Five commercial lettuce cultivars representing different genetic types were grown through aluminum-coated paper, through black polyethylene film, and on bare soil. For each variety, the aluminum mulch reduced the numbers of Macrosteles fascifrons (St~l), reduced the incidence of aster yellows, and increased yields when compared to uncovered controls. The head lettuce cultivar \u27Minetto\u27 was most susceptible on unmulched plots (74.3%) while the leaf cultivar \u27Grand Rapids\u27 was least susceptible (33.8%). The latter also had the greatest infestation of leafhoppers which may indicate either resistance to the aster yellows agent or shorter feeding times by the vector leafhopper. The abundance of aster leafhoppers on the romaine cultivar \u27Valmaine\u27, the butter head cultivar \u27Buttercrunch\u27, and the bibb cultivar \u27Summer Bibb\u27 was much lower than that of the other two and might explain the lower percentage of aster yellows on these types as compared with \u27Minetto\u27

Zalom, Frank G

English

Frank G Zalom

Crossref

 (Homoptera: Cicadelidae), in Minnesota

ValpoScholar

The Great Lakes Entomologist 
Volume 14 
Number 3 - Fall 1981 Number 3 - Fall 1981 Article 4 
October 1981 
The Influence of Reflective Mulches and Lettuce Types on the 
Incidence of Aster Yellows and Abundance of its Vector, 
Macrosteles Fascifrons (Homoptera: Cicadelidae), in Minnesota 
Frank G. Zalom 
University of California 
Follow this and additional works at: https://scholar.valpo.edu/tgle 
 Part of the Entomology Commons 
Recommended Citation 
Zalom, Frank G. 1981. "The Influence of Reflective Mulches and Lettuce Types on the Incidence of Aster 
Yellows and Abundance of its Vector, Macrosteles Fascifrons (Homoptera: Cicadelidae), in Minnesota," 
The Great Lakes Entomologist, vol 14 (3) 
Available at: https://scholar.valpo.edu/tgle/vol14/iss3/4 
This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. 
It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. 
For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 
1981 THE GREAT LAKES ENTOMOLOGIST 145 
THE INFLUENCE OF REFLECTIVE MULCHES AND LETTUCE TYPES 

ON 
THE INCIDENCE OF ASTER YELLOWS AND ABUNDANCE OF ITS 

VECTOR, 
MACROSTELES FASCIFRONS (HOMOPTERA: 

