We have had reports of asparagus rust in new plantings. Now is the time to get out and scout; especially in the two-year old fields and any volunteer asparagus near the production fields. These plants often act as source of inoculum for the commercial crop later in the season.
Severe rust infections cause the plants to die prematurely in the fall, impacting both the vigour of the crown and the following year’s harvest.
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 (figure 1, asparagus rust aeciospores). 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. As harvest concludes, scout all fields regularly during the fern development stage.
Mid-summer infections appear as raised, reddish-brown pustules. These pustules release uredospores that continue to infect the plants throughout the summer (figure 2, asparagus rust uredospores). 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.
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. For the best control, apply fungicides preventatively under these conditions and if the disease is present in the field or local area.
Products currently registered for rust control in asparagus (post harvest) include:
propiconazole (Mission 418 EC, Topas),
metiram (Polyram DF)
For product rates and rotational information and other notes, see the Ontario Vegetable Crop Protection Guide – 2014-15 (publication 838). Copies are available and your local OMAF/MRA Resource Centre or from Service Ontario 1-800-668-9938 or 416-326-5300.