Pests: Time to get out and scout

 

I hope you all are having a good start to the season! As plants are emerging out in the field, and transplants growing in greenhouses are being set out, nefarious forces are emerging too. It’s time to start scouting and making a plan for the inevitable diseases and pests, with all their inbuilt hunger for your precious produce. Here’s a quick list of some common things to watch out for this time of year.

Leek moth was first trapped two weeks ago in the Annapolis Valley. Their first flights should be occurring throughout the province now. They are nocturnal so you may never notice them until the larvae are creating window-pane like damage to your onions, leeks, and garlic. They are difficult to control once they establish themselves, as they live inside of the leaves of onions or will bore their way into the stems of garlic and leeks, making the plants unmarketable. Their presence is relatively new in Nova Scotia but they have quickly established themselves. They generally have two flights here, one early in the spring and another later in the summer before garlic harvest.

Leek moth larval feeding damage on garlic. (Photo: Agriculture and Agri-Food Canada.)

Onion, cabbage, and seed corn maggot. These each overwinter in the soil then emerge in the spring, with cabbage maggot flies appearing first, followed by onion maggot flies, then seed corn maggot flies. We can expect the cabbage maggot flies to start their first flights in a couple of weeks (middle to late May). Emergence happens roughly at the same time as yellow rocket starts to bloom. Generally you’ll first notice the presence of these maggots when transplants start wilting on hot days. This is due to the larvae feeding on roots; plants will eventually die if left unchecked. On a small scale, physical barriers (such as row cover, insect netting, etc) are effective. On a larger scale chemical controls are available to help manage these pests.

Onion maggot damage (Ontario CropIPM)

For those growing in tunnels or seed-starting greenhouses you will start to see thrips, springtails, aphids, and flea beetles emerging soon, or already emerged depending on the specifics of your tunnel setup. Inspect your transplants for feeding damage such as shotgun-like holes on your brassicas in the case of flea beetles, or tiny white spots on leaves in the case of thrips.

Onion thrip damage (Cornell University)

Flea beetle damage (UMN Extension)

While we’ve had relatively good weather for seeding and putting out transplants, the recent cold, dreary, and wet weather has slowed soil microbial metabolism, meaning that overwintering plants like garlic might be showing yellow leaf tips right now. This is most likely due to a slowdown in nitrogen mineralization as soil temperatures reduced. This can be remedied by applying a plant available nitrogen source such as a liquid fertilizer or urea. In addition to reduced mineralization rates, the cold wet weather was an excellent environment for promoting fungi such as Pythium, Rhizoctonia, and Smut.

Damping-off (Pythium spp.) beetroot seedling, (Penn State University Extension)

This is not an exhaustive list by any means, but hopefully gives you a good push to get out and start scouting your crops!

Please reach out to me to discuss any of these pests, or if your crops are suffering for other reasons.

 Happy seeding and transplanting!

Tim (tmorcom@perennia.ca)

Things are Heating Up for Insects

Insect development relies on the accumulation of heat throughout the season to progress through their life stages, allowing their development to be tracked with the use of degree day models specific to the insect. By tracking the degree days, the timing of key activities such as adult flight and egg hatch can be predicted, facilitating scouting and pest management activities. To calculate degree days for a particular insect, there are two pieces of information that need to be known: the base temperature (the minimum temperature required for the development of that insect), and the biofix date (the date on which degree day calculations for that insect will begin). The equation used to calculate degree days for insect development is:

GDD = ((Tmax + Tmin)/2) – Tbase

In the equation, Tmax and Tmin refer to the maximum and minimum temperatures on a single day. Using this equation, the growing degree days can be calculated anywhere that has daily temperature information available, making it possible to tailor the model to a particular geographic area. Being able to customize data is important in Nova Scotia where we have a number of microclimates with sometimes significantly different weather often caused by the geography and proximity to the Atlantic Ocean or the Bay of Fundy. Environment Canada lists all of the weather stations available in Nova Scotia both past and present, and can provide the temperature data needed to calculate degree days. Choose the closest weather station logging hourly data for the current year. It is important to note that while degree day modeling can be a useful tool, development models from other geographic areas are not necessarily validated for use in Nova Scotia. Degree day modelling should be used in conjunction with, not as a replacement for, regular scouting.

