| Material Information
||Effects of Oxamyl insecticide on fungal leaf spot
||ARC-Apopka research report
||4 p. : ; 28 cm.
||Chase, A. R ( Ann Renee )
Osborne, L. S
Agricultural Research Center (Apopka, Fla.)
||University of Florida, IFAS, Agricultural Research Center-Apopka
||Place of Publication:
||Fungal diseases of plants -- Control -- Florida ( lcsh )
Leaf spots -- Control -- Florida ( lcsh )
Insecticides -- Testing -- Florida ( lcsh )
||government publication (state, provincial, terriorial, dependent) ( marcgt )
bibliography ( marcgt )
non-fiction ( marcgt )
||Includes bibliographical references (p. 2).
||Statement of Responsibility:
||A.R. Chase and L.S. Osborne.
||ARC-A research report ;
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Copyright 2005, Board of Trustees, University
)_- EFFECTS OF OXAMYL INSECTICIDE ON FUNGAL LEAF SPOT
DISEASES OF FOLIAGE PLANTS
A. R. Chase and L. S. Osborne
University of Florida, IFAS
Agricultural Research Center-Apopka
ARC-Apopka Research Report, RH-83-8
Nontarget organisms are often affected as strongly by pesticides as
those organisms the pesticides are designed to control. Sometimes the
result is not noticeable but at other times the population of the nontarget
organism is dramatically increased or decreased. There are many documented
cases of this phenomenon involving insecticides or herbicides used on
agronomic crops, but little information is available concerning greenhouse-
grown crops. The following data summarizes results of tests
employing the insecticide/nematicide oxamyl (Vydate L and its effects on
several leaf spot diseases of foliage plants.
The influence of oxamyl on growth of the following plant pathogenic
fungi was tested in culture dishes with medium amended with oxamyl at the
recommended rate (x = 1 pt/100 gal), 1/2 x, 1/4 x, 1/8 x, and an unamended
control: Alternaria panax, Bipolaris setariae, Fusarium moniliforme and
Myrothecium roridum. Plates were inoculated with a disk of one fungus and
growth and sporulation were recorded after 4-10 days.
Oxamyl did not significantly affect growth or sporulation of Fusarium
moniliforme. In contrast, addition of this insecticide to culture medium
reduced growth of the other 3 pathogens (Table 1), e eh?.wen:used~at rateS~
as low as 1/8 the recommended level. The 1/2 x rate resulted in inhnbition
of sporulation for Alternaria panax and Myrothecium roridutirThi ipOhnoneno
could have an influence on disease development through spore dispersal in
HI.!A S. i'(iv r of --: .
the greenhouse. --- L...r ;,
In vitro (laboratory) testing does not always indicate the response of
the plant and pathogen when grown together in more natural greenhouse
conditions. The effect of oxamyl on disease severity of Alternaria leaf
spot of schefflera (A. panax-Brassaia actinophylla) and Myrothecium leaf
spots of dieffenbachia and nematanthus (M. roridum-Dieffenbachia maculata
'Perfection' and M. roridum-Nematanthus sp. 'Tropicana') was therefore
tested in the greenhouse.
Schefflera seedlings were produced in 4" pots containing steam-sterilized
potting medium (2 Canadian peat:l pine bark:l cypress shavings) amended with
slow relea e fertilizer (19-6-12 Osmocote .dolomite and micronutrients
(MicromaxK Three treatments were included: 1. control (sprayed with
tap water only); 2. sprayed with oxamyl (x rate.) 1 week before inoculation;
and 3. sprayed with oxamyl (x rate) 1 day before inoculation. All treatments
were sprayed to runoff. All plants were inoculated with conidia of A. panax
at the rate of 1 x 104 conidia/ml by spraying to runoff. The severity of
leaf spot disease was rated after 4 days (Table 2). In all 3 tests disease
severity was greatly reduced when oxamyl was applied to plants 1 day before
inoculation and, in 2 tests, applications 1 week earlier also reduced
Dieffenbachia and nematanthus were produced from disease-free cuttings
rooted in the potting medium described above. Preinoculation treatments
included: 1. water spray; 2. oxamyl spray 2 weeks before (x rate); 3. oxamyl
spray 1 week before; and 4. oxamyl spray 1 day before. All dieffenbachia
plants were wounded artificially with a sterilized dissecting needle at the
rate of 3 wounds for each of 4 leaves on each plant and sprayed to runoff
with a spore suspension (1 x 106 conidia/ml). The number of leaf spots
(dieffenbachias) or the disease severity rating (nematanthus) was recorded
after 7 days. In general, oxamyl increased disease severity compared to
inoculated control plants (Tables 3 and 4).
