TII K NATIONAL N URSK R Y M A N 
410 
Methods of Prevention of Tree and Plant Diseases 
All address delivered before the Seventh Annual Convention of the California Association of 
yurserymen at San Jose, October 10-13, 1917, by Earl L. Monas, County llorticulturat 
Commissioner, San Jose, Cat. 
T IIR subject on which I have been asked to say a 
few' words is “Tlie AFetliods of Prevention of Tree 
and IMant Diseases.” It is intended, I take it, 
that this subject he treated from the standpoint of the 
nurseryman. This limits the discussion because, of the 
many tree and j)lant diseases, comparatively few' etleet 
vouiiij: trees hv the time thev leave the nurserv. At 
least if such young trees are atl’eeted it cannot be known, 
lienee is a ease of “Ignorance is bliss.” I shall con¬ 
sider four conditions which may occasionally he met in 
trees about the transition stage from nursery to orchard; 
namely, crow n gall [Pseudomonas tumefaciens) , oak 
fungus (Armitlaria mettea), sour sap, and hlackheart. 
Crown gall, well known to all of you, is caused by a 
micro-organism and the condition is termed a bacterial 
disease. It has been studied long and carefully yet w^e 
know' next to nothing of methods of prevention or cure, 
and little concerning methods of distribution. Ground 
badly infested with this organism should not he used for 
nursery ]mr{)oses, or in fact for growing or propagating 
anything known to he susceptible to the disease. In 
some eases it seems to he indigenous to virgin soil. About 
the only sure way to determine whether or not soil is in¬ 
fested is to grow the nursery stock and note the size of 
the bonfire at the harvest. However, it is certainly far 
w iser to use virgin soil than old soil which is known to 
he infested. Since this disease is almost universally 
distrihnted. and may he found in practically all orchards 
and all nurseries, the only thing is to sort out and burn 
the trees with knots or galls on the main roots so near the 
trunk that they will not he removed by the usual root 
])runing required at planting. By some this may not 
seem an orthodox procedure. However, the tree on 
w hich a gall may he situated w ell out on the root w here 
it must he removed w hen the root is pruned is not essen¬ 
tially different from an adjacent tree, the gall on which 
was severed by the tree digger and left in the ground, or 
yet another tree apparently clean which may have an in¬ 
cipient gall in a more injurious location, hut so small it 
cannot he seen at all. The grower has a right to expect 
trees apparently clean. The nurseryman should deliver 
trees apparently clean, hut farther than that, in the case 
of crow n gall, neither party can go w ith any degree of 
accuracy. 
Oak Fungus {Armillajaa motlea) 
Oak-fungus is a disease hut rarelv found in nurseries 
for w hich we may he indeed thankful since it is as fatal 
to plants as is tuhei’culosis to animals. It is a toad stool 
fungus growing as a white felty mass between the hark 
and wood of the roots and trunk under ground. Some¬ 
times it takes the form of black or brown strings about 
the size of tw ine and creeps along the outside of the hark. 
About December in this locality it may show as a mass 
of large brow n toadstools usually at or near the base of 
a tree or where an old root comes near to the surface. 
While it is called “Oak fungus” it is not at all confmed 
to the oak hut infests most of our forest trees more or 
less. Nurseries planted along creeks, or on cleared 
land, or where large trees once stood, mav occasionallv 
have a few' infested trees. There is no known remedy. 
Inspection is the only safeguard. Have some one who 
know s the disease go through the nursery thoroughly and 
map out any diseased area and burn any diseased trees. 
Usually the loss to the nurseryman is very little, not 
more than ten or fifteen trees hut should one of those 
trees he planted in an orchard and start an “oak fungus 
spot” the orchardist would continue to lose trees during 
the entire lifetime of the orchard. That “oak-fungus” 
is found in an orchard is no proof that it was carried 
there on nursery stock. On the contrary most infesta¬ 
tions can he traced hack to diseased native trees which 
once grew there. 
Sour Sap 
Sour sap is a term used to indicate a condition not ne¬ 
cessarily a disease. Any injury to the camhium or 
growing layer between the hark and the wood which 
kills the tissue may result in the souring of the sap. The 
sour sap condition which I shall describe, and which 
causes the greatest annoyance to both nurserymen and 
orchardists. is undoubtedly caused by sudden climatic 
changes. It might he expected after a freezing tem])era- 
ture in the early morning followed by warm sunshine. 
Young orchards, and especially young apricot orchards 
from one to three years old. may fail to start in the 
spring, or having started die in from thirty to sixty days. 
In either case the roots may he in good condition and an 
examination of the above ground portion reveals a dead 
sour camhium layer nearly or quite surrounding the tree 
generally near or at the ground. Usually in such cases 
a vigorous shoot appears just above the union which w ill 
make a large tree much quicker than one can he grow n 
from a replant since the root system is already estab¬ 
lished. If for reasons to he discussed later it seems 
best to replant there need be no fear of a fatal disease 
passing from the dead tree to the replant in the same 
hole. If a tree is grown from the old root and new' 
shoot the giTat danger is that fungi causing w ood decay 
may find entrance where the dead stump has been re¬ 
moved before the new' growih has closed over it. and 
that in ten or fifteen years the tree w ill he weak at that 
point. Great care must he taken to protect the wound 
and even then there is danger of infection. 
^Yhether it is best to try to make a tree from a sound 
root which has been in orchard form more than one year, 
if the whole to]) must he removed, or whether it is best 
to replant, can he determined only by future ohsen'ations. 
That a good growth will come from such a root is cer¬ 
tain, however, two years time and the cost of trees and 
labor is veiy little compared w ith the possible loss of 
trees after they have come into full bearing. There do 
