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Alternaria Leaf Spot of Peanut

Alternaria Leaf Spot of Peanut

Alternaria spp.

fungi

In a Nutshell

    Alternaria arachidis causes small brown spots surrounded by a yellowish haloAlternaria tenuissima produces dark-brown blighting on the apical portions of leafletsAlternaria alternata is characterized by necrotic and brown lesions that affect adjacent veins

Hosts: %1$s

· Peanut

Symptoms

A. arachidis produces small brown, irregular-shaped spots surrounded by an yellowish halo on leaves (leaf spot). A. tenuissima causes a ‘v’ shaped blighting on the apical portions of leaflets. Later, the dark-brown lesion extends to the midrib and the entire leaf shows a blighted appearance, curls inwards and becomes brittle (leaf blight). Lesions produced by A. alternata are small, round to irregular in shape and spread over the whole leaf. They are first chlorotic and water-soaked, but as they enlarge, they turn necrotic and also affect the adjacent veins (leaf spot and veinal necrosis). The central portions rapidly dry up and disintegrate, giving the leaf a ragged appearance and leading to defoliation of the plant.

Trigger

These diseases are caused by three soil-borne fungi of the Alternaria species. Infected seeds can be the primary source of inoculum. If they are planted and the environmental conditions are favorable, severe losses can occur. The secondary spread between plants is facilitated by wind movement and by insects. Temperatures above 20°C, prolonged leaf wetness, and high humidity favor the spread of the disease. The incidence may be important on peanut crops irrigated during the post-rainy season. Depending on the occurrence and severity of the disease, pod and fodder yields can be reduced up to 22% and 63% respectively.

Biological Control

No effective alternative treatment has been found against these diseases so far.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatment if available. Chemical control measures include the foliar application of mancozeb, copper oxychloride or carbendazim.

Preventive Measures

    Use seeds from healthy plant material or certified pathogen-free seedsUse resistant or tolerant cultivarsRemove weeds, alternate hosts and volunteer plants from fieldsCheck the fields for any sign of disease whenever conditions are favorable for the pathogensHandpick and destroy infected plants found in the seedbeds or fieldsCrop rotation with non-host crops is recommended for a minimum of three yearsAvoid working in the field when foliage is wetPlow deep to rid the soil from any remaining pathogen