most economical and least difficult to incorpo- 
rate into an agricultural program, Certainly 
there should be no easing up of the effort in 
these directions, because we have broader 
concepts and new techniques for advancing 
the knowledge on biological control today. 
However, the plant pathologist has been 
sorely disillusioned by the results from this 
effort. The great varieties that were bred to 
complete immunity have fallen by the wayside 
like leaves in the fall as new races of the 
parasite have evolved. Perfectly sound rec- 
ommendations regarding cultural practices to 
promote aeration of tops and suppression of 
inoculum fail at the most awkward moments in 
some seasons, 
The truth of the matter is that all biological 
controls are designed to operate on a set of 
premises that certain normal or average con- 
ditions will prevail wherein there will be a 
balanced condition between pathogen, host, 
and environment. Unfortunately this condition 
rarely prevails year in and year out. Change 
is constant in all three of the components we 
are relying upon. The crop plant may be held 
in a susceptible juvenile state by retarded 
seasonal developments. The low population of 
soil micro-organisms suddenly gets a new 
lease on life, and they multiply wildly when 
there is excess rain to remove natural toxi- 
cants or to force the use of heavy nitrogen 
fertilization to keep the crop vigorous. The 
virulence of the pathogen changes because of 
mutation or reshuffling of its genes during 
sexual reproduction. 
Unfortunately there is no such thing as a 
perfectly balanced biological state that can be 
depended on year after year, The best the 
scientist can do is to accept the parameters of 
variability that will prevail 70 or 80 percent 
of the time and work within these limitations. 
He tries to be ever alert to the shifting abil- 
ities of the pathogens, be it ability to attack a 
supposedly immune variety of the crop or to 
be susceptible to the chemical toxicant used 
in its environment at the most susceptible 
stage of its life cycle. Finally, he must be 
prepared to apply emergency methods to meet 
the unusual circumstances that are certain to 
prevail the other 20 or 30 percent of the time. 
The chemical controls, therefore, are the form 
of crop insurance that are indispensable in 
crises. 
50 
Because of these basic considerations agri- 
culture will never be able to dispense with 
chemicals. In the future they will be used 
more--not less--to control plant diseases. 
This flat prediction is made because (1) we 
are still sustaining over $3 billion damage a 
year; (2) the best laid biological measures 
have a unique way of breaking down ina crisis 
and need a helping hand; (3) crop rotations are 
being shortened as cash crops become more 
important in farm economy with high fixed 
prices; (4) soils are being overworked so 
unbalanced conditions prevail both as to mic- 
robial population and nutritional components; 
(5) crops are being grown so intensively in 
specific areas to facilitate the modern re- 
quirement for economical processing and pres- 
ervation that they are more vulnerable to 
attack; (6) crops have been bred to such high 
standards of uniformity that every change in 
the pathogens becomes a disaster that cannot 
be tolerated under modern farm economy, 
where heavy capital investment must be made 
to pay off every year if financial ruin is to be 
avoided; and (7) present marketing practices 
are so dependent on a uniform productivity of 
high-quality produce that appreciable fluctua- 
tions in volume of crop work to the disad- 
vantage of both the farmer and the consumer. 
The great problem today is to keep the 
research on fungicides and other disease- 
controlling chemicals progressive. There is no 
need to apologize for what has been achieved 
over the past 30 years, because it has been 
tremendous. However, great need still exists 
for better disease control. It can be met by a 
combination of traditional chemical research 
and opening our minds to the new possibilities 
knocking on our doors. The greatest mistake 
that could possibly be made would be to go on 
blindly screening compounds without exploring 
the possibilities of harnessing other forces of 
the environment and the crop to solve the 
problems, 
The industrial chemist is confronted with a 
tremendous challenge. So are the academicians 
of research, for they have failed to keep funda- 
mental knowledge abreast the battlefield. We 
cannot be proud when we simply do not know 
how a molecule permeates a spore, what the 
composition of a fungus cell membrane may 
be, which lipids exist in a fungus and where 
each is located to affect the availability of a 
