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Plant & Pest Advisory – June 4, 2024 – Andy Wyenandt
Asparagus growers should consider scouting their fields regularly during the summer months for foliar
disease development. Important pathogens that growers need to scout for on a regular basis include
Purple spot, Cercospora, and Rust. These pathogens are easily diagnosed by the characteristic
symptoms they produce on infected plants. Purple spot lesions can appear on the spears during
the harvest season and reduce quality, as well as, on fern growth later in the summer months.
Characteristic symptoms of Purple spot include small (1 to 2 mm) slightly, sunken elliptical reddish purple lesions on spears and ferns. Cercospora produces small tan lesions with darker margins on
ferns and stems. Damage to ferns can cause premature defoliation which will reduce carbohydrate
flow and reduce yield for the next growing season. Chopping the fern and incorporating the debris in
the fall after the fern senesces can help destroy overwintering sources of the inoculum, however these
practices may also lead Fusarium infection. Once fern stalks are full-size and/or disease is detected,
fungicide applications of chlorothalonil (FRAC code M5) in rotation with azoxystrobin (FRAC code 11)
should be repeated every two to four weeks until frost.
Rust is another important pathogen of asparagus. Rust can easily be diagnosed in the field early in the
season by the cream-colored oval lesions (6 to 19 mm) its produces. A few weeks later these lesions
will appear reddish-brown. These reddish-brown lesions can produce spores which can cause more
infections leading to further disease development. Control of asparagus rust is extremely important
and necessary in one and two year old beds, even with rust resistant varieties. Growers need to scout
for symptom development in cutting and non-cutting beds and, if not already started, apply fungicides
if necessary. Fungicide applications of chlorothalonil (M05), Folicur (tebuconazole, 3), mancozeb
(M03),or Rally (myclobutanil, 3) rotated on a 7 to 10 day schedule will help control rust.
For more information on controlling these important diseases please see the 2024/2025 Mid-Atlantic
Commercial Vegetable Production Guide.