Spotted Wing Drosophila & Weed Control in Carrots

In this episode, we are joined by Hannah Fraser, Entomologist for horticulture crops and Erica Pate, Fruit Crop Specialist for berries to introduce us to the invasive insect, spotted wing drosophila and how berry and tender fruit growers are dealing with this difficult pest. As well, we hear from Dennis Van Dyk, Vegetable Crop Specialist for root vegetables on weed control in carrots as well as some existing and emerging technologies for getting rid of those pesky weeds. Plus, Ontario crop updates for June 12th, 2020.

For more updates on Ontario horticulture visit:

• www.onvegtables.com
• www.onfruit.ca
• https://onspecialtycrops.wordpress.com/

Have a question or a topic you'd like us to cover? Email us at ONhortcrops@gmail.com 

Music: Aspire by Scott Holmes

Transcript

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.

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0.49
Kristy:  Welcome to our second episode of What's growing ON? I'm very excited about our three guests today – first, we will be chatting with OMAFRA entomologist for horticulture, Hannah Fraser and berry crop specialist, Erica Pate on the invasive insect, spotted wing drosophila and how berry and tender fruit growers are dealing with this difficult pest. 

 Cassie: After, we will be hearing from vegetable crops specialist Dennis Van Dyk who is going to give us an overview of weed control in carrots and discuss some existing and emerging technologies for getting rid of those pesky weeds. 

 Kristy: But first, lets cover some general crop updates for Ontario as of Friday, June 12, 2020.

 Why don't you start us off with vegetables today, Cassie?

Cassie: Sure thing - Well, first we need to acknowledge the crazy storm that blew through Ontario Wednesday evening - what a storm. Lots of strong wind and precipitation and even hail reported in the Windsor/Essex region. Make sure if you haven’t already, check on your crops, especially recently seeded or transplanted vegetables to survey any damage and don't hesitate to reach out to any of the OMAFRA specialists if you have questions or want to send us some photos of what you're seeing out in the field.

Onto some specific vegetable updates, In Brassica Crops – Flea beetles, cutworms and imported cabbageworms are all active and cabbage maggot has reached it’s degree day threshold in all regions except for Sudbury.

For celery, aster leafhopper and tarnished plant bugs are active and thresholds have been reached in all regions.

In Garlic, the number of trapped adult leek moths has been down over the past two weeks and it’s likely that the second flight will be occurring shortly. Make sure to target the next wave of leek moth larvae a week after the next peak of adults have been trapped. Scapes are starting to emerge across Ontario in ‘Music’ and other hard neck cultivars.

Cutworms pressure has been high in leafy greens, and leafminers are also active and will cause damage that looks similar to frost. 

Many direct seeded onions have reached the 3rd leaf stage and some are even a little further along. Onion maggots and cutworms are also active.  

For asparagus - Harvest is wrapping up for this year's crop. Fluctuating temperatures have encouraged Stemphylium purple spot in many areas. Some fields have high incidence so inoculum levels should be assumed to be high. Asparagus should be scouted to determine when spray programs should begin for Stemphylium and for rust. 

Cucumber beetle continues to cause direct damage in cucurbit crops in many areas and vine crops should be scouted. Thresholds are low for this pest because they carry the causative agent of bacterial wilt, of which Cucumbers and melon are more susceptible. If there are beetle emergences in your area, be alert for these during their second emergence later this summer and consider planting trap plants or indicator plants. 

Rhubarb has recovered from earlier season frost damage and harvest is ongoing.

Carrots are almost all seeded now and most have started to emerge and Hopefully the emerged carrot survived the storm and wind on Wednesday night. Carrot weevil are active right now and laying eggs so scout on the field borders and determine if the numbers are at threshold.

Potatoes are planted and many fields are starting to emerge and fill in the row. Overwintering Colorado Potato Beetles are out and laying eggs, so keep an eye out for egg masses under leaves and hatching larvae to determine how your seed or in-furrow insecticide is holding up.

Tomatoes and pepper transplants are coming along well, although some plants were suffering from heat stress and dry conditions prior to the storm.  Early season insect pressure has been low overall so far, but cutworm larvae have been active in other crops, so be sure to maintain your scouting practices. Now is also the time that neighbours might be spraying herbicides on field crops, so make sure you’re having that chat if you have tomatoes growing nearby so that your tomatoes don’t suffer from damaging herbicide drift. 

