Seasonal development
and life cycle—Pear decline
Pear trees are infected with decline when mycoplasma-infected psylla feed on their foliage. Trees planted
on tolerant rootstocks do not decline quickly, but may experience leaf damage, resulting in overall loss
of tree vigor. The mycoplasma in pear leaves causes them to curl and turn red prematurely by plugging
the food conducting cells in the leaf veins and petioles and preventing movement of food products out
of the leaves. First symptoms of leaf curling usually appear in early July and intensify up to leaf fall.
Leaves begin to turn red or purple as early as mid-August. Leaves that fall prematurely carry with them
an abnormally high amount of sugars and nitrogen, which normally would have been stored in limbs and
roots over the dormant season. This loss reduces the tree's vigor the following season.
Mycoplasmas are slowly eliminated by the host tree during the dormant season, and trees recover if
not reinfected by psylla. Some mycoplasmas overwinter within the roots of infected trees growing on tolerant
rootstocks, but the main source of a continued infection is renewed feeding the following season by
infected
pear psylla. | 
Red
foliage is characteristic of pear decline
|