CICADELLlDAE), IN MINNESOTA1 

FrankG. Zalom2 
ABSTRACT 
Five commercial lettuce cultivars representing different genetic types were grown through 
aluminum-coated paper, through black polyethylene film, and on bare soil. For each variety, 
the aluminum mulch reduced the numbers of Macrosteles fascifrons (St~l), reduced the 
incidence of aster yellows, and increased yields when compared to uncovered controls. The 
head lettuce cultivar 'Minetto' was most susceptible on unmulched plots (74.3%) while the 
leaf 
cultivar 'Grand Rapids' was least susceptible (33.8%). The latter also had the greatest 
infestation 
of leafhoppers which may indicate either resistance to the aster yellows agent or 
shorter 
feeding times by the vector leafhopper. The abundance 
of aster leafhoppers on the 
romaine cultivar 'Valmaine', the butter head cultivar 'Buttercrunch', and the bibb cultivar 
'Summer 
Bibb' was much lower than that 
of the other two and might explain the lower 
percentage of aster yellows on these types as compared with 'Minetto'. 
Aster 
yellows is one 
of the most destructive plant diseases of the upper Midwest and the 
prairie provinces of Canada. It has become the limiting factor in the p oduction of lettuce, 
carrots, and celery in Minnesota. Lettuce fields have been reported as suffering 100% loss in 
some 
years (Schultz 1973). 
The principal vector 
of aster yellows is the aster leafhopper, Macrosteles fascifrons (St~l). 
The vector leafhoppers which migrate from southern breeding areas each spring are the 
principal source of primary inoculum. The number of migrants and the percentage infected 
with aster yellows has been used to predict early-season loss potential in Wisconsin, allow­
ing growers to delay initiation of spray programs (Chiykowski and Chapman 1965). Both the 
vector and 
the disease have a wide host range. However, lettuce seems to be preferred 
vegetable host in the midwest (Peterson and Saini 
1964, Schultz 1973). No cultivars of 
commercial lettuce have been developed which are highly resistant to the leafhopper or the 
disease. 
Frequent 
insecticidal applications are often required for commercial production 
of lettuce 
(Richardson an  Westdal 1964, Thompson 1967). Though typically effective (Chapman 
1973), the failure of insecticides to adequately protect plants from insect transmission has 
been 
reported (e.g., 
Lee and Robinson 1958). 
Reflective mulches can decrease the incidence of nonpersistent viruses on lettuce by 
reducing the number of alate aphids alighting upon plants (e.g., Nawrocka et al. 1975, 
Toscano et 
al. 1979). Aluminum foil has been most successfully utilized for this purpose; 
however. black polyethylene plastic was more effective than yellow 
or white plastic in field 
tests (Jones and Chapman 1%8). Similarly, reflective mulches may lower the number of 
aster 
leafhoppers 
in lettuce and reduce infection by aster yellows (Chapman 1973). 
IThis research was supported by the Minnesota Agricultural Experiment Station Project 17-48. Sci­
entific Journal Series Paper No. 11491. 
2Statewide IPM Project-Implementation Group, Department of Plant Pathology, University of Cali· 
fornia. Davis. CA 95616. 
1
Zalom: The Influence of Reflective Mulches and Lettuce Types on the Inci
Published by ValpoScholar, 1981
146 THE GREAT LAKES ENTOMOLOGIST Vol. 14, No.3 
This study evaluated the effect of aluminum and black plastic mu ches on the abundance 
of aster 
leafhoppers, the incidence 
of aster yellows, and yield for five commercial lettuce 
types in Minnesota during the 1980 season. 
METHODS 
Five cultivars of lettuce, representing five distinct genetic types were selected for study: 
'Valmaine', a deep green romaine type; • Buttercrunch', a larger growing butter head type 
making a dense cluster of leaves; 'Grand Rapids', a heavy leaf type with light green, well 
frilled leaves; 'Minetto', a small, firm head lettuce with short cores; and 'Summer Bibb', a 
longer standing bibb type with tight clusters of medium dark green leaves. The plants were 
seeded in wooden flats in a greenhouse, and transplanted to field plots on the St. Paul 
