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© 2007 Plant Management Network.
Accepted for publication 23 October 2006. Published 2 February 2007.


Potato Yield Increases Due to Fungicide Treatment in Argentinian Early Blight (Alternaria solani) and Late Blight (Phytophthora infestans) Field Trials During the 1996-2005 Seasons


Jorge D. Mantecón, Facultad de Ciencias Agrarias, Universidad Nacional de Mar del Plata, Estación Experimental Agropecuaria, INTA, Balcarce, Buenos Aires, Argentina


Corresponding author: Jorge D. Mantecón. jmantecon@balcarce.inta.gov.ar


Mantecón, J. D. 2007. Potato yield increases due to fungicide treatment in Argentinian early blight (Alternaria solani) and late blight (Phytophthora infestans) field trials during the 1996-2005 seasons. Online. Plant Health Progress doi:10.1094/PHP-2007-0202-01-RS.


Abstract

The effect of fungicides on potato yields in separate early blight and late blight trials during the 1996 to 2005 growing seasons at the INTA Balcarce experimental station was determined. Potato cultivars Pampeana INTA were used for early blight trials while Kennebec ones were used for late blight trials. A randomized complete block design with four replications was used in all trials. The fungicides Folicur 25EC at 0.5 liter/ha and Brestan 60WP at 0.5 kg/ha were tested in early blight trials while Dithane M80WP at 2.5 kg/ha and Ridomil Gold 68WP at 1.25 kg/ha were tested in late blight trials. Early blight infections were rated using a 0 to 50 a rating scale. Late blight severity was rated using a disease index of 0 to 5. Potatoes were graded into two categories, marketable (> 60 g) and undersize tuber “seeds” (< 60 g), and then weighed. Data was subjected to analysis of variance. Early and late blight symptoms were present every season. In early blight trials, the efficacy of the systemic fungicide Folicur 25EC was greater than that of the non-systemic Brestan 60WP. The average yield increase due to fungicide treatment during the ten-year period was 22.4% for marketable and 17.9% for total yield. In late blight trials the efficacies of Dithane M80WP and Ridomil Gold 68WP were similar. The average yield increase due to fungicide treatment during the study was 41.23% for marketable and 33.85% for total yield.


Introduction

Early blight of potato, caused by the fungus Alternaria solani, is one of the most destructive foliar diseases of potato and is found in production areas worldwide. The disease causes losses to crop productivity in the field and to tuber quality in storage. It can occur over a wide range of climatic conditions and can be very destructive, sometimes resulting in complete defoliation of plants. Early blight is a particular problem in warmer climates, especially where crops are irrigated. Early infections by A. solani are typically unimportant and the disease does not become problematic until the plants approach senescence. Symptoms usually develop first on the older leaflets of mature plants, spreading to the younger leaves under favorable weather conditions. Late blight, caused by Phytophthora infestans, is potentially the most serious disease of potato and is found in potato-producing areas worldwide. The intensity of the epidemic and consequent level of damage is directly related to the environmental conditions prevailing over the growing season of the crop (4). Climatic conditions in Argentina are favorable for both blights, particularly in southeastern Buenos Aires Province where late blight is endemic.

Both diseases are controlled primarily through the use of resistant cultivars, cultural practices, and foliar fungicides sprays. Field resistance to foliage infection by early blight is associated with plant maturity (2); late maturing cultivars are usually more resistant than early maturing cultivars. The most common and effective control method for early blight is foliar fungicide application (3,5,8). Protecting fungicides recommended for late blight control are also effective against early blight when applied at approximately 7-day intervals (6,11,12). Typical fungicide programs for the control of potato late blight in Argentina consist of a full-season program initiated 30 days after planting with sequential applications made at 7 or 10-day intervals. Systemic fungicides are applied beginning 60 to 90 days after planting with up to 3 applications on a 10-day interval. Before and after this period, farmers apply up to 12 applications of non-systemic fungicides on 7-day interval depending on climatic conditions. The use of fungicides for foliar disease control is a well recognized strategy accepted and adopted by the commercial growers in Argentina. During the crop cycle there are approximately 12 to 15 applications of non-systemic fungicides; this number increases in years with climatic conditions favorable for disease (13). In Argentina, the average loss attributed to late blight between 1986 and 1995 was 50.01% for marketable tubers and 42.55% for total yield (10). The economical losses for the growers were bigger because marketable tubers are the main product of the crop.

