Best Management Practices for Producing Clean Nursery Stock

6.5. Other cultural inputs

Objective:  manage all cultural inputs to minimize the risk of contamination and facilitate rapid detection of root disease if it develops

What you need to know:  Phytophthora-caused diseases, as well as those caused by many other plant pathogens, are favored by the moist and crowded conditions found in many plant nurseries. Chemicals that suppress Phytophthora symptom expression in the nursery do not eliminate Phytophthora infections.

Best practices:

6.5.1. Use low water pressure and small droplet sizes when irrigating to minimize splash between containers. 

6.5.2. Schedule overhead irrigations to minimize the duration of leaf wetness. 

6.5.3. Avoid excessive irrigation or stressing plants with inadequate water.  Consider water loss from evapotranspiration, inputs from rainfall, plant and pot size and other factors when scheduling irrigations.

6.5.4. Keep irrigation wands, nozzles, and hose ends at least 3 feet (1 m) off the ground on clean, sanitized hooks or racks.  The same standard applies to any portion of a hose that may come in contact with or will be held over plants or benches during use.  Resanitize these items after any contact with the ground or other potentially contaminated surfaces.  Overhead hose reels (like those used in auto shops) are somewhat expensive, but potentially an easy way to avoid contaminated hoses in a small nursery.

6.5.5. Do not apply materials to plants (e.g., compost tea, organic amendments, organic fertilizers) unless you have reliable documentation that they

6.5.6. Do not use systemic oomycete suppressive compounds (“fungicides”) because they suppress Phytophthora but do not eliminate infections. These include fertilizers containing phosphite or phosphonate salts (note: phosphites have suppressive activity against Phytophthora diseases; phosphates are fertilizers with no such activity). By suppressing Phytophthora symptom development, these chemicals mask introductions of Phytophthora into the nursery. When such symptomless but infected plants are planted, the suppressive activity declines as the chemicals degrade. The pathogens can resume activity, leading to both plant decline and infestation of the planting site.  See How Using Fungicides in Nurseries Can Increase the Risk of Moving Phytophthora to Planting Sites for a more complete discussion on this topic.