1. New leaves are small and defoliation occurs from root rot.
Figure 2. Size of infected area can be marked by plant death and the
presence of water-loving plants.
Figure 3. A field with heavy infection. The improved drainage is helping
is soil-borne and root infection is favored by saturated soil moisture.
Zoospores (swimming spores) produced by the fungus infect blueberry
roots. As the infection spreads, roots collapse and decay. Early above-ground
symptoms include yellowing of leaves with some burning of the margins
and lack of new growth. As the disease progresses, terminal leaves
1) become small, and excessive defoliation occurs because of severely
On chronically infected older bushes, nearly all the leaves on the
bush can be stunted and wilt-prone. Affected plants will often have
a restricted root system that allows them to be easily rocked back
and forth or pulled up. Plants in low areas in affected fields are
characterized by dead or prematurely defoliating bushes.
Defoliation and poor growth follow the contours of the low areas where
excessive soil moisture is present. The presence of sedges (Figure
2) and other water-loving plants is an indicator of the size and
shape of these areas.
Lasting control of phytophthora root rot on blueberries is accomplished
by improving drainage (Figure
3). Adequate ditching and raised, single-bedded rows are usually
sufficient. Rows are most easily bedded up prior to planting. In
existing fields, taper-disking or sweep-blading can be used. Field
drains using "sock pipe" and other types of pipe normally used for
residental septic fields have been effective for draining small
areas. Homeowners and pick-your-own growers often encounter problems
on wet clay or clay loam soils; the problem is often diagnosed as
"planted too deep". On these sites, growers should incorporate peat
or bark mulch before planting, then plant shallow and use additional
mulch to form beds.
fungi, chiefly Armillaria species, occasionally cause root
rot on blueberries. If Armillaria is present, a white layer
of fungal growth can usually be found just under the bark near the
soil. This fungal layer is not present with Phytophthora root rot,
and its presence or absence can be used to help distinguish between
the two types of root rot. Armillaria rot is most likely to occur
in newly cleared areas that have lots of old tree roots remaining
in the soil. Control is aided by removal of old dead roots and stumps
or by simply not planting in newly cleared areas.