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How Processed Wood Substrate Affects Damping-Off Disease Suppression

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How Processed Wood Substrate Affects Damping-Off Disease Suppression

Benjamin Brown; Kevan W. Lamm, Ph.D.; Brian Jackson, Ph.D.; Tope Arayombo

Extension Explainer Publication S3-1007 published on January 28, 2026

Why This Matters

  • Growers are exploring processed wood as a partial peat substitute. In this radish damping-off model, peat+wood blends were never worse than peat+perlite and were often better, especially with disc-refined (FG) and hammer-milled (PTS) wood.
  • Results are crop- and pathogen-specific; treat as promising evidence, but not universal proof. Because of this new substrate mixes such as engineered wood are being considered as a replacement or partial substitution.
  • This study helps answer a few preliminary questions about disease spread in processed wood substrates but also serves as a starting point for deeper and more varied analysis of alternative soilless substrates.

Background & Research Insights

  • This study observed the effects of Raphanus sativus (Radish) infested with Rhizoctonia solani (fungus that causes damping off) in a mixture of three different engineered wood substrates mixed with peat at three different ratios and a control of perlite.
  • Evidence from this study suggests that engineered wood substrate mixed with peat does not increase the severity of damping off in Raphanus sativus
  • Results suggest that processed wood may be disease-suppressive, but all factors affecting disease rate were not studied. The results were also specific to Raphanus sativus.
  • These results should encourage growers, as processed wood substrate mixes do not have a negative effect and may be beneficial for disease rates in some crops. Results may vary with different species of crops but are worth testing

Materials & Inputs Needed

  • Substrate(s): 4 different substrates were used:
    • Commercial wood product produced with a disc refiner (disc-refined FG); product produced with a screw extruder (extruded GF); Manufactured hammer-milled material (Hammer-milled PTS); Control blend made up of 70% peat and 30% horticultural perlite (peatlite)
  • Ratios: Substrates were hand-mixed into peat (Canadian raw sphagnum peat) 3.56 kg m 3 at three ratios (10%, 20%, and 30%)
  • Additives: Carbonate dolomitic limestone added to adjust pH to 5.8; and wetting agent (PsiMatric, Aquatrols) 100 mL m -3
  • Crop tested: Raphanus sativus L. “Early Scarlet Globe” radish
  • Pathogen: Rhizoctonia solani (Rice inoculation)
  • Tests: pH, electrical conductivity, and substrate moisture were used to ensure uniformity between treatments and controls

Step-by-Step Guidelines

1. Prepare Substrate Mixes:

  • Obtain each of the wood-processed substrates (disc-refined FG, extruded GF, and Hammer-milled PTS) as well as commercial horticulture perlite.
  • Hand mix each of the substrates with raw Canadian sphagnum peat at ratios of 10:90, 20:80, and 30:70.

2. Analyze Substrate Mixes:

  • Adjust pH to 5.8 by adding carbonate dolomitic limestone.
  • Add wetting agent (PsiMatric, Aquatrols) 100 mL m-3; seal substrate mixes in 114 L plastic bins and allow them to equilibrate for 7 days.

3. Test and Measure Substrate Mixes:

  • Test pH and Electrical conductivity of 3 samples from each group. Find substrate moisture content with a moisture analyzer and add clear water to achieve a 60% gravimetric substrate moisture content for all treatments.
  • Measure porosity, container capacity, air space and dry bulk density for each treatment.

4. Pathogen Prep. and Inoculation:

  • Take samples from 2-week-old Rhizoctonia solani and autoclave for 60 min at 121 oC and 15 psi. Incubate samples for 7 days and then pulverize in a mortar and pestle.
  • Sieve through 2mm mesh and then add .5 g of infested rice per liter of substrate.

5. Crop establishment:

  • Sow thirty-two organic radish seeds (Raphanus sativus L. “Early Scarlet Globe”) by hand in each pot and hand water with 200 mL of clear water.
  • After inoculation, allow pots to sit in 24-hour illumination.

6. Measuring disease severity:

  • Seven days after seeding, measure disease severity on a scale of 1 = symptomless, 2 = small root or stem lesion but not damped-off, 3 = large root or stem lesion but not damped-off, 4 = post-emergence damping-off, 5 = pre-emergence damping-off.
  • Take the average for each pot and then measure fresh above ground biomass for each pot.

Tips & Pitfalls

  • If you’re trialing wood in peat: start at 20–30% wood with FG or PTS; expect equal or lower damping-off than peatlite in this model. GF can work but avoid very low (10%) where disease was higher.
  • Watch germination & background loss: FG tended to have better germination; GF lower (non-infested). If stands lag, adjust moisture/temperature and recheck seed-to-substrate contact.
  • Boundaries: evidence here is for radish + R. solani, 7-day window. Other crops/pathogens may differ, pilot small batches is therefore suggested before scaling.

Expected Outcomes

  • Across all tests, peat+wood was not worse than peatlite; with and PTS, more wood generally meant less disease; GF showed a best range (20–30%).
  • When trying to replicate this experiment growers should expect to see a higher fresh weight yield and lower rates of disease in crops similar to those used in this experiment
  • It is important to note this study only looked at relatively low percentages of processed wood mixes, if the percentage of wood was >30% it could lead to different results.

Additional Resources

Poleatewich, A., Michaud, I., Jackson, B., Krause, M., & DeGenring, L. (2022). The effect of peat moss amended with three engineered wood substrate components on suppression of damping-off caused by rhizoctonia solani . Agriculture, 12(12), 2092. https://doi.org/10.3390/agriculture12122092


Visuals and Graphs

Radish plants grown in non‐infested or Rhizoctonia solani ‐infested peat blended with hammer milled PTS compared to peat blended with perlite. Images were taken 7 days post‐infestation.