Various methods can be used to detect root-infecting Phytophthora species in plants. We decribe a method for testing leachate from container grown plants in our BMPs for Producing Clean Nursery Stock pages. The most practical methods for monitoring large numbers of plants in a nursery involves capturing irrigation that drains from the bottom of continers during irrigation and baiting that water with a Phytophthora -specific bait such as a green pear. This system allows for testing of relatively large blocks of plants at one time without requiring that the plants be moved from the benches upon which they are situated. Such testing can be done on a spot basis during an inspection, but more importantly, can be run by the nursery on an ongoing basis to monitor plants for infection. Drought tolerant plants growing in the nursery with frequent irigation and low evaporative demand will commonly not show obvious top symptoms even when root rot is extensive.
To run this test, we need two pieces of equipment:
- a collection system that is placed under a nursery bench that will capture the leachate from the irrigated nursery plants on the bench and direct it into a zoospore collection vessel
- a zoospore collection vessel, which is a container that will tend to accumulate zoospores from the large volume of water that is being leached from the irrigated plants
Collection system (universal fit)
This page describes how to make a universal collection system that can be suspended under a variety of greenhouse benches. This is useful if you are running tests in multiple nurseries, which tend to have a wide variety of bench arrangements. As with many universal-fit devices, this collection system can be made to fit many different situations, but is not necessarily going to be the simplest or most efficient design for any given bench. If you are doing repeated tests in your own nursery, it will be simpler to design the collection system for the specific dimensions of your benches. Instead of suspending your custom-made collection system, it may be more convenient to make it free standing or cart-mounted to make it easier to slip under benches to be tested.
- vinyl flashing - 20 inch (51 cm) wide. Each standard system requires three pieces cut to 52 inches (152 cm) lengths (13 ft or about 4 m total), which will work on benches up to about 48 inches (122 cm) wide and will cover a length of about 54 inches (138 cm). We have used Amerimax 205008W Duraflash 20 Inch By 50 Foot White Vinyl Flashing. If you only make one collection system, you will have a lot of flashing left over, so consider making a couple at least. Also, vinyl flashing turns out to be pretty useful for all sorts of applications, so you can probably find good uses for the leftover material over time. It won't go bad.
- plastic grommets - 4 per vinyl flashing sheet, so 12 total for each full (3 section) system. We prefer Coghlan's 706 Snap 'n Tap Grommets (8 per pack). We have used the Camco 51046 Plastic Tap-In Grommets as well, but the batch we got had excessive amouts of blue dye that kept leaching out of the plastic, which we were not keen on. They also seemed to be more brittle. If you use the Camco grommets leach them well before using.
- plastic spring cord locks - 4 per vinyl flashing sheet, 12 total for each full system. These vary widely in cost, but in shopping for them, make sure that the hole will be large enough to accommodate two strands of the nylon cord you will be using. We found it pretty difficult to judge this from the online vendor pictures - the ones we ordered were much smaller than they looked. Also found in hardware and sporting-goods stores, but often hard to find.
- small S hooks - the minimum needed is 12 total for each full system. Typically easiest to pick up at a hardware store. We use hooks that are 1.25 inch (3 cm) long and are made of 0.125 inch (3.2 mm) diameter zinc-coated steel, You will need one end open and one end closed, so you can buy either the open or closed S hooks and plan to bend one end open or closed as needed.
- braided nylon cord - 0.125 inch (3.2 mm) diameter, or similar; make sure that two cords will fit in your cord locks. We have also used paracord, but find the ends are difficult to sear. For each full system, you will need 8 pieces, each about 14 inches (36 cm) long, for a total of about 9.3 ft (2.90 m). You will save a lot of trouble by getting the braided cords rather than the cheaper twisted type that unravels and frays a lot more readily.
- 1 inch diameter class 200 (thin walled) PVC pipe - two lengths, each about 20 inches (51 cm) long.