Sweet potato planting is currently underway. New growers are reminded that many herbicides registered on sweet potatoes, as well as insecticides registered for white grubs (one of the main insect pests of sweet potatoes in Ontario) must be applied early in the season, either pre-plant incorporated or shortly after planting. A full list of pest control products and herbicides currently registered on sweet potatoes in Ontario is available in OMAFRA publications 838 and 75B.  

And lastly, for any Hops growers out there, Downy mildew has been under control in yards with regular spray programs, but recent rain will encourage development of the disease.  Significant basal growth remaining at the base of plants after training can encourage development of the disease, particularly around irrigation lines. Minimal flea beetle damage, not requiring control, has been reported in some areas and Potato leafhopper has also been observed in southern yards where surrounding hay fields have been cut.  

Alright well that’s it from me, for more detailed information and other vegetable specific updates – check out the weekly vegetable crop report, that’s released each Thursday on our vegetable blog, Onvegetables.com

Ok Kristy, lets move onto fruit. Hearing of any impacts from the storm on Wednesday?

Kristy: Yeah, a lot of areas finally got some much needed rain with that storm. Other areas still not as much as they had hoped. But with it came some pretty strong winds and even hail in some regions. As you mentioned already Cassie, don’t hesitate to reach out to your OMAFRA specialist if you are seeing crop damage or have any concerns.

One thing with these storms, there is a big risk of insect and disease movement both coming in over the lakes as well as moving between fields. For instance, we typically see a flush of potato leafhopper following the first large storms of the season as they’re blown in from the south. Another example is the fire blight bacteria, Erwinia amylovora. It can move really well on wind currents so can spread between apple and pear orchards in a region during storm events like what we had this week. Be sure to keep a regular monitoring program to stay ahead of any issues that may have come from this storm. 

Strawberries harvest is underway for day neutrals and early June bearing. Blueberries are not far behind, having reached petal fall in most areas. Raspberries have begun to bloom this week so harvest is likely in about 3 weeks time. Birds have begun feeding on developing haskap berries.  Bird netting or other protective devices should be in place at this time as birds can rapidly remove haskaps from unprotected fields. Spotted wing drosophila traps have now been installed but no adults detected yet.

Grapes are growing well though the hot, humid weather has been optimal for fungal diseases such as phomopsis, downy mildew, suscepted black rot and powdery mildew. Scale and mealybugs are moving back down to the grapevine trunks. Stippling leafhoppers are present but in low numbers and phylloxera and erineum mite galls have been found. 

Fruit are sizing nicely in apples. Fruitlet thinning programs have begun. Weather conditions have been fairly good for these thinning products since they are more effective in warm temperatures. There is some concern in some areas though that have had lower rainfall amounts as this is the key time for fruit development to obtain good size. Growers who have irrigation will be irrigating. Fire blight symptoms are starting to show in some orchards after the last few weeks of high to extreme infection risk potential. Trauma blight may come out of the storm from this week but many growers followed up with a preventative spray after the bad weather cleared. Powdery mildew and frog eye leaf spot, or black rot have also really taken off in some susceptible varieties. Codling moth flight has begun so control for this pest will be applied shortly.

The severe weather continues to create high risk conditions for fire blight in pears. Plum curculio activity has begun in orchard margins where there is a history of damage. Peach leaf curl damage is sporadic in peach and nectarine blocks.  With shuck fall occurring, apricot, peach and nectarines are susceptible to infection by powdery mildew, bacterial spot and peach scab.  Bacterial spot lesions have been observed in some peach and nectarine blocks. Fruitlets damages by hail in the Niagara region last week have scarred over and are not susceptible to pathogen infection. Most of these fruit will either drop naturally or be removed during fruit thinning. Tart cherry growers that sustained significant crop loss due to hail will still have to protect trees from cherry leaf spot and powdery mildew in order to maintain tree health. 

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.
 
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11.08
SEGMENT 1: Spotted Wing Drosophila

Kristy: On today’s fruit segment, I’m joined with Erica Pate, OMAFRA’s Fruit Crop Specialist for berries and Hannah Fraser, Entomologist for Horticulture crops to talk about a little pest that’s causing big problems in Ontario.  Hannah & Erica, welcome and thanks for being here.   