European corn borer (ECB) is a pest of a number of crops in Nova Scotia. There are two types of ECB, with significantly different development schedules. The univoltine type completes one life cycle in a growing season while the bivoltine type can have two lifecycles in a growing season, though in cool summers the second generation of the bivoltine corn borer may not be able to complete its development.

European corn borer larva in a corn stalk. Photo: https://extension.entm.purdue.edu/fieldcropsipm/insects/euro-cornborer.php  

Both univoltine and bivoltine types of European corn borer use a base of 10°C and a start date of April 1st for degree day development models. As of June 21^st, 239* degree days had been accumulated in Kentville and 190 in Debert. According to the model, at 231 degree days, about 5% of pupae are emerged for univoltine types, with egg laying starting to occur around 425 degree days. For bivoltine types, about 50% of 1^st generation adults are emerged by  281 degree days, with a second generation starting their flight around 792 degree days.

For more information on European corn borer in Nova Scotia, check out Perennia’s new fact sheet!

*These numbers were generated with CIPRA software, AAFC, Saint-Jean-sur-Richelieu, Quebec.

Changes Coming for the Use of Chlorothalonil (Bravo®) Products

By Jill MacDonald, Perennia Research Associate

Chlorothalonil is a contact and protectant fungicide that controls a broad range of fungal diseases. It is used on a number of crops. Due to the recent re-evaluation of chlorothalonil by the Pest Management Regulatory Agency (PMRA) there are changes that will affect how growers use the product, in relation to how it is mixed, loaded and applied. The re-evaluation has caused a discontinuation of Bravo 500 and Ridomil Gold SL/Bravo Twin-Pak formulations. The final day that these products will be available for purchase is May 10th, 2020, and the final day that growers will be able to make applications of these products is May 10, 2021.  After this time, it will be the responsibility of the grower to properly dispose of any leftover product.

How will these changes affect how I use chlorothalonil products?

Changes to Number of Applications Permitted

There have been several changes made to the number of applications that are permitted on fruit and vegetable crops, it is important to check how your crop is affected. The full list of changes, including application rates and REIs can be found here.

A few of the crops that are undergoing changes to the number of applications permitted per season:

Crop	2019	2020
Blueberry (HB)	3	2
Cabbage	5	2
Celery, field	9	2
Cherries (sweet and sour)	4	3 (2 spring + 1 post-harvest)
Cole Crops	5	1
Cranberries	3	1
Cucurbit Vegetables	7	2
Onion, dry bulb	3	2
Onion, green bunching	5	2
Peach, nectarine	4	3 (2 spring + 1 dormant)
Potato, table	12	3
Tomato (not for processing)	9	2
Wheat	3	2

Additional PPE, Buffer Zone Changes and REI

New requirements have been put in place to protect the applicator and persons who are handling the product, by increasing the amount of personal protective equipment (PPE) required. It is recommended to read the revised product label to obtain information on PPE and changes to the buffer zone requirements and restricted entry intervals (REI) for certain activities. Growers are reminded to have the updated label available to staff members who may come in contact with the product, as well as making them aware of the changes.

Implementation of Vegetative Filter Strips

Use of chlorothalonil requires a 10 meter (32’) vegetative filter strip (VFS) to be planted, if there is an aquatic ecosystem downhill from the field or sprayed area. A VFS is different than spray buffer zones: the filter strip is typically perennial, hardy, deep-rooted native vegetation that can slow runoff and filter out any pesticides that the runoff may contain. 

