DECIDUOUS FRUITS 193 



account of the large size the trees attain, they are planted 

 farther apart than are other orchard trees. They are propa- 

 gated by budding or grafting the best varieties of Persian 

 walnuts upon black walnut stock. 



When the walnuts become mature on the trees, most of 

 them drop and are picked up by hand. Those which do not 

 drop are shaken from the tree by the use of poles with hook? 

 at the ends. Many of the nuts drop free of the hulls and 

 those which do not are hulled by hand or are run through a 

 revolving cylinder which removes the hulls readily. The nuts 

 are left to cure in trays or in well-ventilated drying bins for 

 a few days. After the curing process, the nuts are sorted and 

 are bleached by being run through a bleaching solution. They 

 are then graded according to size and are ready for marketing. 

 Most of the Persian walnut crop in this country is placed on 

 the market by a cooperative association of growers known as 

 the California Walnut Growers' Association. 



Blight is a common disease affecting the walnut. This 

 bacterial disease is especially destructive to the young and 

 tender growth and to the nuts. When blight attacks the 

 nuts early, they turn black and drop, and when it attacks 

 them later their development is hindered. The walnut aphis 

 is a troublesome insect pest. It is controlled by applying a 

 nicotine dust preparation (made of nicotine dust mixed with 

 finely powdered kaolin) by means of a dusting machine. In 

 recent years the codlin-moth has been troublesome, the larva 

 of which enters the nuts. 



285. The pecan is native to the United States. Wild 

 forms are found in several of the southern states in the 

 Mississippi basin. From these a number of excellent varie- 

 ties have been derived. The pecan has become one of the 

 most popular of the nuts and the best varieties sell at good 

 prices. It is planted widely in southeastern United States, 

 the most extensive plantings being in Georgia, Alabama, and 

 northern Florida. As pecans do not come true to seed, the 



