330 THE MONTHLY BULLETIN, 



COUNTY COMMISSIONERS' DEPARTMENT. 



APRICOT GUMMOSIS AND SOUR SAP— REPORT ON OBSERVA- 

 TIONS AND INOCULATION EXPERIMENTS. 



By Leonard H. Dat, County Horticultural Commissioner, HoUister, California. 



Disease of the apricot tree, accompanied by more or less copious 

 gumming, is very common in the coast regions of California. On 

 taking up his work in San Benito County in the winter of 1907-1908, 

 the writer found that one of the most common calls for information 

 on the part of apricot growers was in relation to what they called sour 

 sap and black heart, the two forms of gumming which they recognized 

 as separate troubles. The latter term was applied to that disease in 

 which dark streaks develop inside the wood, and the former to various 

 gumming manifestations of the bark which appeared to kill the tree or 

 limb affected, either cjuickly or slowly. It seemed apparent that by 

 the term sour sap the growers were covering several entirely distinct 

 diseased conditions. Fielcl studies of these troubles have- convinced the 

 writer that several distinct parasitic diseases, in which gumming is 

 the first externally evident sympton, are commonly classed as sour 

 sap. In fact, he feels safe in asserting that true souring of the sap 

 is of comparatively rare occurrence in this district. 



Among the first cases of sour sap to which the writer was called 

 for consultation was in a twelve or fourteen year old apricot orchard, 

 where over a hundred trees had, shortly after growth started in the 

 spring, suddenly sickened and died. Pints of sour-smelling gum had 

 exuded from the trunks. Close examination revealed large plow scars 

 on the crown, and roots of considerable size broken in recent plowing 

 operations. Very few of the healthy trees bore these sears and broken 

 roots. It seemed very evident that here was a case of an infection. 

 The soil moisture conditions were excellent, as far as we could .iudge. 

 In some trees soured gummy areas of bark extended some distance 

 around these wounds, but had not girdled the tree sufficiently to cause 

 them to wilt. Many isolated cases of ''sour sap" developed at this 

 time in the orchards about the valley — both young and old trees being 

 affected. 



This and subsequent observations led the writer to suspect fungous 

 or l)acterial origin of most of the common forms of gumming and 

 "sour sap" in apricot trees. This conviction was strengthened after 

 Fawcett had traced the gummosis of citrus trees to definite fimgi. The 

 fimgi M-hich the writer has suspected of being the causal agent of 

 certain forms of gumming, including the case above recorded, are 

 Sclcrofinia Ubcrfiana and Botrytis vulgaris, both of which R. E. Smith 

 (California Experiment Station, Bulletin 218), holds to be the cause 

 of the blossom rot of the green apricot fruit early in the spring, and 

 Sclerotinia fructigena, the causal agent of the brown rot of the' ripe 

 fruit. Some seasons one or both of these diseases of the fruit are 

 quite prevalent here and in certain cases produce disastrous results, 

 destroying not only a large amount of the fruit, but continuing the 

 infection into and killing the fruit spurs on which the rotting fruits 

 are located. This latter contingency is especially common with the 



