Corn: Rust

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Corn: Rust (Puccinia sorghi)

Author:	OMAFRA Staff
Creation Date:	04 July 2005
Last Reviewed:	28 July 2007

Pub 812: Field Crop Protection Guide > Chapter 2 : Corn > Rust

Excerpt from Chapter 2, Field Crop Protection Guide, Order this publication

Integrated Pest Management Options
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Description

Early 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.

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Integrated Pest Management Options

Rust 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.

propiconazole – Tilt 250 E, Bumper 418 EC
	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, a third application 14 days later can be made. 14 days to harvest.

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 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/yr. 48 hrs re-entry period.