Controlling Soil-Borne Pests andDiseases by Managing Soil Health

Dr. Paul Struik, ProfessorWageningen University

Netherlands

Controlling soil-borne pests and diseases by managing soil health

Paul C. Struik, Crop and Weed Ecology, Wageningen University

Outline

Introduction

DefinitionsPotato diseases and pestsApproaches

Soil disinfectionCrop rotation

Outline (continued)

Trap cropsOrganic amendmentsEnhancing disease suppressivenessSolarizationChanging biological diversityA systems approachConclusions

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

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.

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.

Soil health:

Physical fertilityChemical fertilityBiological fertility

Focus on the biological fertility

Biological soil quality includes:

Biomass and biological activityBiodiversity (no. of species and their abundance) Disease suppression (various mechanisms)

Potato diseases and pests

Over 300 potato pests and diseases world-wideAbout 140 are seriousInclude viroids, viruses, phytoplasmas, bacteria, fungi, nematodes, insects and parasitic weedsMany are soil-borne

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)

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)

Silver scurf and black dot

Approaches to enhance soil health

Soil disinfectionCrop rotationSpecial trap cropsOrganic amendmentsManagement of crop residuesEnhancing disease suppressivenessSolarizationChanging biological diversity

Soil disinfection

Effects of soil disinfection (in the absence of PCN)

No nematicide With nematicideStem infection (%)Rhizoctonia 26 37Verticillium 40 26Colletotrichum 31 31

Crop rotation

Crop rotationMore or less fixed pattern in the succession of crops on a certain field.

Relevant aspects are:Which crops are part of the rotationFrequency of each cropSequence of crops

All aspects affect disease pressure.

Potato stems affected by Rhizoctonia (%)

Rotation No nematicide With nematicide Average

P 48 62 54MP 22 41 32SP 23 32 28MSBBP 9 14 12

Average 26 37

Potato stems affected by Verticillium (%)

Rotation No nematicide With nematicide Average

P 49 34 42MP 39 20 30SP 50 38 44MSBBP 21 13 17

Average 40 26

Potato stems affected by Colletotrichum (%)

Rotation No nematicide With nematicide Average

P 35 32 34MP 29 30 30SP 33 36 35MSBBP 28 27 28

Average 31 31

Average (6 years) early tuber dm yield (g/m2)

Rotation No nematicide With nematicide Average

P 99 122 111MP 131 144 138SP 118 154 136MSBBP 152 167 160

Average 125 147

Comments on these results:

Synergistic and antagonistic effects occurIt is possible to influence such effects by cultural practiceLevel of other inputs must be adapted

Special trap crops

A new trap crop

Two greenhouse experiments (2003 and 2004) withcontainers 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

0

20

40

60

80

100

0 1 2 3 4 5 6 7

Root length density (cm cm-3)

Lurin

g of

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atod

es fr

om th

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)

BintjeRaketblad

Organic amendments (green manure)

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 67Oats 127 123 1043* 10* 51*

Management of crop residues

Effects of debris removal (R) on Verticillium inoculumSampling in March year 4

Isolate Crop sequence (Year) no. cfuper g

1 2 3P P P PR 126P PR PR PR 51***F F P PR 199F FR PR PR 28***

Enhancing disease suppressivenessExample: Rhizoctonia-decline

Use your own seed tubers (farm-specific seed)

potato

disease suppressing

microorganisms in the soil

Rhizoctonia-population in the soil

Figure 1.

Schematic representation of interactions that may play a role in Rhizoctonia-decline in seed potatoes

Disease suppression:Trial field Wildekamp, The Netherlands, sandy soil

Arable land (20 years) ⇒⇒

A → G grasslandA → M monoculture maizeA → R crop rotation (oats, maize,

barley, potato)

Grassland (50 years) ⇒ ⇒G permanent grasslandG → AM monoculture maizeG → AR crop rotation (oats, maize,

barley, potato)

(Garbeva, 2004)

Disease suppression(Potato with Rhizoctonia)

Diversity: Shannon Weaver index with PCR-DGGE

rotation %healthy

bacteria fungi Bacillus actinomycetes

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)

Solarization

Control of Ralstonia solanacearum through solarization

A: soil microcosmos

B: Field plots

Schonfeld et al., 2003

Changing biological diversity

Changing biological diversity by importing beneficial micro-organisms

Effective and Beneficial Microorganisms (EM) include1. Photosynthetic bacteria 2. Lactic acid bacteria3. YeastsThey provide useful substances to the soil fauna and stimulate breakdown of organic matter.They also contribute to suppressiveness?

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 techniquesMethod: Grow potato in a narrow rotation (1:2), infest with nematodes and fungi, and clean with several techniquesGrow potato cultivars highly resistant, moderately resistant and susceptible to Globodera pallida.

Soil infestation:

Nematodes: Meloidogyne hapla, M. chitwoodi, Pratylenchus penetrans, P. crenatus and Globodera pallidaFungi: Rhizoctonia solani, Verticillium dahliae

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 replicatesExperiment duplicated and each duplicate running for 5

years

Experiment stopped after 5 years because of budget cuts and early retirement of principle researcherEffects of use of trap crop on all pathogens knownResults averaged over 3 green manure crops x 2 haulm treatments x 3 cultivar combinations

Main results of system experiment for one duplicate

Control Trap Pcrop

No. Meloidogyne spp. / 100 ml soil 0 36 <0.001No. Pratylenchus crenatus / 100 ml soil 184 190 nsStem infections with R. solani (index 0-100) 52 50 nsBlack scurf on tubers (index 0-100) 22 10 <0.001Stem infections by V. dahliae for cv. S (%) 42 22 <0.05No. cfu per g soil of V. dahliae 61 37 <0.01Fresh tuber yield for cv. S (g/m2) 4540 5210 <0.05

Note trap crop is for PCNcv. S is PCN susceptible cultivar

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.

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

Thanks for your attention !