campus of the University of Minnesota four weeks after seeding (early June). The bed was 
disced and leveled prior to planting. 
One third of the plots were covered with Reynolds'" aluminum-coated construction paper, 
one third with black polyethylene plastic film, and one third remained uncovered. Each plot 
measured 5.4 m on a side, with I m between plots. There were four replications of each 
mulch type. The reflective mulches were held in place by 12-gauge galvanized steel wires 
100 
cm long, bent 
at the ends to pierce the mulch and continue into the soil. Circular holes, 
15 cm 
diam, were 
cut out of the mulches through which the lettuce was transplanted. Plants 
within a row were spaced at 45 cm, with 10 plants in a row. Rows within plots were spaced 
at 75 
cm. Each 
of the five rows within a plot was planted with a different cultivar selected at 
random. No insecticides, herbicides, or fertilizers were applied to the plots. Weeds were 
rogued from the plots when necessary. 
One 
week after transplanting and twice weekly thereafter, the plots were sampled for aster
leafhoppers and aster yellows. The relative abundance 
f aster leafhoppers was esti­
mated by sweeping each lettuce plant in a row four times with a standard 40-cm insect net. 
Therefore, insect abundance was obtained on both a cultivar and plot basis. The abundance 
of aster 
leafhoppers among the five cultivars for each mulch treatment was compared by Friedman's 
analysis 
of variance by ranks. The cultivar most heavily infested with the insect 
on 
a given sampling date was assigned the rank 
of I. 
The lettuce was hand harvested by cultivar 5.5 weeks after transplanting (mid-July), 
weighed individually, and examined for symptoms of aster yellows. After determining the 
percentage of plants with aster yellows in each cultivar for the reflective mulch treatments 
and among all replications, the differences between the cultivars and between the reflective 
mulch treatments were analyzed by Duncan's multiple range test. The mean weight of 
lettuce from the reflective mulch plots and the uncovered controls was compared by one­
way analysis of variance. 
RESULTS 
Leafhopper abundance. The mean number of aster leafhoppers per 40 sweeps from lettuce 
grown on bare soil exceeded that from lettuce grown through plastic and aluminum mulch on 
each 
sampling date (Fig. 
1). Their abundance over plastic was greater than over aluminum 
mulch. The peak abundance of aster leafhoppers on the lettuce plants occurred in mid-July. 
The 
difference in aster leafhopper abundance between the five lettuce cultivars grown on 
bare soil and through the plastic mulch was significant (P 
< 0.05). The leaf lettuce (Grand 
Rapids) and the head lettuce (Minetto) had the greatest infestations (Table I). No significant 
difference (P > 0.05) was found among cultivars grown through the aluminum mulch. 
Aster yellows. At harvest, the percentage of plants with aster yellows in each cultivar for 
the reflective mulch treatments among all replications was determined. A significant differ­
ence 
(P 
< 0.05, F = 21.0626) was found by mulch treatment but no significant difference 
(P> 
0.05, F 
= 2.2345) was found by cultivar. Aphid-borne lettuce viruses were not present 
in 
the study area. 
2
The Great Lakes Entomologist, Vol. 14, No. 3 [1981], Art. 4
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1981 THE GREAT LAKES ENTOMOLOGIST 147 
en 
a. 
w 
w 
ffi ~ 30 
I­
~ ~ 25 
LLa: 
o ~20 
a: en
wa:EDw 
::Eo. 
::Jo. 
Z 010 
IX l:LL 
<I( 
W 
....J 
-o-NO MULCH 
-e-ALUMINUM MULCH 
-*- PLASTIC MULCH 
o~~~~~~..~~--~~--~--~~~-
6/13 6/16 6/20 6/23 6/26 7/1 7/3 
SAMPLING DATE 
Fig. I. Mean (n 4) number of aster leafhoppers per 40 sweeps on lettuce grown through aluminum 
mulch, plastic mulch. or no mulch. 
Table I. Abundance of aster leafhoppers on five lettuce cultivars grown on bare soil and 
through revlective mulches. 
Treatment 
Cultivar 
Bare soil Plastic mulch Aluminum mulch 
Buttercrunch 
Grand Rapids 
Minetto 
Summer Bibb 
Valmaine 
x" 
3.40 
1.65 
1.85 
4.20 
3.90 
22.22a 
3.65 
1.05 
2.25 
4.70 
3.35 
31.2oa 