During the period of this study, the dithiocarbamate fungicide mancozeb (Dithane M80WP, Dow AgroSciences LLC, Indianapolis, IN) and the phenylamide fungicide (mefenoxam) in co-formulation with mancozeb (Ridomil Gold 68WP, Syngenta Crop Protection, Greensboro, NC) were evaluated for the control of potato late blight and subsequent effect on yields. Mancozeb is a protectant fungicide and needs to be applied to the crop prior to infection in order to achieve satisfactory control (7,16). Mefenoxam is a systemic phenylamide funguicide. Despite the occurence of phenylamide resistance in Phytophthora infestans, co-formulations with multi-site protectants such as mancozeb tend to give better control of foliar blight than the dithiocarbamate alone (1,14). Mixtures of systemic and non-systemic fungicides were far more effective than the fungicides applied singly (9). On commercial crops, periodic applications of fungicides offer the only available control of early and late blight. There are no real data on potential yield losses caused by early blight under Argentine conditions. Therefore, the purpose of this work was to determine the effect of fungicide treatment on the tuber yield of early blight-infected plants. Data was collected over the past decade. We also present the results of a ten-year study on the effect of fungicide treatment on the tuber yield of late blight-infected plants under Argentine conditions.


Determining Effects of Fungicides on Potato Yields

Field trials were performed at the INTA Balcarce experimental station in a Brunizen soil with 4.5 to 6.0% of organic matter. Virus-free seed tubers, sliced or whole, were machine planted at 0.20-m intervals in rows spaced 0.80-m apart. For the early blight study, during the 1996-2002 seasons, the Pampeana INTA cultivar was used, which was susceptible to early blight and resistant to late blight; during the 2003-2005 seasons, the Kennebec cultivar was used, which was susceptible to both diseases. All the plots were sprayed several times weekly with Previcur 72 SL (propamocarb) (Bayer CropScience, Research Triangle Park, NC) at 1 liter/ha to control late blight. For the late blight study, the potato cultivar Kennebec, which is susceptible to this disease, was used in all trials. In all trials a randomized complete block design with four replications was used. Each plot contained four rows, each 5 m long, and was bordered on all sides by a planted and unsprayed guard row 2 m long and designed to promote greater disease development and to minimize drift of fungicide sprays to nearby experimental plots. Irrigation was used every 7 days (30 mm each). Fertilization with 18-46-0 N-P-K was used every year at seeding. Weeds were controlled with Sencor 48SC (metribuzin) (Bayer CropScience) at 0.75 liter/ha + Dual Gold 96EC (s-metolachlor) (Syngenta Crop Protection) at 2 liter/ha applied pre-emergence and Sencor 48SC at 0.75 liter/ha applied post-emergence of the crop. Moreover, grass weeds were controlled with post-emergence applications of Poast 18.4EC (sethoxidin) at 2 liter/ha. Insects were controlled with foliar applications of Lorsban 48E (chlorpyrifos) (Dow AgroSciences LLC) at 0.3 liter/ha. For the early blight assays, the test fungicide Folicur 25EC (tebuconazole) (Bayer CropScience) at 0.5 liter/ha was applied at biweekly intervals and the test fungicide Brestan 60WP (triphenyl tin acetate) at 0.5 kg/ha was applied at weekly intervals according to commercial recommendations. There was an untreated control for each fungicide trial. Applications begun 70 days after planting and continued to harvest. Every year there were four Folicur 25EC and six Brestan 60WP sprays. Although the potato cultivar Pampeana INTA was resistant to late blight, early blight trials were cover sprayed with propamocarb (Previcur 72SL) for late blight control on a 7-day schedule of 40 to 70 days after planting. Plots were evaluated visually for early blight symptoms four times each year, starting when symptoms first appeared. Disease severity was rated using a 0 to 50 rating scale (14). For the late blight trials the test fungicides Dithane 80WP (mancozeb) at 2.0 kg a.i./ha and Ridomil Gold 68WP (mefenoxam + mancozeb) at 0.8+0.05 kg a.i./ha were applied (according to commercial recommendations) weekly during 40 days after planting up to harvest. Each year, the total number of sprays for late blight was 10. An unsprayed check plot was always included. Applications were made with a boom sprayer equipped with Teejet (Spraying Systems Co., Wheaton, IL) ceramic disc-type cone nozzles at 240 PSI at a rate of 300 liter/ha. Plots were evaluated visually for late blight symptoms four times a season starting when symptoms first appeared. Each year, the trials were naturally infected and irrigation was used to encourage disease development. Late blight disease severity was rated using a disease index (0 = no infection; 0 to 1 = first foliar symptoms are present; 1 to 2 = up to 25% of defoliation; 2 to 3 = up to 50% of defoliation; 3 to 4 = up to 75% of defoliation; and 4 to 5 = maximum defoliation; 5 = maximum defoliation). Plants were allowed to senesce naturally. In all trials, tubers were harvested from the two center rows of each plot. The potatoes were graded into two categories, marketable (+60 g) and undersize tubers “seeds” (-60 g) and then weighed in order to calculated total yield. Data from each year was subjected to analysis of variance. ANOVA was not conducted on the entire 10-year data set. Means from each year were compared by LSD at P = 0.05.


