Phytophthora & Me

Written by Mary & Tim Bergstrom
Reviewed by Dr. Steven Jeffers, Clemson University

This is an educational and editorial story of our ongoing experience with Phytophthora, the “plant destroyer”, at our farm, Southern Hills Lavender. Pretty much, if you think you know what it is, you really don’t – we surely didn’t. So keep reading – it could save your lavenders’ lives.

Phytophthora causes a disease casually called “root rot” or “the landscape fabric killed it”. Phytophthora is also called a fungus, but it’s actually not. Phytophthora is also usually overlooked and not tested for – but it is a stealthy, and common, killer. Phytophthora is essentially like getting an incurable STD in your field and can affect your farm for the rest of the life of your farm. Yes, pay attention.

Our story

On May 2^nd, 2015, we planted 500 plants. Over the next 2 weeks, we planted an additional 600 plants. In the next 4 weeks, we didn’t get any rain, but we had our temporary irrigation in place as we planted each row, so the young plants received water on a regular schedule. On May 27^th, we received 0.30 inches of rain. During the month of May we had temperatures warmer than normal—even for South Carolina. On May 29^th, we had massive plant death in one cultivar in our field. We made anxiety-filled calls to the grower and sent pictures of the young plants to get their help. They did try to help and looked at pictures and pointed us to our local ag-college, Clemson University. We talked to a professor there and he referred us to the Clemson University Problem Plant Clinic (PPC). We learned about the PPC, figured out what we needed to send in, and drove 3 samples 1 hour away the next day. We got results back – Phytophthora nicotianae. The next day, we spoke with the PPC to get more details on the report and were referred to a Plant Pathologist that specializes in Phytophthora. We contacted Dr. Jeffers, the specialist, and drove 1 hour again to deliver a whole car full of samples to him the next day. Over the next several weeks, we took additional samples to Dr. Jeffers and learned about Phytophthora. We researched and tracked down treatment chemicals and created a treatment plan with Dr. Jeffers. We are still developing that treatment plan in hopes to make more headway against this almost permanent disease. We also had to pull out all the dead plants while attempting to limit the spread of contamination.

We communicated with the grower of those plants and they got part of the plants from another source originally. They believe that’s where the infection came from. This was a lesson for them as well about quarantining incoming plants. Even though the infection didn’t originate with this grower, they were gracious enough to refund our money.

Dying plant	Dead plant in tray
Dead plant pulled out of tray (notice black roots)

What it is – and isn’t

Phytophthora is:

“the plant-destroyer”, a genus of plant-damaging Oomycetes—fungus-like microorganisms (but not a fungus) often called water molds, whose member species are capable of causing enormous economic losses on crops worldwide (as a general, introductory reference: https://en.wikipedia.org/wiki/Phytophthora)
responsible for potato late blight that caused the Great Irish Famine in the mid-1800s; species of Phytophthora also attack tobacco, citrus trees soybeans, oak trees, cocoa trees, strawberries, coconuts, cucumbers, squash, rhododendrons, and many other ornamental plants–just to name a few
cosmopolitan and wide spread, and many are naturally present in agricultural and forest soils
extremely easy to spread and contaminate otherwise healthy plants and clean soil
adapted to different climates, soil types, and temperature ranges so that there are species that live in cold climates, moderate climates, and warm climates

Interesting facts:

There are over 100 described species and these species attack a wide variety of agricultural crops, landscape plants, as well as trees and plants in forests and natural ecosystems.
Most species are soilborne—which means they live and survive in soil; therefore, they frequently attack roots and the lower stem on plants but they also can attach foliage, flowers, and fruits.
These Oomycetes produce a swimming spore called a zoospore that moves very well in water—like irrigation water, runoff water, streams, and ponds.
Because of these zoospores, Phytophthora is most active under wet conditions when soils become saturated.
Disease symptoms are most pronounced when temperatures get hot because the diseased roots cannot move enough water to satisfy the needs of the plants, so plants wilt and die.
These pathogens can produce survival structures that allow them to persist in soil for many years-even under adverse conditions.
Disease management can be expensive, time-consuming, and a never-ending process.

Phytophthora is NOT:

an automatic death sentence just because you are using weed or landscape fabric
easily cured in an active field
the only type of “root rot” affecting plants; other microscopic organisms also can attack plant roots—Pythium, Fusarium, Rhizoctonium, nematodes are some of the majors ones

Testing

We’ve heard people talk about plant deaths, and some may sound like Phytophthora symptoms, but they are not getting the plants tested. Testing is VERY important to know exactly what you are dealing with no matter what the cause. It cost us $10 to get a sample tested at the Clemson University PPC and that gave us definitive results. Most states should have some type of diagnostic service associated with their agriculture university or other state agency. After testing, talk to your cooperative extension agent to dig deeper and get additional details. While you should expect a certain percentage of loss when planting a field, don’t assume that plant death is “just a part of farming”. Every death has a cause and you could learn the cause and then create a management plan to improve your farm business.

If you want to test your plants for Phytophthora, you can send a plant sample to the Clemson University Plant Problem Clinic for testing (they are serving as a consolidation point for consistent testing methodology):

The Clemson University Plant Problem Clinic [PPC] can accept samples, and there is a $20 fee for out-of-state samples. The PPC will process the samples and then send the cultures for identification.
Here is the link for the PPC website and information and here is the link to fill out their form.
The menu on the right side has links for sampling & submission guidelines as well as a sample submission form.

