United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
DD FOR PECAN WEEVIL CONTROL IN THE SOUTHEASTERN STATES
By G. 7. Moznette
Division of Fruit Insect Investigations
In the Piedmont areas of the Southeastern States the pecan weevil
(Curculio caryae (Horn)) (fig. 1) causes serious losses in many orchards.
The pest is also gradually becoming abundant and causing serious losses
in pecan chards in an iv;reasing number of localities in the Coastal
Plains areas of these States.
Pecan varieties differ widely in their susceptibility to attack.
Ihe early maturing varieties, such as the Schley, Stuart, Mahan, and
Moneymaker, are the most subject to infestation, because the weevils
seek nuts with early developing kernels in which to lay their eggs.
The late maturing varieties, such as the Success, Mobile, and Van Deman,
are not usually attacked, unless the crop on the early maturing varie-
ties is very light or has been destroyed early in the fall.
Pecan weevil damage is of two types-(l) that resulting from attack
before the shell-hardening period in July and August and causing all
affected nuts to drop, and (2) that resulting from attack after kernel
formation and usually causing the shuck of infested nuts to stick tight
to the shell instead of opening normally. Weevil-injured nuts of the
second type contain grubs (fig. 2) which destroy the kernels, or they
contain holes about one-eighth inch in diameter (fig. 3) which mature
grubs have bored and through which they escaped after destroying the
kernels. The first type of damage often passes unnoticed an& is due
to the feeding of early emerging weevils, which puncture the immature
nuts with their long lancelike beaks to feed on the juices within.
Since all nuts punctured in this way before the shell-hardening period
drop to the ground, the entire crop may be lost if weevils are abundant
and the crop is light. Such damage may be heavy even when a large crop
is attacked. The second type of damage is generally noticeable at
harvesttime in October and November, and in seasons when large numbers
of weevils have been present practically the entire crop may be wormy
Since the weevils do not feed very much on the outer surface of
developing pecan nuts, stomach poisons applied to trees have been of
little practical value in control. In 1944, however, laboratory tests
showed that DDT could kill the adults, and that it was worthy of field
MAY 2,3 1947
Preliminary orchard tests with DDT were carried out in 1945 at
Fort Valley, Ga., on trees known to be severely infested according to
records maintained since 1942. All the trees were sprayed four times
during the season with bordeaux mixture to control pecan scab. The
first application of DDT against the weevil was combined with the last
application of bordeaux mixture on July 23. Seven Schley pecan trees
were used for each of three plates, two sprayed and one unsprayed. The
details of the treatments and the results obtained are given in table 1.
Table i.--Field tests with DDT for control of the pecan weevil, 1945.
.DDT : Dosage per Nuts harvested
D 100 gallons. : Marketable
wettable treatments Marketable
powder Powder' DDT : Total : Infested : yield per
........ .powder _......; tree
Percent Pounds Pounds HNumber Percent Pounds
50 8.0 4.o July 23, 41,817 1 86
Aug.6 and 21
4o 4.5 1.8 July 23 25,286 14 39
Check None 23,018 21 33
The results of these tests showed that a high degree of control of
the pecan weevil could be obtained with three applications of a spray
containing 8 pounds of a 50-percent DDT wettable powder in 100 gallons
of water and that such control would be reflected in increased yields
of good nuts at harveattime. It was also apparent that more than one
application of DDT would probably be necessary. The evidence was not
clear on this point, however, since the single-application treatment
was made at a reduced strength of DDT and heavy rains may have removed
some of the insecticide.
In 1946 additional field tests were made with DDT on Schley trees
that had been severely infested with weevils in previous years. All treat-
ments were replicated four times avd each plot received four bordeaux
sprays for pecan scab control. The last bordeaux application was de-
layed until July 30, when it was combined with the first of the two
DDT applications given each plot. This application was made before
there was much weevil emergence, to prevent, if possible, the losses
that result from the feeding punctures made by the pecan weevil between
the time of emergence and egg laying. The second application of DDT
was made on August 9. In two of the treatments a latex material known
as polyethylene polysulfide was included as a sticker. A total of
26,077 nuts were examined in determining the results of the tests,
which are summarized in table 2.
which are summarized in table 2.
