(1832) Alternaria alternata is a fungus causing leaf spots, rots, and blights on many plant parts, and other diseases.

It can also cause upper respiratory tract infections[1] and asthma in humans with compromised immunity.

[5] In addition to necrotic leaves and petioles, plants are found to have severe defoliation, with considerable yield losses when it occurs before flowering.

In addition, a tomato cultivar's resistance to a toxin produced by AAL also affects disease development.

Additionally, when dead infected debris is added to compost pile it can spread to other vegetables throughout the garden.

If monitoring indicates the presence of AAL, it is suggested to begin late-spring treatments of fungicide about mid-April[clarification needed].

This can be done by treating tomatoes in mid to late April[clarification needed] and 2 to 3 weeks later by applying a fungicide.

This causes the moisture to remain on the leaf tissue and increase susceptibility to the disease and provides an optimal environment for the fungus to survive and grow.

While γ-aminobutyric acid (GABA) has no direct fungicidal activity on A. alternata,[9] it does induce resistance in tomato (Solanum lycopersicum).

[12] A. alternata's conidia disperse via air currents, and their release from the lesions can be triggered by rainfall, or even just a sudden drop in humidity.

It was identified and confirmed by research conducted on fast atom bombardment and ion spray mass spectrometry.

[dubious – discuss] However, sensitivity to the fumonisin B1 gene is controlled by a single locus with two alleles expressing incomplete dominance when heterozygous.

[citation needed] A fungicide may be used to save the plants once they are infected; however, the disease cannot be completely eradicated.