Rust disease of asparagus detected

Recent wet weather favors rust disease outbreak and fern should be protected.

The recent wet weather has likely contributed to reports of the early stage of rust on asparagus fern. Asparagus rust has the potential to ramp up quickly, causing the fern to brown prematurely. Once the rust is well-established, fungicide applications are unlikely to deter the epidemic. Michigan State University Extension states it is key to protect the fern early as soon as harvest concludes.

Rust lesions on asparagus stem in the field.

Young fields that are not being harvested should be protected immediately, even if rust symptoms are not evident. A program of Folicur alternated with Bravo has long been the mainstay of an effective rust management program. As the industry has shifted from more rust tolerant cultivars to those that are more rust susceptible, preventive fungicide sprays for rust become especially important. It has been a few years since growers have seen a significant rust outbreak, so it is important to emphasize that without preventive fungicide applications, asparagus fern is at risk in 2013.

Field epidemic caused by asparagus rust.

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.

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.

Infected asparagus spear.

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 Disease Cycle
View larger image.

Rust damage is most severe when the ferns are diseased for two or more 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 identify and halt early signs of the aeciospore phase of the disease.

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 the table below for fungicide products applied after harvest to fern growth only.

Fungicide products


A. I.


Bravo (Ultrex, Weather Stik), Echo 720, Equus (720, DF)


Should be applied preventively and can be used in rotation with Folicur. Applications of Bravo also protect against purple spot.

Dithane (DF Rainshield, M-45, F-45 Rainshield), Manzate 75DF, Penncozeb (4F, 75DF, 80WP)


Folicur 3.6F


Maximum three applications per season; 12 h REI.

Kumulus DF, Sulfur DF, Thiolux Jet


Limited control under heavy disease pressure.

Rally 40WSP


Maximum six applications per season.

Dr. Hausbeck’s work is funded in part by MSU‘s AgBioResearch.

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