Avoid yield loss now

Prevention is the only option when dealing with early blight


Early blight is caused by Alternaria solani and it is certain that it will infect your potatoes if preventative control measures are not taken. Early blight typically affects older plant tissue more severely than young tissue and usually only becomes a problem later in the season. However, in areas where potatoes are grown season after season the disease can cause problems earlier in the season.

The disease symptoms are angular dark brown to black lesions with concentric rings (see figure 1). Older lesions are surrounded by a yellow halo as the fungus produces toxins that move into the healthy cells that surround the infection and start killing off the tissue. Lesions usually start on the bottom older leaves and is spread upward in the plant. Early blight is a polycyclic disease which means it has many disease cycles during one season. A disease cycle is the period from infection, till new spores are formed and spread to infect again. Spores are spread primarily by water and wind.

Figure 1: Early blight lesion on potato leaf 
(Photo: Adri Anthonissen, Syngenta)

Moisture and temperature are the main factors controlling infection and disease development. The minimum temperature for infection is around 10°C and the maximum higher than 35°C, however the optimum temperature for infection is from 20°C to 30°C. No infection can take place in the absence of free moisture or high humidity.

The time it takes from infection to the development of symptoms can vary as it is influenced by many factors such as the age and susceptibility of the plants, temperature and moisture availability. The severity of disease development is mostly dependent on moisture. The longer the period of leaf wetness, the more severe the disease development. Any stress on the plants, such as overcrowding and insufficient nutrition will lead to an increase in disease severity.

An integrated control strategy is necessary to best avoid yield losses due to early blight. The pathogen survives on crop residues in the soil and removing as much of the material as is practical, will reduce the inoculum for the next season. Well-managed fertilization and irrigation schedules will be part of the disease control strategy, combined with an effective fungicide spray program.

When planning a fungicide spray program it is important to always alternate with fungicides containing active ingredients with different modes of action to avoid the development of resistance. Syngenta will soon be launching a new fungicide for control of early blight on potatoes and this will add another option to include into a fungicide program. More info to follow, watch the media!

Figure 2: Early blight control achieved by new Syngenta fungicide (Photos: Adri Anthonissen, Syngenta). 

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Issue 46


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