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Ministry of Agriculture, Food and Rural Affairs

Rust

Rust Light Orange Lesion Rust Pustules Rust Pustules
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Beginner

Scientific Names
Puccinia asparagi

Identification

  • Look for cream to dark-reddish-brown, oval-shaped, raised pustules on the stems and fronds after harvest.
  • Rust-coloured spores are often easily seen in the centre of the lesions.

Often Confused With
Purple Spot (Stemphylium)

Period of Activity
Infection of growing foliage can occur from May through to early September. Warm weather with heavy dew or light rainfall promotes rust development.

Scouting Notes
Carefully inspect 10 groups of 10 plants across the field. Look for lesions at the base of the plants. Rust is often first identified in 2nd year asparagus plantings, wild asparagus or immature fields as they begin to develop ferns. These fields act as an additional source of inoculum for the production fields later in the season.

Thresholds
None established.

Advanced

Scientific Names
Puccinia asparagi

Identification
The early infections are slightly raised, light green lesions 10 to 20 mm in length. As they mature, the lesions turn cream to light orange. These initial infections generally appear at the base of the stalks. Look for these lesions early in the season on volunteer asparagus or two-year old fields. If they are present, it will be important to be on the lookout for mid-summer infections in production fields.

Mid-summer infections appear as raised, reddish-brown pustules. These pustules release uredospores that continue to infect the plants throughout the summer. These dark orange blisters occur on all plant parts.

The overwintering spores, or teliospores, begin to appear in the upper canopy in late-summer to early-autumn. These lesions are almost black in colour. Once these have started to be abundant, the disease is moving into its overwintering phase, making further fungicide application less effective.

Severe rust infections cause the plants to die prematurely in the fall, impacting the vigour of the crown and the following year’s harvest.

Often Confused With
Purple Spot (Stemphylium)

Biology
Asparagus rust overwinters as teliospores on asparagus debris. Teliospores germinate in spring, producing small, basidiospores which are blown onto emerging spears and cause the initial infection. The initial infections produce small raised, light-green, oval lesions on the lower portion of the infected fern stalks. As the lesions turn creamy orange in color, they release aeciospores. The aeciospores produce further infections under cool, humid conditions. During mid-summer, raised tan blisters called uredia appear on asparagus stalks and foliage. The uredia break open to expose masses of rusty-colored spores called uredospores. Uredospores repeatedly re-infect asparagus from June until September.

In the late-summer, blackish lesions develop in the upper canopy. These lesions produce the overwintering teliospores.

Warm weather with heavy dew, fog, or light rainfall enhances rust development. Infection can occur with as few as 3-9 hours of leaf wetness.

Period of Activity
Infection of growing foliage can occur from May through to early September. Warm weather with heavy dew or light rainfall promotes rust development.

Scouting Notes
Carefully inspect 10 groups of 10 plants across the field. Look for lesions at the base of the plants. Rust is often first identified in 2nd year asparagus plantings, wild asparagus or immature fields as they begin to develop ferns. These fields act as an additional source of inoculum for the production fields later in the season.

Thresholds
None established.

Management Notes

  • Some asparagus varieties have moderate levels of rust resistance.
  • Protect plantings as soon as the fronds are about 30 cm high. This usually occurs in late May for new plantings or early July for established ones.
  • Inspect new plantings for rust as soon as they develop fern. Infected immature fields may act as a source of infection for the commercial plantings.
  • Maintain a 7- to 21-day fungicide spray schedule until late August to protect the fern growth.
  • Thorough coverage of the entire canopy is important.