In this episode, we are joined by Erica Pate, Fruit Crop Specialist for berries to talk weather-based models and how they can be used to manage issues like anthracnose in strawberries. For more information on anthracnose management, click here. As well, is it a yam or sweet potato? Melanie Filotas, Horticulture IPM Specialist for specialty crops sets the record straight on Ontario sweet potato production. Plus, Ontario crop updates for July 3rd, 2020.
Editor's note: Since the recording of this podcast, cucumber downy mildew has now been detected in Kent County, Ontario.
For more updates on Ontario horticulture visit:
Have a question or a topic you'd like us to cover? Email us at ONhortcrops@gmail.com
Music: Aspire by Scott Holmes
In this episode, we are joined by Erica Pate, Fruit Crop Specialist for berries to talk weather-based models and how they can be used to manage issues like anthracnose in strawberries. For more information on anthracnose management, click here. As well, is it a yam or sweet potato? Melanie Filotas, Horticulture IPM Specialist for specialty crops sets the record straight on Ontario sweet potato production. Plus, Ontario crop updates for July 3rd, 2020.
Editor's note: Since the recording of this podcast, cucumber downy mildew has now been detected in Kent County, Ontario.
For more updates on Ontario horticulture visit:
Have a question or a topic you'd like us to cover? Email us at ONhortcrops@gmail.com
Music: Aspire by Scott Holmes
0.00
Kristy: This is What’s Growing ON? A show where we dig up the latest dirt on Ontario horticulture production, helping producers navigate best management practices and taste the sweet success of a quality crop. My name is Kristy Grigg-McGuffin.
Cassie: And I’m Cassie Russell. Join us as we talk to specialists in the field of fruit, vegetables and specialty crops to find out what’s really growing on.
Music transition
0.38
Kristy: Hi everyone, we are back after a week break. Hope everyone had a great Canada Day and finding ways to enjoy this hot weather.
On today’s episode of What’s Growing ON?, we talk weather-based models with OMAFRA’s berry specialist, Erica Pate and how models can be used to manage issues like anthracnose in day-neutral strawberries.
Cassie: After that, I’ll be chatting with Melanie Filotas horticulture IPM specialist, about a speciality crop we grow here in Ontario, the sweet potato.
But as always, let’s start with some general horticultural crop updates as of Friday July 3rd 2020. Kristy, why don’t you start us off with fruit this week.
Kristy: Thanks Cassie.
Great news from pick your own operations. So far overall, demand for pick your own strawberries has been good with lots of interest from customers. Harvest continues with mid-season varieties sizing well. Insect activity has been relatively low. Leafhoppers, two-spotted spider mites and winged aphids have been found. More anthracnose and botrytis infections are showing up. Raspberry harvest has started, and blueberries will start in about a week in early areas. Crops are looking good.
Spotted wing drosophila monitoring continues with catch confirmed in Essex, Kent, Norfolk, Elgin, Niagara, Oxford and Halton. Counts are similar to 2017 which was an early and challenging year so be sure to follow the ONfruit blog at onfruit.ca for regular updates and management recommendations. Keep in mind spraying for SWD isn’t necessary until there is ripe fruit present and the pest is active in your area.
Bloom has finished in grapes. We are seeing a considerable amount of vigour in some vineyards which is causing lateral breaking earlier than normal. Powdery mildew, downy mildew and black rot have been found. Grape mealybug populations are in adult and egg cluster stage of development.
Sweet cherry harvest has begun while tart cherry harvest is anticipated to start mid-July.
Hand thinning has started in most tender fruit and apple orchards. Frost damage varies from orchard to orchard with some areas having a reduced crop or signs of russetting and deformed fruit.
In apples, the extent of hand thinning that is needed really depends on the variety and region. Some areas are reporting light fruit set in varieties like Ambrosia, Mutsu and Empire. While spot thinning is needed in other varieties like Honeycrisp or Gala.
While fire blight continues in apples and pears, spread is slowing as we approach terminal bud set. The hot, dry weather has helped to slow this spread and provide a window for pruning out strikes.
Potato leafhopper, Japanese beetle and mite activity has picked up with this heat. San Jose scale crawler emergence is on-going. As well, obliquebanded leafroller control timing is beginning in most areas.
Bacterial spot is present in peach, nectarine, apricot and plum blocks.
Hazelnut development is advanced enough now to see the crop. Growers should start to be able to determine the percentage of shells that contain a developing kernel versus shells that are blank, or empty. This would be a sign of freezing damage that may have occurred in the early spring.