Hannah & Erica:  Thanks for having us.

Kristy: I was thinking of the two of you the other day. I was doing my usual routine of kids in bed and vegging out on the couch getting caught up on social media and gossip columns. There was a thread about someone who found out when they put their fruit in salt water, creepy crawlies came out. It just snowballed from there with everyone being so disgusted. But no one asked what it actually was. So I’m happy to be talking to you to get the grower perspective and how they are dealing with this.

But let’s start from the beginning here. Hannah, what is this pest we’re talking about?

 Hannah: Spotted wing drosophila or SWD for short is an invasive fruit pest from Asia that has recently undergone a range expansion to other fruit producing regions around the globe.  It was recorded as invasive in Hawaii in 1980 and then simultaneously in California and in Europe in 2008. Since 2008 it has spread rapidly throughout the temperate regions of North America and Europe.  

 Kristy: When did SWD first show up in Ontario?

 Hannah: We first heard about SWD in 2009, when reports of injury were coming out of California, and when it was identified in BC.  The Canadian Food Inspection Agency conducted surveys in other provinces in 2010.  Late that year – I think it was November – we learned that SWD had been found in Ontario.  OMAFRA conducted province-wide surveys in 2011, and SWD started to show up mid-August.  We still didn’t know if this pest could become established in Ontario.  In 2012, SWD showed up at the end of June, and by the end of the summer, we had found it across southern and central Ontario, and as far north as Temiskaming.  This was also the first year we confirmed injury in berry crops.  We’ve since learned SWD is a serious pest and that it’s here to stay. 

 Kristy: You mentioned berry crops are impacted. What crops are at risk?

 Hannah: SWD is a pest of soft-skinned fruit.  Berries, including strawberry, raspberry, blueberry, and other small fruit including cherries are at high risk if SWD are present near harvest.  Other stone fruit are less susceptible as they are typically still firm at harvest.  But SWD is an opportunist …

 Kristy:  Opportunist? 

 Hannah: Yes.  SWD has a wide range of hosts that includes many berry-producing wild hosts.  SWD populations can build up on these hosts in unmanaged areas.  They move between wild hosts and crops through the season.  For this reason, we refer to SWD as a landscape level pest.  It’s an aspect of this pests’ biology that makes it more challenging to manage.      

 Kristy:  But we’re talking about a fruit fly or a vinegar fly, right? I just know of the ones that come out when I’ve let something in the fruit bowl get too ripe or you see them near compost bins.  What makes SWD different?

 Hannah:  Related vinegar flies lay eggs in fruit and vegetables that are past-peak, in other words plant substrates that are starting to decay.  Over-ripe or damaged fruits and vegetables often have breaks in the skin where females can lay their eggs directly on the exposed pulp. SWD has evolved to exploit a resource that other vinegar flies can’t: healthy, sound fruit that is beginning to ripen.  This is because the females have a large, serrated ovipositor that helps them saw through the skin of ripening fruit and allowing them to deposit their eggs inside.  Other vinegar flies can’t do that.  

 Kristy: Eggs inside the fruit and right before harvest.  That doesn’t sound good.

 Hannah: Definitely not. The larvae that feed inside the fruit will cause it to break down quickly, reducing the quality, and rendering the fruit unmarketable.  Although there are signs of infestation that an experienced person will pick up on when fruit is being harvested, sometimes fruit with SWD eggs or small larvae might end up in the basket.  There is a very low tolerance for insects in fruit. That’s why it’s important to manage SWD so that females don’t have the opportunity to lay their eggs in the first place.  Growers have to use a number of strategies to manage this pest effectively, and in some years, when the pest pressure is high, it’s really tough to keep up.  

 Kristy: Does SWD show up around the same time every year?

 Hannah:  No, it doesn’t.  The first few years after SWD was found in Ontario, we noticed that it seemed to be showing up earlier and earlier.  Every year is different.  Some years it shows up in early June, but it can be later.  Bumper years for SWD – when numbers surge earlier in the season – put more crops at risk than in years when populations start their exponential growth later.  

 Kristy: Is there any way to predict how a given year is shaping up?

 Hannah: We’re often asked about how the year is shaping up in term of SWD numbers. Researchers at Michigan State University have access to a data set that has allowed them to pin down factors that drive the interannual variability of their populations.  Environmental conditions can be used in northern temperate regions like ours to provide risk warnings as a component of IPM.  

