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Asparagus

Rust

Pathogen: Puccinia asparagi

(Reviewed 11/05, updated 11/05)

In this Guideline:

Symptoms
Comments on the disease
Management

SYMPTOMS
Rust is most common on fern growth after the harvest season is over. Infections begin in spring from spores that overwintered on crop debris. These infections produce the orange stage (pycnia and aecia) of the disease. Occasionally, this stage can be found in spring on emerging spears from new or established plantings. The orange stage is characterized by light green patches on new spears that mature into yellow or pale orange pustules in concentric ring patterns. Spores produced by these spring stages are airborne to new fern growth. Infection occurs and brick red pustules develop on stalks, branches, and leaves of the fern. These red pustules produce airborne, rust-colored spores (urediospores) in a powdery mass, which can reinfect the fern and increase disease incidence. Fern yellowing and browning, defoliation, and dieback may occur. As ferns mature and senesce, or autumn weather begins, the black spore stage may develop. The same pustules that produced the red spores begin producing black spores (teliospores). The pustule will slowly convert in appearance to a powdery mass of jet black spores. These black spores are the overwintering stage of the fungus.

The overall effect of rust on asparagus is reduced plant vigor the following year and reduced yields.

COMMENTS ON THE DISEASE
Rust diseases have several stages, some of which may occur on different hosts. In asparagus rust, however, all the life stages (orange spore in spring, red spore in summer, and black spore in fall and winter) occur on asparagus. Therefore, what may appear to be a different disease, could be a different stage of rust.

Rust is favored by temperatures between 55° and 90°F. Several hours of dew or rain (free water) are necessary for spores to germinate and infect the host.

MANAGEMENT
Good field sanitation and irrigation practices are important components of managing rust. Treatments are necessary when monitoring indicates rust is present.

Cultural Control
Provide adequate irrigation during the spring/summer fern period so that plants are neither over-or under-watered. Orient rows with the prevailing wind, if possible, to allow free flow of air through the field. This will allow faster drying of the soil surface when irrigations or rainfall occur. At the end of the fern season, cut and destroy diseased ferns. One of the best solutions is to incorporate the cut fern with a power driven rotary tiller two times, once in each direction. The fern may also be removed from the field or burned (not allowed in all districts). Cut young spears to keep infections from occurring, thus breaking the cycle of the fungus in spring. Destroy volunteer asparagus within 400 yards of commercial asparagus fields.

Organically Acceptable Methods
Cultural control and sulfur dust treatments are acceptable to use in an organically certified crop.

Monitoring and Treatment Decisions
Monitor spears and ferns for the appearance of rust lesions. Begin treatments when rust first appears.

Common name

Amount/Acre

P.H.I.+

(trade name)

(days)

MYCLOBUTANIL

(Rally) 40WSP

5 oz

See label

MODE OF ACTION: A DMI (Group 3)¹ fungicide.

COMMENTS: Begin applications to the developing ferns after harvest has taken place. See label for restrictions.

MANCOZEB

(Penncozeb, Manzate, Dithane) 75

2 lb

120

MODE OF ACTION: A multi-site contact (Group M)¹ dithiocarbamate fungicide.

COMMENTS: Apply at first sign of rust and repeat at 10-day intervals until disease pressure subsides. Do not apply during harvest. Do not apply more than 6.4 lb a.i./season. Apply only on asparagus ferns after spears have been harvested.

MICRONIZED SULFUR#

(Thiolux) DF

10–30 lb

MODE OF ACTION: A multi-site contact (Group M)¹ inorganic fungicide.

COMMENTS: Although this material is registered, it does not provide very effective control. Use after cutting stops. May repeat at 7- to 10-day intervals throughout the season.

+	Preharvest interval. Do not apply within this many days of harvest.
¹	Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different group number are suitable to alternate in a resistance management program. For more information, see www.frac.info/.
#	Acceptable for organically grown produce.

PUBLICATION

UC IPM Pest Management Guidelines: Asparagus
UC ANR Publication 3435
Diseases
R. M. Davis, Plant Pathology, UC Davis
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara Co.
Acknowledgment for contributions to the diseases section:
R. J. Mullen, UC Cooperative Extension, San Joaquin Co.

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