  

Figures were obtained from: https://www.syngentaebiz.com/dotnetebiz/imagelibrary/Vegetative_Strip_ECU_Bulletin_2019.pdf?utm_source=pardot&utm_medium=lp&utm_campaign=895&utm_content=en

Introduction of Closed-system Transfer

The PMRA will now require growers, under certain circumstances, to use a closed-transfer and application system. The closed-system transfer specifically focuses on mixing and loading of the product. All potato applications, or any applications when more than 340 kg a.i. are handled in one day will be subject to these requirements.  When product is directly transferred from the tote to the sprayer tank, this will now require dry poppet connections which comply with closed-transfer. Dry poppets are available from several manufactures and are also known by several names, such as dry poppet couplings or valves. Syngenta currently supplies a female dry poppet to male cam lever adapter with each tote of Bravo Zn. Many chemical handling systems and sprayers are fitted with cam lever connections from the factory, in this case you can purchase a dry poppet to cam lever adapter. The existing dry poppet valves on the 450L totes of Bravo®ZN are already compliant with the closed-system transfer requirement and will not need to be altered.

Figures were obtained from: https://www.syngentaebiz.com/Media_Upload/Pdfs/SY_19_WhitePaper_BravoZNClosedSystem_R3.pdf?utm_source=pardot&utm_medium=lp&utm_campaign=895&utm_content=en

Additional Important Changes

Hand harvesting of processing tomatoes and application through irrigation systems on strawberries and cucurbits (cantaloupe, muskmelon, honeydew, squash, pumpkin, watermelon and cucumber) is now prohibited.

For further details, please visit Syngenta.ca.

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Tortoise beetles on sweet potatoes

These fascinating beetles are a minor pest of sweet potatoes.  Early in the season, damage can look quite alarming, but rarely hits yield-limiting or economically damaging levels.  The Golden Tortoise Beetle (Charidotella bicolor) and the Mottled Tortoise Beetle (Deloyala guttata) will often come in on slips.  Areas that are protected from predators (i.e. under row cover) tend to show greater damage.  In Nova Scotia, there is typically only one generation per year and they do not overwinter.  Growers typically start noticing feeding damage in early July.  Not to get wildly dorky, but the adults look like if C3PO and R2D2 had a baby (Figure 1).  Adults are 5 – 7 mm in length and are metallic gold or orange, but can shift to a redder colour when disturbed.

Figure 1. Adult tortoise beetles.

You may also notice golden tortoise beetle larvae in your sweet potatoes (Figures 2, 3).  Larvae yellowish to reddish-brown and are broad and flat with spikes.  They have an anal fork and will use it to shovel old skin and fecal matter onto the spines on their back.  This creates a "poop shield", which, unsurprisingly, deters predation.

Figure 2. Tortoise beetle larvae with "poop shield".

Figure 3. Clearly an effective predation deterrent.

Both adults and larvae will feed on sweet potatoes and other members of the Convolvulaceae family, such as field bindweed and morning glory, causing irregular small- to medium-sized holes (Figure 4).  Tortoise beetles are a minor pest of sweet potatoes and chemical control is usually not warranted.  Sweet potatoes are a vigorous crop and will typically outgrow the damage (Figure 5).

Figure 4. Tortoise beetle damage, July 11, 2017.

Figure 5. Tortoise beetle damage in the same field on August 30th, 2017. 

Written in part by Cassidy Coombs, Perennia summer student.

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Growing degree days and crop and pest development

I was talking to Michelle Cortens, Perennia's Tree Fruit Specialist, this morning and she mentioned something interesting...  By June 5^th, we had achieved the status of ‘coldest spring in the last 20 years on record’. I'm sure none of you are surprised to hear that.  Many crops use a 5℃ Growing Degree Day model, while many insect pests use a 10℃ Growing Degree Day model.  

Graph courtesy of Orchard Outlook.  Click here to subscribe or read past issues.

We were pretty far behind in insect degree days by about 44-49% less than average.  By comparison, the plant development heat units were at about 21-28% of average.  Some growers may be noticing this in their fields - pests that you normally expect at, say the end of May/early June showed up later, and are continuing to cause problems longer than they normally would (i.e. flea beetle).

The good news is, now that we're starting to get some heat, Growing Degree Days are starting to look more like what you'd expect at this time of year.  We're still about 13% less plant development heat units (base 5℃) compared to the 5 year-average, and 17% less compared to the 10-year average as of July 2.  We have 25% less insect development heat units compared to the 5-year average (10℃ base), and 27% less compared to the 10-year average.

Graph courtesy of Orchard Outlook.  Click here to subscribe or read past issues.