 Predicting fly capture includes looking at overwintering and spring conditions, and to a lesser extent the pressure and peak activity of the previous season.  Winter is an important bottleneck for SWD.  Even though this pest has a winter morph that is better adapted to surviving adverse conditions such as cold temperatures and desiccation, less than 1% will typically overwinter.  Spring activity begins with low abundance of adult flies.  

 The greatest initial growth and subsequent peak activity in season occurs in years where winter and spring conditions are warm.  The fewer winter days with temperatures below 0°C and the more winter and spring days above 10°C result in earlier activity and higher population growth.  As the season approaches, spring conditions need to be considered, as cold springs delay population growth.  

 Kristy: Why does this matter?  

 Hannah: Being able to provide a general estimate of future fly activity helps us to evaluate seasonal levels of risk.  If it’s been a mild winter, such as the one we’ve just had, conditions are set in place for a potentially risky year.  Taken together, winter and spring conditions have utility in predicting severity before fruit becomes susceptible during the late spring and early summer. This can be useful intel for growers who produce crops that ripen when SWD transitions from low activity to exponential growth, such as June strawberries, cherries, and summer raspberries.  

 Kristy:  That’s a lot to take in.  Erica, I’m going to bring you in now. How do you build an IPM program for a pest like SWD?

 Erica: One of the things we tell growers is that (ripening fruit + SWD) = time to spray.  Monitoring to determinine what the SWD population is doing in your region is a key component to managing this pest effectively. Monitoring tools have improved over the last decade, but we still do not have highly sensitive and selective tools like pheromones.  Commercially available baits are much more effective than the apple cider vinegar or the messy homemade sugar yeast baits, although these do work.  These can be paired with either sticky cards or liquid traps or both to track SWD presence and to look for signs the population is starting to surge.  We also recommend the use of plastic baggie tests or salt water tests to detect any larvae in fruit at harvest.  Finding larvae in fruit means it’s time to ramp up management, if you haven’t already.    

 We are currently working on a couple projects to develop quick and practical monitoring tools for growers, including using sticky cards baited with commercial lures and another one using a molecular test to detect and quantify the number of SWD in the traps. If anyone is interested in learning more check out our blog at onfruit.ca or contact me, Hannah or our colleague in tender fruit, Wendy McFadden-Smith. 

 Kristy: Fruit flies are pretty small and you’re identifying them in a trap? How can you tell what you’re looking at? 

 Erica:  SWD is a small insect, about 2 mm in length.  Only the male have spots on their wings, one per wing, near the tip.  Once you learn to recognize the males, they are relatively easy to spot on cards or in liquid.  Double checking suspects with a hand lens, or better yet, using your cell phone to magnify, will help you to confirm.  Females can be tricky.  The ovipositor is easy to find once you know what you are looking at … which can take a lot of practice.  And this requires magnification.

 Kristy:  OK, so I’m finding SWD in my traps.  What’s next?

 Erica: Females can lay hundreds of eggs in their lifetime, (380-560) and there are multiple, overlapping generations. Once SWD has emerged in the spring the population continues to increase, and they are active for the rest of the season.  SWD also has a wide host range, which means SWD can fly in from perimeter hosts throughout the season. Growers will need to continue to manage for SWD until their season is over

 There are a number of insecticides registered for SWD control or suppression. Once SWD has emerged growers will need to apply an insecticide weekly and will need to re-apply after a rain. Less effective products need to be applied more often. Consider weather conditions when choosing products.   Each product has specific re-application intervals and maximum number of applications/season. Take a look at this now so you have an idea of how many applications you have to get you through the season.

Keep pesticide resistance in mind. Repeated use of an insecticide group may result in its loss as a management tool due to the development of resistance. Use a wide variety of different insecticides and rotate between insecticide groups.

 Kristy: Apart from insecticides, what are the other IPM practices that need to be implemented?

 Erica: Insecticides are only part of the strategy to control SWD. The goal with insecticides is to kill SWD before the female lays eggs in the crop.  Once the eggs are under the skin of the fruit and the larvae have hatched, they are protected from sprays.  Research indicates that less than 10% of the SWD population at any given time are adults; the rest are eggs, larvae, or pupae protected in the fruit. That’s why cultural practices are also very important.  

