30 
Colorado Experiment Station 
may be either hard or soft. In some instances instead of galls large 
bunches of small fibrous roots are formed. This gives rise to the 
name ''hairy root” which is sometimes applied to the disease. 
Crown gall is caused by bacteria which live in the tissues of the 
plant stimulating it to abnormal growth. The same bacteria may 
cause galls on many other plants besides the apple. 
Plant only disease free nursery stock and destroy all infected 
plants. Avoid injuring the roots in any way. In grafting care 
should be taken to use root and scion of approximately the same 
size. Most states have horticultural inspectors who inspect all 
nurseries at least once a year, and condemn all infected stock. This 
greatly aids in controlling the disease. 
Nitre Injury (14), (15) — As stated in Part I of this bulletin, cer- 
tain Colorado soils have the power of fixing atmospheric nitrogen in 
excessive quantities. The accumulation of large quantities of nitrates 
in the soil in this way is extremely injurious to many plants. The 
apple is extremely susceptible to nitre injury. 
The leaves of affected trees have a characteristic appearance. A 
burning and drying begins at the tip and progresses rapidly along 
the margin and finally involves the entire trees and even whole 
orchards are completely killed. The process is a rapid one, whole 
trees being killed in a period of three weeks. Injury frequently fol- 
lows irrigation. The Avater of irrigation brings the nitrates into solu- 
tion, the condition in w^hich they are the most injurious. 
It has been shown that clean cultEation tends to hasten the 
accumulation of nitrates. PloAving under of cover crops is said 
to be an effective means of checking the formation of nitrates. This 
not^ only retards the accumulation of nitrates but vegetable matter, 
Avhich is needed by the soil of most orchards, is added. 
Good drainage is also an important factor in preA^enting nitre 
injury. Well drained soil Avill often take off sufficient nitrates in 
solution to prevent excessive accumulation. 
Experiments have shoAvn that soils containing large amounts of 
nitre and on AAdiich nothing Avill groAV, can be reclaimed by flooding. 
Flooding is accomplished by preparing the ground in the usual 
manner for soAving grain. The area to be flooded is surrounded 
Avith an embankment of earth and Avater is led into the enclosure so 
that the entire piece of ground is covered to a depth of several 
inches. As the Avater see])s into the soil and drains off moi-e Avater 
»hould be supplied keeping the surface covered for ten days. In this 