3.19 1.44 
2.69 
3.75 44
1.05 
ap < 0.05. 
The head lettuce (Minetto) exhibited significantly higher incidence of aster yellows than 
did the other cultivars when grown on bare soil (Table 2). The leaf lettuce (Grand Rapids) 
had the lowest 
incidence. 
For each cultivar, the percentage of plants with aster yellows was 
significantly reduced when grown through aluminum mulch instead of bare oiL Aster yel­
lows 
did 
not occur on 'Valmaine', 'Buttercrunch', and 'Summer Bibb' when grown through 
aluminum mulch and was greatly reduced on 'Grand Rapids' and 'Minetto'. The effect of the 
plastic 
mulch was variable with respect 
to cultivar and the other mulch treatments. 
3
Zalom: The Influence of Reflective Mulches and Lettuce Types on the Inci
Published by ValpoScholar, 1981
148 THE GREAT LAKES ENTOMOLOGIST Vol. 14, No.3 
Lettuce yields. Lettuce plants of each cultivar were significantly larger (P < 0.0l) from 
reflective mulch plots than from uncovered control plots. In every instance, the weight of a 
plant grown through aluminum mulch was greater than a plant of the same cultivar grown 
through plastic mulch or on bare soil. When plants infected with aster yellows were elimi­
nated 
from 
the calculation of yield per plant, the differences were still significant (Table 3). 
Table 2. Mean (:;: SD; n 4) percentage of aster yellows infected plants among five lettuce 
cultivars grown n bare soil and through reflective mulches. 
Treatment 
Cultivar Bare soil Plastic mulch Aluminum mulch 
Buttercrunch 
Grand Rapids 
Minetto 
41.0±17.2a 
33.8:;: 11.1 a 
74.3±16.9c 
30.0:;: 16 911 
8.3± 9 1 b 
38.5±16.5a 
O.O±O.Ob 
8.3±9.1b 
2.8±4.8b 
Summer Bibb 
42.3±Il.oa 5.5± 9.5 b O.O±O.Ob 
Valmaine 41.8±14.2a 19.5±15.7d O.O:;:O.Ob 
a, b,c.dNo significant difference belween values with same superscripl. Values wilh differenl superscripls 
significantly different (P < 0,05), 
Table 3. Mean (± SD, n = 4) weight (g per plant) of (I) all plants and (2) all plants excluding 
those infected with aster yellows. 
Treatment 
Cultivar Bare soil Plastic mulch Aluminum mulch F 
(1) ALL PLANTS 
Buttercrunch 249.4± 84.9 458.1± 50.5 733.9±165.2 35.51 
Grand 
Rapids 368.5± 24.2 675.2± 60.1 868.2± 
165.2 18.14 
Minetto 255.2:;: 68.3 526.1:;:109.5 775.9:;:145.4 16.15 
Summer 
Bibb 142.3:;: 19.4 357.0± 61.0 488.7± 64.7 32.22 
Valmaine 440.8:;: 78.8 849.3:;:1l0.5 1258.8:;:152.5 
36.13 
(2) 
PLANTS NOT INFECTED WITH ASTER 
YELLOWS 
Buttercrunch 296.0:;: 95.1 544.0:;: 46.7 783.0:;: 72.2 26.41 
Grand 
Rapids 411.7:;: 32.0 702.9:;: 41.3 932.6:;: 133.6 29.83 
Minetto 381.4:;: 37.9 654.0:;: 85.8 806.0±147.1 
10.39 
Summer 
Bibb 182.3:;: 22.6 372.4:;: 69.2 488.7:t: 64.7 22.70 
Valmaine 569.8± 151.4 894.5± 
116.8 1258.8:;: 1 2 5 18.23 
DISCUSSION 
The results indicated that reflective mulches would lower the abundance of aster leaf­
hoppers, lower the incidence of aster yellows, and increase yields with respect to uncovered 
controls. In most cases, the aluminum-coated construction paper was superior to black 
plastic. 
The greatest abundance of the aster leafhopper in this study occurred in early July. This 
might have been the result of planting date and hostplant attractiveness. As the plants 
increased in size more aster leafhoppers would be drawn to them. The numbers would fall as 
4
The Great Lakes Entomologist, Vol. 14, No. 3 [1981], Art. 4
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1981 THE GREAT LAKES ENTOMOLOGIST 149 
the plants reached maturity. No nymphs were found on the lettuce plots until adults were 
present 
for 
3.5 weeks. 
Although both reflective mulch treatments significantly lowered the incidence of aster 
yellows on the lettuce plantings, no significant difference was found in cultivar susceptibility 
to the disease. In New York, Linn (1940) determined that romaine and head lettuce were 
similarly susceptible to aster yellows. The data obtained in Minnesota indicated that the 
head lettuce cultivar 'Minetto' was more attractive to leafhoppers, which might explain the 
higher incidence of aster yellows on the cultivar. Interestingly, the leaf lettuce variety 
'Grand 
