1070 
not killed by gophers or mice, it is safe 
to conclude that it is often caused by 
the attacks of these animals. 
Crown Gall on Almond 
+R. E. Smith reports crown gall on the 
almond in California as somewhat serious. 
“Large swellings appear on the main 
roots just below the ground and to some 
extent on the smaller roots. This results 
in a gradual failure and dying of the 
trees. This is one of the commonest 
troubles of our stone fruit trees, being 
found both in the nursery and on the 
mature orchard soils. The organism 
would seem to be abundant in California 
soils, since cases are not rare of infec- 
tion on the roots of trees grown from 
pits in virgin soil.” 
Woolly Aphis Galls 
*R. I. Smith, in treating the subject of 
woolly aphis, says: “The woolly aphids 
occur in damaging numbers, principally 
on the roots, and are responsible for the 
stunted, unhealthy growth and even death 
of hundreds of apple trees each year. In 
spite of this, their presence often remains 
unnoticed except by orchardists who give 
strict attention to the condition of their 
trees. The extent of the damage must be 
far greater than is commonly supposed, 
when the number of infested trees in nur- 
sery blocks, together with those in both 
young and older orchards is considered. 
In short, the woolly aphis is one of the 
most serious apple pests, ranking with the 
San Jose scale and the codling moth. 
For DESCRIPTION OF WooLLy APHIS, see 
Aphids. 
Similar to all plant lice, the woolly 
aphids subsist on the plant juices, feeding 
by means of piercing and sucking beaks. 
Wherever they feed, galls of greater or 
less size are produced, the exact reason 
for which is not fully understood. It is 
due probably to some poison injected by 
the insect into the tissue of the plants. 
The galls formed on the soft root tis- 
sue are of large abnormal growths which 
soon commence to decay, their destruc- 
tion being hastened by the entrance of 
218 California Experiment Station, Bulletin 
a North Carolina Experimen - 
tin DOR periment Station, Bulle 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
fungi and bacteria. As the roots weaken 
and die, the aphids die also, or move to 
other roots, so that when looking for the 
first time for signs of woolly aphis, one 
may find badly injured roots from which 
the insects have all disappeared. By 
further search, live aphids may be discov- 
ered on the few live roots remaining, or 
close by the trees. The continual weak- 
ening and rotting of the infested roots is 
what renders woolly aphis damage so 
disastrous. The drain on the vitality of 
the tree soon results in a sickly dwarfed 
appearance of the root. 
Nematode Root Gall or Root Knot 
*The nematode is not an insect nor is 
it related to the insects. It belongs to 
the class of animals known as vermes or 
true worms. The common earth worm is 
the best known example of the class, al- 
though it occupies a position in a high- 
er group than that of the nematodes. 
There are a good many species of nema- 
todes, some living in the ground, some 
parasites on animals, and a few live para- 
sitically on plants. Often in moist soil, 
rich in humus, such as vegetable gardens, 
there may be large numbers of white 
transparent worms. These are nematodes 
however, that do no appreciable injury to 
plants, and it is only the parasitic species 
of which this subject is an example. 
The Heterodera radicicola is widely dis- 
tributed over the world and attacks large 
varieties of plants. In the Argentine Re- 
public it is said to be the most destruc- 
tive pest of the vine occurring in that 
country. In the United States it is chiefly 
destructive in greenhouses. 
This parasitic species is an exceedingly 
small worm-like creature about one-sev- 
enty-fifth of an inch long, and of a trans- 
parent whitish color. It has a sharp slen- 
der organ on the head that enables it to 
make its way into the more tender por- 
tions of the roots, where it embeds it- 
self in the tissues. Here it develops and 
lays eggs, from which succeeding genera- 
tions arise. These may scatter through 
the soil and attack other portions of the 
roots. It is not so much the direct drain 
upon the roots, however, that causes the 
Quavle, Calltornis Experiment Sta- 
* FH. 
tion Bulletin No. 192 
