PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Disease cycle
The disease cycle is quite simple (see Fig. 155
below). Susceptible healthy plants become infected
when planted into infested soil.
‘Overwintering’
In galls on host plants (especially nursery stock)
and in soil.
The bacteria can live as saprophytes in the soil
for years, but in the absence of hosts, the
population gradually declines. A. vitis can be
detected in plant debris in soil for at least 2 years.
Main source of infection is planting material.
If healthy vines are planted in old vineyard soils
containing contaminated debris the new plants
will be become infected.
Spread
By movement of infested soil on machinery, in
soil deliveries and containers, infected plants and
contaminated soil water.
By propagating from infected plants.
On pruning, budding and grafting tools. Nursery
plants may become infected through budding and
grafting scars.
Conditions favoring
Wounding of roots, crowns, stems or seeds by
cultivation, insects or animals. On grapevines
and Rubus spp. aerial galls are formed, thought
to be associated with frost damage to the stems
and canes.
The repeated planting of susceptible species into
infested soil.
Fig. 155. Disease cycle of crown gall (Agrobacterium sp.) (adapted from Agrios, 1997).
Bacterial diseases 305