Quite a number of fruit and nut orchards across the province have seen higher than normal gypsy moth activity this year causing defoliation. This is a pest that has a boom/bust life cycle, where activity can peak some years before predators and pathogens catch up and cause a collapse in numbers. We’re currently in the midst of this sort of upswing which is why this pest is so prevalent. The good news though is that there is only one generation in a year, and we are nearing the end of the destructive life stage. Generally, defoliated trees should have enough energy reserves to develop replacement canopy during July and August. However, a tree may struggle to bounce back in a year like this where there are multiple stresses, such a dry weather on top of the insect damage.
In other specialty crops, ginseng growers are facing higher than normal disease pressure due to earlier frost damage. Otherwise, the crop is progressing as normal. Lavender bloom has started this week and will continue until late July.
The big issue for most is how hot and dry many areas of the province are which is putting a lot of stress on the plants and may impact fruit sizing as well as fruit set for next year. People are irrigating where they can because, unfortunately, it doesn’t look like much rain is in the long-term forecast.
That’s it from my side. How are things looking in vegetables around the province, Cassie?
Cassie: Thanks Kristy, Lets start with some root vegetables today:
For carrots; Carrot weevil activity is drawing to a close and its Weed control that is the topic of the week as pigweed takes advantage of this stretch of warmer weather. If any weeds are escaping control of your herbicides take advantage of the free testing available through Kristen Obeid, weed management specialist with OMAFRA and more information can be found on our vegetable blog.
Potatoes have really popped the last couple weeks and many fields are starting to flower. This is a critical time in development and adequate water is important. With a lot of first cuts around the province, also be on the lookout for a flush of leafhoppers. We've seen high numbers in some fields but no hopper burn symptoms reported yet. There has also been some air pollution injury in some areas as well, so ensure any damage is protected with a fungicide.
Moving into fruiting vegetables, Most tomatoes are just beginning to flower and some early plantings have developed small fruits. Insect pressure overall has been low, but hot/dry conditions are conducive for rapid insect development. Corn earworm (tomato fruit worm) have been caught in low numbers in traps in southeast Michigan and could make their way to Ontario soon where adults may look to lay eggs on flowering tomato plants in the absence of suitable corn.
Peppers are holding up well with the heat and some of the earlier plantings are just starting to flower. Pepper weevil pheromone traps have been put up across Chatham, Essex and some other pepper growing regions, and no weevils have been caught so far.
In Cucurbits; Downy Mildew has now been found in Southeast Michigan, following last week's confirmed case in Southwest Michigan. Check out our post at onvegetables.com on cucurbit downy mildew in the Great Lakes region for more details. We are continuing to monitor for the arrival of both downy mildew spores and symptoms in Ontario and will provide updates if it is found. Make sure to also be scouting for spider mite damage as populations can thrive in the hot dry weather and damage can resemble drought stress.
Sweet corn harvest is approaching in a few weeks. Lepidopteran and other pest populations are building. Armyworm continues to be a concern in sweet corn fields that have not been sprayed, but corn is moving into maturity where this crop is more tolerant of armyworm feeding. Check for the presence of parasitoid eggs on the larvae, this indicates that parasitic wasps are active and sprays may not be required. Look for European Corn Borer damage starting in Univoltine and overlap regions, as well as Corn Earworm, Western Bean Cutworm, and Corn Leaf Aphids. Common Stalk Borer has also been found so check areas adjacent to grasses.
For beans and Peas - Insect pressure is building including aphids which are major vectors for viruses. Fields should be scouted for virus symptoms such as mosaic patterned leaves, leaf curling, dwarfing, and irregular pods. Watch for hopper burn from the Potato Leafhopper, as well as the bacterial Common Blight starting in areas that had heavy rain leading to soil splashing before the current dry spell.
In Brassica Crops, Lepidopteran pests continue to be an issue across the province for a lot of brassica crops. Eggs laid from the second generation peak of seedcorn maggot is causing damage to small transplants in some areas. Sclerotinia or white mould has been seen in a few fields. For more details about what to look for and suppression options for sclerotinia, see the vegetable crop report from July 3, 2020.
Garlic harvest is quickly approaching and there are a few things to consider. Depending on how quickly your soil dries out, avoid irrigating too close to harvest as soil stuck to the bulb will make it more difficult to achieve a clean wrapper. If black plastic has been used for weed control, cutting it open to allow the soil to dry before harvest can also help with wrapper cleaning. If leek moth counts were high last week, consider targeting the larvae that are now feeding on the crop. Many products available for control are most effective when they make contact with the larvae, and control now will help reduce the amount of overwintering moths and potential damage to future crops.
In onions, the warm weather has created favourable conditions for Stemphylium leaf blight. IF you are applying chemical controls to onions, avoid applying products from the same chemical group one after the other. The pressure of thrips in onions is low but will increase dramatically as we see more hot and dry weather. If you are looking for more information on products to help control Stemphylium and thrips in onions, vegetable specialist Travis Cranmer has outlined some management strategies in the July 2nd vegetable crop report.
