What is blight in tomatoes?
Blight
Blight is a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral organs.[1] Accordingly, many diseases that primarily exhibit this symptom are called blights. Several notable examples are:
Monilinia laxa
 "Monilinia laxa" is an ascomycete fungus that is responsible for the brown rot blossom blight disease that infects many different types of stone fruit trees, such as apricots, cherries and peaches. It can also occasionally affect some pome fruits; for example, apples and pears. The pathogen overwinters on infected plant parts, particularly on infected twigs, branches, old flower parts or mummified fruits. In spring, the pathogen produces asexual conidia on the aforementioned infected plant debris. In addition, apothecia, which are small, open cup, mushroom-like sexual propagative structures of "M. laxa" that produce ascospores, also develop on the fallen fruits on the ground. Both asexual (conidia) and sexual (ascospores) spore types are spread during the spring via wind and rain in which they infect blossoms and young shoots. Floral tissue is the most susceptible to both spores’ infection when the trees are in full bloom. The infected floral tissues are responsible for the production of the secondary inoculums that further continues the disease cycle during the spring season. If the environmental conditions are very conducive (i.e. warm and wet environments), infection can also occur in non-flowering shoots or leaves. Infection is sometimes not visible until after the fruit begins to ripen and the pit hardens. These ripe fruits are at a high risk of being infected and passing the disease onto other plants during harvest.