Rapids' had the greatest infestation 
of leafhoppers, yet the lowest incidence of aster 
yellows on the uncovered plots. Perhaps 'Grand Rapids' was resistant to the aster yellows 
agent, or the leafhoppers had a shorter feeding time, preventing a high level of transmission 
of 
the disease agent. The relative abundance 
of aster leafhoppers on the cultivars 'VaI­
maine', 'Buttercrunch', and 'Summer Bibb' was much lower than that of 'Minetto' and 
'Grand 
Rapids', and might explain the lower percentage 
of aster yellows on these cultivars 
as compared with 'Minetto'. 
Yield for each cultivar was greatest on the aluminum mulched plots even when the plants 
infected with aster yellows were-eliminated, indicating additional benefits to the planf from 
the treatment. In Maine, Hilborn et aI. (1957) found that head weight of lettuce grown 
through black plastic was ca. 33% greater than head weight from nonmulched plots owing to 
higher soil temperature, weed suppression, moisture conservation, and lack of plant contact 
with the soil which reduced plant diseases such as bottom rot and bacterial soft rot. Addi­
tional advantages to the plant from an aluminum soil covering might include increased light 
reflection to leaf surfaces, and higher air temperatures immediately over the mulch. 
Aluminum mulching is routinely used on a commercial scale tor aphid management on 
tomatoes and peppers in Florida. The benefits derived from the technique including reduced 
disease incidence, increased yield, and weed suppression lend promise to the technology for 
production of high value crops and home gardens elsewhere. 
ACKNOWLEDGMENT 
The 
contribution 
of D. W. Davis, Professor of Horticulture and Landscape Architecture, 
University of MiImesota, to this study is gratefully acknowledged. M. A. Ascemo critically 
reviewed the manuscript. 
LITERATURE CITED 
Chapman, R. K. 1973. Integrated control of aster yellows. Proc. North Cent. Branch 
Entomol. Soc. Amer. 28:70-92. 
Chiykowski, L M. and R. K. Chapman. 1965. Migration of the six-spotted leafhopper 
Macrosteles fascifrons (soo). Univ. Wisconsin Res. Bull. 26:21-45. 
Hilborn, K. T., P. R. Helper, and G. R. Cooper. 1957. Plastic films aid control of lettuce 
diseases. Maine Farm Res. 5:11-17. 
Jones, F. R. and R. K. Chapman. 1968. Aluminum foil and other reflective surfaces to 
manipUlate the movement of aphid vectors of plant viruses. Proc. North Cent. Brdflch 
EntomoL Soc. Amer. 23:146-148. 
Lee, P. E. and A. G. Robinson. 1958. Studies on the six-spotted leafhopper, Macrosteles 
fascifrons (StliI), and aster yellows in Manitoba. Canadian J. Plant Sci. 38:320-327. 
Linn, M. B. 1940. The yellows disease of lettuce and endive. New York Agric. Expt. Sta. 
Bull. 742, 33 pp. 
Nawrocka, B. Z., C. J. Eckenrode, J. K. Uyemoto, and D. H. Young. 1975. Aphid borne 
viruses in lettuce. J. Econ. Entomol. 68:694-698. 
Peterson, A. G. and R. S. Saini. 1964. Relation of aster-yellows infection in host plants to 
increase of six-spotted leafhopper. Proc. North Cent. Branch Entomol. Soc. Amer. 19:99. 
Richardson, H. P. and P. H. Westdal. 1964. Experiments on control of the six-spotted 
5
Zalom: The Influence of Reflective Mulches and Lettuce Types on the Inci
Published by ValpoScholar, 1981
150 THE GREAT LAKES ENTOMOLOGIST Vol. 14, No.3 
leatbopper, Macrosteles fascifrons, and aster yellows on head lettuce with contact and 
systemic insecticides in Manitoba. Canadian J. Pl nt Sci. 44:393-396. 
Schultz, G. A. 1973. Plant resistance to aster-yellows. Proc. North Cent. Branch Entomol. 
Soc. Amer. 28:93-99. 
Thompson, L. S. 1967. Reduction of lettuce yellows with systemic insecticides. J. Econ. 
Entomol. 60:716-718. 
Toscano, N. C., J. Wyman, K. Kido, H. Johnson, and K. Mayberry. 1979. Reflective 
mulches foil insects. California Agric. 33: 17-19. 
6
The Great Lakes Entomologist, Vol. 14, No. 3 [1981], Art. 4
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The Influence of Reflective Mulches and Lettuce Types on the Incidence of Aster Yellows and Abundance of its Vector, \u3ci\u3eMacrosteles Fascifrons\u3c/i\u3e (Homoptera: Cicadelidae), in Minnesota

