Alright folks, this will be my last project update for a little while! That was a whirlwind of information, but I hope that you were able to take the time and read through the work over the last few weeks.
As we are right on the cusp of April, I figured I can share a few upcoming events and other newsletter updates alongside this post as well. Based on the size of this list, we are officially transitioning out of event season, and transitioning into the growing season!
Upcoming Events/Perennia Updates
- Tunneltalk Webinar Series
- April 7 - Irrigating Soil-based Crops in High Tunnels (pt 2)
- check out the recording for part 1 here if you haven't already!
- May 4 - Enterprise Budget for High Tunnel Tomatoes
Recent Project Work: Assessing the Efficacy of Disease Protectants Against Pythium
Based on the varied and inconsistent disease results we saw following anaerobic soil disinfestation (ASD) implementation on farm, we decided to dedicate some of our project funding through Horticulture Nova Scotia to assessing the efficacy of some of the commercial root protectants that are available on the market. We have a wide host of products with notable price tags, looming expiration dates, and a lot of uncertainty on efficacy...so this seemed like a great opportunity to try and add some clarity on what is available on the market, and what these products can do!
In a perfect world, we would be able to implement this project in a commercial greenhouse, dose certain plants with disease, and follow a handful of plant productivity metrics over time gaining valuable information on what each product was able to offer in terms of protection. This is just not feasible with our current resources. We went back to the drawing board to see what we could pull off, and landed on a tomato seedling assay. This way we are able to test the products in a 'living' situation, while addressing our space restrictions and desire to keep inoculated trials contained and far away from commercial production. You can see the project setup below in Figure 2.
I wanted to assess product efficacy in two scenarios with these trials:
- Seeds are planted into infected media with and without preventative products applied
- Healthy seedlings are transplanted into infected substrate with and without preventative products applied
Both scenarios give the plants 3-4 weeks of growth in their respective treatment, giving the disease some time to take hold and lend us some information on product efficacy.
Due to the sheer number of products available for biological control of Pythium root rot, we decided to focus on representation of active ingredients as opposed to each individual product on the market. We settled on a list of 6 active ingredients to test in our growing rack, one of which serves as a conventional chemical control. Each product is applied preventatively according to the label recommendations throughout the duration of our trial.
The active ingredients we decided to include are:
- Trichoderma harzianum
- Streptomyces lydicus
- Gliocladium catenulatum
- Bacillus amyloliquefaciens
- Mono- and di-potassium salts of phosphorous acid
- Propamocarb (conventional chemical control)
The main metrics we were observing through the trial was root development and root disease, however we took notes on percent germination, wilt, and vigor on the seedlings as well. Figures 3 and 4 showcase healthy plants compared to diseased ones to provide context to our rating systems.
Figure 3. An example of a healthy seedling on the top of the image, compared to the seedling on the bottom which is experiencing disease symptoms on the root and lower portion of the stem. Photo credit: Talia Plaskett
So what did we find? Figure 5 outlines the disease symptoms observed on plants that were direct seeded into diseased growing medium. I wanted to mimic what might happen if we are starting plants in dirty seeding trays, irrigating with water that may contain fungal spores, and/or the media was contaminated somewhere between our last use of it, storing for the season, and bringing it back out for the spring.
The plants were scored from 1 (assigned to plants with roots that are disease free and well developed) to 5 (assigned to plants with high disease severity and poor development). If we start out by looking at our water control, we did have some underlying disease showing up even though the plants were not inoculated. My guess is that came from the water that we used to irrigate the entire trial with. If we take a look at the results we can see that there is a difference in the degree of protection offered to the plants depending on the active ingredient. The taller blue bars indicate more disease compared to short blue bars. We also see some significant differences in the amount of root development observed: the shorter green bars are more representative of what I would like to see for root development compared to the taller bars which had very poor root development.
Figure 5. A graph outlining the root development and root disease across inoculated, disease susceptible tomato seedlings. Credit: Talia Plaskett
A few noteworthy take-homes:
- Plants treated with Trichoderma harzianum had better root development compared to plants that were treated with our conventional chemical intervention.
- Plants treated with Trichoderma harzianum had the lowest disease incidence across the plants that were inoculated with our Pythium cocktail.
Figure 6. A graph outlining the root development and root disease across inoculated, disease susceptible tomato seedlings. Credit: Talia Plaskett
This assay proved to be a little bit trickier to make judgements on! If we look at the plant health rating on the y-axis of Figure 6, you'll notice that there isn't a very large range here. Plants scored between 1 and 2 across the board, making it hard to tease apart significant differences across treatments. I would say this is largely a result of the time we were able to run the trial - the plant rack did not have enough space between each level to support the plants growing taller than they were at assessment, and now that the plants are a bit more established, the root disease we introduced didn't have enough time to really get going compared to the seedling assay.
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I would love to hear feedback on your experience using these products to protect against root disease through a full season of production! I'm hopeful one day we can repeat this work in a more commercial setting, so fingers crossed that is a possibility in the future! And hopefully the results that we were able to generate here give you a bit of a leg up on what active ingredients you want to try on farm compared to others.
I still believe that these products offer a leg up in terms of root development and ability to withstand disease pressures in our highly sought-after high tunnel soils, so I do recommend adoption where possible to give our crops their best chance at success for a long season ahead.