Potato Yields in Early and Late Blight-Infected Fields

Early blight foliar symptoms were present each season and reached a maximum disease severity rating in untreated plots (Tables 1 and 2). Efficacy in the control of foliar symptoms by the systemic fungicide Folicur 25EC was higher than that of the non-systemic fungicide Brestan 60WP during the 1996, 1997, 1999, 2001, 2003, and 2004 seasons. Yield increases were high in these seasons. Increases in marketable yield and in total yield were similar. In Pampeana INTA the average increase in yield for fungicide-treated plants during the seven year study was 26.6% for marketable and 19.2% for total yield. In Kennebec cultivar the average increase in yield for fungicide-treated plants during the three year study was 27.6% for marketable and 26.3% for total yield. In general, fungicide application did not increase the undersize tuber yield. Data on “seed” yields is not shown because no significant differences were detected between treatments during this study. The disease did not affect the number of tubers but did appear to reduce tuber size.


Table 1. Effect of fungicides on early blight foliage infection and potato yields in 1996-2000 field trials.

Treat-
ments
Days after planting Yield
(tons/ha)
Yield
(% increase)
Foliage infection
1996 season 86** 91 102 110 Market Total Market Total
Untreated check 2.5* a 25.0 a 50.0 a 50.0 a 19.9 b 25.9 b
Brestan 60WP 0.0 b 5.0 b 15.0 b 25.0 b 25.9 ab 29.9 b 23.1 13.4
Folicur 25EC 0.0 b 0.0 b 5.0 c 5.0 c 32.5 a 36.0 a 38.8 28.0
1997 season 86** 94 100 106 Market Total Market Total
Untreated check 2.5* a 25.0 a 25.0 a 50.0 a 22.0 b 27.5 b
Brestan 60WP 0.0 b 5.0 b 10.0 b 25.0 b 28.4 a 32.8 a 22.5 16.2
Folicur 25EC 0.0 b 0.0 b 2.5 c 12.5 c 32.2 a 35.3 a 31.7 22.1
1998 season 88** 100 108 116 Market Total Market Total
Untreated check 5.0* a 15.0 a 25.0 a 50.0 a 15.6 b 19.9 b
Brestan 60WP 0.0 b 5.0 b 10.0 b 15.0 b 20.8 a 25.4 a 25.0 21.7
Folicur 25EC 0.0 b 0.0 b 10.0 b 15.0 b 22.9 a 26.3 a 31.9 24.3
1999 season 93** 99 103 111 Market Total Market Total
Untreated check 5.0* a 15.0 a 25.0 a 50.0 a 11.6 b 19.8 b
Brestan 60WP 5.0 a 5.0 b 15.0 b 25.0 b 13.3 b 22.4 b 12.8 11.6
Folicur 25EC 0.0 b 0.0 b 10.0 c 15.0 c 16.9 a 26.7 a 31.4 25.8
2000 season 85** 99 108 116 Market Total Market Total
Untreated check 0.0* a 5.0 a 10.0 a 15.0 a 16.1 a 22.4 a
Brestan 60WP 0.0 a 0.0 a 5.0 b 5.0 b 18.4 a 24.5 a 12.5 8.6
Folicur 25EC 0.0 a 0.0 a 5.0 b 5.0 b 19.1 a 23.1 a 15.7 3.0

Within a column, means followed by the same letter are not significantly different (P = 0.05).

 * Foliar disease severity scale, where: 0 = no symptoms, 50 = maximum infection (15).

** Days after planting time.


Table 2. Effect of fungicides on early blight foliage infection and potato yields in 2001-2005 field trials.

