COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
STATE OF FLORIDA
COLLEGE OF AGRICULTURE, AGRICULTURAL EXTENSION SERVICE
UNIVERSITY OF FLORIDA, AND tl Crop C ilCOUNTY AGENT AND
UNITED STATES DEPARTMENT vegetable Crop pecialsts HOME DEMONSTRATION WORK
OF AGRICULTURE, COOPERATING GA1NESVILLE, FLORIDA
December 22, 1954
MR. COUNTY AGENT:
DO WE RECOiMEHD PCNB FOR THE CONTROL OF DAMPING-OFF AND ROOT ROT OF VEGETABLES?
No....and that about answers it for any other indicated use in vegetables, if
we are to rely on research of our Florida Agricultural Experiment Stations. We in-
tend to continue doing so.
However, since it is difficult to separate the wheat from the chaff, we feel
that you as a group should be currently well briefed on the material. We've talked
to many of you individually and are presenting it to agent training sessions. This
is in nature of a summary and reference. iore detail can be supplied.
First. Dr. W.D. Moore, USDA at Ft. Lauderdale, gives the following recommenda-
tion for the use of the material, and this at best was qualified recently under
some very definite limitations: "on beans on soils known to be heavily infected
with Rhizoctonia, and with the possibility that Pythium is not a factor in the root
rot complex, then I would recommend PCNB. But with the reservation that we do not
know what effect it will have upon yields. Some farmers just want the disease con-
trolled and in those cases it is O.K." Specific application rates and methods
accompany these limitations.
How note very closely that Dr. Hoore's recent account carries a suggestion for
only one crop, for only one organism damaging in the absence of another, and with
the reservation that there is not known -hat yield effect will be derived. Further
comment would reveal that Rhizoctonia and various species of Pythium are associated
with this root rot complex, and that there are distinct possibilities of other or-
ganisms. PCNB may control Rhizoctonia, but "in no instance have we found PCNB to
be of apparent value in controlling Pythium." Dr. Moore also says in effect that
the Rhizoctonia population is only reduced, PCNB does not eradicate the mass of or-
ganisms throughout the soil, Pythium can cause serious damage acting alone and may
be a factor in ag;ravatinr the activity of Ihizoctonia, there are 5 different spe-
cies of Pythium, and 15 or more strains of Rhizoctonia in South Florida.... and also
influences by such factors as temperature, moisture, and organic content of the soil.
All of the above seems to add up to the fact that even to recommend its use on
beans, the one crop, you would have to predict that only the organism Rhizoctonia
would be active in the root rot complex, and then even if you could be accurate in
this, you would not be able to say that from this data controlling the organism
would have any effect on yields. There may be some other "ifs" but we feel that
these define what would appear to be a rather precarious position for you as a
WHAT RESEARCH IS THERE ON COMBIHIHIG PCNB WITH OTHER WATERIALS-FOR SOIL TREATY EUT?
Your next logical question from the above might go something like this:
"Granted that PCNB controls Rhizoctonia but not Pythium, and that in the past 'root
rot' was loosely attributed to Rhizoctonia whereas now it looks like Pythium was
definitely in the picture, what about combining some materials and controlling
That was some of the thinking developed during the course of Dr. Moore's work,
too. He says, "On the basis of one test captain and vancide $1 looked most promis-
ing in combination with PCNB from an all-round standpoint....i.e., appreciable
reduction in disease without any apparent effect on germination and early growth of
beans. In addition to these materials the comparisons included nabam, crag 400,
dowicide A, thiram and chloranil. There is no data on what proportions of the
various materials would be effective combinations."
Note particularly 'one test,' and 'no data on what proportions.'
GOING BACK TO EFFECT OF RHIZOCTONIA CONTROL ON YIELDS, IS THERE RESEARCH ELSE-
WHERE IN THE FLORIDA STATIONS?
Since we have about narrowed this down to PCNB and beans, here is possibly a
good place to follow in with some work by Dr. Bob Conover at the Sub-Tropical Sta-
tion. Good control of Rhizoctonia stem cankers, following specific methods of
application, is reported in four replicated tests and several commercial fields. In
these tests 3 or 5 pounds active PCNB per acre gave good control; 10 lbs. caused
"injury" but was not reflected in decreased yield while 20 lbs. caused a short delay
in germination, but apparently not in stand. The material is not recommended for
general use by the Sub-Tropical Station.
