Evaluation of a Biologically Intensive Integrated Pest
Management System for Sclerotinia Drop on Lettuce:
2006 Study
Michael E. Matheron and Martin Porchas
Abstract
Sclerotinia drop of lettuce, caused by the pathogenic fungi Sclerotinia minor and
S. sclerotiorum, is a serious disease in most regions were this crop is grown.
Conventional fungicides, such as Rovral (iprodione) and Endura (boscalid), are
usually applied after lettuce is thinned and once more 2 to 3 weeks later. Two
biological products, Contans (Coniothyrium minitans) and Serenade (Bacillus
subtilis), are also available. In earlier field trials conducted from 2001 to 2004
in the presence of S. minor, the mean reduction in disease by Contans, Serenade
and Endura was 36, 21 and 51%, respectively. The main objective of the
current study was to determine the efficacy of the biological products Contans
and Serenade, applied alone or in combination with each other or the
conventional fungicide Endura, within a biologically intensive integrated pest
management system for Sclerotinia drop on lettuce caused by S. minor. The
study was conducted at the The University of Arizona, Yuma Valley Agricultural
Center. Sclerotia of Sclerotinia minor were produced in the laboratory. Lettuce
‘Winterhaven’ was seeded and sclerotia were applied to the plots on Nov 14,
2005 and the final disease assessment at plant maturity was made Mar 13, 2006.
There was a high degree of variability among the replicate plots for each
treatment in this trial, as well as an overall low disease incidence, which made
statistical comparisons of data difficult. The only treatment in this trial that
significantly lowered disease incidence compared to nontreated plots was an
initial application of Contans at seeding followed by Endura at thinning. This
study was established in a field containing well-draining loam soil, which
combined with the lack of any rainfall and the use of furrow irrigations in
January and February, which kept the tops of beds dry, likely contributed to the
excessive variability and low incidence of disease.
Introduction
Sclerotinia drop of lettuce, caused by the pathogenic fungi Sclerotinia minor and S. sclerotiorum, is a serious disease
in most regions were this crop is grown. In the southwest Arizona production region, the disease can appear in
lettuce fields from November through March. Annual losses attributable to Sclerotinia drop vary from year to year;
however, a small crop loss of even1% would total 720 acres with a value of $5.9 million, using 2004 Arizona lettuce
production data of 72,000 acres with a value of $590,000,000. Conventional fungicides, such as Botran (dicloran),
This is part of the University of Arizona College of Agriculture 2006 Vegetable Report, index at:
http://cals.arizona.edu/pubs/crops/az1419/
Rovral (iprodione), and Endura (boscalid), are usually applied after lettuce is thinned and once more 2 to 3 weeks
later. Two biological products, Contans (Coniothyrium minitans) and Serenade (Bacillus subtilis), are also
available. In earlier field trials conducted from 2001 to 2004, the efficacy of Contans and Serenade have been
evaluated along with Endura. In the presence of S. minor, the mean reduction in disease in four field trials by
Contans, Serenade and Endura applied alone was 36, 21 and 51%, respectively. The objective of the current study
was to demonstrate the efficacy of the biological products Contans and Serenade, applied alone or in combination
with each other or the conventional fungicide Endura, within a biologically intensive integrated pest management
system for Sclerotinia drop on lettuce caused by Sclerotinia sclerotiorum. The efficacy of two additional
conventional products, Rovral and V-10116, and the biological product Sonata (Bacillus pumilus) was also studied.
Materials and Methods
This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-siltclay, pH 7.2, O.M. 0.7%). Sclerotia of Sclerotinia minor were produced in 0.25 pt glass flasks containing 15-20
sterilized 0.5 in. cubes of potato by seeding the potato tissue with mycelia of the fungus. After incubation for 4-6 wk
at 68°F, mature sclerotia were separated from residual potato tissue by washing the contents of each flask in running
tap water within a soil sieve. Sclerotia were air-dried at room temperature, then stored at 75°F until needed. Lettuce
‘Winterhaven’ was seeded Nov 14, 2005 on double rows 12 in. apart on beds with 40 in. between bed centers.
Sclerotia were applied on Nov 14 as well by distributing 0.13 oz (3.6 grams) of sclerotia evenly on the surface of
each 25-ft-long plot between the rows of lettuce and incorporating them into the top 1-inch of soil. Lettuce seed was
germinated with sprinkler irrigation from Nov 17 to 22. Additional sprinkler irrigations were performed Dec 1 and
14, followed by furrow irrigations Jan 13 and 30 and Feb 16 and 28. Treatments were replicated five times in a
randomized complete block design. Treatment beds were separated by single nontreated beds. Each replicate
consisted of 25 ft of bed, which contained two 25 ft rows of lettuce. Plants were thinned Dec 28 at the 3-4 leaf stage
to a 12 in. spacing.