Valparaiso University

The Great Lakes Entomologist Volume 14 Number 3 - Fall 1981 Number 3 - Fall 1981 Article 4 October 1981 The Influence of Reflective Mulches and Lettuce Types on the Incidence of Aster Yellows and Abundance of its Vector, Macrosteles Fascifrons (Homoptera: Cicadelidae), in Minnesota Frank G. Zalom University of California Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation Zalom, Frank G. 1981. "The Influence of Reflective Mulches and Lettuce Types on the Incidence of Aster Yellows and Abundance of its Vector, Macrosteles Fascifrons (Homoptera: Cicadelidae), in Minnesota," The Great Lakes Entomologist, vol 14 (3) Available at: https://scholar.valpo.edu/tgle/vol14/iss3/4 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 1981 THE GREAT LAKES ENTOMOLOGIST 145 THE INFLUENCE OF REFLECTIVE MULCHES AND LETTUCE TYPES ON THE INCIDENCE OF ASTER YELLOWS AND ABUNDANCE OF ITS VECTOR, MACROSTELES FASCIFRONS (HOMOPTERA: CICADELLlDAE), IN MINNESOTA1 FrankG. Zalom2 ABSTRACT Five commercial lettuce cultivars representing different genetic types were grown through aluminum-coated paper, through black polyethylene film, and on bare soil. For each variety, the aluminum mulch reduced the numbers of Macrosteles fascifrons (St~l), reduced the incidence of aster yellows, and increased yields when compared to uncovered controls. The head lettuce cultivar 'Minetto' was most susceptible on unmulched plots (74.3%) while the leaf cultivar 'Grand Rapids' was least susceptible (33.8%). The latter also had the greatest infestation of leafhoppers which may indicate either resistance to the aster yellows agent or shorter feeding times by the vector leafhopper. The abundance of aster leafhoppers on the romaine cultivar 'Valmaine', the butter head cultivar 'Buttercrunch', and the bibb cultivar 'Summer Bibb' was much lower than that of the other two and might explain the lower percentage of aster yellows on these types as compared with 'Minetto'. Aster yellows is one of the most destructive plant diseases of the upper Midwest and the prairie provinces of Canada. It has become the limiting factor in the p oduction of lettuce, carrots, and celery in Minnesota. Lettuce fields have been reported as suffering 100% loss in some years (Schultz 1973). The principal vector of aster yellows is the aster leafhopper, Macrosteles fascifrons (St~l). The vector leafhoppers which migrate from southern breeding areas each spring are the principal source of primary inoculum. The number of migrants and the percentage infected with aster yellows has been used to predict early-season loss potential in Wisconsin, allow­ing growers to delay initiation of spray programs (Chiykowski and Chapman 1965). Both the vector and the disease have a wide host range. However, lettuce seems to be preferred vegetable host in the midwest (Peterson and Saini 1964, Schultz 1973). No cultivars of commercial lettuce have been developed which are highly resistant to the leafhopper or the disease. Frequent insecticidal applications are often required for commercial production of lettuce (Richardson an  Westdal 1964, Thompson 1967). Though typically effective (Chapman 1973), the failure of insecticides to adequately protect plants from insect transmission has been reported (e.g., Lee and Robinson 1958). Reflective mulches can decrease the incidence of nonpersistent viruses on lettuce by reducing the number of alate aphids alighting upon plants (e.g., Nawrocka et al. 1975, Toscano et al. 1979). Aluminum foil has been most successfully utilized for this purpose; however. black polyethylene plastic was more effective than yellow or white plastic in field tests (Jones and Chapman 1%8). Similarly, reflective mulches may lower the number of aster leafhoppers in lettuce and reduce infection by aster yellows (Chapman 1973). IThis research was supported by the Minnesota Agricultural Experiment Station Project 17-48. Sci­entific Journal Series Paper No. 11491. 2Statewide IPM Project-Implementation Group, Department of Plant Pathology, University of Cali· fornia. Davis. CA 95616. 1Zalom: The Influence of Reflective Mulches and Lettuce Types on the InciPublished by ValpoScholar, 1981146 THE GREAT LAKES ENTOMOLOGIST Vol. 14, No.3 This study evaluated the effect of aluminum and black plastic mu ches on the abundance of aster leafhoppers, the incidence of aster yellows, and yield for five commercial lettuce types in Minnesota during the 1980 season. METHODS Five cultivars of lettuce, representing five distinct genetic types were selected for study: 'Valmaine', a deep green romaine type; • Buttercrunch', a larger growing butter head type making a dense cluster of leaves; 'Grand Rapids', a heavy leaf type with light green, well frilled leaves; 'Minetto', a small, firm head lettuce with short cores; and 'Summer Bibb', a longer standing bibb type with tight clusters of medium dark green leaves. The plants were seeded in wooden flats in a greenhouse, and transplanted to field plots on the St. Paul campus of the University of Minnesota four weeks after seeding (early June). The bed was disced and leveled prior to planting. One third of the plots were covered with Reynolds'" aluminum-coated construction paper, one third with black polyethylene plastic film, and one third remained uncovered. Each plot measured 5.4 m on a side, with I m between plots. There were four replications of each mulch type. The reflective mulches were held in place by 12-gauge galvanized steel wires 100 cm long, bent at the ends to pierce the mulch and continue into the soil. Circular holes, 15 cm diam, were cut out of the mulches through which the lettuce was transplanted. Plants within a row were spaced at 45 cm, with 10 plants in