PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Management (IDM)
Are you a commercial grower or home gardener?
1.Prepare a plan that fits your situation.
2.Crop, region. Recognize variations.
3.Identification of disease must be confirmed.
Consult a diagnostic service if needed (page xiv).
4.Monitor disease and/or damage and record results
as recommended. Check sources of all planting
material and inspect all new stock. Remember know
when, where, what and how to monitor.
5.Threshold. How much damage can you accept? Do
you need to calculate a threshold for your particular
crop? This will depend on whether you are a
commercial grower or a home gardener.
6.Action. Take action when any threshold is reached.
Remember crown gall is a sporadic disease and is
mainly a serious problem on nursery stock. If the
disease is a regular problem commercial growers should
treat susceptible planting material (Table 55).
7.Evaluation. Review IDM program to see how
well it worked. Recommend improvements if
required. Monitor treated nursery stock, etc for the
next few years after treatment where practical.
Control methods
Once a plant is infected with crown gall there is no
reliable effective eradication treatment.
Cultural methods.
Avoid wounding roots of trees and nursery stock
when planting and during subsequent cultivation,
crown gall enters only via relatively fresh wounds.
Make sure graft union is above ground level.
There is a greater incidence of crown gall on
grafted nursery stock rather than on bud unions.
Do not unnecessarily lime soil or add wood ash.
Avoid repeatedly planting susceptible crops into
infested soil unless roots, etc are treated with
Nogall. Some crops, eg corn or other grain
crops, are resistant and would reduce the amount
of inoculum in the soil.
Sanitation.
Destroy young plants with galls at the graft
union or near soil level. Remember older plants
may tolerate infection.
Infected plants should be dug up and burnt,
and if practical, eg in a home garden, also dig up
surrounding soil and burn, sterilize or replace.
Contaminated containers, seed boxes and
benches must be disinfected so that treated soil
or healthy seed, cuttings and other nursery stock
do not become infected.
Budding and grafting tools must be
disinfected to stop bacteria from spreading via
budding and grafting (page 309).
Table. 55. Crown gall – Biocontrol agent.
What to use?
PRE-PLANT DIPS
Seeds, roots of seedlings and cuttings
Nogall (Agrobacterium radiobacter var. radiobacter strain
K102.)
Biological control.
Nogall . Where crown gall is a recurring
problem, protect new plantings from attack by
dipping planting material (seeds, cuttings or
roots of young plants) in Nogall . This a nonpathogenic
strain of Agrobacterium sp. which
produces an antibiotic, that inhibits the growth
of the gall-forming strain of Agrobacterium. The
non-pathogenic bacteria grow on wound sites
produced during striking, root pruning, repotting,
digging, planting, weeding, and frost.
Susceptible plants are protected during their
initial growth stage when they are likely to suffer
severe damage if infected with crown gall.
Very occasionally, strains of crown gall, eg
those that infect grapevines, are not controlled by
this method. Research is under way to use nonpathogenic
strain of A. vitis.
Resistant varieties.
Within the known host groups there are no known
resistant cultivars. Overseas research is attempting
to develop resistant rootstock.
Plant quarantine. Avoid introducing crown
gall to disease-free areas by purchasing from
reliable suppliers of disease-tested planting
material and avoiding introductions of infested
soil. Make an effort to keep crown gall out of
nurseries and gardens by inspecting all new stock
and rejecting infected plants.
Disease-tested planting material.
Main source of infection is planting material.
Do not propagate from infected plant material.
unless treated with a biological pesticide.
Treated planting material must be planted in
disease-free soil.
Disease-free soil must only be planted up with
disease-tested planting material, eg diseasetested
nursery stock. Growers should purchase
and plant only crown gall-free trees.
Physical & mechanical methods.
Where crown gall is a problem in small areas
such as seedbeds and cutting beds, soil can be
pasteurized (60 o C for 30 minutes).
Bactericides.
There are no non-fumigants that will kill
crown gall bacteria in soil.
Gall paints have been researched for decades to
eradicate gall from established woody plants. The
usual method is to remove the gall and then apply
paint to the raw surface. Gallex (2,4-xylenol
plus meta-cresol) is still being researched for the
eradication of crown gall in established roses in
the USA (Anyango and Odhiambo 2000).
Controlling root chewing insect on grapevine stems
in nurseries reduce wounds which are entry points
for crown gall.
When and how to apply?
On stone fruit, almonds, pecans, walnuts, roses...
Seeds, cuttings, bare plant roots may be dipped in a
prepared suspension prior to planting in contaminated soil.
Trim damaged roots before dipping.
Used to protect propagation material before planting.
Very effective on Rosaceous plants but not as useful on
other plants such as chrysanthemum and grapevines.
Treatment is ineffective once infection has occurred.
306 Bacterial diseases