Table 2.-Field tests with DDT for control of the pecan weevil, 1946
: Material per : : Yield per tree :
Treat-: 100 gallons :Weevil- : :Approxi- :Value of
ment :50% DDT : Poly- :infested: Noa- :Market-:mate coat:market-
No. :wettable:ethyleae:nuts at :infested: able :of DDT :able nuts
:.powder : poly- :harvest nuts : nuts :per tree :per tree
Pounds Pounds Percent Pounds Pounds Dollars Dollars
1 2 0 9 10 7 .60 3.15
2 4 0 5 11 8 1.20 3.60
3 4 2 3 12 10 1.20 4.50
4 6 2 1 26 23 1.80 10.35
5(Check) 0 43 4 1/4 .11
Even though it was a poor crop year and severe weevil infestations
were expected, all the DDT treatments in the 1946 tests significantly
reduced the percentages of weevil-infested nuts at harvesttime. The
best results were obtained with 6 pounds of a 50-percent DDT wettable
powder with 2 pounds of polyethylene polysulfide to 100 gallons of
spray. The differences in the average yields of noninfested nuts and
marketable nuts, and in the value of the marketable nuts between
treatments Nos. 1, 2, and 3, were not significant. As there were in-
dications that the DDT applications were effective against other
insects that often limit nut production, the differences in nut yields
may not have been due entirely to the effect of the treatments on the
pecan weevil. The results of treatments Nos. 2 and 3 indicate that the
polyethylene polysulfide that was used as a sticker did not appreciably
increase the effectiveness of the DDT.
From the results obtained in 1945 and 1946 it appears that at
least two applications of DDT will be necessary for the effective
control of the pecan weevil; however, the possibilities of one appli-
cation have not been fully investigated.
The results of the tests in 1946 show that in a poor crop year
the pecan weevil may destroy practically all the crop. In the un-
treated plots 43 percent of the nuts were infested with weevils at
harvesttime. The yield of noninfested nuts in these plots was only
4 pounds per tree, of which 1/4 pound was marketable.
The effectiveness of two applications of DDT at the rate of 6
pounds of a 50-percent wettable powder to 100 gallons of water in re-
ducing harvest infestations to 1 percent gives rise to the hope that
this treatment, applied for several seasons, will eliminate a pecan
weevil infestation in an orchard, or will reduce it to such an extent
that spraying every year will not be necessary.
DDT is the most effective poison yet found for the protection of
pecans from weevil attack, but there remains much to be learned before
a final recommendation can be made. However, for the benefit of those
pecan growers who wish to try this material, the following tentative
recommendation is made based on the time of weevil emergence: Make two
applications of DDT at the rate of 6 pounds of a 50-percent wettable
powder to 100 gallons of spray, the first during the last week in July
and the second 10 days later in Georgia, Alabama, and Mississippi. In
South and North Carolina the first application should be made during
the first and second week in August, respectively, and thu second 10
days later. When bordeaux mixture is being used for pecan scab control,
the last seasonal application of this fungicide can be delayed and.
combined with DDT in the first application of DDT for weevil control,
since the two materials can be used together.
The time of the first application of DDT cannot be based on the
time of the first drop of nuts, because other pecan insects also cause
the nuts to drop during July and August. However, pecan growers who
wish to make the effort can time the first application accurately by
spreading a sheet on the ground beneath an infested tree and lightly
jarring the branches to dislodge the weevils. When the weevils are
disturbed they fall and "play possum" and can be easily collected.
When a minimum of six weevils can be taken by Jarring the branches
on any one tree, it is time to make the first application.
In handling DDT one should use the same care as with other known
insecticides, such as lead arsenate, calcium arsenate, and nicotine.
ZA--Z, i -
Figure l.-Pecan weevils on Schley pecans.
Figure 2.-Grubs of the pecan weevil in Stuart pecans.
UNIVERSITY OF FLOR IDA
3 1262 09239 1373
Figure 3.-Grubs of the pecan weevil emerging through
holes in pecan nuts.