50 



1917 ANNUAL REPORT 



Time When Irrigated. — The evidence on the effect of irrigation 

 is very meager, but there are some observations to indicate that trees that 

 were suffering for water and needed irrigation when the freeze came, suf- 

 fered rather severely, as did also trees that had been irrigated three to five 

 days before the freeze and were thus gorged with water. The least injury 

 seemed to be on trees that had been thoroughly irrigated two or three weeks 

 before the freeze, and had water supposedly in what might be termed 

 optimum amount. This degree of injury, with reference to water condi- 

 tion in the soil following irrigation, was very clearly brought out with 

 citrus trees in the great freeze of 1913 and evidently applies also with 

 the avocado. 



Comparative Hardiness of Varieties 

 The data regarding the comparative hardiness of the different varie- 

 ties is so conflicting that only a few statements can be safely made. 



All observers agree in placing the Mexican varieties as the most hardy, 

 with the Guatemalan varieties coming second and the West Indian and 

 Hawaiian sorts, third. Several cases were reported where a tree of a 

 Mexican variety was more injured than similar-aged trees of Guatemalan 

 varieties nearby, but in all such cases the greater injury of the Mexican 

 tree was apparently due to the sappy, growing condition in which the tree 

 was caught. 



Of the Mexican varieties, the Knowles and Sein Sebastian appear to 

 be slightly the most hardy, but the degree of difference between the true 

 Mexican sorts is very slight. Queretaro, which may be a hybrid and not 

 a true Mexican type, proved rather tender. Puebla, which is thought to 

 be a Mexican-Guatemalan hybrid, in general proved to be about as hardy 

 as the true Mexican. 



Observations on the various Guatemalan varieties were very conflict- 

 ing, and no very positive statements can be made. Apparently, the fol- 

 lowing classification of the degree of hardiness of a few varieties is about 

 correct : 



Most hardy — Fuerte and Lyon; 



Medium hardy — Taft, Spinks, Sharpless, Dickinson, and Challenge; 

 Most tender — Meserve and Miller. 



The following statements of temperature endurance is based on a 

 very large number of observations made in different places and is as nearly 

 correct as can be determined from the data collected: 



30° F. — Nothing injured so far as could be observed. 



29° F. — No injury of account; only traces on most tender growth 

 of West Indian and Guatemalan varieties. 



28° F. — New foliage scorched on Guatemelan t>T3es; West Indian 

 varieties showang considerable foliage damage. 



27° F. — Mexican varieties, with new tips slightly scorched; Guate- 

 malan, with almost all new foHage injured; West Indian- 

 badly damaged. 



25° to 26° F. — Mexican varieties, with new foliage injured but 

 some dormant trees uninjured; all Guatemalan sorts, with 

 new foliage badly injured and some old fohage scorched. 



24° F. — Some dormant Mexicans uninjured; Guatemalan varieties 

 badly injured, small limbs frozen back. 



