swelling. At 

 that time the insects are hatching on the tree and can be more easily 

 destroyed than at any other time. 



The writer sees no good reason why the aphis should cause such crack- 

 ing and does not presume to state whether they are the direct or indirect 

 cause. Some discussion of this might prove beneficial. 



