Friday, June 26, 2015

Tomato Leaf Spot Diseases

Brown spots on a tomato leaf
Early blight
(Photo: NMSU-PDC)
Featured Diagnosis: Tomato leaf spot diseases - Two different fungi which cause leaf spots on tomatoes have recently been identified in the NMSU Plant Diagnostic Clinic: early blight, caused by Alternaria solani, and Phoma rot, caused by Phoma destructiva. These two leaf pathogens occur under similar environmental conditions and produce similar symptoms on plants. Test, don't guess! A laboratory test is recommended to properly identify the causal agent. Samples can be submitted to the NMSU - Plant Diagnostic Clinic through the County Extension Offices.

For homeowners, cultural practices that reduce humidity and leaf wetness are essential for good management: avoid overcrowding and avoid wetting the foliage. If plants are irrigated in a manner that wets the foliage, water early in the day so that the leaves dry quickly. When conditions are highly favorable for disease development, fungicides may be helpful in reducing the severity of the disease. Both organic and synthetic fungicides are registered to help manage these diseases. If fungicides are used, all label instructions should be followed very carefully. Some tomato cultivars are tolerant of early blight and are recommended in areas where this disease is common.

A tomato plant in a pot with yellowing leaves
Phoma rot
(Photo: NMSU-PDC)
A microscope photo of a egg-shaped brown fruiting body of a fungus with round spores around it.
Pycnidia and spores of
Phoma destructiva,
the causal agent of Phoma rot
(Photo: NMSU-PDC)
A microscope photo of multi-celled, elongate spores.
Spores of Alternaria solani,
the causal agent of early blight
(Photo: NMSU-PDC)

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