Corn:
Rust (Puccinia sorghi)
| Author: | OMAFRA Staff
| | Creation Date: | 04
July 2005 | | Last Reviewed: |
15 June 2009 |
Excerpt from Chapter 1, Field Crop
Protection Guide, Order this publication
Table of Contents - Integrated Pest Management
Options
- Related links...
DescriptionEarly symptoms of rust infection are yellow flecks or spots
on either side of leaf. These develop into small, brick-red pustules that break
through the surface (epidermis). The brick-red colour is the result of spores
being released from these oval or elongated lesions (2-10 mm (1-4 in.) long).
Yellowing of the leaf occurs around these lesions. Dead, brown (necrotic) areas
of the leaf develop, and in severe cases the entire leaf dies. The brick-red spores
mature and turn black as they mature, causing the lesions and leaf surface to
appear black. 
Image 1. Common rust symptoms range from yellow flecks
to red pustules.
Integrated
Pest Management OptionsRust is generally not a problem in Ontario except
when infection begins early in the season. Field corn has good resistance when
compared to seed corn, sweet corn, and specialty corn hybrids. As a result, foliar
fungicides in field corn are not needed unless significant disease appears before
corn tassels. Humid, cool conditions favour the disease.
azoxystrobin – Quadris |
Active ingredient | azoxystrobin | |
Trade name | Quadris | | Rate
per hectare (product) | 453 mL per ha | |
Rate per acre (product) | 183 mL per ac | Comments
Ground application only. Apply prior to disease development. Second
application may be made 7-14 days later. Maximum 2 applications per season. 7
days to harvest.
pyraclostrobin – Headline EC
| Active ingredient | pyraclostrobin |
| Trade name | Headline EC |
| Rate per hectare (product) | 400-600
mL per ha | | Rate per acre
(product) | 160-240 mL per ac | Comments
Ground and aerial application only. Use a minimum water volume of 100 L/ ha. For
optimal disease control, begin applications prior to disease development. Do not
graze treated crop within 6 days of last application. 7 days to harvest. Maximum
of 2 applications per year.
azoxystrobin + propiconazole – Quilt
| Active ingredient | azoxystrobin
+ propiconazole | | Trade
name | Quilt | | Rate
per hectare (product) | 0.75-1.0 L per ha | |
Rate per acre (product) | 305-406 mL per ac | Comments
Ground and aerial application. Apply when disease first appears, followed
by a second application 14 days after the first, if environmental conditions are
favourable for disease development. Do not apply to field corn or field corn grown
for seed after brown silk. 30 days to harvest for forage. 14 days to harvest for
sweet corn. Maximum 2 applications per season.
| | Tilt 250 E | Bumper
418 EC | propiconazole – Tilt 250
E, Bumper 418 EC | Active
ingredient | propiconazole | propiconazole | |
Trade name | Tilt 250 E | Bumper 418 EC | | Rate
per hectare (product) | 500 mL per ha | 300 mL per ha |
| Rate per acre (product) | 200
mL per ac | 121 mL per ac | Comments
Ground
and aerial application. Apply when rust pustules first appear. Can be tank-mixed
with Ripcord or Matador insecticide for insect and disease control. Under severe
disease pressure, a second application 14 days later may be necessary. Only in
seed corn, under severe disease pressure, can a third application 14 days later
be made. 14 days to harvest.
Related
links... For more information:
Toll Free: 1-877-424-1300
Local: (519) 826-4047
E-mail: ag.info.omafra@ontario.ca
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