BIOEFFICACY EVALUATION OF ANTRACOL 70 WP AGAINST HELMINTHOSPORIUM LEAF SPOT OF SWEET CORN
(ZEA MAYS L. var. RUGOSA)
INTRODUCTION Corn is an important crop in the Philippines as another staple food of many Filipinos next to rice. Yellow corn or grain corn is the type of corn mainly produced in the country because of the growing demand as component for animal feeds. But aside from grain corn, sweet corn production is also a growing trend in the Philippines with the introduction of new supersweet corn varieties with higher sugar content and longer postharvest life. However, these varieties are also exposed to different fungal diseases causing significant yield losses. One of these is Helminthosporium leaf spot. Corn leaf spots or Helminthosporium leaf spots caused by Helminthosporium maydis Nishekado & Miyake are small, spindle-like or oblong, reddish-brown to brown spots on the leaves of corn. This disease causes significant yield losses when corn is not treated with protectant fungicides. Frequent rainy periods enhance disease development.
Antracol 70 WP is an organic fungicide containing propineb, an active ingredient belonging to the dithiocarbamate group of compounds. It is a product of Bayer CropScience. It is a protectant foliar fungicide with long residual activity and it is used across the world as a protective treatment on several crops for the control of various fungi, especially Oomycetes, Ascomycetes, Basidiomycetes and Fungi imperfecti. In various countries, propineb can be used to control blights on potatoes and tomatoes, downy mildew on grapes and also apple scab.
Antracol 70 WP is a wettable powder containing 70 % ai /kg propineb. WHO classified its active ingredient and the product itself as slightly hazardous. Propineb is a dithiocarbamate fungicide with the multisite activity characteristic of the group. Conidia or germinating conidia are killed by contact with propineb.
Objectives:
The objectives of this field experiment are the following: 1. To determine the effectiveness of Antracol 70 WP against Helminthosporium leaf spot of corn; 2. To determine the most effective rate of Antracol 70 WP against Helminthosporium leaf spot of corn; and 3. To generate bioefficacy data to be used for the registration of Antracol 70 WP with FPA against Helminthosporium leaf spot of corn
Location of the study
There will be two trials to be conducted in two locations:
Luzon - Pangasinan State University-Sta. Maria Campus Experimental Station
Mindanao – Mindanao State University – General Santos City
Name of the FPA-accredited researcher (applicant) Mr. Oliver C. Caasi
Duration of the study July-September, 2013 for a duration of 75 days (Wet Season)
Treatments
Treatment No. | Treatment | Application rate | 1 | Antracol 70 WP (1/2 RR) | 20 g/16 L | 2 | Antracol 70 WP (RR) | 40 g/16 L | 3 | Antracol 70 WP (1 ½ RR) | 60 g/16 L | 4 | Dithane M-45 NEOTEC 80 WP (Mancozeb) –standard check | 60 g/16 L | 5 | Untreated Check | No treatment |
METHODOLOGY
Experimental Design
This study will use the Randomized Complete Block Design with five treatments and 4 replications (blocks).
Plot Size and Buffer Zone
The treatments will be randomly distributed to 20 plots with a plot size of 5m x 6 m or 30 m2. A buffer zone of 2 m fallow in between blocks and in between treatments within a block will be established to avoid cross contamination.
Isolation
A 200 m distance isolation or 2 week time isolation will be established to prevent cross pollination from other varieties.
Variety
A supersweet corn variety, Sweet Grande F1 (East-West Seed Company) will be used for the testing. This variety is susceptible to Helminthosporium leaf spot based on initial field survey at Sta. Maria, Pangasinan.
Production Technology Land selection -The testing will be conducted in well-drained soil with a pH of 6.0-6.5. The area has a deep-well irrigation system with a motorized pump as the source of water for irrigation. The area has perimeter fence. Land preparation – The land will be thoroughly plowed twice, each plowing followed by one harrowing. Furrowing - After the last harrowing and when there is adequate moisture, furrows will be laid-out at 65 cm apart at a depth of approximately 8 cm. Nutrient management – Basal fertilizer will be applied along the furrows. Rate will be based on the result of soil analysis. Seeds will be moistened with water then thoroughly mixed with Bio-N at the rate of 200 g Bio-N per 3 kg of seeds. This will reduce the approximately 50% of the N requirement.
Planting – Seeds will be sown 1 seed per hill using a distance of 25 cm between hills. Weed control – Spaces in between rows will be cultivated at 15 DAP. Hilling-up will be done at 25-30 DAP to control weeds within the rows. Other pesticide management – Recommended insecticides will be applied after monitoring of the field. Water management – Irrigation will be done when necessary especially during the critical growth stages. Harvesting - Corn will be ready for harvest approximately 18-22 days after completion of pollination (indicated by drying of silk).
Adequate natural source of inoculum
Natural disease infection will be the source of inoculum.
Treatment application
Application of the fungicide will be done starting at early vegetative stage (V3 stage or when the plants are approximately 8 inches. Subsequent applications will be done at 10 days interval but not later than 7 days before harvest.
Data to be gathered
Bioefficacy assessment – Percent leaf area following the rating scale (Table 1) will be taken and percent disease severity will be computed using the formula below: Table 1. Disease severity rating scale Scale | % area infected | 0 | None | 1 | 1-5 | 3 | 6-12 | 5 | 13-25 | 7 | 26-50 | 9 | >50 | Calculations:
%DS = n(0) + n (1) + ….. + n(9) x 100 N x 9 where : n = number of infected plants classified by grade (scale) N = no. of samples Number of samples = 30 Sequential severity measurement will be conducted by stage at the following growth stages: early vegetative stage (15-20 DAP), late vegetative stage (30-35 DAP), reproductive stage (45-50 DAP), at harvesting stage (70-75 DAP).
Other data Phytotoxicity – Phytotoxicity rating will be determined following the crop injury rating for herbicides.
Yield – Ear weight of the green corn from the inner plots will be determined at harvest and converted to kg/ha.
Effect on other diseases – Severity of the other diseases will be assessed using appropriate rating scale.
Effect on non-target organisms – effect of the fungicide on other non-target organisms such as pollinators and natural enemies especially parasitoid wasp, earwigs, spiders and ants.
Environmental data – The following environmental data will be collected: rainfall, temperature, relative humidity, dew, wind velocity, and direction.
Sampling procedure Thirty plants per plot will be used as sample plants for observation of diseases and actual yield from the whole plot (inner rows) for yield data.
Data analysis Parametric data will be analyzed using ANOVA and non-parametric data will be analyzed using the Kruskal-Wallis test and significant differences between treatment means will be compared using Tukey’s test.