Treatments were applied to soil on Nov 16, 2005 (after seeding) and Jan 5, 2006 (after thinning). All tested
materials were appled to the bed surface between the two rows of lettuce (where sclerotia of the pathogen had been
incorporated) in 1.0 gal of water, followed by an additional 1.0 gal of water per plot to further incorporate each
material into the soil. Mean soil temperature (°F) at the 4 in. depth was as follows: Nov, 62; Dec, 53; Jan, 54; Feb,
60; Mar, 65. No rainfall was recorded for the duration of the trial. The severity of disease was determined at plant
maturity (Mar 13) by recording the number of dead plants in each plot. As a point of reference, the original stand of
lettuce was thinned to 50 plants per plot.
Results and Discussion
There was a high degree of variability among the replicate plots for each treatment in this trial, as well as an overall
low disease incidence, which made statistical comparisons of data difficult, as shown in the data table. The only
treatment in this trial that lowered disease incidence compared to nontreated plots was an initial application of
Contans at seeding followed by Endura at thinning. This study was established in a field containing well-draining
loam soil, which combined with the lack of any rainfall and the use of furrow irrigations in January and February,
which kept the tops of beds dry, likely contributed to the excessive variability and low incidence of disease. Wet
soil conditions, especially on the tops of beds, promote Sclerotinia drop in lettuce.
The objective of this study was to demonstrate the efficacy of the biological products Contans and Serenade, applied
alone or in combination with each other or the conventional fungicide Endura, for management of Sclerotinia drop in
lettuce. In a similar trial conducted in 2005, in the presence of Sclerotinia sclerotiorum, the biological material
Serenade reduced the number of infected lettuce plants as well as the conventional fungicide Endura. Furthermore,
the biofungicide Contans provided significantly better control of disease than Endura. These data from this 2005
trial supporting the efficacy of Contans and Serenade for control of lettuce drop caused by Sclerotinia sclerotiorum
are encouraging; however, the results from this initial field trial will need to be confirmed by additional field trials.
Funding for the current research project as well as the one conducted in 2005 was provided, in part, by the IR-4
project under a cooperative agreement with the U.S. Environmental Protection Agency.
2005-2006 evaluation of a biologically intensive integrated pest management system for Sclerotinia drop on
lettuce caused by Sclerotinia minor
Mike Matheron and Martin Porchas, The University of Arizona, Yuma Agricultural Center, Yuma, AZ
Treatment
Rate of product
per acre
Treatment
dates 1
Diseased
plants per 25 ft
plot 2
Untreated control
-------
1,2
14.0
Contans WG
Endura 70WG
4.0 lb
0.69 lb
1
2
6.6
Contans WG + Serenade AS
Endura 70WG
4.0 lb + 4.0 qt
0.69 lb
1
2
7.6
Endura 70WG
0.68 lb
1,2
8.2
V-10116 50DW
0.25 lb
1,2
8.4
Serenade AS
Endura 70WG
4.0 qt
0.69 lb
1
2
9.2
Contans WG
Sonata AS
Endura 70WG
4.0 lb
4.0 qt
0.69 lb
1,2
1,2
2
10.2
10.2
10.4
Serenade AS
Rovral 4F
Serenade AS
4.0 qt
1.0 qt
4.0 qt
1,2
1,2
1
11.2
11.8
13.2
Contans WG + Serenade AS
Serenade AS + Sonata AS
Contans WG+ Serenade AS
Contans WG
Serenade AS + Sonata AS
Contans WG
Serenade AS
4.0 lb + 4.0 qt
2.0 qt + 2.0 qt
4.0 lb + 4.0 qt
4.0 lb
4.0 qt + 4.0 qt
4.0 lb
4.0 qt
1,2
1,2
1
1
1,2
1
2
14.2
14.8
15.2
16.5
16.8
19.0
LSD (Least Significant Statistical Difference, P=0.05) 3
1.
Treatments were applied to soil on 1) Nov 16, 2005 (when lettuce seed was sown); 2) Jan 5, 2006 (after
thinning). All tested products were applied to the bed surface between the two rows of lettuce (where
sclerotia of the pathogen had been incorporated) in 1.0 gal of water per plot. An additional 1.0 gal of water
was applied to further incorporate Contans and Serenade into the soil.
2.
Disease assessment was performed at plant maturity (Mar 13). All diseased plants were dead or dying.
3.
Least Significant Difference at P = 0.05.