Often considered a minor pathogen, angular leaf spot caused by the bacterium, Xanthomonas fragariae, can cause serious leaf and calyx infections ruining the marketability of fruit if left uncontrolled. [Read more…]

Often considered a minor pathogen, angular leaf spot caused by the bacterium, Xanthomonas fragariae, can cause serious leaf and calyx infections ruining the marketability of fruit if left uncontrolled. Like all bacterium, the pathogen will infect leaves and the calyx through natural openings or wounds. Primary infections of new growth in the spring originate from systemically infected overwintered plants and dead leaves in which the bacterium survives the winter; or from infested transplants. The pathogen is very resistant to desiccation and can survive in old, dried leaves or infected plant debris buried in the soil. The pathogen will not survive free in the soil so it originates primarily from infected leaf debris and infected crowns.

Infections can often start in production operations and come in on infected bare root transplants or cuttings. Symptoms on leaves include initial small, irregular water-soaked lesions (Fig. 1). Young, actively growing leaves are most susceptible, especially on vigorously growing plants. Disease development is favored by moderate to low daytime temperatures, low night time temperatures – near or below freezing, and high relative humidity. Long periods of precipitation, overhead irrigation used to establish plantings or protect plantings from freezing, and heavy dews favor disease development.
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There have been a few reports of angular leaf spot (ALS) caused by the bacterium, Xanthomonas fragariae, in strawberry in the northern part of New Jersey. Often considered a minor pathogen, ALS can cause serious leaf and calyx infections ruining the marketability of fruit if left uncontrolled. Like all bacterium, the pathogen will infect leaves and the calyx through natural openings or wounds.

Infections can often start in production operations and come in on infected bare root transplants or cuttings. Symptoms on leaves include initial small, irregular water-soaked lesions (Figure 1).


As disease progresses lesions will enlarge and coalesce forming reddish-brown spots on leaf surfaces which later become necrotic and translucent (Fig. 2). Holding infected leaves up to the light will reveal this diagnostic feature.


Importantly, in severe outbreaks in the spring, the bacterium can spread to fruit causing the calyx to turn brown and dry out ruining the marketability of infected fruit (Figs. 3 & 4).

The pathogen is easily spread via overhead irrigation and during rain and can be moved around the field during harvest. The bacterium may overwinter on infected plant debris buried in the soil for up to one year. The best method for controlling angular leaf spot is to buy clean transplant material. Conventional or organic copper-based products can help suppress the development of ALS, and should be applied at a low rate to avoid phytotoxicity in leaves. Weekly, preventative applications of 0.3 lb fixed copper have been shown to be effective in reducing ALS if applied early enough when disease pressure was still low.