How it spreads

We had to ask a lot of questions about this. It can spread in one drop of water, but does it spread when it’s dry? Does it spread on implements and shoes? Does it spread in blowing wind or water running down your field or on the ground? The answer is yes to all of these. Many species of Phytophthora, including the one that attacks lavender, naturally live in soil. Once an infected plant is placed in the field, it becomes the source from which the pathogen can become established in your soil and spread to other plants. Therefore, the plant and surrounding soil need to be removed and, even with that effort, the pathogen still may remain in the soil. But if you don’t remove the plant, the pathogen will continue to produce inoculum and increase the likelihood of spreading to other plants.

Phytophthoras produce a unique spore called a zoospore, which is a motile, swimming spore. This allows these pathogens to move very easily in any form of water. It can spread if you have trays of plants side by side. Let’s say you’re ready to plant a new field and you have multiple orders of plants coming in. So you line up all the trays beside each other as they come in until you are ready to plant. If that first tray has Phytophthora and, as you water the plants in these trays, the water from it runs into the other trays, they can become contaminated. Then, you put those plants into the field and the contamination runs into other rows and other plants—wherever the water flows. Also, because the soil becomes contaminated with the pathogen, anything that moves soil has the potential to move the pathogen.

Sanitation is a very important part of disease management. Once we got the report that we had Phytophthora in our field, we researched what we could and listened to Dr. Jeffers at Clemson. We removed all the dead plants and started cleaning tools and our shoes when working in or leaving the field. We threw away any plants left in pots that had any symptoms. Even though there are some small areas we haven’t seen plants die yet in the field, we still need to consider the whole field contaminated so we don’t get complacent. It is still possible to spread the contaminated soil to other parts of our farm too – with our feet, tools, and maybe even by wind.

So, how does a nursery or grower not know they have Phytophthora? It might be that they are using a preventative fungicide as part of their regular treatments and the plants are not affected while that preventative is being used. As soon as the plants come to you, however, and the preventative is no longer being applied, the infection can start. Then, as you transplant the young plants, they are stressed and the infection has an even bigger opportunity to get a foothold. Then, as the summer warms up, the infection starts to kill the plant. On young plants, Phytophthora can kill them in a matter of days. In older, more established plants, it can kill one stem or section of the plant at a time and an infected plant may hang on for weeks or months.

Treatment

Phytophthora is very difficult to manage once it becomes established in a field because it is nearly impossible to eradicate it in soil without the use of soil fumigation. Now that our field of established plants is contaminated, we have to treat the entire field regularly for the life of the field. All of the registered fungicides primarily are preventatives instead of curatives, so the only way to kill Phytophthora with pesticides is with fumigation. Fumigation kills everything in the soil and it’s extremely costly for an entire field. However, some species of Phytophthora that normally occur in warmer climates, like the species that typically attacks lavender (P. nicotianae), is sensitive to cold temperatures and probably will not survive winter in locations where winter temperatures stay below freezing for long periods of time. In addition, prolonged periods of heat also can kill Phytophthora in soil, but this requires the use of a portable aerated steam generator or a process called solarization.

We are working with Dr. Jeffers on an experimental treatment for our situation that has not been tested before, and we will have to determine if the treatment will harm the plants. It is still possible that even though we’ve been treating with preventatives, that the plants had a low level infection before treatment started and the whole field could slowly die.

For those invested in Organic Certification, there is at least one option on the OMRI list. Talk to your Organic Certification specialist.

What can we do as an industry?

One lesson is when ordering plants, order 3-4 more than needed of each cultivar from each nursery for testing; don’t assume that because plants in previous orders were clean that plants in subsequent orders will be clean as well. When the order comes in, quarantine the shipment and send the extra plants for testing. Quarantine means to put the plants where their soil and water run off won’t get on/contaminate/mix with any other soil or plants. This can sound like a hardship or large task, but everything from Rubbermaid bins to a tarp on a carport could help even the slightest bit. The key is not to mix the plants in with other orders, plants, or soil until you get a clean bill of health from the test results.

The second lesson is to test—not just when you get the plants, but when any plant dies. Testing is another tool in our agricultural bucket and should be used appropriately. Again, plant death has a cause and you need to know what the cause is to run your farm as a business and keep a possible infection from spreading. If you suspect plant death is not cultural (ie: drought, too much water, sun, etc.), then employ testing. Find your closet ag college or extension agent and identify the plant clinic to send material to, have the submission process identified and ready to go. We’ve heard so many farmers talk about plants dying and they didn’t go beyond just thinking about why to get concrete evidence. It is also possible that the testing will show it’s not Phytophthora and you’ll have other things to research!

Also, be aware that testing is necessary to present an informed, fact-based case to others in the industry, growers, and nurseries.

The last lesson is to have a “systems approach” to your farm and business. A systems approach includes steps such as: points of control, development and implementation of best practices, monitoring and recording of issues, risk analysis, recording of production and training methods, documenting sources and movements, and recording incoming and outgoing materials to create traceability. Just like the ornamental fish industry knows that you have to quarantine a new Koi before putting it into your Koi pond, the US lavender industry needs to employ more scientific and business approaches to running our farms (I’m speaking for us too!). We need to take examples from other industries and apply them to even the smallest farm to make the entire industry stronger.

Phytophthora & me Tomorrow

Our farm was “virgin soil” before we began, having only been in pasture for many years. Our farm is young, with plants only in the ground for several months. We have plans to plant several more acres of lavender on our land over a period of years. These plant deaths, testing, clean up, and treatments have taken time and money out of our budget and put us behind in some plans. We will also have to live with this the rest of the time we own this land. But because we have a dream and a plan to make the dream happen, we are going to keep trying to understand Phytophthora, how to deal with it, and how to protect our plants. Phytophthora is now a part of our lives and our business plan.