Cultural Management of Armillaria Root Rot
Cultural management of Armillaria root rot (ARR). Several studies
have demonstrated that partial excavation of the crown of trees to
expose primary roots to air and solar heating (collar excavation) can
reduce Armillaria colonization and prolong the productivity of infected
fruit trees. For example, in an orchard survey collar excavation
prevented tree mortality at 35 sites in an 8-year-old citrus plantation
infested with Armillaria for over 11 years. Since cambial temperatures
and moisture contents of exposed roots never reach levels reported to
directly kill Armillaria in vitro, they suggested that Armillaria fails
to colonize the exposed crown of infected trees in the field due to a
continuous effect of mild heating and drying.
Root
collar excavation (RCE) has been applied to established citrus trees and
grapevines for Armillaria root rot (ARR) control but despite its demonstrated
effectiveness this cultural management system is not routinely used for ARR
protection in disease-infested replant sites. One major drawback is the difficulty
of excavating the below-ground root collar, the potential of excavated roots to
be covered again with surrounding soil and the associated labor cost. We studied a new cultural method was investigated that resulted in trees with above-ground
excavated root collars potentially eliminating many of the drawbacks.
Experimental peach trees were planted in two commercial orchards (designated Landrum
and Monetta) in South Carolina (SC); each tree replaced one that had declined
from ARR disease the year before. Trees were planted approximately 40 cm higher
than normal in open bottom Smart Pots and root collars were excavated above
ground level 8 months later. Five years after planting 30 and 70% of all
control trees (planted according to grower standard) had declined from ARR
disease in Landrum and Monetta, respectively, whereas only 0 and 10%,
respectively of trees in the above-ground root collar excavation (AG-RCE)
treatment had declined. The difference in disease pressure between the two
locations could not be attributed to differences in nematode pressure. Non
excavated trees in Smart Pots revealed significantly less tree decline (
P < 0.05) compared to the
control but tree decline in both locations was greater compared to the AG-RCE
treatment (
P < 0.05). Trees
in the AG-RCE treatment were as vigorous as the controls but produced more root
suckers. In this ‘prototype’ study, we demonstrate the potential of above-ground
root collar excavation for ARR management. Its potential for commercial use is
discussed. A manuscript is in press in the journal 'Plant Disease'.
