fungus on peas

[vegaenglit]

i planted some alaska peas and for a while they did really well.  then they got some powdery mildew or fungus of some kind.  the package said to water the ground, not the plant because of this problem and tried to keep water off the leaves as much a possible, but what abour rain?

the plot is in a semi-shaded spot to keep the hottest sun off the plants during the day.  do the peas need more sun?  what organic thing can i use?  ive got a plant or two chugging along, but would like to plant some more and dont want to lose them.