 Good spray coverage is essential.  Insecticides registered against SWD target the adult flies, either by direct contact or when they land on treated surfaces, before females lay eggs inside the fruit.  Adults prefer cool, moist, and shaded environments. Manage the crop environment to make it less favourable by increasing sunlight and reducing humidity, and to improve coverage. Calibrate your sprayer, use a high water volume, do not cut rates, and don’t go too fast.

 Kristy: Does the frequency of harvest have any impact on extent of damage?

 Erica: Plan now to pick regularly and often. Ideally, pick every other day and remove unmarketable fruit from the field. Regular harvest can make a big difference. This will prevent the build up of ripe and over-ripe fruit. Make sure to destroy cull fruit as well. Renovate June-bearing strawberries as soon as possible to dry up the remaining fruit, making it less attractive to SWD.

 Kristy: You’ve both mentioned wild hosts.  Is there anything to do to help reduce pest pressure from unmanaged areas?

 Erica: It may not be practical or desirable to manage all wild hosts, especially since they may also contain beneficial species.  However, it may be advantageous to keep field edges tidy and free from wild hosts (honeysuckle, wild brambles, pokeweed, mulberry, pin cherry, elderberry, and others). If it is not possible to remove wild hosts, try to cut them back below the fruiting zone. Do not apply insecticides to non-crop areas.  

 Kristy: How about any infested fruit that get harvested … what can be done?  

 Erica: Cool fruit as soon as possible after harvest and keep it cool. This will slow or stop the development of larvae and eggs in the fruit. Pick-your-own customers should be encouraged to follow this strategy to improve fruit quality at home.  

 Growers should use as many of these tools as possible to help manage SWD!

 Kristy: That sounds like a lot of work!

 Erica: Yes it is- the key to SWD management is for growers to use as many of these as possible. 

 Although it is a challenging pest, it is manageable. Growers need to take a season long approach and use as many management practices as possible. Early detection and management are very important to limit economic damage. There is also a lot of research going on with alternative management tools - maybe we should talk again about those some day.

 Kristy: That sounds great! So now that we are nearing harvest in some berry crops, what’s happening in Ontario presently in terms of SWD activity?

 Erica: We just started putting traps out last week, so we will start to have regular counts available to growers. However, New York has been monitoring for a couple weeks and they have found 1 SWD at a few cherry sites. We will post the results from our monitoring regularly on our blog at onfruit.ca or in the Berry Bulletin. We encourage everyone to check the emergence or monitor themselves on their farm. The important thing to remember is that once SWD is active in your area and there is ripe fruit present, it is time to spray!

 Kristy: Well, thanks so much to you both for joining me today and sharing your information about SWD. As I mentioned before, it’s a small pest but sounds like it really causes big problems. 

 Hannah & Erica: Thanks for having us, Kristy.

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32.58
SEGEMENT 2: Weed control in carrots

 Cassie: For todays vegetable segment, I’m here with Dennis Van Dyk, vegetable specialist covering root vegetables such as carrots, potatoes and rutabaga. Thanks so much for joining me today, Dennis. 

 Dennis: Thanks for having me Cassie. 

 Cassie: In Ontario, there are approximately 9000 acres of carrots grown throughout the province and as most growers have just finished seeding their crop, now is a great time to chat about managing early season weeds. So Dennis, I guess a great place to start here is, why are carrots so susceptible to weed competition in the first place? 

 Dennis: Carrots are notoriously slow to germinate and establish. Often need to be babied a bit with good soil preparation and soil moisture, often need to be irrigated after seeding, especially later seeded carrots. When they do germinate they’re also slow to grow and establish early so weeds often get ahead of them. That’s a big problem in carrots especially because they’re susceptible to significant yield losses from weed competition. 

 Research at the U of Guelph by Clarence Swanton found that the critical weed free period for carrots is up to the 4th leaf stage for late seeded carrots and the 12th leaf stage for early seeded. That’s a long time to keep weeds out of the crop, especially with a fairly limited herbicide toolbox.

 Cassie: Right, and what are some of the typical weeds Ontario carrot growers have to deal with? 