- flat PVC moulding, 3/4 inch (2 cm) wide, 1/4 inch (0.6 cm) thick (available at home improvement stores) or similar. We use this to make connectors that are used to link the vinyl sheets together at the seams. Other materials will work. You need something that will fit through the grommet hole (about 1 cm diam max), is long enough to go through two grommets and have room for a 4 mm diameter hole on top (about 4 cm), and has one wide end that will not slide through the grommet hole. It should ideally be plastic or someting similarly easy to clean and sanitize. A metal clevis or hitch pin of the right diameter will work, but may be subject to corrosion when treated with bleach.
- scissors or a utility knife to cut the vinyl flashing and nylon cord
- square or straight edge to mark the cut lines
- sharp steel punch or dividers to cut the holes (about 0.5 inch or 13 mm diameter) in the flashing for the grommets. The vinyl flashing is too thick to be cut by the plastic grommets
- measuring tape
- heat source to sear the ends of the cut nylon cord (not strictly necessary, but helpful)
- fine tooth backsaw or similar thin fine-toothed saw
- drill motor and 4 mm diam drill bit if making PVC connectors. The drill bit needs to make a hole large enough to accomodate the S hook end.
What to do:
- Cut three 52 inch (152 cm) lengths of vinyl flashing.
- Cut or punch holes in each corner of each sheet. The holes are centered 1-3/8 inch (3.5 cm) from the edges at the corners. Note: you can make additional holes along the short edge to make the sheet adjustable for additional lengths.
- Fold a partial crease in the center of the long edge of each sheet. The crease should extend only about 1/3 of the way across the sheet. The fold should create a depressed V in the glossy side of the flashing.
- Snap the plastic grommets into the holes in the corners of the each sheet.
- Cut 8 lengths of the nylon cord, each about 14 inches (36 cm) long. Sear the cut edges.
- On two of the sheets, you can tie one end of the cord through the grommet. For one sheet (this will be the upslope sheet), tie the cord on the two corners on the uncreased end of the sheet. For the other sheet (the downslope sheet), the cords will be tied to the end with the crease.
- On the other end of each of these cords, make a loop that is closed by the cord lock. Put an S hook on this loop and pinch it closed with a pair of pliers to keep it attached to the cord. Knot the end of the cord to keep the cord lock from slipping off. You can do the same thing with one end of each of the remaining cords.
- Pinch one end closed on the remaining S hooks. Tie the closed end onto the free, unknotted end of the cord.
- Draw a straight line down the length of each of the PVC pipes. Using a fine saw, cut a slit along the pipe down this line.
- To make the connectors out of PVC molding, mark as shown in the image. Drill the holes first, then cut along the lines. Use a file or sandpaper to clean up rough edges.
Vinyl flashing, sowing grommets (inset and right) and placement of crease. Nylon cord with S hook can be tied through the grommet as shown for the four corners that will not overlap with other sheets (the high corners of the upslope sheet and the lowest corners of the downslope sheet).
Configuration of cords that are not tied to the sheet corners. Note that all S hooks are pinched closed on one end so they will stay attached to the cords.
Connectors used to join vinyl flashing sheets at seams. Bottom image shows marked cut lines and drill points on PVC molding.
Setting it up:
- You will need to be careful not to let the top or edges of the vinyl flashing contact the ground to avoid containation. Have one person on each side of the bench when setting up to support and connect the vinyl flashing.
- Starting at the upslope side, attach the first sheet, glossy side up, under the bench using hooks.
- Place the uphill side (no crease) of the second sheet under the free edge of the first sheet. Line up the holes in both sheets and insert a connector through the stacked grommets of both sheets. Hook one end of a free cord through the connector hole and attached the other end to the bench.
- Repeat the above procedure with the third sheet, overlapping the second (middle) sheet over the third (downslope) sheet. Attach the hooks from the downslope cords to the bench.
- Slip the slit PVC pipes along the downslope edge of the final (downslope) sheet, leaving a gap of about 8-10 cm on each side of the central crease. These pipes make the edge of the sheet more rigid and serve as a dam to help direct the runoff into the center of the crease. It will be easiest to slip these on if you start at the edge of the pipe at the corner of the sheet and slip it straight along the edge (see image below).
