For a printable brochure on the top 10 tips for preventing disease in your nursery using cultural controls, see Managing Phytophthora by J. Parke, attached below.

Purchase Clean Stock

Buy only clean, disease-free stock.

  • Purchase plants only from state certified suppliers (see Module 3 for details)

  • Inspect all incoming plants for symptoms of disease. Keep new shipments separate from the rest of your nursery stock until you are sure they are free of disease

Sanitation Steps for Pots and Potting Media

  • Ensure that potting media or potting media components are pathogen-free by purchasing soilless media or by treating potting media components with aerated steam (see Module 3 for details).

  • Store and mix potting media components on a cement slab, not on soil. Do not contaminate clean potting media by using dirty, infested tools, equipment, vehicles, and water.

  • Use new pots, or disinfest used pots. Disinfest pots by treating them with aerated steam, or by washing them to remove old potting media and soaking them in a disinfectant.

Sanitation Steps for Propagation

  • Keep the propagation area extremely clean. Between crops, thoroughly disinfect your potting area, sorting area, cutting benches, machines, tools, propagation mist beds, and greenhouses.

  • Prevent contaminating propagation areas with soil potentially infested with Phytophthora. Field workers should clean their shoes and wash their hands or change gloves before entering propagation areas. Equipment, tools, and vehicles used in the field should not be used in the propagation area.

  • Do not place flats or containers directly on soil. Place them on raised benches or on a 6-inch layer of gravel.

  • Never allow sick or dead plants, or their fallen leaves, to remain in the propagation areas. These can harbor Phytophthora and spread disease to healthy plants.

  • Select cuttings from disease-free plants. Ideally, these should be from stock plants, or “mother blocks,” that are separate from plants grown for sale. Treat mother blocks with protectant chemicals to reduce diseases.

  • Use several pairs of pruning shears or knives when making cuttings, so that one can be soaked in disinfectant solution while others are being used. Change the disinfectant solution regularly to retain its effectiveness.

  • Soak cuttings in an approved disinfectant solution before sticking them in flats.

Sanitation Steps for Production

  • Scout your nursery regularly and remove any sick or dying plants right away.

  • Place your cull pile away (and down the slope) from propagation and production areas, potting media storage, and water sources.

  • Do not make compost from diseased plants unless your composting procedures meet EPA standards (a minimum temperature of 131 F for 2 weeks with 5 turnings for windrow composting, or 131 F for 3 consecutive days for forced air static piles.)

  • Rotate crops. If you grow a crop susceptible to Phytophthora, then follow it with a crop that is not susceptible. This applies to plants grown in greenhouses, in can yards, and/or in the field.

  • If field soil becomes heavily infested, plant it to a nonsusceptible cover crop or a green manure crop. Use fumigation only as a last resort.

  • Never place container plants directly on soil; place them on raised benches or on a 6-inch layer of gravel.

  • Avoid excessive applications of nitrogen fertilizers. The resulting succulent new growth is very susceptible to Phytophthora.

  • Avoid excessive applications of nitrogen fertilizers. The resulting succulent new growth is very susceptible to Phytophthora.

  • Do not let leafy debris accumulate in nursery beds. If you use a weed barrier mesh, keep it free of debris.

  • To prevent contaminating clean areas with mud or soil from potentially infested areas, wash vehicles, tools, and shoes before moving into a new area of the nursery.

  • Prune and harvest susceptible plants during dry weather. Wounds provide entry points for Phytophthora, especially if wounds stay wet or muddy.

 

Host Resistance

Planting resistant hosts is an effective way to manage Phytophthora disease, but market demands may make this difficult.

  • Grow genetically resistant species and cultivars whenever possible. Use disease resistance as a tool to market your products.

Chaemacyparis is a good example. Chaemacyparis is one of the most highly prized trees in horticulture, but it is very susceptible to Phytophthora root rot caused by Phytophthora lateralis. In recent years, native Port-Orford-cedar (Chaemacyparis lawsoniana) was part of a selection and breeding program by the U.S. Forest Service and Oregon State University to find resistant varieties.