How to Manage Pests

UC Pest Management Guidelines



Pathogen: Puccinia asparagi

(Reviewed 6/09, updated 6/09)

In this Guideline:


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.


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.


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. 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 per Acre R.E.I.‡ P.H.I.‡
(example trade name)   (hours) (days)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
The following materials are listed in order of usefulness in an IPM Program. Also, consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
  (Chlorothalonil 720) SC 2–4 pt 12 see comments
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
  COMMENTS: Do not apply within 120 days of spear harvest for the following season. Research from Michigan indicates very effective.
  (Rally) 40WSP 5 oz 24 See label
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Begin applications to the developing ferns after harvest has taken place. See label for restrictions.
  (Penncozeb, Manzate, Dithane) 75 2 lb 24 120
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
  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.
  (Thiolux) DF 10–30 lb 24 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  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.
Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1,4,9,11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.
# Acceptable for organically grown produce.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Asparagus
UC ANR Publication 3435


  • B. J. Aegerter, UC Cooperative Extension, San Joaquin County
  • R. M. Davis, Plant Pathology, UC Davis
Acknowledgment for contributions to Diseases:
  • R. J. Mullen, UC Cooperative Extension, San Joaquin County
  • F. F. Laemmlen, UC Cooperative Extension, Santa Barbara County

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