A1 and A2 nuclei fuse together to form sexually produced spores, which reproduce in the same way as asexual spores. Sexual reproduction is possible if both mating types (A1 and A2) are present on the same host foliage.In warmer conditions, instead of releasing the zoospores, the spore will produce a tube that directly penetrates the host and provides nutrients directly to the zoospores still inside the spore. Under cool and wet conditions, spores release mobile reproductive units called zoospores that use a flagellated tail to find a suitable site for penetration and infection on host foliage.Spores produced on host foliage are carried by wind or water to other host plants.Weed hosts include nightshade and petunia.Ideal conditions for development include temps of 60-80 F for 8-10 hours with high moisture and/or humidity.Has proven to be resistant since the 1980s to some previously efficacious chemical controls.Inside the tuber, the initial infection will look dry and corky with a dark reddish-brown appearance. Infection causes tubers to be vulnerable to many other infections that lead to complete rotting and foul smell. Infection on tubers appears as reddish-brown, brown, or purple discoloration.Bottoms of leaves have similar spotting overlain by thin, white, cottony growths containing spores.
Legions may be surrounded by light green halo. Appears on foliage as irregular brown or black spots on top of leaves and stems.Classified as a water mold, not a fungus.Responsible for Great Irish Famine in the mid-1800s.Late blight hosts include: potato and tomato.Disease Summary Report Phytophthora infestans
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