Abiotic problem with Lavender plug production

A propagator brought in a flat of lavender plugs (Lavandula x intermedia cv. Grosso) showing dieback and plant death. The grower has an intense fungicide rotation for Pythium so it was unlikely to be the cause. Soil pH and salt levels were within range for plug production. When the plants were removed and washed, no roots were seen on the affected plants. This indicates a rooting problem, not a disease. Several plants in the flat were able to root and mature althought they weren't at 100% (see above. Note:this photo was taken after holding in the lab for a week so the plants have deteriorated somewhat). It is possible that fertilizer levels were a problem earlier or growth temperatures were not in the range that lavender prefers. At this point, the exact cause of this problem is unknown.

Photo below shows rooted cutting (left) compared to an unrooted cutting (right) 30 days after sticking. A variety of secondary pathogens were isolated from the decaying stem of the unrooted cutting.

Verbena-Thielaviopsis Root Rot

A recent sample of Verbena cv. Valley Lavender from propogation stock showed stunting, poor root formation, and plant death. Roots were light brown and failed to grow beyond the original plug. The problem was diagnosed as root rot caused by the fungus Thielaviopsis basicola.

The above photos shows chlamydospores in crushed root tissue under magnification - this a characteristic diagnostic sign of T. basicola infection.

For more detailed information on Thielaviopsis root rot and management, check out this article in Greenhouse Product News.

Pythium root rots of bean and watermelon seedlings

Today was a day of root rots! Two samples of pythium root rot but both came in with complaints of foliage problems on field transplants (browning and death of bean leaves & wilting of watermelon). Luckily, the submitters had included the full root system and soil so we were able to quickly make an accurate diagnosis. Pythium agar was used to confirm the presence of Pythium spp. Note the characteristic stem lesions.
Pythium root rot on snap bean transplants:

And Pythium root rot on watermelon transplants:

What's your plant's problem?

Did you know that most U.S. states have a clinic that will diagnose your sick plant for a small fee? The American Phytopathological Society maintains a list of all university clinics. Click here to find one in your state!

Fennel-Unknown problem

Another delicious smelling sample- fennel (Foeniculum vulgare). This sample presented with browning on the edges of stems at the bulb. The very oldest leaves are yellowing and dying. The main cause is likely that the plant is pot bound (roots are curling around at the bottom). There was no internal decay in the bulb and the majority of the foliage was fine. The bulb is incubating to double check.Above photo is a little bleached out, note that the Jiffy pot has been pulled away for the photo.



Cut edges are starting to brown as I took the above photo ~10 mins after cutting.

Rust on Agastache

Another good smelling herb sample! Agastache sp. (pronounced ah gas TAH kee) is a perennial herb which smells like fruity, minty, licorice. This sample presented with raised rust colored pustules on the upper and lower leaf surfaces. All leaves were affected, but the disease appeared to affect the lower leaves first as many had fallen from the plant. Slightly crushing under a plastic coverslip, a wet mount of the pustules revealed characteristic telia of the rust Puccinia. (The morphology of the telia tells me it is in the genus Puccinia.) Some of the characteristic tails, or stalks, of the telia were broken off but many remained intact (see the last photo).




I need to remember to burn the scale into each picture! The software shows the scale on the screen, but doesn't burn into the image unless you go through an extra step. The leaf pictures were taken under the dissecting scope. I don't like this camera as the resolution isn't that great. The teliospore photos are taken using an Olympus camera and their software, MicroSuite Five. I tried using the merge function on the last photo (big clump of spores) to show the 3D effect, but it appears I need more practice. I saved leaves from this sample and will attempt better photos when time permits.

Venus Flytrap-Diagnosis in progress

A very cool sample came into the clinic this week-Venus flytraps!



Venus flytraps (Dionaea muscipula) are native to North & South Carolina (their natural habitat is only within a 100 mi radius of Wilmington, NC). They are, however, a very popular plant and considered easy to grow as long as you treat them right. 'Right' for a Venus flytrap is a humid swamp! Check out this site for detailed info on Venus flytraps (disclaimer: I can't vouch for complete accuracy on this site as I'm not a D. muscipula expert!).

The sample presented with blackened petioles and traps. Many of the older leaves were dying. The plants were being grown commercially and Phytophthora cinnamomi had caused problems in previous years. Leaves and rhizomes were plated for Pythium and Phytophthora.
Diagnosis is pending....