Develop a Water Management Plan
Water management is the most important step you can take to control Phytophthora diseases in the nursery. If you ignore this aspect, it is virtually impossible to avoid serious disease outbreaks and plant losses.
The main steps in water management for disease control are:
Water used to irrigate nursery crops should be free of Phytophthora spores.
This water should be applied in ways that avoid prolonged periods of wetness.
The irrigation system should apply water uniformly and match the needs of plants.
Carefully engineered surface and subsurface drainage systems should move excess water away from the root system and prevent standing water that favors disease.
While irrigation, rain, and misty conditions throughout the year often create conditions favorable for disease, following a good water management plan will help to minimize these risks.
The first steps in planning are to:
Observe how water moves around the production area, and note where water collects.
Measure how uniformly the irrigation systems apply water, and look critically at your irrigation guidelines. For example, if you are watering until the driest pot has had enough water, many pots probably will get too much water-which encourages disease.
Since rain contributes to the amount of water a nursery must deal with, it will help to know the average and maximum rainfall patterns for your location. In western Oregon, field-grown nursery crops use about 2.5 acre feet of overhead irrigation water in a single warm season. Container crops require about three times that amount: 7.5 acre feet. (This is one reason container nurseries recycle excess water.) Design and maintain drainage systems to handle heavy rain events to avoid flooding and having plants sit in water. To prevent over-watering, plan to adjust the irrigation schedule to account for the amount of rain that occurs during the growing season. After your evaluation, see what aspects the nursery does well and which ones need improvement.
Try to develop a plan that is achievable, recognizing that changing the way water is managed can be difficult. A water management system affects so many nursery operations and is costly. Remember, your goal is to control the most serious disease of nursery crops. A costly change in water management might be a good investment in the long run, if it allows you to avoid disease problems.