Treat-
ments
Days after planting Yield
(tons/ha)
Yield
(% increase)
Foliage infection
2001 season 82** 95 102 106 Market Total Market Total
Untreated check 5.0* a 15.0 a 30.0 a 50.0 a 19.2 b 26.0 b
Brestan 60WP 0.0 b 0.0 b 10.0 b 25.0 b 22.2 b 29.1 b 13.5 10.6
Folicur 25EC 0.0 b 0.0 b 5.0 b 5.0 c 26.6 a 34.2 a 27.8 24.0
2002 season 90** 94 107 114 Market Total Market Total
Untreated check 0.0* a 0.0 a 10.0 a 20.0 a 15.6 a 18.6 a
Brestan 60WP 0.0 a 0.0 a 0.0 a 5.0 b 16.8 a 19.5 a 7.1 4.6
Folicur 25EC 0.0 a 0.0 a 0.0 a 2.5 b 17.2 a 20.1 a 9.3 7.5
2003 season 90** 97 103 110 Market Total Market Total
Untreated check 2.5* a 10.0 a 25.0 a 25.0 a 23.2 b 23.6 b
Brestan 60WP 0.0 b 0.0 b 5.0 b 15.0 b 26.9 b 28.0 b 13.8 15.8
Folicur 25EC 0.0 b 0.0 b 5.0 b 5.0 c 31.5 a 33.8 a 26.4 30.2
2004 season 84** 95 107 114 Market Total Market Total
Untreated check 0.0* a 5.0 a 15.0 a 25.0 a 24.5 b 27.7 b
Brestan 60WP 0.0 a 0.0 a 10.0 ab 15.0 b 30.7 a 34.4 a 20.2 19.5
Folicur 25EC 0.0 a 0.0 b 0.0 b 5.0 c 33.7 a 35.6 a 27.3 22.2
2005 season 92** 98 108 115 Market Total Market Total
Untreated check 5.0* a 15.0 a 25.0 a 25.0 a 22.9 b 27.5 b
Brestan 60WP 0.0 a 0.0 b 0.0 b 5.0 b 31.4 a 35.5 a 27.1 22.5
Folicur 25EC 0.0 a 0.0 b 0.0 b 5.0 b 32.4 a 37.4 a 29.3 26.5

Within a column, means followed by the same letter are not significantly different (P = 0.05).

 * Foliar disease severity scale, where: 0 = no symptoms, 50 = maximum infection (15).

** Days after planting time.


Late blight foliar symptoms were observed every year (Tables 3 and 4). The two tested fungicides were effective at reducing foliar infection and were not significantly different in their effect on yield. Yield increases as a result of fungicide treatment appeared greater in marketable tubers than in total tubers. The average increase in yield during the ten-year study was 41.23% for marketable tubers and 33.85% for total yield. Every year, except in 1998, 2001, 2003, and 2004, fungicide treatment did improve seed tuber yield. Results are not shown because differences between treatments were not significant.


Table 3. Effect of fungicides on late blight foliar disease severity and potato yields in 1996-2000 field trials.

Treat-
ments
Days after planting Yield
(tons/ha)
Yield
(% increase)
Foliage infection
1996 season 93** 96 100 105 Market Total Market Total
Untreated check 1.2* a 3.4 a 4.6 a 5.0 a 37.6 b 45.8 b
Dithane 80WP 0.0 b 1.0 b 2.6 b 3.1 b 59.3 a 66.5 a 36.6 31.1
Ridomil Gold 68WP 0.0 b 1.0 b 2.7 b 3.1 b 57.6 a 65.1 a 34.7 29.6
1997 season 74** 88 93 100 Market Total Market Total
Untreated check 2.0* a 3.5 a 5.0 a 5.0 a 14.4 b 21.0 b
Dithane 80WP 0.0 b 0.5 b 2.0 b 2.0 b 26.8 a 33.5 a 46.2 37.3
Ridomil Gold 68WP 0.0 b 0.5 b 2.5 b 3.0 b 26.2 a 33.7 a 45.0 37.7
1998 season 93** 99 102 106 Market Total Market Total
Untreated check 1.5* a 2.8 a 3.8 a 4.8 a 8.5 b 16.6 b
Dithane 80WP 0.0 b 0.4 b 1.5 b 2.3 b 15.1 a 23.6 a 29.7 29.7
Ridomil Gold 68WP 0.0 b 0.6 b 1.1 b 1.8 b 13.8 a 21.0 a 21.0 21.0
1999 season 80** 92 1.4 111 Market Total Market Total
Untreated check 1.5* a 3.0 a 5.0 a 5.0 a 9.1 b 17.6 b
Dithane 80WP 0.0 b 1.0 b 2.0 b 2.5 b 19.2 a 28.4 a 52.6 38.0
Ridomil Gold 68WP 0.0 b 0.5 b 1.5 b 2.2 b 21.4 a 29.5 a 57.5 40.3
2000 season 75** 88 95 101 Market Total Market Total
Untreated check 1.0* a 1.8 a 4.0 a 5.0 a 18.2 b 22.1 b
Dithane 80WP 0.0 b 1.0 b 2.2 b 3.1 b 23.5 a 30.9 a 22.5 28.5
Ridomil Gold 68WP 0.0 b 0.3 b 1.8 b 2.4 b 27.1a 34.8 a 32.8 36.5

Within a column, means followed by the same letter are not significantly different (P = 0.05).