a row. Rows within plots were spaced at 75 cm. Each of the five rows within a plot was planted with a different cultivar selected at random. No insecticides, herbicides, or fertilizers were applied to the plots. Weeds were rogued from the plots when necessary. One week after transplanting and twice weekly thereafter, the plots were sampled for asterleafhoppers and aster yellows. The relative abundance f aster leafhoppers was esti­mated by sweeping each lettuce plant in a row four times with a standard 40-cm insect net. Therefore, insect abundance was obtained on both a cultivar and plot basis. The abundance of aster leafhoppers among the five cultivars for each mulch treatment was compared by Friedman's analysis of variance by ranks. The cultivar most heavily infested with the insect on a given sampling date was assigned the rank of I. The lettuce was hand harvested by cultivar 5.5 weeks after transplanting (mid-July), weighed individually, and examined for symptoms of aster yellows. After determining the percentage of plants with aster yellows in each cultivar for the reflective mulch treatments and among all replications, the differences between the cultivars and between the reflective mulch treatments were analyzed by Duncan's multiple range test. The mean weight of lettuce from the reflective mulch plots and the uncovered controls was compared by one­way analysis of variance. RESULTS Leafhopper abundance. The mean number of aster leafhoppers per 40 sweeps from lettuce grown on bare soil exceeded that from lettuce grown through plastic and aluminum mulch on each sampling date (Fig. 1). Their abundance over plastic was greater than over aluminum mulch. The peak abundance of aster leafhoppers on the lettuce plants occurred in mid-July. The difference in aster leafhopper abundance between the five lettuce cultivars grown on bare soil and through the plastic mulch was significant (P < 0.05). The leaf lettuce (Grand Rapids) and the head lettuce (Minetto) had the greatest infestations (Table I). No significant difference (P > 0.05) was found among cultivars grown through the aluminum mulch. Aster yellows. At harvest, the percentage of plants with aster yellows in each cultivar for the reflective mulch treatments among all replications was determined. A significant differ­ence (P < 0.05, F = 21.0626) was found by mulch treatment but no significant difference (P> 0.05, F = 2.2345) was found by cultivar. Aphid-borne lettuce viruses were not present in the study area. 2The Great Lakes Entomologist, Vol. 14, No. 3 [1981], Art. 4https://scholar.valpo.edu/tgle/vol14/iss3/41981 THE GREAT LAKES ENTOMOLOGIST 147 en a. w w ffi ~ 30 I­~ ~ 25 LLa: o ~20 a: enwa:EDw ::Eo. ::Jo. Z 010 IX l:LL <I( W ....J -o-NO MULCH -e-ALUMINUM MULCH -*- PLASTIC MULCH o~~~~~~..~~--~~--~--~~~-6/13 6/16 6/20 6/23 6/26 7/1 7/3 SAMPLING DATE Fig. I. Mean (n 4) number of aster leafhoppers per 40 sweeps on lettuce grown through aluminum mulch, plastic mulch. or no mulch. Table I. Abundance of aster leafhoppers on five lettuce cultivars grown on bare soil and through revlective mulches. Treatment Cultivar Bare soil Plastic mulch Aluminum mulch Buttercrunch Grand Rapids Minetto Summer Bibb Valmaine x" 3.40 1.65 1.85 4.20 3.90 22.22a 3.65 1.05 2.25 4.70 3.35 31.2oa 3.19 1.44 2.69 3.75 441.05 ap < 0.05. The head lettuce (Minetto) exhibited significantly higher incidence of aster yellows than did the other cultivars when grown on bare soil (Table 2). The leaf lettuce (Grand Rapids) had the lowest incidence. For each cultivar, the percentage of plants with aster yellows was significantly reduced when grown through aluminum mulch instead of bare oiL Aster yel­lows did not occur on 'Valmaine', 'Buttercrunch', and 'Summer Bibb' when grown through aluminum mulch and was greatly reduced on 'Grand Rapids' and 'Minetto'. The effect of the plastic mulch was variable with respect to cultivar and the other mulch treatments. 3Zalom: The Influence of Reflective Mulches and Lettuce Types on the InciPublished by ValpoScholar, 1981148 THE GREAT LAKES ENTOMOLOGIST Vol. 14, No.3 Lettuce yields. Lettuce plants of each cultivar were significantly larger (P < 0.0l) from reflective mulch plots than from uncovered control plots. In every instance, the weight of a plant grown through aluminum mulch was greater than a plant of the same cultivar grown through plastic mulch or on bare soil. When plants infected with aster yellows were elimi­nated from the calculation of yield per plant, the differences were still significant (Table 3). Table 2. Mean (:;: SD; n 4) percentage of aster yellows infected plants among five lettuce cultivars grown n bare soil and through reflective mulches. Treatment Cultivar Bare soil Plastic mulch Aluminum mulch Buttercrunch Grand Rapids Minetto 41.0±17.2a 33.8:;: 11.1 a 74.3±16.9c 30.0:;: 16 911 8.3± 9 1 b 38.5±16.5a O.O±O.Ob 8.3±9.1b 2.8±4.8b Summer Bibb 42.3±Il.oa 5.5± 9.5 b O.O±O.Ob Valmaine 41.8±14.2a 19.5±15.7d O.O:;:O.Ob a, b,c.dNo significant difference belween values with same superscripl. Values wilh differenl superscripls significantly different (P < 0,05), Table 3. Mean (± SD, n = 4) weight (g per plant) of (I) all plants and (2) all plants excluding those infected with aster yellows. Treatment Cultivar Bare soil Plastic mulch Aluminum mulch F (1) ALL PLANTS Buttercrunch 249.4± 84.9 458.1± 50.5 733.9±165.2 35.51 Grand Rapids 368.5± 24.2 675.2± 60.1 868.2± 165.2 18.14 Minetto 255.2:;: 68.3 526.1:;:109.5 775.9:;:145.4 16.15 Summer Bibb 142.3:;: 19.4 357.0± 61.0 488.7± 64.7 32.22 Valmaine 440.8:;: 78.8 849.3:;:1l0.5 1258.8:;:152.5 36.13 (2) PLANTS NOT INFECTED WITH ASTER YELLOWS Buttercrunch 296.0:;: 95.1 544.0:;: 46.7 783.0:;: 72.2 26.41 Grand Rapids 411.7:;: 32.0 