1. Controlling Soil-Borne Pests and
Diseases by Managing Soil Health
Dr. Paul Struik, Professor
Wageningen University
Netherlands

2. Controlling soil-borne pests and
diseases by managing soil health
Paul C. Struik, Crop and Weed Ecology, Wageningen University

3. Outline
Introduction
Definitions
Potato diseases and pests
Approaches
Soil disinfection
Crop rotation

4. Outline (continued)
Trap crops
Organic amendments
Enhancing disease suppressiveness
Solarization
Changing biological diversity
A systems approach
Conclusions

5. Definitions (1)
Soil:
An ecological system consisting of inorganic
minerals, decomposing organic matter, living
organisms and growing plants.
Soil is a complex living system:
>> 10,000 different species in 1 g of soil
>> 1.5 as many individual organisms in a
teaspoon of soil as people on earth

6. Definitions (2)
Soil health (synonym soil quality):
Ability of a soil to
* enhance productivity;
* regulate water flow;
* buffer environmental changes;
* support environmental, animal and human
health;
in a sustainable way.

7. Definitions (3)
Soil health according to SSSA:
Capacity of specific kind of soil to function, within
natural or managed ecosystem boundaries, to
sustain plant and animal productivity, to maintain
or enhance water and air quality, and to support
human health and habitation.

8. Soil health:
Physical fertility
Chemical fertility
Biological fertility
Focus on the biological fertility

9. Biological soil quality includes:
Biomass and biological activity
Biodiversity (no. of species and their abundance)
Disease suppression (various mechanisms)

11. Potato diseases and pests
Over 300 potato pests and diseases world-wide
About 140 are serious
Include viroids, viruses, phytoplasmas, bacteria,
fungi, nematodes, insects and parasitic weeds
Many are soil-borne

12. Main soil-borne potato pests and diseases (1)
Bacteria:
Ralstonia solanacearum (bacterial wilt, brown rot),
Streptomyces scabies (common scab)
Fungi:
Fusarium (dry rot),
Fusarium spp. (Fusarium wilt),
Helminthosporium solani (silver scurf),
Macrophomina phaseolina (charcoal rot),
Phoma exigua var. foveata (gangrene),
Phytophthora infestans (late blight),
Rhizoctonia solani (Rhizoctonia black scurf / stem canker),
Spongospora subterranea (powdery scab),
Synchytrium endobioticum (wart disease),
Verticillium spp. (Verticillium wilt)

13. Main soil-borne potato pests and diseases (2)
Nematodes:
Globodera rostochiensis (golden nematode),
Globodera pallida (white potato cyst nematode),
Meloidogyne chitwoodi (root-knot nematode),
M. incognita (root-knot nematode),
M. hapla (northern root-knot nematode),
M. javanica (root-knot nematode),
Nacobbus aberrans (false root-knot nematode),
Pratylenchus penetrans (lesion nematode),
Pratylenchus spp. (lesion nematode)

14. Silver scurf and black dot

15. Approaches to enhance soil health
Soil disinfection
Crop rotation
Special trap crops
Organic amendments
Management of crop residues
Enhancing disease suppressiveness
Solarization
Changing biological diversity

16. Soil disinfection

17. Effects of soil disinfection (in the absence of PCN)
No nematicide With nematicide
Stem infection (%)
Rhizoctonia 26 37
Verticillium 40 26
Colletotrichum 31 31

18. Crop rotation

19. Crop rotation
More or less fixed pattern in the succession of crops
on a certain field.
Relevant aspects are:
Which crops are part of the rotation
Frequency of each crop
Sequence of crops
All aspects affect disease pressure.

20. Potato stems affected by Rhizoctonia (%)
Rotation No nematicide With nematicide Average
P 48 62 54
MP 22 41 32
SP 23 32 28
MSBBP 9 14 12
Average 26 37

21. Potato stems affected by Verticillium (%)
Rotation No nematicide With nematicide Average
P 49 34 42
MP 39 20 30
SP 50 38 44
MSBBP 21 13 17
Average 40 26

22. Potato stems affected by Colletotrichum (%)
Rotation No nematicide With nematicide Average
P 35 32 34
MP 29 30 30
SP 33 36 35
MSBBP 28 27 28
Average 31 31

23. Average (6 years) early tuber dm yield (g/m2)
Rotation No nematicide With nematicide Average
P 99 122 111
MP 131 144 138
SP 118 154 136
MSBBP 152 167 160
Average 125 147

24. Comments on these results:
Synergistic and antagonistic effects occur
It is possible to influence such effects by cultural
practice
Level of other inputs must be adapted

25. Special trap crops

26. A new trap crop
Two greenhouse experiments (2003 and 2004) with
containers cropped to susceptible potato cv. Bintje,
S. sisymbriifolium (sticky nightshade) and fallow
- Cysts in nylon bags buried in soil with different
crops or fallow and dug up at different times
- Assessment of root density around each bag