 Dennis: Well we get the usual weed pressure across Ontario, Lambsquarters, Purslane, velvet leaf, ragweed, fleabane but we also have some real problem weeds that are a real problem in vegetables and carrots specifically. Nutsedge is a perennial problem especially since there’s not very many herbicides available to manage it in carrots. Once nutsedge is germinated in the season it’s next to impossible to effectively control. Higher rates of Lorox might set it back but because it’s growing from a nut in the ground it just keeps coming. It’s really a weed that has to be managed in the rotation outside of when carrots are grown.

 Another problem weed that has popped up recently across a number of vegetable crops is Group 1 resistant crabgrass in SW Ontario. It’s an interesting problem that’s currently being researched on how to better manage. But really, the main weed in much of our carrot growing areas are pigweed species. The real issue is triazine resistant pigweed so triazines are the Group 5,6,7 herbicides. In carrots specifically, Group 7 herbicides like Lorox is a main concern but we also have populations resistant to Group 7 and Group 5 are your Gesagard/Sencor herbicides.

 Cassie: So you’ve mentioned a few options already, but can you talk a bit more about what herbicides are available to carrot growers? 

 Dennis: Yeah sure so whether you’re on muck or mineral soil, the cornerstone of any carrot herbicide program is still Lorox. Lorox is the only post-emerge product that controls emerged broadleaf weeds. Our toolbox is different depending on whether you are on muck or mineral soil. So on a mineral soil you have three group options. You have group 3 products – trifluralin (Treflan/Rival/Bonanza) pre plant incorporate, Prowl H2O is also in that group 3 and is a pre-emerge but it has a 90 day PHI so that might not always work for you. Group 5 you have Guesagard, and then you have group 15 - Dual Magnum as a pre-application. In terms of pre-emergence for muck soils. Muck soils you don’t have trifuralin, you just have prowl, Guesagard and Dual, but then on muck soils you also have a group 6 Pardner registered as a stale seedbed burndown. You apply it right before emergence to get rid of weeds that have come up. Post emergence, the products are similar, you have Lorox as I’ve mentioned before as the cornerstone, you also have Dual 2 Mangnum you can apply between the 3-6 leaf stage and then you have Aim registered as a non selective herbicide that you can spray in between the rows. In terms of grasses, we have three products, post, select and venture all group 1s to spray off any grasses, and we also have Sencor registered which is a group 5 but it requires PRE application of Lorox which is a bit of a waste, Lorox is better used POST. You might also run into issues with differences in tolerance for some varieties and rotational crop problems, especially with onions.

So that’s our current situation when it comes to carrots, a couple pre-emergent options but a real reliance on Lorox post-emergence.

 Cassie: I guess that’s why we’re hearing and growers are seeing so much Group 5 and Group 7 resistant weed issues pop up in these crops?

 Dennis: Yeah absolutely. Another contributing factor to that is a lot of carrot fields had or still do have potatoes in their rotation which is another crop which is heavily reliant on Sencor/Lorox Group 5 and Group 7 herbicides for weed control so it’s difficult to get a good herbicide rotation in and a heavy selection pressure on those type of products.

 Cassie: And what could they do if they know or suspect they have these resistant weed issues in their crops?

 Dennis: First thing I would say is to confirm whether or not your weed escapes are due to resistance. It’s important to know the difference between application error and resistance because it drastically changes your management strategy. If you have resistant pigweed in your field is should be top priority to prevent escapes from going to seed. Our colleague Kristen Obied is working with weed scientists at AAFC and the University of Guelph are doing some awesome work with resistance testing and developing quick tests that are available free to growers right now.

 Cassie: That’s great, so no excuse to not get your weeds tested for resistance. 

 Dennis: Ya, you can’t beat free. 

 Cassie: Alright so what about organic carrot growers out there, do they have tools available to them for managing weeds in carrots?

 Dennis: Organic carrots really have to rely heavily on mechanical cultivation and hand-weeding for weed control. I think we’re also seeing more conventional growers incorporating mechanical cultivation back into their strategies. There’s not many weeds resistant to steel so it’s a great way to deal with herbicide resistant weeds. 

 One key part of organic carrot weed control that conventional growers can use as well is a stale seedbed technique. With organic carrots it’s critical to do this in order to reduce the burden on cultivation and hand-weeding. 

 Cassie: Sorry, what’s a stale seedbed technique? 

