Aeciospores found on asparagus volunteers

Asparagus rust can reduce yield and longevity of an asparagus field. Scout early in the growing season and remove volunteer plants on edges.

Asparagus rust, caused by the fungus Puccinia asparagi, is a single-host disease (Most rusts require two hosts.) that affects the fern portion of the crop. Puccinia asparagi produces four distinct spore types that can cause infection. Basidiospores that develop on leftover, infested asparagus debris begin new infections in the spring, causing oval-shaped, light-green lesions. These lesions become sunken and turn orange with the onset of aeciospore production.

Rust lesions on asparagus stem in the field
Rust lesions on asparagus stem in the field.

Aeciospores are often visible on young asparagus or early volunteer plants and are responsible for infecting the healthy branches or cladophylls (needle-like leaves) via air currents or rain splash in early summer. This early source of inoculum infects new material through wounds or stomata (the pores of a plant used for gas exchange) in the presence of water or moisture. Once the fungus is established, it produces pustules that release brick-red colored uredospores in large numbers – giving the disease its name – to create the epidemic phase in mid- to late summer. Large-scale epidemics are dependent on foliar wetness from rain, dew, or overhead irrigation. Uredospores germinate in the presence of moisture, similar to basidiospores and aeciospores, and yield new generations of spores every 10 to 14 days. In early fall, the fungus gives rise to black teliospores that enable it to overwinter on plant debris.

The following spring, these teliospores will produce basidiospores to begin a new cycle of disease. Rust damage is most severe when the ferns are diseased for several years in succession. Because the pathogen can stunt, kill or defoliate young plants, carbohydrate reserves become depleted for the following year’s crop. Plants stressed from rust disease may become more susceptible to Fusarium and Phytophthora crown and root rot. As a result of the pathogen’s ability to reduce the yield and longevity of an asparagus field over time, using disease-resistant varieties is an important management tactic that has been found to reduce the intensity of infection. Scouting early in the growing season and removing volunteer plants on field edges can help growers to identify and halt early signs of the aeciospore phase of the disease.

Rust disease cycle
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Interrupting this phase with fungicide applications can decrease development of the uredospore phase, thereby inhibiting the repeated spore cycle that causes large epidemics. In addition to scouting and using fungicides, planting crop rows with ample spacing and in the direction of prevailing winds can increase air movement and minimize periods of prolonged foliar wetness. In asparagus growing regions, destruction of abandoned fields will minimize disease pressure on neighboring production systems. See below for fungicide products (apply after harvest to fern growth only).

Infected asparagus spear
Infected asparagus spear.

Field epidemic caused by asparagus rust
Field epidemic caused by asparagus rust.

Product A. I. Comment
Bravo (Ultrex, Weather Stik)
Echo (720, 720 SST)
Equus DF
chlorothalonil Apply every 14 to 28 days
Dithane (DF Rainshield, M-45,
F-45 Rainshield)
Manzate Pro-Stick
Penncozeb (4F, 75DF, 80WP)
mancozeb
Folicur 3.6F tebuconazole Max. three applications per season; 12-hour REI
Kumulus DF
Sulfur DF
Thiolux Jet
sulfur Limited control under heavy disease pressure
Rally 40WSP myclobutanil Max. six applications per season

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