And lastly, for asparagus – Continue to scout ferns for insects such as Aphids and Japanese Beetles, as well as fungal disease. Be on the look-out for rust developing, especially on young plantings, which can then move to mature fields.
Kristy: For more detailed information on these and other fruit and vegetable crops, check out our weekly crop updates at onvegetables.com and onfruit.ca.
11.45
SEGMENT 1: Weather-based models for strawberry anthracnose
Kristy: On today’s fruit segment, I’m joined by Erica Pate, OMAFRA’s Fruit Crop Specialist for berries to talk about the challenges and successes of using weather-based models. Welcome Erica. It’s nice to talk to you so soon after our spotted wing drosphila chat a couple of weeks ago.
Erica: Thanks Kristy. Thanks for having me back.
Kristy: I wanted to talk to you today about weather stations and modelling. I don’t know about you but I’m finding growers are asking more often about the benefits of having weather stations on-farm. And in particular with that, the focus is on being able to integrate weather-based models to predict pest development, whether that’s insect activity or either disease infection potential or if infection has already happened.
The first question is usually why they should consider an on-farm station as opposed to using regional weather stations available across the province by Environment Canada.
So, I’m curious about your opinion, whether you think it’s worthwhile for a grower to have these on-farm stations?
Erica: Well, first of all anything is better than nothing at all. If cost is prohibiting the purchase of a station on farm, then regional information is perfectly fine to use.
But if you have a weather station on your own farm, you’re going to get a little bit more accurate information. There are microclimates so if you have that information coming directly from your farm or even a specific field, you’re going to get more accurate information. In dry years – and it's been fairly dry the last few weeks – often you hear that you really need some water and then your neighbour one concession over gets a good drink. There can be changes and that’s where a value of a weather station would come in.
As well, some models require more data than maybe aren’t included in a standard weather station like a leaf wetness monitor.
Kristy: And I find too with the regional stations, with some of the models that I’ve run, the locations are really applicable for the agricultural areas. They might be at an airport or in some cases at an actual port somewhere. It can be quite a drastic difference from one region to another if you’re basing it on those regional stations.
Now, in terms of running those weather-based models, what information is a person actually looking to pull from those weather stations?
Erica: There’s a few things: minimum and maximum temperature, relative humidity, precipitation. And then some models require a bit more detail like leaf wetness from within the canopy.
Kristy: Just kind of a side note, with using leaf wetness sensors and how they can be used with models. There’s a disease in apples called flyspeck and there is a model that has been developed for it. It was originally developed using the old mechanical sensors like the De Wit string recorders. Whereas now, most sensors are electronic and more precise so the timing for the model has been adjusted. So, it’s important that if a person is using an on-farm station – and there are some growers that I talk to that still have their string recorders up and running – it's important to know what the instrument is and how it affects the model.
When you’re running these models though, what exactly do they do?
Erica: All insects and disease have environmental conditions in which development, growth and – for disease - infection occurs. Above and below this range, activity decreases dramatically. If growers can use these models, they can accurately predict critical life events of a pest such as egg laying for example. This will help growers move from more calendar-based sprays, like weekly spraying for example to more precise timings. This can be important for newer target-specific pesticides which are more effective early in infestation when pest populations are low or for pests where resistance is a concern. It helps reduce the pressure on resistance developing.
Kristy: Are there forecasting models that are used in berries?
Erica: Yes, so there are degree day models for tarnished plant bug and spotted wing drospholia. And we’ve been doing some work on a weather-based model for anthracnose.
Kristy: What’s anthracnose?
Erica: Anthracnose fruit rot is serious fungal disease for strawberry growers caused by the fungus Colletotrichum acutatum.
Kristy: What does the damage look like?
Erica: The lesions on the fruit are distinct, brown or black sunken circular lesions, and can be on green or ripe berries. It’s pretty recognizable. You can also see salmon coloured spores ooze from the lesions in humid conditions. They can attack blossoms, petioles, runners and crowns too. These lesions can cause daughter plants to die out, outer leaves to die prematurely, or the plant to collapse from crown rot. For today and the model I’m talking about, C. acutatum is the main cause of anthracnose fruit rot.
Kristy: Does it show up every year?
Erica: It’s really weather dependent. Anthracnose infections need warm, humid weather (between 20-32C), and splashing rain or irrigation, especially between bloom and harvest. So when you have those conditions during that period, it’s conducive to anthracnose infection. It’s been dryer this year so disease pressure has been fairly low but I am starting to see infection starting to show up. Because of these conditions, that’s why anthracnose is more of a challenge for day-neutral growers, because day-neutral varieties are more likely to be exposed to these conditions because they fruit during the warm summer months when we have hot, humid temperatures. One other factor for day-neutral strawberries is that they are grown on plastic, which favours the rain splashing and spreading the disease, leaving plasticulature systems at a higher risk of anthracnose.