In light of the lack of yield data mentioned above you will be particularly in-
terested in Dr. Conover's following comment: "Control of Rhizoctonia stem cankers
did not result in a yield increase in one experiment (only yield o-pi.riment made)
even when 57% of the chock plants were rated as severely infected, i.e., had girdling
lesions, or elongated lesions exposing vascular elements. While these results tempt
one to think that the damage caused by stem canker has been overrated, one should
remember that Rhizoctonia can cause a loss in stand sufficient to necessitate re-
planting. On the cther hand, since root rot is a complex disease caused by several
organisms, it is p..a_-iblc that the control of one component of the complex might
result in heightened activity of the other components with the result that over-all
damage is about equal."
Dr. Conover relates a situation showing the complexity of the problem: "In one
experiment in a commercial field it was very plain that PCNB is specific in its
action. mcrc.-icc of bans in this field seemed to be affected by a complex involv-
ing several organisms. PCNB at 4 lbs. (active) per acre did not improve the stand
at all whereas captain applied as a seed treatment produced approximately 100% in-
crease in stand. Within a short time the captan-troated plants were badly damaged
by stem cankers but the PCNB-treated plants were singularly free of them."
WHAT HAS BEEN THE EXPERIENCE OF RESEARCH WITH PCNB AS SOIL TRhEATiIEJJT AT OTHER
In citing the instances below in such a general fashion, we want it realized
that more specific information can be given, such as rates and methods of applica-
tion. We present it in this fashion as a means of oxpressinc the experience of the
research people when using the material according to information at hand, and to
indicate why research experience over the state indicates that we should not recom-
mend PCNB at this time. Thcso remarks include other "combination" materials
mentioned above as promising.
At the Belle Glade Station, Dr. R.S. Cox has been checking PCNB and captan for
possible use in celery seedbeds. In before seeding tests, as mixed in soil or
drench, captain gave stand reduction and PCNB was ineffective. In after sccding
tests, both materials were among the best for Rhizoctonia post-oncr enco damping-off
control, neither gave control of Fusarium-Pythium root rot or Bacterial leaf blight,
PITT, gave slight and captain severe injury to seedlings.
In an attempt to use the material where he could not get a tomato stand on
second-scason planting, Dr. C.H. Coc at the Ft. Fierce station, tried PCNB as a
pro-emergence application. No control of damping off resulted; Pythium was the
primary offender. Under hot weather conditions some injury to "crooks" occurred.
At Bradenton, Dr. Walter does not report any advantages in terms of final stand
counts of pole beans from PCNB applied before or after planting or captain applied
after seeding. In a more recent observation of FCNB he relates an instance of
resulting poor emergence of pole beans....valuable seed stock, we believe. Mr. Don
Burgis, also at the Gulf Coast Station relates instances of phytotoxicity from PCNB,
vancide 51 and captan to eggplant and peppers, and phytotoxicity to cabbage and
tomatoes from captain.
WHAT OTHER USES OF PCNB HAVE BEEN EXPLORED BY THE STATIONS?
Transplant water treatments for damp-off control?
Dr. Moore, USDA, says very limited trials indicated Rhizoctonia may be con-
trolled on pepper and tomatoes by application in the transplantin water at the time
of setting. He refers to this work as hardly worth mentioning.
Dr. Conover at the Sub-Tropical Station says since study of the operation of
tomato transplanters made it rather plain there is no practical way for the starter
solution to be applied to both roots and the area affected by Rhizctonia, experi-
ments with these mixtures were discontinued. He indicates loss of transplants due
to Rhizoctonia has not been serious enough to justify either the cost of control or
work on the problem.
At the Ft. Pierce Station, Dr. Coo to date observes that PCNB in the tomato
transplanting solution appears no better than the check, that zineb and panogen
appeared to give a measure of control, and that captain ranked first. Early losses
were due to Pythium and later to Rhizoctonia. He's currently repeating the test
for closer study and analysis.