It is possible that oxamyl could act as a fungicide on scheffleras
infected with Alternaria panax, but since no tests were conducted to test the
efficacy of oxamyl for control of this leaf spot compared to standard fungi-
cides, its usefulness is not known. The difference between the influence of
this insecticide-nematicide when applied to one plant compared to another
indicates that its role is not always fungistatic or fungicidal and should
not be considered for use interchangeably with fungicides for leaf spot
control. In some cases, leaf spot diseases were actually more severe when
oxamyl was applied. In instances when disease control has not been successful,
application of another pesticide, such as oxamyl, may increase severity of
the disease over the benefit of the fungicide application.
1. Chase, A. R. and L. S. Osborne. 1982. Orthene 75S and its influence on
two leaf spots of foliage plants. ARC-Apopka Research Report, RH-82-25.
2. Chase, A. R. and L. S. Osborne. 1983. Influence of insecticidal soap on
several foliar diseases of foliage plants. Plant Disease 67. (Submitted)
3. Osborne, L. S. and A. R. Chase. 1983. Influence of acephate on Alternaria
leaf spot of schefflera, and the pathogen,Alternaria panax. J. Econ. Ent.
Table 1. Influence of oxamyl insecticide on growth and sporulation of four
.plant pathogenic fungi on culture medium.
Rate of oxamyl
23 / 0
28 / 0
34 / 28
38 / 28
59 / 57
Bipolaris Fusarium F
72 / 0 76 / 100
75 / 0 78 / 100
78 / 0 78 / 100
83 / 0 78 / 100
84 / 0 79 / 100
30 / 0
39 / 0
48 / 0
51 / 100
62 / 100
a = Growth was recorded in mm and
7 plates with sporulation.
b = Recommended rate of oxamyl is
sporulation represents the percentage of
2.5 mVl (x rate) or 1 pint/100 gal.
Table 2. Effect of oxamyl insecticide on severity of Alternaria leaf spot
Oxamylb week before
Oxamyl day before
-Disease severity for 10 plants
Test 1 (11-23-82) Test 2 (12-17-82) Test 3 (1-24-83)
3.1 10.2 15.2
1.3 5.0 14.1
1.1 0 2.1
a = Number of leaf spots per plant
b = Oxamyl was applied at 1 pint/100 gal rate.
Table 3. Effect of oxamyl insecticide on severity of Myrothecium leaf spot of
Average number of leaf spots per 5 plantsa
Treatment Test 1 (9-28-82) Test 2 (10-20-82) Test 3 (11-17-82)
Water 2.0 1.0 5.2
Oxamylb 2 weeks before 2.2 NT c 6.2
Oxamyl 1 week before 2.6 2.8 7.7
Oxamyl 1 day before NTc 0.8 8.5
a = A total of 12 leaf spots was possible for each of the five plants.
b = Oxamyl was applied at 1 pint/100 gal rate.
c = Not tested.
Table 4. Effect of oxamyl insecticide on severity of Myrothecium leaf spot of
Disease severity rating for 7 plants
Treatment Test 1 (11-17-82) Test 2 (12-17-82)
Water 2.4 2.6
Oxamyl 1 week before 2.6 2.6
Oxamyl 1 day before 3.7 2.7
a = Disease severity was rated on the following scale: 1 = no disease; 2 =
slight disease; 3 = moderate disease and 4 = severe disease.
b = Oxamyl was.applied at 1 pint/100 gal rate.