Historic note

Group Title: Mimeo report - UF Central Florida Experiment Station ; CFES-68-2
Title: Ametryne as a pre-harvest desiccant for Irish potatoes
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00075854/00001
 Material Information
Title: Ametryne as a pre-harvest desiccant for Irish potatoes
Series Title: Mimeo report - UF Central Florida Experiment Station ; CFES-68-2
Physical Description: Book
Language: English
Creator: Scudder, W. T.
Publisher: Central Florida Experiment Station, University of Florida
Publication Date: 1968
 Record Information
Bibliographic ID: UF00075854
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 123229274

Table of Contents
    Historic note
        Historic note
        Page 1
        Page 2
        Page 3
        Page 4
Full Text


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source

site maintained by the Florida
Cooperative Extension Service.

Copyright 2005, Board of Trustees, University
of Florida


Sanford, Florida APR 22 1963

Mimeo Report CFES 68-2 [.F.brdjry'l1 ~i9 a


W. T. Scudder, Associate Horticulturist

Chemical vine killing is commonly practiced in many of the early potato
producing areas in order to permit the setting of the skins on the tubers and
to facilitate harvesting. The effectiveness and low cost of inorganic sodium
arsenite, a non-proprietary chemical, precludes the use of the newer foliage
desiccants by most potato growers at the present time. Because of the high
mammalian toxicity of sodium arsenite, several states have recently dropped it
from their list of recommended potato vine killers. For years, U. S. grade
standards for potatoes have had a zero tolerance for arsenicals on the marketed
crop. This bars the use of sodium arsenite whenever there are exposed tubers
in the field at the time of treatment. Anticipated prohibition of the use of
inorganic arsenicals on all food crops by the USDA has stimulated a renewal of
the search for effective vine killers for Irish potatoes.

During the last five years, several potato desiccation trials have been
conducted by the Central Florida Experiment Station using potatoes grown on
both sand soil at Sanford and peat soil at Zellwood. In addition to sodium
arsenite, DNBP at the rate of 2 pounds of active ingredient plus 5 gallons of
emulsified diesel oil per acre was used as a standard for comparison. Approxi-
mately 20 different chemicals were tested in the trials, including several new
materials under development such as ametryne and paraquat. The desiccants were
applied shortly before natural maturity of the vines, using tractor sprayers.
Three nozzles per row were arranged to give thorough coverage.

Tables 1 and 2 summarize the observed data for ametryne, sodium arsenite,
DNBP + oil, and paraquat in comparison with the untreated check plots from four
typical trials. All of these chemicals were highly effective, producing com-
plete or nearly complete desiccation in approximately 10 days. The time re-
quired for complete drying of the vines varied among the chemicals and from
season to season. In most cases, ametryne acted similarly to sodium arsenite,
more slowly than the other organic desiccants. At rates of lY2 pounds or more
per acre, it was equally effective.

Subsequent to harvesting the potatoes, several chemical-sensitive indi-
cator crops were planted to determine the persistence of residues of these
potato vine desiccants in the soil. Table 3 shows the effects of ametryne
residues in the sand soil at Sanford following a mid-winter vine-killing trial.
The desiccants were sprayed and the potatoes were harvested in January. The
first indicator crop planting, made 44 days after the ametryne was applied,
showed evidence of considerable residues in the soil. A small amount of ametryne
residue was still present in the soil 80 days after application, but at the third
120 day planting, there was no evidence of residues remaining. By this time,
soil temperatures were high permitting rapid microbiological degradation of the

200 copies


Table 1. Efficacy of ametryne in comparison with other chemicals when used for
killing potato vines, Central Florida Experiment Station, 1963.

Treatment Desiccation ratings
Rate Exp. I (Sanford)b Exp. II (Zellwood)c
Chemical lb ai/a 10 days 5 days 10 days

Ametryne 2z 6.7 9.7
5 8.5
Sodium arsenite 8 6.5 4.0 6.3
DNBP + oil 2 + 5 gal 6.5 7.7 8.3
Paraquat 1/2 8.0 5.3 8.0
Check 0.0 0.0 0.0

aRating scale (0 to 10): 0 = no effect; 10 = complete desiccation.
Experiment I (Sanford) data are means of 4 replications. The treatments
were applied on May 9.
CExperiment II (Zellwood) data are means of 3 replications. The treatments
were applied on June 7.