702.9:;: 41.3 932.6:;: 133.6 29.83 Minetto 381.4:;: 37.9 654.0:;: 85.8 806.0±147.1 10.39 Summer Bibb 182.3:;: 22.6 372.4:;: 69.2 488.7:t: 64.7 22.70 Valmaine 569.8± 151.4 894.5± 116.8 1258.8:;: 1 2 5 18.23 DISCUSSION The results indicated that reflective mulches would lower the abundance of aster leaf­hoppers, lower the incidence of aster yellows, and increase yields with respect to uncovered controls. In most cases, the aluminum-coated construction paper was superior to black plastic. The greatest abundance of the aster leafhopper in this study occurred in early July. This might have been the result of planting date and hostplant attractiveness. As the plants increased in size more aster leafhoppers would be drawn to them. The numbers would fall as 4The Great Lakes Entomologist, Vol. 14, No. 3 [1981], Art. 4https://scholar.valpo.edu/tgle/vol14/iss3/41981 THE GREAT LAKES ENTOMOLOGIST 149 the plants reached maturity. No nymphs were found on the lettuce plots until adults were present for 3.5 weeks. Although both reflective mulch treatments significantly lowered the incidence of aster yellows on the lettuce plantings, no significant difference was found in cultivar susceptibility to the disease. In New York, Linn (1940) determined that romaine and head lettuce were similarly susceptible to aster yellows. The data obtained in Minnesota indicated that the head lettuce cultivar 'Minetto' was more attractive to leafhoppers, which might explain the higher incidence of aster yellows on the cultivar. Interestingly, the leaf lettuce variety 'Grand Rapids' had the greatest infestation of leafhoppers, yet the lowest incidence of aster yellows on the uncovered plots. Perhaps 'Grand Rapids' was resistant to the aster yellows agent, or the leafhoppers had a shorter feeding time, preventing a high level of transmission of the disease agent. The relative abundance of aster leafhoppers on the cultivars 'VaI­maine', 'Buttercrunch', and 'Summer Bibb' was much lower than that of 'Minetto' and 'Grand Rapids', and might explain the lower percentage of aster yellows on these cultivars as compared with 'Minetto'. Yield for each cultivar was greatest on the aluminum mulched plots even when the plants infected with aster yellows were-eliminated, indicating additional benefits to the planf from the treatment. In Maine, Hilborn et aI. (1957) found that head weight of lettuce grown through black plastic was ca. 33% greater than head weight from nonmulched plots owing to higher soil temperature, weed suppression, moisture conservation, and lack of plant contact with the soil which reduced plant diseases such as bottom rot and bacterial soft rot. Addi­tional advantages to the plant from an aluminum soil covering might include increased light reflection to leaf surfaces, and higher air temperatures immediately over the mulch. Aluminum mulching is routinely used on a commercial scale tor aphid management on tomatoes and peppers in Florida. The benefits derived from the technique including reduced disease incidence, increased yield, and weed suppression lend promise to the technology for production of high value crops and home gardens elsewhere. ACKNOWLEDGMENT The contribution of D. W. Davis, Professor of Horticulture and Landscape Architecture, University of MiImesota, to this study is gratefully acknowledged. M. A. Ascemo critically reviewed the manuscript. LITERATURE CITED Chapman, R. K. 1973. Integrated control of aster yellows. Proc. North Cent. Branch Entomol. Soc. Amer. 28:70-92. Chiykowski, L M. and R. K. Chapman. 1965. Migration of the six-spotted leafhopper Macrosteles fascifrons (soo). Univ. Wisconsin Res. Bull. 26:21-45. Hilborn, K. T., P. R. Helper, and G. R. Cooper. 1957. Plastic films aid control of lettuce diseases. Maine Farm Res. 5:11-17. Jones, F. R. and R. K. Chapman. 1968. Aluminum foil and other reflective surfaces to manipUlate the movement of aphid vectors of plant viruses. Proc. North Cent. Brdflch EntomoL Soc. Amer. 23:146-148. Lee, P. E. and A. G. Robinson. 1958. Studies on the six-spotted leafhopper, Macrosteles fascifrons (StliI), and aster yellows in Manitoba. Canadian J. Plant Sci. 38:320-327. Linn, M. B. 1940. The yellows disease of lettuce and endive. New York Agric. Expt. Sta. Bull. 742, 33 pp. Nawrocka, B. Z., C. J. Eckenrode, J. K. Uyemoto, and D. H. Young. 1975. Aphid borne viruses in lettuce. J. Econ. Entomol. 68:694-698. Peterson, A. G. and R. S. Saini. 1964. Relation of aster-yellows infection in host plants to increase of six-spotted leafhopper. Proc. North Cent. Branch Entomol. Soc. Amer. 19:99. Richardson, H. P. and P. H. Westdal. 1964. Experiments on control of the six-spotted 5Zalom: The Influence of Reflective Mulches and Lettuce Types on the InciPublished by ValpoScholar, 1981150 THE GREAT LAKES ENTOMOLOGIST Vol. 14, No.3 leatbopper, Macrosteles fascifrons, and aster yellows on head lettuce with contact and systemic insecticides in Manitoba. Canadian J. Pl nt Sci. 44:393-396. Schultz, G. A. 1973. Plant resistance to aster-yellows. Proc. North Cent. Branch Entomol. Soc. Amer. 28:93-99. Thompson, L. S. 1967. Reduction of lettuce yellows with systemic insecticides. J. Econ. Entomol. 60:716-718. Toscano, N. C., J. Wyman, K. Kido, H. Johnson, and K. Mayberry. 1979. Reflective mulches foil insects. California Agric. 33: 17-19. 6The Great Lakes Entomologist, Vol. 14, No. 3 [1981], Art. 4https://scholar.valpo.edu/tgle/vol14/iss3/4

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The Influence of Reflective Mulches and Lettuce Types on the Incidence of Aster Yellows and Abundance of its Vector, \u3ci\u3eMacrosteles Fascifrons\u3c/i\u3e (Homoptera: Cicadelidae), in Minnesota

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