Kristy: Interesting. I didn’t think of the splash that can happen from plastic. So, since it’s so weather dependent, is there any way growers can predict infection?
Erica: Yes there is. We’ve actually worked on a project on this for the past few years. My predecessors at OMAFRA Mike Celetti and Pam Fisher began a project in 2016 evaluating a weather-based model to time fungicide applications for anthracnose control. The model used in the project was developed by researchers at the University of Florida , Natalia Peres and Steven Mackenzie. And the model determined when there was a low, medium or high risk of anthracnose infection. Because Ontario has a different climate, weather and production systems, we needed to validate the model here to see if we could use the same thresholds for growers and if it was practical. This study found that using the model when it indicated a ‘high’ or ‘medium’ risk reduced fungicide applications by 7-33%, reduced the cost of fungicides, time which growers spend spraying and didn’t affect the incidence of diseased berries, compared to the standard 7 day trial.
Kristy: Wow, over 30% reduction in fungicide applications! From a cost savings standpoint, that’s pretty huge but are there other reasons why reducing fungicide applications would be important for a grower?
Erica: Well there were two parts of this project. This project also included testing for any fungicide resistance in Ontario. Anthracnose was confirmed resistant to pyraclostrobin (Group 11), the active ingredient in Cabrio and one of the active ingredients in other registered products. While these products may still be effective at some farms we don’t recommend anyone rely on them for control alone since resistance is presumed to be widespread. If growers can reduce the number of fungicide applications, they are reducing the number of times they are relying on these Group 11 products.
Kristy: Are there other options for control products?
Erica: There are fairly limited options which is where a weather-based model comes into play and can be a practical tool. I can send you a list to share with listeners of registered products in Ontario, but it includes Diplomat, Pristine, Cabrio, Switch, Quadris Top and Luna Sensation.
Four of these products have a Group 11 in them, which is the group that resistance was identified. So we recommend if growers are using these products, that they tank mix with a broad-spectrum fungicide for resistance management. Group M fungicides are registered for botrytis but will provide resistance management as well as some control for anthracnose. So it’s a fairly short list when you look at it, especially with so many containing Group 11. To avoid the further development of fungicide resistance to Group 11s, growers should not apply sequential applications of products from this group.
I also mentioned Group M or captan products are also important to the program. The challenging part there is that there was a recent re-evaluation and the REI has increased to 6 days for captan in strawberries. The maximum application per season has also decreased to only 6 applications. Strawberry growers have a fairly long season going into October. With only 6 applications, growers will be very limited. As well, with that 6 day re-entry interval, it is not very practical to use in-season.
So, we’re limited with our number of options and with the practicality of some of the products we have relied on in the past. That’s really where this weather-based model comes into play to time the fungicides that we do have and reduce resistance pressure on some of those fungicides that we use.
Kristy: Ok so with limited options and risk of resistance developing, is there anything else growers can do?
Erica: To begin, growers should start with clean plants from an accredited program. If possible, growers should apply Bravo or captan before bloom for botyris control which may provide some anthracnose control. During bloom include those broad spectrum fungicides. Then during harvest, growers will be more limited because of the re-evaluations I mentioned, leaving growers with Switch, Diplomat and Quadris Top.
During harvest, clean up diseased fruit and remove it from the field. Where pressure is high and a lot of anthracnose damage is present, workers should strip off any diseased blooms or berries, apply a group M, and begin again in 6 days.
Avoid over-applying Nitrogen and not let the crop canopy get too thick.
If possible, growers and workers should sanitize between fields and work in older fields last where there may be more infection present.
Finally, there are some new varieties that have a tolerance or resistance to anthracnose, so growers can try those out if they are interested.
Oh, and then a disease prediction model can also be used to potentially reduce the number of sprays!
Kristy: Ok, so back to this prediction model. I’m curious, is anyone using weather stations to run this model on farm?
Erica: So, I mentioned that first project we did in 2016/2017 that validated the model in Ontario. In 2019, we wanted to get experience of trying this on a farm to see how practical it is and if it fits in with a regular program.
We worked with 5 day-neutral strawberry growers across the province who set up these models on their farm. The model told them whether they had a medium or high risk and if they needed to spray. So we worked with them to see how this fit onto a practical strawberry management program.
All of the growers who participated liked using the model and seeing the information. They could learn a lot about the weather conditions that would trigger a high or medium warning and when they could anticipate needing to spray.