Table 2. Efficiency of ametryne in comparison with other chemicals when used
for killing potato vines, Central Florida Experiment Station, 1965
and 1966.

Treatment Desiccation ratings
1965 Exp. (Zellwood)b 1966 Exp. (Sanford)c
Chemical lb ai/a 3 days 10 days 10 days

Ametryne 3/4 5.3 10.0
1z 7.0 10.0 7.0
3 7.3 10.0 8.0
Sodium arsenite 10 8.3 10.0 8.0
DNBP + oil 2 + 5 gal 7.0 9.7 6.0
Paraquat 1/2 5.3 8.7 8.5
Check 0.0 4.7d 0.0

aRating scale (0-10): 0 = no effect; 10 = complete desiccation.
b1965 Experiment (Zellwood) data are means of 3 replications. The treat-
ments were applied on June 1.
C1966 Experiment (Sanford) data are means of 2 replications. The treatments
rere applied on May 16.
dNormal maturity effect.


Table 3. Persistence of phytotoxic residues of ametryne in sand soil at
Sanford, Florida following its use for killing potato vines,
winter 1966.

Residue crops planted Evidence of residue (crop injury)b
Days after Indicator Ametryne rate (lb ai/a)
Date treatmenta crop 0 1Y2 3

Feb. 16 44 Cabbage +++ ++++
Cucumbers ++++ +++++
Oats ++++ +++++
Mar. 24 80 Cucumbers + ++
Oats + +++
Tomatoes + ++
May 3 120 No evidence of residue with any crop.

Ametryne treatments were applied January 3.
bResidue effect indicated by: "-" = no effect; "+" = slight stunting;
"+++++" = no crop growth.

Results from a similar series of residue crop plantings, following a late
spring potato harvest, are given in Table 4. Since the soil moisture and tem-
perature were already high at the time the ametryne was applied, dissipation
of the chemical was rapid from the start. There was evidence of small amounts
of ametryne residue in the soil 38 days after application, but it was not pos-
sible to detect this at either of the later plantings. Analyses of soil samples
taken from these plots at the time of the first and second plantings confirmed
the observations made using the indicator crops,

On the peat soil at Zellwood, specific tests to determine the persistence
of ametryne residues have not been conducted. However, work with other triazines,
including simazine, atrazine, and prometryne, has indicated much more rapid dis-
sipation of these chemicals from the peat soil than from the sand soil at

These trials indicate that ametryne at 12 to 3 pounds of active ingredient
per acre is potentially a good chemical for use as a pre-harvest desiccant for
potatoes. Its slow though thorough action may be an advantage over more rapid-
acting chemicals which may encourage stem-end discoloration in the tubers. This
discoloration results occasionally from the use of rapid vine-killing procedures,
including the use of mechanical rotary-beaters. Further, ametryne is relatively
non-toxic and non-corrosive, a safe chemical in comparison to most other defo-
liants and desiccants now available.


Table 4. Persistenceof phytotoxic residues of ametryne in sand soil at
Sanford, Florida following its use for killing potato vines,
spring 1966.

Residue crops planted Field bio-assay Soil analysis
and soil sampled b
and soil s d Crop injury Soil Residue (ppm)
Days after Indicator ametryne rate depth ametryne rate
Date treatmenta crop 0 12 3 (in.) 0 1l2 3

Jun. 24 38 Beans ++ +++ 0-3 (.04 x.04 .06
Cucumbers + + 3-6 (.04 ,.04 .04
Tomatoes -
Millet ++
Oats -
Sesbania -

Jul. 12 56 No evidence of residue 0-3 <.04 -- .04
with any crop or 3-6 (.04 -- <.04
ametryne rate.

Aug. 15 90 No evidence of residue Not sampled.
with any crop or
ametryne rate.
aAmetryne treatments were applied May 16.
Residue effect indicated by: "-" = no effect; "+" = slight stunting;
"+++" = moderate stunting.
Ametryne analyses by ultraviolet method in the Geigy Research Laboratories.

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