The species name infestans is the present participle of the Latin verb infestare, meaning "attacking, destroying", from which the word "to infest" is derived.

The zoospores released from sporangia are biflagellated and chemotactic, allowing further movement of P. infestans on water films found on leaves or soils.

People can observe P. infestans produce dark green, then brown then black spots on the surface of potato leaves and stems, often near the tips or edges, where water or dew collects.

Infected tubers develop grey or dark patches that are reddish brown beneath the skin, and quickly decay to a foul-smelling mush caused by the infestation of secondary soft bacterial rots.

Under most conditions, the hyphae and asexual sporangia can survive for only brief periods in plant debris or soil, and are generally killed off during frosts or very warm weather.

In particular, volunteer plants sprouting from infected tubers are thought to be a major source of inoculum (or propagules) at the start of a growing season.

[12] Clonal lineages of A1 include: Discovered by John Niederhauser in the 1950s, in the Toluca Valley in Central Mexico, while working for the Rockefeller Foundation's Mexican Agriculture Program.

It also contained a diverse variety of transposons and many gene families encoding for effector proteins that are involved in causing pathogenicity.

[21][22] A study published in 2014 evaluated these two alternate hypotheses and found conclusive support for central Mexico being the center of origin.

Support for a Mexican orgin – specifically the Toluca Valley[20] – came from multiple observations including the fact that populations are genetically most diverse in Mexico, late blight is observed in native tuber-bearing Solanum species, populations of the pathogen are in Hardy–Weinberg equilibrium, the two mating (see § Mating types above) types occur in a 1:1 ratio, and detailed phylogeographic and evolutionary studies.

She pointed to the absence of potato exports during the 1840s, which posed a challenge to the notion of a Mexican origin for the blight's migration to the US and Europe [24].

In 2016, the Ristaino lab with collaborators Mike Martin and Tom Gilbert, at the University of Copenhagen, conducted the largest whole genome sequencing project to date with historic and modern day lineages of P infestans (25).

Analysis of these  more extensive genomic dataset that included both P. infestans and P. andina isolates documented an  Andean origin of the species [25].

Coomber et al., examined the evolutionary history of Phytophthora infestans and its close relatives in the 1c clade using whole genome sequence data from 69 isolates of Phytophthora species in the 1c clade and conducted a range of genomic analyses including nucleotide diversity evaluation, maximum likelihood trees, network assessment, time to most recent common ancestor and migration analysis [26}.

Furthermore, the distinction between modern Mexican and South American P. infestans proved less discrete, suggesting gene flow between populations over time.

Migrations from Mexico to North America or Europe have occurred several times throughout history, probably linked to the movement of tubers.

[13] The co-occurrence of the two mating types is significant due to the possibility of sexual recombination and formation of oospores, which can survive the winter.

[33] This is notable since different forms of P. infestans vary in their aggressiveness on potato or tomato, in sporulation rate, and sensitivity to fungicides.

[34] Variation in such traits also occurs in North America, however importation of new genotypes from Mexico appears to be the predominant cause of genetic diversity, as opposed to sexual recombination within potato or tomato fields.

If adequate field scouting occurs and late blight is found soon after disease development, localized patches of potato plants can be killed with a desiccant (e.g. paraquat) through the use of a backpack sprayer.

This management technique can be thought of as a field-scale hypersensitive response similar to what occurs in some plant-viral interactions whereby cells surrounding the initial point of infection are killed in order to prevent proliferation of the pathogen.

To increase the probability of successfully storing potatoes from a field where late blight was known to occur during the growing season, some products can be applied just prior to entering storage (e.g., Phostrol).

Maincrop varieties which are very slow to develop blight include Cara, Stirling, Teena, Torridon, Remarka, and Romano.

Defender is an American cultivar whose parentage includes Ranger Russet and Polish potatoes resistant to late blight.

[48] By using weather forecasting systems, such as BLITECAST, if the following conditions occur as the canopy of the crop closes, then the use of fungicides is recommended to prevent an epidemic.

Several studies have attempted to develop systems for real-time detection via flow cytometry or microscopy of airborne sporangia collected in air samplers.

In some regions of the world during the 1980s and 1990s, most strains of P. infestans became resistant to metalaxyl, but in subsequent years many populations shifted back to sensitivity.

Given the dangers of copper toxicity, other organic control options that have been shown to be effective include horticultural oils, phosphorous acids, and rhamnolipid biosurfactants, while sprays containing "beneficial" microbes such as Bacillus subtilis or compounds that encourage the plant to produce defensive chemicals (such as knotweed extract) have not performed as well.

This normally involves piling soil or mulch around the stems of the potato blight, meaning the pathogen has farther to travel to get to the tuber.

[63][64] The disease being first identified in Europe around Kortrijk, Belgium, in June 1845, and resulted in the Flemish potato harvest failing that summer, yields declining 75–80%, leading to an estimated forty thousand deaths in the locale.