However, there were limitations as to how practical this weather model is and whether growers are going to start using it. One of the big comments is using this model with other pests. In the last podcast episode, I spoke about spotted wing drosophila and recommend that everyone spray every 5-7 days. So, that becomes challenging when this model is triggered every 10 days. This could potentially be doubling the number of passes in a sprayer or time spent in the sprayer so that’s not really very practical and difficult for a grower to manage.
There's also the picking schedules that growers need to manage. They need to watch those re-entry and preharvest intervals if they want to get their berries for a Saturday market for example.
Lastly, the cost may also be prohibitive. It can be fairly expensive to have the weather stations and run the model so if it’s not going to reduce the number of applications, it all comes down to the cost and whether or not it’s worth it.
So, it’s positive. We learned a lot and growers liked using it. There are just some things we need to work out and make it more practical. Maybe this fits better in the spring. When we did the project in 2019, we did it in July and August when we had those hot, humid conditions where the model would be triggered fairly regularly so growers may not see a big reduction in the number of fungicides that they’re using. But, in the spring or in June we might see less if the weather that would trigger the model and might see a bigger reduction in the number of fungicides. It might be a bigger benefit to use it then.
Or maybe this model could be used to time your best fungicide. If you still wanted to use your regular program, maybe you could use the model information to time certain fungicides.
As well, we are looking into regional options. The hard part there - as we were speaking about at the beginning – is with the leaf wetness monitor. So, right now we are looking into options and how to get this information to growers. Whether we can get regional information that growers can tap into or have their own leaf wetness monitor. There is interest out there. There is just some of these factors we need to address and see how it really fits into a regular program.
Kristy: So it sounds like your approach is using a model as another decision making tool for a grower to apply to their own unique situation and how control may fit into their pre-existing program and they options they have.
Erica: Yes, for sure. Especially when they have multiple other pests that they’re managing. Maybe this can help decide when they’re going to go back in or what product they’re going to use. So, it’s just part of the decision making tools.
Kristy: And I find that that’s often the hardest part to integrating models. Because – as you said earlier – our products are getting really target-specific and we now have to deal with the recent re-evaluations and loss of products so we don’t really have a lot of choices left. You have to be really strategic with what and when you spray. I think models can really help with that but it definitely needs to be incorporated into their own individual operation.
Erica: Yeah, and I think models like this are going to become more important as we become more restricted because of the re-evaluations like with captan. Growers are really just going to start to see the changes this year and next. It’s fairly new and we’re just adjusting our spray program. That’s where these kinds of decision-making tools come into play.
Kristy: So, it’s good that you’re being proactive. Do you think that it’s good for a grower to play around with these models while they still have more tools to work with?
Erica: Yes, I think it’s good to learn. That was some of the comments from growers. Even if they’re not necessarily going to run the model next year, at least now they know more about the conditions that lead to an infection and they can time their sprays based on similar conditions. Some growers are doing this already without models, but it is always helpful to spray at more effective times.
Kristy: I’m going to put you on the spot then – going back to the first couple of questions – do you think it’s better for a grower to run these models on-farm? Is it worth the investment of a weather station or is that still to be determined once you look into how regional models could work?
Erica: That’s a good question. The leaf wetness is an important component of this specific model so that is what is needed on your farm because it can vary so much even from field to field. But I think there is potential for regional monitoring. Some of this technology is beyond me but we are looking into it and hopefully there’s more practical solutions. I think it’s great that people have weather stations on their farm, but maybe more growers can use these tools in the future as we figure out different options.
Kristy: I think a regional approach would be really nice because like you said more growers can tap into that resource and you’re not so limited by the cost aspect of it.
Well, with anthracnose, in the meantime while we wait for these models to be developed, are there resources available for anyone who is looking for anthracnose management?
Erica: Yes, berry consultants and our OMAFRA pathologist, Katie Goldenhar have helped me put recommendations all together into one resource, which is on our blog. I can share it with you today. It lists various programs for spring-planted day-neutrals, overwinter day-neutrals and June-bearing strawberries since there are some differences with how you’d manage those fields.
Kristy: Definitely. We can put the link up in the show notes for this episode so listeners can go to that and get access to it. Thanks!
Erica: Great. Thanks Kristy.
Kristy: Well, really appreciate you chatting with me today. I think the topic of models is going to be in more discussions as we see our tools change. From our availability of tools to the resistance issues many growers are facing as well as climate change and the expanding pest activity ranges, I think models are really going to come into play with helping us. So, I appreciate hearing more about anthracnose and how you’re working with all that. Thanks for your time today.
Erica: Thanks for having me on again.
Kristy: I was just speaking with Erica Pate, Fruit Crop Specialist for berries with the Ontario Ministry of Agriculture, Food & Rural Affairs.
