135 



excessive fertilisation or to improper soil conditions, and it is probable 

 that the real cause will be found to be the same in both cases. Both 

 forms of the disease appear to be greatly aggravated by excessive cul- 

 tivation, which apparently destroys the sarface roots and forces the 

 tree to feed lower down. 



Treatment. — When die-back is due to the excessive use of highly 

 nitrogenous organic fertilisers, an effective remedy consists in simply 

 ceasing to cultivate and allowing all weeds to grow. In fertilising, 

 omit entirely all highly nitrogenous organic manures, but use about the 

 normal quantity of potash and phosphoric acid. As the tree recovers 

 a small amount of nitrogen should be given, preferably in the form of 

 nitrate of soda or sulphate of ammonia, until the tree is brought up to 

 its normal condition. If the disease is produced by the close proximity 

 of privies, chicken houses, barns, etc., removing these will usually 

 result in the recovery of the affected trees. In the case of barns 

 which can not be removed it has been found effective in some cases 

 to dig trenches between the trees and the barn to prevent the feeding 

 roots from running under the former. Of course the caution in regard 

 to the use of organic nitrogenous feJtilizers given above is applicable 

 in this case also. When the malady is caused by planting on die-back 

 lands, treatments vary according to the character of the soil. If the 

 grove is on low, wet soil, through drainage will usually be found an 

 effective remedy without other treatment If the soil is underlaid 

 with hardpan, mulching the trees with pine straw, oak leaves, or some- 

 thing of this nature, and stopping cultivation will allow the f eedin g 

 roots to develop near the surface and usually bring about a cure. The 

 latter has been found an effective treatment in many instances. Good 

 drainage is also beneficial in such cases. 



SCAB OR VERRUCOSIS OF THE LEMON AND OTHER CITRUS FRUITS. 



The introduction of this disease into the United States is compara- 

 tively recent. It first appeared in Florida about the year 1884 and 

 spread rapidly over the State and to Louisiana. Although many 

 thousands of trees affected with scab have been sent to California, it 

 seems that the nisease is unable to exist there permanently. The rea- 

 son for this will appear later. The malady also occurs in Australia 

 and Japan, from which latter country it was undoubtedly introduced 

 into America. So far it is not known to occur in Europe or Africa. 

 The first account of the disease was publishe i by F. Lamson-Scribner 

 in October, 1886 (Bulletin of the Torrey Botanical Club, New York, 

 Vol. XIII, No. lU, pp. 181-183), at which time Professor Scribner was 

 Chief of the Section of Vegetable Pathology of the Department of 

 Agriculture. A fuller account, with a coloured plate, was published in 

 the Annual Report of the Commissioner of Agriculture for 1886, pp 120, 

 121. A disease undoubtedly the same was reported from Australia 

 on orange and lemon leaves by Henry Tyron. {^} 



The principal loss from scab occurs in Florida, where it often renders 

 lemon groves so unprofitabie that they are cut off and budded to other 

 citrus fruits. In many cases a very large percentage of the fruit i* 

 rendered unsaleable, sometimes one-third or even one-half being unfit 



(1) Report on Insect and Fungous Pests, No. 1, Queensland, 1889, pp. 144, 145. 



