Laboratory tests of the repellent activity of selected chemicals for
protecting corn from damage by cotton rats (Sigmodon hispidus)

In parts of Latin America, cotton rats (S. hispidus) often cause
extensive damage to young corn plants by direct cutting of the stalk
or digging the roots from the base of the plant. Damage is sometimes
so severe that fields must be replanted several times before adequate
corn stands can be raised. Our laboratory research on this problem
has been aimed toward development of repellent chemicals that will
alleviate rat damage to young plants. Four chemical formulations
were evaluated using topical (surface) treatments on growing corn
plants (<15 cm high). The only treatment that produced a consistent
decrease in damage was a 1-percent solution of red squill, a
commercial rodenticide. This effect is shown in Table 10, with
comparative results for R-55 (commercial rodent repellent) and
acetone extracted tannins from a bird-resistant variety of sorghum.


Numbers (mean SD) of corn plants
(n = 3) of cotton rats. Plants (n
day for 5 days during the baseline


damaged by small groups
= 10-15) offered each
and treatment sessions.


 Baseline Treatment
 No. plants No. plants
 No. plants cut and No. plants cut and
Treatment cut eaten cut eaten

1% R-55 8.00.0 4.01.4 8.22.2 5.44.2

1% Red Squill 10.00.0 10.00.0 5.82.9 5.82.9

1% Tannin 10.57.8 5.53.5 7.64.8 4.62.1

5% Tannin 10.57.8 5.53.5 10.00.0 6.20.8


Additional tests with 5 percent red squill and an
rodenticide are in progress. Closed circuit videotaped
the treatment periods (4 p.m. 8 a.m. each night) should
refined analysis of the repellency effects.


experimental
sessions of
allow a more


Table 10.