HOLD-OVER BLIGHT IN THE PEAR 
BY WAI/TER G. SACKETT 
There seems to be some difference of opinion among the fruit 
growers in this state as to whether the microorganisms which produce 
fire blight in the pear, apple, quince and apricot can live through the 
winter in the diseased limbs, twigs and fruit of the previous season 
under Colorado conditions and still retain their virulence in a degree 
sufficient to start off a new attack in the spring. Practically all agree 
that the hold-over form of the malady exists in the old cankers of the 
trunks, such as are found in the Ben Davis tree, and most of them are 
familiar with the characteristic oozing of the sticky gummy material in 
the spring, but the disagreement which has arisen has been concerning 
its persistence in the smaller limbs and twigs. 
On the one hand, if the germs can survive the cold weather 
and the drying, then there is the greatest necessity for thorough in¬ 
spection and careful removal and destruction of every infected portion 
of the tree before any new growth begins; on the other hand, if the 
causal organisms are destroyed by natural agents, there could be a 
big saving of labor at the time of the year when the orchardist’s 
services are in demand for the routine pruning. He would not 
feel the urgent need of cutting out the blighted wood before doing 
anything else, and could postpone this to a more opportune time. 
Furthermore, the usual precautions to disinfect the tools and freshly 
cut surfaces, when working in blighted material, would be unnecessary, 
and there would be no objection to removing the diseased limbs 
while the general pruning was being done, so far as spreading the 
contagion is concerned. 
It is not at all uncommon to find in the literature on this sub¬ 
ject such statements as the following: “the germs gradually die, due 
to drying out of the canker so that at the beginning of the dormant 
season very few * such cases show live germs present“The key to the 
whole situation is found in those cases of active blight (comparatively 
few) which hold over”; “These few cankers in which the bacteria 
survive the winter are called ‘hold-over’ cankers.” The writer is 
likewise guilty of having made a similar statement in a former pub¬ 
lication, not upon its own authority however, but from information 
furnished him by a well known horticulturalist, familiar with Colorado 
conditions. Everywhere the tendency has been to underestimate 
the prevalence of hold-over blight, in spite of the recognized fact 
that were it not for this form of the disease, blight could not be carried 
from one season to another. 
* Italics by author. 