- Place the zoospore collection vessel at the downhill side centered at the crease. Use the cord locks to adjust the height of the sheets so that they slope slightly downhill so that all water hitting the flashing will run into the collection vessel. Make sure there are no gaps at the junctions between the sheets. Spray some water on to the flashing from under the bench to rinse it off and check that all of the runoff is going into the collection vessel. Empty and rinse out the collection vessel before starting the test.
Left - linking of two adjacent sheets using the PVC connector and attachment to bench. Right - attachment of cord from non overlapping corner (upslope) to bench.
Cords can be hooked to containers if there are no places to hook on the bench top.
Variation of attachment due to supports in center of bench. Two sheets are linked together on the right side of the vessel, a sinle separate sheet is directed into the vessel from the other side. The vinyl flashing sheets can be used singly or linked together (2 or 3 sheets) to form a larger catchment area.
Slitted PVC pipe dams are easier to slide onto the edge of the flashing sheet if you start with the end of the pipe at the corner and slide stright down as shown in top image. When installed, edges of pipes should be inside of the rim of the zoospre collection vessel (lower image).
Zoospore collection vessel
To optimize the detection of zoospores, this device takes two facts into account. First, zoospores swim upward, so they will therefore concentrate near the top of a water column. Second, debris that may contain sporangia or oospores tends to either float or settle to the bottom of a water column. A large amount of water will be leached out of the irrigated plants, so the objective of this vessel is to concentrate inoculum where it can be detected by the bait. To accomplish this, excess water drains from the middle portion of the water column rather from the top or bottom.
The other main design consideration is that the container outflow needs to be sized large enough to accomodate the maximum amount of water flowing into the vessel. A 1 inch (2.54 cm) PVC pipe has sufficient flow to handle peak drainage from a set of plants covering about 10.8 sq ft (1.5 sq m) of bench, which can be captured using the collection system above.
- 2 gallon (7.6 L) insulated plastic beverage jug with an internal depth of 12 inches (30 cm). We use an Igloo Sport 2 Gallon Cooler / Jug / Beverage container
- Three 1 inch (2.54 cm) PVC slip-slip elbows
- One 1 inch (2.54 cm) PVC FPT-F slip coupling
- One 1 inch (2.54 cm) PVC MPT-F slip coupling
- One 1 inch (2.54 cm) ID rubber gasket (could use a rubber O ring)
- Three sections of 1 inch (2.54 cm) PVC pipe - schedule 40 or class 200: one piece 7.25 inches (18.5 cm) long; two or three pieces about 2 inches (5 cm) long. We have used sch 40 for the long section and schedule 200 for the short ones, but you can use class 200 for everything if you prefer.
- Short section (about 3/8 inch=1 cm long) of 2 inch (5 cm) ID ABS or PVC pipe. This is used to make a guard that keeps the pear bait from blocking the outflow inside of the vessel. Yo can come up with other types of pear exclusion devices, but the key points are that it should not have sharp edges that could wound the pear and should be easy to clean and sanitize.
PVC fittings and pipe sections (all 1 inch diameter), pear exlusion device (black ABS), gasket, and 2 gallon beverage container needed to assemble the zoospoire collection vessel. Existing spigot has been removed from the container and a larger hole has already been made.
- 1.25 inch (3.18 cm) diameter hole saw - this diameter should make a hole just large enough to thread in the male end of the 1 inch MPT coupling
- drill motor or drill press. If using a drill motor, you will need some wood blocks to fit in tightly across the bottom of the vessel, as shown in the video
- adjustible pliers (Channellocks or similar) to help tighten the threaded coupling
What to do:
See this video to see how to construct this vessel. In short:
- the existing spout is removed
- a larger hole is drilled out around the existing hole to accomodate the threaded coupling. Make sure the bottom of the hole is not too close to the bottom of the vessel or your fitting many not fit.
- assemble the pieces as shown in the images. All fittings can be simply pressed in as there is very little pressure in this system. Depending on the height of the hole at the bottom, you may need to adjust the length of the long PVC pipe slightly. The target is to leave the water level in the vessel about 2.5 inches (6 cm ) below the rim to prevent any overflow out the top.
Top view of the assembled zoospore collection vessel. Note rubber gasket to inside and pear exclusion device (black ABS ring) over the elbow that serves as the outflow.