 Dennis: A stale seedbed approach is when you make beds, allow weeds to germinate, kill them off by flaming or cultivation or in the case of conventional growers with herbicides. The idea is to drain that top portion of the beds of germinating weeds. You can seed the crop before and do this right before emergence or make the beds prior to and seed after. What it does is give the carrots a better chance of getting ahead of that first flush or two of weeds.

 Cassie: You mentioned some growers are starting to adopt more mechanical cultivation which is great to hear from a resistance management perspective, can you talk a bit more about that?

 Dennis: Yeah definitely, growers had gotten away from cultivation a little bit because of a number of reasons; soil health, worried about allowing more weeds to germinate, not having a good setup to get good weed control without hurting the crop, but there’s definitely more scuffling or cultivation going on now. There’s been some great work recently out of Michigan State University, Dan Brainard’s group have been some interesting work in carrots with mechanical weed control. They have some good resources on different types of cultivation tools like knives and tines and hooks and finger weeders and equipment that will work in carrots so if you’re interested you can check their work out.

 Cassie: Any work on robotic weeders in carrot fields? 

 Dennis: I would say we’ll probably see a commercial robotic weeder in Ontario within the next decade. There’s already some units out there with visual guidance systems that are close but a true robotic weeder that’s eliminating or picking weeds in-between the carrots is not here yet but it’s coming. It would definitely have a fit in carrots because of the reliance of hand-weeding in the crop. It’s a huge expense, growers can pay a couple thousand dollars per acre in labour costs in a weedy field. It’s also getting more difficult to find workers willing to weed all day in the middle of July and August. In Ontario if you’re growing carrots commercially it’s pretty difficult to grow a crop without having to hand-weed at least once.

 Cassie: Is there anything else growers could try if they are dealing with really high weed pressure and maybe don’t have the labour capacity to hand weed?

 Dennis: One thing I think could really work for growers is building or buying a band sprayer or hooded sprayer.  I’m sure most people are familiar with the concept but the general idea is you have a hooded sprayer in-between the rows where you spray a non-selective herbicide and it’s protected from getting on the crop.

 Cassie: Do you see a lot of growers using band sprayers?

 Dennis: There are some out there for sure, mostly growers are building their own and I think they actually have a great fit in carrots especially for growers with resistance issues. With band sprayers if you do it right, you can really focus on just worrying about the top of the hill and in-row weeds.  With the hoods or shrouds you can get on a burndown product like Aim and some growers have a second tank and nozzle setup which can apply a crop tolerant herbicide to the carrots on top of the bed to get any in-row weeds. So that would be carrot oil or Lorox, something like that which will get those in row weeds. 

 Cassie: What in the world is carrot oil?

 Dennis: Carrot oil is a product that carrot growers have historically used to clean up really weedy fields. Carrot oil is actually mineral spirits and it’s registered for use on a couple crops including carrots as Guardsman Agricultural Weedkiller No. 1.  Growers really only use it as a last resort as it is very expensive and not very nice to work with. But there have been fields that look like they’re growing weeds one day and the next day it’s a carrot field again so it seems to have taken on this magical, secretive persona that growers only whisper about.

 Cassie: That’s so interesting, trade secrets! 

 Dennis: Yeah, a not so well kept trade secret for sure. 

 Cassie: Anything else that’s new and coming down the pipeline?

Dennis: Yeah actually, there have been a few Minor Use Priorities for carrot herbicides over the last few years. Ones that are currently in progress Blazer and Zidua which currently being worked on. Blazer is a soybean herbicide, Group 14 so more of a contact herbicide and can be pretty hot on the crop but the carrot rate would be much lower than the soybean. It’s very effective against pigweed so could be a nice addition to the toolbox when that registration eventually comes through.

 Zidua is a Group 15 herbicide like Dual Magnum that has excellent pre-emerge activity against pigweed. So there has been some great background work on this product and a push to get it registered. It would be applied early post and really help with resistant pigweed. It looks like at this point it’s only safe of muck soils unfortunately for mineral growers, that might not be an option. We are also exploring a Goal registration for use early post specifically targeting resistant pigweed. With the changes in the Minor Use System due to Covid, this might have to wait another year but we’ll see how that goes. 

 Cassie: Anything else that you could see coming down the pipeline?