29. 100
Luring of nematodes from their
80
60
cysts (%)
40
20 Bintje
Raketblad
0
0 1 2 3 4 5 6 7
-3
Root length density (cm cm )

30. Organic amendments
(green manure)

31. Effects of oats on relative numbers (%) of
mesofauna and Rhizoctonia index
Rel. no. of Rel. no. of Disease index (0-100)
collemboles nematodes
Year 1 Year 2 Year 2 Year 1 Year 2
Control 100 100 100 26 67
Oats 127 123 1043* 10* 51*

32. Management of
crop residues

33. Effects of debris removal (R) on Verticillium inoculum
Sampling in March year 4
Isolate Crop sequence (Year) no. cfu
per g
1 2 3
P P P PR 126
P PR PR PR 51***
F F P PR 199
F FR PR PR 28***

34. Enhancing disease suppressiveness
Example:
Rhizoctonia-decline

35. Use your own seed tubers (farm-specific seed)
Figure 1.
Schematic
representation of
interactions that may
play a role in potato
Rhizoctonia-decline in
seed potatoes
disease
Rhizoctonia-
suppressing
microorganisms population
in the soil in the soil

36. Disease suppression:
Trial field Wildekamp, The Netherlands, sandy soil
Grassland (50 years) ⇒ ⇒
G permanent grassland
G → AM monoculture maize
G → AR crop rotation (oats, maize,
barley, potato)
Arable land (20 years) ⇒ ⇒
A→G grassland
A→M monoculture maize
A→R crop rotation (oats, maize,
barley, potato)
(Garbeva, 2004)

37. Disease suppression
(Potato with Rhizoctonia)
Diversity: Shannon Weaver index with PCR-DGGE
rotation % bacteria fungi Bacillus actinomycetes
healthy
G → AM 100 3.51 3.26 2.85 2.75
G → AR 60 3.55 3.24 2.85 2.55
G 60 3.24 3.35 2.85 2.34
A→M 30 3.10 2.90 2.25 2.45
A→R 17 3.10 3.02 2.13 2.40
(Garbeva, 2004)

38. Solarization

39. Control of Ralstonia solanacearum through
solarization
A: soil microcosmos
B: Field plots
Schonfeld et al., 2003

40. Changing biological
diversity

41. Changing biological diversity by importing beneficial
micro-organisms
Effective and Beneficial Microorganisms (EM)
include
1. Photosynthetic bacteria
2. Lactic acid bacteria
3. Yeasts
They provide useful substances to the soil fauna
and stimulate breakdown of organic matter.
They also contribute to suppressiveness?

42. An example of system experiment to test how far
we can go with non-chemical enhancement of soil
health
Aim: control a complex of soil-borne pathogens
with ecologically sound techniques
Method: Grow potato in a narrow rotation (1:2),
infest with nematodes and fungi, and clean with
several techniques
Grow potato cultivars highly resistant, moderately
resistant and susceptible to Globodera pallida.

43. Soil infestation:
Nematodes: Meloidogyne hapla, M. chitwoodi,
Pratylenchus penetrans, P. crenatus and
Globodera pallida
Fungi: Rhizoctonia solani, Verticillium dahliae

44. Non-chemical control techniques:
Use of resistant cultivars (3 levels; HR, MR, S)
Use of green manure crops (3 levels: fallow, African
marigold, oats)
Use of trap crop against PCN (2 levels: control (fallow),
potato)
Use of removal of potato haulm (2 levels: left on the field
or removed)
36 treatment combinations in three replicates
Experiment duplicated and each duplicate running for 5
years

45. Experiment stopped after 5 years because of
budget cuts and early retirement of principle
researcher
Effects of use of trap crop on all pathogens
known
Results averaged over 3 green manure crops x
2 haulm treatments x 3 cultivar combinations

46. Main results of system experiment for one duplicate
Control Trap P
crop
No. Meloidogyne spp. / 100 ml soil 0 36 <0.001
No. Pratylenchus crenatus / 100 ml soil 184 190 ns
Stem infections with R. solani (index 0-100) 52 50 ns
Black scurf on tubers (index 0-100) 22 10 <0.001
Stem infections by V. dahliae for cv. S (%) 42 22 <0.05
No. cfu per g soil of V. dahliae 61 37 <0.01
Fresh tuber yield for cv. S (g/m2) 4540 5210 <0.05
Note trap crop is for PCN
cv. S is PCN susceptible cultivar

47. Conclusions:
Interactions between soil organisms are important
for control of soil-borne pathogens (sbp);
Soils can suppress certain sbp;
Organic amendment approaches are most likely
more successful in controlling sbp than
introductions of single species;
Root length density is important for trap crops;
Biodiversity is important to make management
strategies reliable.

48. Acknowledgement
This contribution was partly based on the heritage
of Dr K. Scholte, former co-worker at the former
Department of Agronomy, WU
Other information came from the Crop and Weed
Ecology group (WU), Soil Quality group (WU),
Louis Bolk Institute, numerous websites and
Science

49. Thanks for your attention !