In testing several rates of PCNB in setting water applied by a continuous
stream cart, Dr. Sowell at Bradcnton indicates no reduction of damping-off suf-
ficient for practical control. Rhizoctonia was consistently isolated from seedlings,
but he says this does not eliminate possibility that such trouble was caused by
Pythium, although this would not seem likely.
As a control of Sclerotinia?
Dr. Mloore, USDA, indicates he does not have enough information to even suggest
a recommendation, but after this year hopes to have a little dope on the subject.
Dr. Conover at the Homestead station has what appears to be some very pertinent
remarks. PC'TB broadcast and disked in to the soil at 75 to 150 lbs. (active) per
acre significantly reduced the number of apothecia of Sclerotinia sclerotiorum
appearing in treated areas. However, in the same experiment, calcium cyanamide was
much more effective. Actual figures were (in numbers of apothecia per 36 sq. ft.):
check, 29.2; PCNB (7r), 12.h; PCI'B (150/), 12.8; calcium cyanamide (290#), 0.8;
calcium cyanamide (500# or more), 0. According to Dr. Conover, 1 or 2 apothecia per
36 sq. ft. evenly distributed in a field would be ruinous. He has no experiments
with PCNB to control Sclerotinia in a vegetative condition.
Dr. Cox at Belle Glade reports no data on Sclerotinia.
Dr. Sowoll at the Gulf Coast Station has some phytotoxicity studies in con-
junction with attempts to use PCOB directly on pole beans, lettuce and endive for
Sclerotinia control. To date no disease or injury has developed in the plots as
As a control of soil rot on tomatoes?
Dr. Conover at Homestead reports that results of 2 experiments with PCNB show
a significant reduction of soil rot of tomatoes when applied to the soil surface
after "lay-by." The reduction was from 19% soil rot in the check, to 14% for the
8 Ibs. (active) per acre dosage, and to 11% for the 32 lb. dosage. He states he is
not one who considers a reduction of 30 to 50% as "control" even if significant.
Furthermore, PCNB caused injury to fruit (inadvertently applied) where the spray
collected in the depression around the stem. These experiments were discontinued
2 years ago.
Dr. Coe at Ft. Pierce is now taking data on PCNB applied as alternate pre- and
post-layby application, mixed with nabam, and directed on plant foliage and soil
around plants. To date no evidence of injury or retarding of growth, and F'CN'
appears compatible with nabam. Concerning soil rot, on first and second harvest
no evidence of anything showing in the data to date.
As a control of gray mold on tomatoes?
Dr. Darby, now at the Central Florida Station, reports on some work done while
he was back at the Ft. Pierce location. On applying PCNB 6 times as an alternate
for zineb in a regular 22-application zineb program, wetting entire plant and soil
surface by run-off, he reports no difference in marketable yield, slight reduction
of gray mold on foliage and fruit, but no other disease reduction was noted. He
adds it warrants further test but does not warrant suggestion it looks promising as
control for gray mold or any other disease.
As a control of Helminthosporium on sweet corn?
Dr. Cox at Belle Glade reports that the material at 2 lbs./l0 gallons was
applied as a foliage spray in regular fungicide screening rro -rnr. In his w-ords,
it was "absolutely ineffective."
Very truly yours,
F. S. Jamison
Vegetable Crop Specialist
P.S. 12/21/54 Received this morning some results of current readings by Dr.
John Darby, at the Sanford station. We appreciate this excellent cooperation in
getting to us the latest data available. 1Hore details can be furnished, as
indicated also on other preliminary reports, but these in general indicated:
Lettuce Drop Trial (Bibb): Testing PCI0B at several rates and captan alone
in drench mixed with top soil prior to transplanting; as of December 15
(month after transplanting) no phytotoxic symptoms apparent, no difference
in number of dead plants per treatment, no disease present to date in
Celery Seedbed: Testing captain solution applications starting at germina-
tion, and at 1, 2, 3 or 4 weeks after germination. Applications have
now been made at germination and at 1 and 2 weeks after germination.
As of December 17 no phytotoxic symptoms a-parent; no damping-off present;
treatment starting at germination has received 3 applications to date
with no ill effect apparent.