 Dennis: There are also a few other weed related things that we are looking into as well. Belchim has an older Group 6 herbicide (Pardner and Basagran) called pyridate that has shown good crop tolerance in carrot in trials in the UK and with Clarence Swanton with the University of Guelph. So it’s a contact herbicide but could be a good rotational partner for Group 14 contact herbicides like Goal or Chateau because there are Group 14 resistant pigweed out there.

 There’s been some reports of Eptam being very effective as a pre-plant incorporate treatment so that is worth some follow-up as well. One project I’m working on along with Kristen Obeid this year is a large-scale demonstration of different herbicide programs. One of the main purposes will be to compare different combinations of Gesagard/Dual/Prowl as pre-emergence treatments. But what we are also investigating Gesagard for use as a POST treatment. So, it’s labled for some use in the States as a post application at the 3-5 leaf stage, so we would really like to see if that would be an effective use here in Ontario. Hopefully we learn some really interesting lessons that we’ll be able to share on the onvegetables blog. 

 Cassie: And you mentioned earlier how carrots are terrible competitors early in the season, so aside from herbicides, is there any way to make the carrots more competitive to weeds?

 Dennis: That’s another area that I’ve been looking into, there is a plant hormone called gibberellic acid that is used in a number of different crops for various effects. What gibberellic acid does (GA, ill refer to it as GA) in carrots is it stimulates the plant to increase leaf growth. So Jed Colquoun’s group at the University of Madison Wisconsin has done some work on this and I trialed it in Ontario last year by using GA early on in the growth stages like the 3-5 leaf stage to see if we could increase weed competitiveness.  We applied is twice, one week apart at different rates and found that it actually worked quite well in getting increased top growth. So, 1 week after application the canopy was 1 inch bigger and 2 weeks after application the carrots with GA were 3 inches taller than untreated carrots. Those treatments also filled in the carrot canopy 2 weeks ahead of the untreated at the high rate and 1 week earlier at the lower rates. 

 So, there may be a fit here to make the carrot more competitive to weeds early on in the season and fill in that row a little faster so you mostly have to worry about the in-between row area which is easier to control weeds in.

Cassie: Integrated Weed Management might be a term people have heard before. What would be your ideal weed management strategy in carrots?

 Dennis: That’s a tough question, each grower is going to have their own recipe of what works for them on their different soil types. There are some tips that might be helpful. Try and use a pre-emerge herbicide that buys you some time but allows the carrots to germinate and get out of the ground quickly without slowing them down too much. 

 Consider using primed seed for June seeded crop when germinating pigweed is the biggest problem. Prime seed might be worth the investment. Mechanical scuffle to kill any small emerged weeds in between the rows and then come back with a band sprayer for example and maybe put down a herbicide with some pre-emerge between the rows so prevent further emergence. And any escapes later in the season, just send them in for testing. It’s free and it doesn’t take long and it’s important to know how seriously you need to take those weed escapes.

 If they are resistant, you really need to get rid of them. Hand-weed and remove from the field or wick-weed them, just make sure you get them before they set seed. In pigweed for example, one plant is going to leave like half a million seeds in your field. So, if you don’t take care of them and get them before they seed, they’ll still be coming up and causing problems when your kids are farming that land. It will make for more problems down the road. 

 Cassie: Absolutely, resistant and resilient. Like you said, these resistant weeds are a problem in a lot of crops we deal with and if they aren’t managed appropriately, they will be here to stay and just continue to cause more problems down the road. 

 So, you provided quite a number of recommendations here for carrot growers, but is there anything else you’d like to add or maybe provide some contact info if any growers have questions?

 Dennis: If you want a follow up with any question you might have, my email is dennis.vandyk@ontario.ca and I can be reached at 519 766 5337.

 Cassie: Thanks again for coming on the podcast today Dennis, I really hope this will help out carrot growers across Ontario better understand the tools they have available to combat weed pressure. 

 Dennis: Thanks for having me, I really enjoyed it. 

 Music transition
 
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Kristy: That brings us to the end of our second episode.  This has been Kristy Grigg-McGuffin 

Cassie: - and Cassie Russell, 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.

Kristy: A big thanks again to our three guests this week, Dennis Van Dyk, Hannah Fraser and Erica Pate.

Another big shout out goes to Michael Pupulin for the editing of our episodes.  Music from this episode is the track Aspire from Scott Holmes.

Cassie:  If you have questions, comments or have a topic you would like us to cover, email us at ONhortcrops@gmail.com.   See you soon!