New sporangia are then carried by wind and splashed water to new plant tissue, creating new infections. After just 4-5 days of sufficient moisture and moderate temperatures, a new phase of sporulation can occur at the site of the initial infection. In cooler wet weather, however, sporangia produce motile zoospores that can infect host tissues. In warm weather, sporangia land on susceptible host tissue and directly germinate to create an infection. Phytophthora infestans reproduces asexually (via sporangia and zoospores). Wisconsin residents can refer to the disease prediction and weather models available at Vegetable Disease and Insect Forecasting Network (VDIFN) website. Mycelia prefer temperatures around 73☏ for optimal growth. Sporangia may germinate at 64-75☏, and zoospores are released at 46-64☏.

The production of pathogen spores is promoted by moist conditions (90-100% relative humidity) with moderate temperatures (60-80☏). The pathogen invades host plant cells causing plant death. The pathogen spreads by movement of asexual spores: sporangia (airborne spores) and zoospores (water-swimming spores). In some countries of Europe and South America, the pathogen can produce a soil-persistent spore known as the oospore, but this spore has not been identified in the United States. In the united states, this fungus-like organism overwinters primarily in plant debris as mycelia, a filamentous thread-like growth of the pathogen.

Phytophthora infestans is the oomycete, or water mold pathogen, responsible for tomato late blight. White, fuzzy pathogen growth can also be found in association with the fruit lesions. Symptomatic tomato fruits appear mottled, often with golden to dark brown, firm, sunken surfaces. Discoloration may also occur on the flowers, causing them to drop. Stem and petiole lesions are brown and are typically not well defined in shape. White, fuzzy growth may be found on the undersides of leaves or on lower stems. When the weather is very humid and wet, late blight infections can appear water-soaked or dark brown in color, and are often described as appearing greasy. Infected leaves typically have green to brown patches of dead tissue surrounded by a pale green or gray border. Symptoms of late blight may be found on any above-ground part of the tomato plant. However, it is most infamously known for its destruction of potato, S. Late blight is a plant disease that affects a variety of Solanum spp., including eggplant, pepper, nightshade weeds, and petunia.

Late blight of tomato