35.32
SEGEMENT 2: Sweet potato production
Cassie: For today’s vegetable segment, I’m here with Melanie Filotas, Horticulture IPM Specialist covering pest management of a variety of specialty crops such as hazelnuts, haskaps, hops, and sweet potatoes just to name a few. Thanks for joining me today, Melanie.
Melanie: Thanks for having me Cassie.
Cassie: Let’s start by clearing something up. Is it called a yam or a sweet potato?
Melanie: It’s definitely a sweet potato! People use “yams” for sweet potatoes all the time, but actually they are completely different. They’re both root vegetables but they’re not even related - sweet potatoes are part of the morning glory family while yams are more closely related to lilies and grasses. The sweet potatoes you are used to seeing in the store are moist and sweet, have thin, variably coloured skin, with orange or white flesh. True yams are dry, starchy and not sweet, they have brown, tough skin that looks like bark and white flesh, and they’re much longer. Yams are much less common then sweet potatoes and are more likely to be found in specialty grocery stores.
Cassie: So we’re growing sweet potatoes here in Ontario, not yams?
Melanie: Yes, we grow sweet potatoes in Ontario. It is a bit confusing because nowadays the US department of agriculture actually requires sweet potato labelling in stores always say both “yams” and ‘sweet potatoes” to avoid confusion. But it doesn’t really seem to be working since people are still confused.
Cassie: OK, let’s talk about how sweet potatoes came to be grown commercially in Ontario. My understanding is that it’s more of a southern crop?
Melanie: It is a southern crop. Sweet potatoes are actually tropical perennial plants native to Central and South America. In North America, the plant is grown as an annual, but still mostly in southern states like North Carolina, California and Louisiana, where they have high temperatures and very long frost-free periods. Ontario is kind of on the northern edge of where sweet potatoes can be grown.
As far as we know, the first significant production in Ontario was during the Second World War, when several hundred acres were grown for canning. By the late 1940s, production dropped off and there were only limited amounts grown for fresh market sales. But then, in the mid-1980s, researchers from OMAFRA and Agriculture Canada began doing trials looking at whether sweet potatoes would be a viable alternative crop for tobacco growers the Sand Plains region. A commercial crop was produced for the first time in 1987 with 25 acres. That has waxed and waned over the years, but now there’s a about 2000 acres of sweet potatoes grown in Ontario, which is a lot less than the 95,000 acres that North Carolina grows, but it’s actually more than a lot of northern US states. So sweet potatoes are actually one of our more successful specialty crops in the province.
Cassie: Can you grow sweet potatoes anywhere in Ontario? Or do they have specific temperature requirements?
Melanie: Well of course you can grow small quantities in a garden in most parts of Ontario, but for large scale commercial production it’s a bit more limited. The roots take anywhere from 90-120 days to reach maturity, depending on variety, and to get there they need long frost-free growing periods with hot days and warm nights. They can grow at temperatures as low as 18 degrees C, but they are happiest when it’s 25 degrees C or higher.
The key thing about growing them in Ontario is the low temperatures we experience at either end of the growing season. They can’t tolerate freezing temperatures, so you have to wait until any danger of frost has passed to plant them. That basically means you don’t plant the until early June, or maybe the end of May if you want to push it. But you have to really rush to get that crop planted so the plants have their 90-120 days to get to maturity before the fall. And that’s because the roots get chilling damage if exposed to temperatures below 10-12°C for more than a few hours, so you have to harvest them before soil temperatures drop that low. So even in southern Ontario, you really want to be finishing harvest by October to try to get them out of the ground before the soil gets too cold.
As a general guideline, we estimate that commercial production of any significant acreage of current varieties of sweet potatoes requires at least 3000 Corn Heat Units or above, so really the southern regions of the province, especially the sandy soils along the north shore of Lake Erie. You may be able to grow them in areas with less heat, but yields will be lower and more variable from year to year.
Cassie: Is there anything a grower can do to alter the temperatures, like maybe using black plastic?
Melanie: Sure, that type of thing is used by sweet potato growers in cooler regions. And research out of the US has shown that black plastic, clear plastic and row covers can all up the soil temperature and help sweet potatoes mature faster. But that has to be balanced with the cost of buying and disposing of the plastic and removing it prior to harvest. Depending on where you are marketing your sweet potatoes and what price you are getting, this may or may not be economical. If your buyer is willing to pay a premium for local sweet potatoes that could work, but if you are competing with imported sweet potatoes you need to consider how that added cost of plastic affects your bottom line.
Cassie: What about soil requirements?
Melanie: Soil type is really important. In Ontario, sweet potatoes grow better on deep, fine sandy soils with relatively low levels of organic matter and clay content. These types of soils warm up more rapidly in the spring, but they also have a big influence on the shape of the roots. You need the right root shape for it to be a number 1 grade root which gets you the highest price.
