This week a grower called to report an area of stunted strawberry plants, first noticed after removal of the row covers in April. There may have been overwatering on occasion.
If you read the 2016 Commercial Vegetable Production Recommendations, you’ve seen the page, Diagnosing Vegetable Crop Problems (A27). Stepping through the diagnostic process with a grower is mutually satisfying – there’s nothing better than getting to the root of a problem so it can be minimized or avoided altogether in the future. The process involves tracing the history of the field and the development of the problem, then closely examining the soil and plants.
Field and Crop History
Our grower said that the field previously had summer cover crop, which was tilled under while green. A couple of weeks later, raised beds were made with plastic mulch applied. The strawberry plugs were set into the beds in late summer. The growth differences that caused him to call weren’t noticed until after the row covers were removed in April.
Field, Soil, and Plant Inspection
Driving up to the field, it was easily seen that plants near the middle of the field were stunted. Noting the slight depression in the same area of the field, we talked about the likelihood of increased soil water at that location. The grower did indicate that the beds may have been overwatered on occasion. With the sandy loam textured soil, the wetting pattern did not reach the edges of the bed we were examining. Pulling plants out of the bed showed great differences in root growth on the sides of individual plants. Roots near the drip line were severely affected, while roots towards the outside of the bed were mostly healthy. Using fingers, the root sheath slid off when pulled, leaving only an inner wire-like portion of the root.
Diagnosis – Pythium Root Rot
We concluded that the problem was Pythium root rot that most likely began in the fall in the area of the field that had risk factors for water saturation. Fortunately the sandy loam soil prevented further spread, and the rest of the plants looked great with excellent production.
Plans – Now and Future
For now we want to avoid over-irrigating which increases the spread of Pythium in the field. Soil fungicide is not an option in this field that is so close to harvest.
In the future, we want to wait 3 to 4 weeks after the cover crop is tilled under (other options are to mow or use a burn-down herbicide) before proceeding with mulch application and planting. This way we can influence the plant (rotting cover crop), environment (over watering, field depression), pathogen factors that support plant disease.
Baysal-Gurel’s (OSU) presentation on Management of Soil-Borne Diseases in Organic Vegetable Production is an excellent resource on the subject of management practices for cover crops to avoid soil-borne disease.