Valdensinia leaf spot
Valdensinia infects all clones of lowbush blueberry and both prune and crop plants. The spots are typically round, large, and brown, and can have a “bull’s eye” appearance. Leaves can have from 1 to about 10 spots that can be from ⅛ to ½ inch and larger. These spots rapidly enlarge on the leaves and can spread from stem to stem within a few days. This leaf spot causes early leaf drop, and young leaves drop off when infected by only one spot and while still green. Stems can have complete leaf drop or only have a few infected leaves at the top of the stem. Older infected leaves will remain on the plant until leaf drop in the fall. In prune fields, stems with complete leaf drop will not produce flower buds for the next year. Crop fields with leaf drop will have decreased yields and smaller berries. The fallen infected leaves are the source of new spores to cause more infections. The spores are large and very efficient at infecting blueberry leaves. The spores can be produced in 2 days on wet, dead infected leaves on the ground. Mature spores are shot off, up to 8 inches high, and typically land on the underside of leaves. The spores will attack all ages of blueberry leaves and will also try to infect all plants they land on so you may see small spots on nearby weeds. The fungus requires about 6 to 8 hours of wet weather (rain or fog) for the spores to infect new leaves. The disease will rapidly spread out from infected stems to adjacent plants as long as the leaf litter remains wet and there is occasionally wet weather for 6 to 8 hours. This fungus produces large, heavy spores that are not carried by the wind so this fungus cannot move across large bare areas or roads without human help.