Cassie: And what about drought tolerance in sweet potatoes? Are they a crop that typically needs lots of irrigation?
Melanie: It’s interesting you mentioned that, because you hear that a lot about sweet potatoes being drought tolerant. It’s true that because they are deep-rooted, they can withstand quite a bit water stress. But it’s kind of misleading because under low water conditions they might not die, and you can even get a crop, but you won’t get the best yield or root shape. In Ontario we often have enough rain that you don’t need a lot of supplemental water, but if it’s really dry you want to consider irrigating, especially during the first few weeks after planting, because water is one of the things that really influences how many storage roots the plant will form.
Cassie: I guess most Ontario sweet potato producers will be long past planting stage by now, but can you tell us a bit about that process?
Melanie: Planting is done in Ontario but might still be wrapping up in the southern US, where they can harvest much later than we can. A lot of people think sweet potatoes are planted as seed pieces, like you do with potatoes, but they’re not. Instead you are planting “slips” which are basically unrooted vine cuttings. Propagators bed out specially selected mother roots which sprout and produce above ground vines, which they cut to make the slips. The slips need to be planted pretty soon after they have been cut, into pre-formed hills that are between 4 and 8 inches high. The slips are planted fairly deep, to get quite a few nodes under the soil, because that’s where the roots form.
Cassie: Where do you get slips? Can you buy them locally? Or grow them yourself?
Melanie: That’s probably the number one question I get about sweet potatoes! Sweet potato mother roots need to be bedded out really early, like March or April, in order to have slips ready for an early June planting. So, the only way slips can be grown in Ontario is in a greenhouse, which is not as practical or cost effective as purchasing them from the southern US, where slips can be produced in the field.
Right now, all of our major Ontario growers source their slips from suppliers in North Carolina. At the beginning of June, they send trucks down there to pick them up and drive them back up to Ontario.
Cassie: Haha that must be a nice long roadtrip - They don’t ever consider mailing them?
Melanie: Well it’s really not a great idea. The problem is that the slips need to be planted within a week of being cut, and if they’re stressed before planting that can really affect not only survival, but the number of roots the plant will produce. As we all know, there can be unexpected delays with the mail, plus the slips can be overheated during shipping. You get really inconsistent results with mailed slips, so most growers use trucks.
Cassie: What do you do if you’re a small grower who’s only buying a few slips?
Melanie: You can try to partner with a larger grower and get a couple of boxes on one of their trucks or try your luck with the mail. There are some garden supply companies and others within Canada that will mail slips domestically, which is usually faster than from the US. Staff from the Vineland Research and Innovation Center are hoping to work with people interested starting up a slip production business in Ontario, so maybe in the future there will be a local source of slips.
Cassie: Is there anything else you need to know about buying slips if they are interested in planting sweet potatoes?
Melanie: I’m glad you asked! First, it’s really important to get disease-free plants from a certified slip supplier. Sweet potatoes accumulate viruses really quickly, which can greatly decrease yield and quality, and this happens when slips are started from the previous season's roots year after year. So certified disease-free slips come from micropropagated plants to eliminate viruses. The propagators also follow cultural practices like crop rotation and cutting slips several inches above the soil to avoid introducing other sweet potato diseases into the slips. So that is key to a good crop.
The second biggest mistake is waiting too long to order slips. I get a lot of calls from people trying to find a source of slips in May, and that’s generally way too late. If you’re interested in trying out sweet potatoes, start looking into placing your order during the winter.
Cassie: You said planting has been done for a while. What else is going on in the field right now?
Melanie: If you walked into a field shortly after planting and you don’t know sweet potatoes, you might think the plants looked pretty bad! Basically like a bunch of sticks, because the leaves that come with the slips fall off and it takes a while for the new leaves to form.
But even though above ground they look almost like they’re dead for a little while, underground things are really happening. The first 30 days or so after planting are actually one of the most critical times for determining how good the sweet potato crop will be.
Cassie: And so what would be going on underground during that critical period?
Melanie: If you look at the nodes of a slip, you’ll see little white bumps. Those are primordial roots, and if they are planted underground each one of them has the potential to form 4-10 baby roots, called adventitious roots. And these, together with roots that come from the cut end of the slip, make up the root system of the sweet potato.
Those adventitious roots can then become one of three types of root. If growing conditions are right, they become storage roots, which are what you want – they are the marketable root. But if the adventitious roots are damaged at or before planting, they make fibrous roots and will not become storage roots. And, if environmental conditions are unfavourable shortly after transplanting, they may become pencil roots, which are skinny, elongated roots that are not marketable.
Cassie: So what you want is for the adventitious roots to turn mostly into storage roots, right?
Melanie: Exactly! To get the best marketable yield, you want to maximize your number of storage roots. And research has shown that is determined within the first two weeks to 30 days after planting.