 * Disease severity scale 0 = no infection and 5 = maximum defoliation, where: 0 to 1 = first foliar symptoms present; 1 to 2 = up to 25% defoliation; 2 to 3 = up to 50% defoliation; 3 to 4 = up to 75% defoliation; and 4 to 5 = maximum defoliation.

** Days after planting time.


Table 4. Effect of fungicides on late blight foliar disease severity and potato yields in 2001-2005 field trials.

Treat-
ments
Days after planting Yield
(tons/ha)
Yield
(% increase)
Foliage infection
2001 season 71** 85 93 99 Market Total Market Total
Untreated check 1.4* a 2.5 a 5.0 a 5.0 a 10.4 b 13.5 b
Dithane 80WP 0.5 b 1.7 b 2.6 b 3.5 b 17.7 a 22.5 a 41.2 40.0
Ridomil Gold 68WP 0.5 b 1.0 c 2.0 b 3.0 b 19.8 a 23.7 a 47.5 43.0
2002 season 74** 88 96 104 Market Total Market Total
Untreated check 2.0* a 3.0 a 5.0 a 5.0 a 15.6 b 16.2 b
Dithane 80WP 0.5 b 1.0 b 1.5 b 3.0 b 25.0 a 25.5 a 37.6 36.5
Ridomil Gold 68WP 0.0 b 0.5 b 1.0 b 1.5 c 27.9 a 28.2 a 44.1 42.5
2003 season 87** 96 104 110 Market Total Market Total
Untreated check 2.5* a 3.5 a 4.0 a 5.0 a 26.4 b 33.2 b
Dithane 80WP 0.0 b 1.0 b 2.0 b 2.5 b 39.7 a 46.8 a 33.5 29.1
Ridomil Gold 68WP 0.0 b 1.0 b 1.5 b 2.0 b 44.0 a 51.3 a 40.0 35.3
2004 season 85** 90 95 105 Market Total Market Total
Untreated check 2.0* a 3.5 a 5.0 a 5.0 a 22.4 b 30.5 b
Dithane 80WP 0.0 b 1.5 b 2.0 b 3.0 b 38.7 a 43.5 a 42.1 29.9
Ridomil Gold 68WP 0.0 b 1.0 b 1.5 b 2.5 b 41.0 a 46.0 a 45.4 33.7
2005 season 80** 87 92 100 Market Total Market Total
Untreated check 1.0* a 2.5 a 4.0 a 5.0 a 20.4 b 30.7 b
Dithane 80WP 0.0 b 1.0 b 1.5 b 2.0 b 33.8 a 41.9 a 39.6 26.7
Ridomil Gold 68WP 0.0 b 0.5 b 1.0 b 1.5 b 36.2 a 44.3 a 43.6 30.7

 Within a column, means followed by the same letter are not significantly different (P = 0.05).

 * Disease severity scale 0 = no infection and 5 = maximum defoliation, where: 0 to 1 = first foliar symptoms present; 1 to 2 = up to 25% defoliation; 2 to 3 = up to 50% defoliation; 3 to 4 = up to 75% defoliation; and 4 to 5 = maximum defoliation.

** Days after planting time.


Potato late blight was a significant problem in each year of the present study but it did not eliminate potato production completely. In Argentina, potato production without fungicides is not economically profitable. The systemic phenylamide fungicide Ridomil Gold 68WP showed the highest efficacy on late blight in years that were climatically conducive for disease development. In these years, total yield for the Ridomil Gold 68WP-treated plants was numerically higher than that for Dithane 80WP-treated plants, although no statistical difference according to the LSD test was observed. Tuber blight is an important phase of the disease in Argentina. However, it was not evaluated in this study since no relevant data could be collected because of the potato cultural practices used in these trials. These cultural practices included early soil removal for the application of post-emergence herbicide to control weeds, strong hilling that produces a very high border in the plots preserving the elevated row over the entire potato crop, and finally the fulfillment of a complete mechanical harvest.


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