Viruses consist only of protein and genetic material (DNA or RNA) and cannot replicate (reproduce) on their own, instead needing to infect cells to complete the process. Phytoplasmas are essentially a type of bacteria without cell walls. Both become systemic throughout the plant.
Stunt is a very important disease of blueberry throughout the United States and eastern Canada. Most varieties of highbush blueberry are susceptible. Stunt can be found in wild highbush and lowbush in the woods. No yield data are available on the losses caused by stunt, but symptomatic bushes are usually less than half the size of healthy bushes, and crop yields vary from very light to none.
Overall dwarfing of the bush is the primary symptom, hence the name "stunt." Small leaves that are cupped downward or puckered are characteristic symptoms. Leaves of infected bushes are often yellow, with yellowing most pronounced along leaf margins and between lateral veins. Midribs and lateral veins usually retain normal green coloration. Yellow areas often turn a brilliant red in the late summer. Stem internodes become shortened, and growth of normally dormant buds causes twiggy branching.
Stunt is actively spread in the field by the sharpnosed leafhopper. The pattern of stunt disease spread appears random. Leafhoppers are strong fliers and may come into a field from a great distance. Insecticides applied on a timely basis to control the leafhopper help keep the disease in check. Also use virus-tested planting stock when establishing a new field.
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