Cassie: Is there anything a grower can do to influence storage root formation?
Melanie: Well some of it is out of their control. Soil and air temperatures are pretty important. Research in Mississippi has shown that daytime temperatures less than 25 degrees C and nighttime temperatures less than 17 degrees C can have a negative impact on storage root initiation.
Cassie: And that doesn’t always happen in Ontario in June!
Melanie: Definitely! And that’s probably got a lot to do with why sweet potato yields in Ontario aren’t as high as in places like North Carolina and California! Which means that optimizing what we can control is that much more important. For example, making sure soil is moist but not too wet. Really dry soils for the first two weeks after planting can lead to pencil roots or misshapen storage roots. Ideally you want soil moisture around 50% of field capacity before and after planting.
Other things you can do include avoiding excess nitrogen prior to planting, making sure you plant high quality slips at least 10-12 inches long and planting them at least 5 inches deep, which puts more nodes (so more roots) underground but also puts the roots deeper, where soil moisture and temperatures are less variable.
Cassie: And after those storage roots form in those first 30 days, what happens after that?
Melanie: Underground the storage roots then need to get bigger. Above ground, those “sticks” I mentioned earlier start to produce leaves and then eventually vine out. The vines can spread to cover the rows so that by the end of the summer most of the field is covered in foliage.
Cassie: OK, and can you just briefly talk about harvesting and storage. Is it basically the same as for potatoes?
Melanie: Not really. The skin of sweet potato roots is much more delicate than a potato’s and needs to be handled extremely carefully to avoid wounding it. Typically, the vines are mowed about a week before harvest, which helps to prevent “skinning” which is when the outer layer of the skin tears from the root. Sweet potato diggers are often modelled after potato diggers but they have been modified to avoid damaging the roots. The roots basically move slowly down a conveyor belt behind the digger and are placed into bins.
Next, as I mentioned before, sweet potatoes are prone to chilling injury if they are exposed to temperatures of 10 degrees C or below. Chilling injury can be breakdown, decay or other things, but it’s not evident right after it happens. You only see it quite a bit later when you have problems in storage. So to avoid that you need to harvest the roots before it gets too cold, and also start curing them within a couple of hours of harvest.
Cassie: And what's involved in the curing process?
Melanie: Yes! Sweet potatoes aren’t sweet at harvest. They have to be cured to convert the starches in the roots to sugars. Curing also thickens the skin of the root and heals wounds, which is important to being able to store them for a long time. If you don’t do it properly, your roots could start to rot or break down prematurely.
Curing involves placing the roots at temperatures between 26 and 29 C and 90-95% humidity for 4 to 7 days. But it’s really important that these exact conditions be maintained this way for all the roots even in a giant stack of bins. So ventilation and circulation is critical. Most growers who end up growing any significant acreage of sweet potatoes end up investing in constructing a specialized curing and storing facility.
Cassie: And they need specialized storage after the curing process as well?
Melanie: After the roots are done curing, they need to be stored at a temperature of 13-15 degrees C and a humidity level of 85-90%. Ventilation is really important for storage as well.
Cassie: How long can you store them for?
Melanie: If you’ve cured them properly and you are maintaining good, consistent storage conditions, you can store sweet potatoes for as long as 9-12 months. The roots will shrink over time, and the sugar content also changes somewhat, but with proper storage there is the potential to sell the crop almost year-round.
Cassie: And just as we wrap up here, if there’s anyone out there looking for more information about sweet potatoes in Ontario, can you provide some contact information?
Melanie: Sure. You can reach me at melanie.filotas@ontario.ca or by phone at 519-428-4340. I also post the odd article about sweet potatoes on our specialty crops blog onspecialtycrops.wordpress.com.
Cassie: Great, well thanks Melanie for coming on the podcast today.
Melanie: Thanks for having me!
Cassie: That was a lot of great information. Hopefully it answered some questions about sweet potatoes production here in Ontario.
Melanie: I hope so!
Cassie: And that was Melanie Filotas, Horticulture IPM Specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs.
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Cassie: Thanks for tuning into our episode today. This has been Cassie Russell -
Kristy: - and Kristy Grigg-McGuffin, for the What’s Growing ON podcast. For more information on horticulture grown in Ontario, check out the links to our fruit, vegetable and specialty crop blogs in the show notes.
Cassie: A big thanks again to our guests this week, Erica Pate and Melanie Filotas. Another big shout out goes to Michael Pupulin for the editing of our episodes, and music from this episode is the track Aspire from Scott Holmes.
Kristy: We will be back next week with an all new episode of What’s growing ON. In the meantime, if you have questions, comments or suggestions for a topic you would like us to cover, Please send us an email us at ONhortcrops@gmail.com. We would love to hear from you.