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.

Time to keep an eye out for cabbage maggot

With a cool start to the spring this year, insect pests have been a little later getting out and about than we would typically see. Now that there are warmer days upon us, it's important to pay attention to when those insect pests will be active so that control measures can be taken in a timely fashion.

Cabbage maggot (Delia radicum) is a particular challenge in brassica crop production. It overwinters in the pupal stage, emerging in the spring, usually coinciding with the bloom of yellow rocket and serviceberry. From a degree day perspective, emergence begins around 161 Degree Days (DD) at a base of 4°C, with peak flight occurring around 250 DD for the first generation of cabbage maggot. As of Friday May 22, 2020, 175 DD (base 4°C) had been accumulated in Kentville. Other Delia species, Delia platura (seedcorn maggot) and Delia florilega (bean seed maggot) are also on the move in the Valley.

Cabbage maggot larvae in soil. Photo UMass Extension.

Once the first generation of adults has emerged in the spring, they take flight and lay their eggs. It is important to know when peak flight is taking place so that you have the opportunity to alter planting times or deploy control measures, such as insect netting, accordingly.  For scouting purposes, eggs can usually be found small clumps on the soil around the base of your seedlings. For more information on cabbage maggot, including concerns about pesticide resistance, check out Perennia’s fact sheets “Cabbage Maggot” and “Chloropyrifos Resistance in Cabbage Maggot”.

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.

Sprayer Efficacy Workshop - Location

The Sprayer Efficacy Workshop will take place on Thursday, July 20, 2017 from 1:00 - 3:00 pm.  The approximate street address is 9780 NS-201, Wilmot, NS.  Keep your eyes peeled for Perennia signs!
 


If you contact Gail Walsh 1-877-710-5210 (toll-free) she will email you a map.


Perennia IPM Specialist Peter Burgess and Vegetable Specialist Rosalie Madden will discuss nozzle selection, canopy penetration, and the importance of water volume!  Pesticide points available.

Thursday, July 20, 2017 

Spurr Brothers Farms, Melvern Square 

1:00 p.m. - 3:00 p.m.

Sprayer Efficacy Workshop

Please join Perennia Integrated Pest Management Specialist Peter Burgess and Vegetable Specialist Rosalie Madden for a discussion about sprayer efficacy.

We will discuss nozzle selection, canopy penetration, and the importance of water volume!  Pesticide points available.

Thursday, July 20, 2017 

Spurr Brothers Farms, Melvern Square 

1:00 p.m. - 3:00 p.m.

Please contact Gail Walsh 1-877-710-5210 (toll-free) or gwalsh@perennia.ca to register by July 17, 2017.

Be sure to give Gail your e-mail address as we will send out a map of the field locations the day before the workshop.

 

Cucumber beetles are here

Stripped cucumber beetle, illustration by Jessica MacDonald

Striped cucumber beetles have made their annual debut in the Annapolis Valley.  These pests are problematic in many ways.  Feeding damage can stunt plants, and when flowers are predated, it can reduce fruit set and yield.  Cucumber beetles also vector bacterial wilt.  Scarring on fruit by adult beetles reduce the marketability of the crop. 

Newly emerging cucurbit plants are particularly susceptible to stunting and bacterial wilt, while older plants can withstand up to 25% defoliation.  Early season control is essential with this pest, and it is important to scout your fields regularly. 

For more information on cucumber beetle biology, beneficial insects, and organic management, check out Managing Cucumber Beetles in Organic Farming Systems on eXtension.
 
Please click here for Perennia's Pest Management Guides for Cucumbers and for Melons.  For Perennia's Pest Management Guides for Pumpkin and Squash, please click here.  Insect netting can also be an effective control option for this pest, but netting must be removed at flowering for pollination to occur.

Wireworm updates

Dr. Christine Noronha is an entomologist with Agriculture and Agri-Food Canada in PEI with a particular interest in wireworms.  She will be visiting Nova Scotia this week and will give an overview of wireworms and their lifecycle (similar to last year’s presentation), as well as the most recent updates and highlights from her research into this pest. 

The presentation will take place at the Kentville Research Station (32 Main Street, Kentville) on Friday, May 12^th, 2017 at 9 am in the Perennia Training Room.  I know it’s a busy time of year, but we hope you can join us! 

Field Day: What's the Deal with Delia?

Join us on a field tour on Thursday, July 9th, 2015 from 8:15 am to noon!  

Come learn more about onion maggots (Delia antigua) and other Delia species that attack onions, corn, beans, and Brassicas such as cabbage, broccoli, cauliflower, radishes, kale and Brussel sprouts.

Figure 1. Onion maggot damage.

AAFC is currently conducting research to determine which Delia species are present in Nova Scotian onion fields and to determine if surrounding vegetation or field history can influence Delia populations and subsequent damage.

Netting and floating row cover can be powerful tools to combat insect pests such as cabbage root maggot (Delia radicum). Perennia and AAFC are currently conducting research into the efficacy of different netting mesh sizes. A Wondermesh Netting/Row Cover Retriever will be on hand to demonstrate technology that makes using netting and row covers easier!

Figure 2. Wondermesh Netting/Row cover Retriever.

Carrot weevils (Listronotus oregonensis) are sporadic pests of carrots. Current AAFC studies are evaluating the carrot weevil’s movement within the field and identifying overwintering sites.

Please call Gail at (902) 678-7722 or visit www.perenniaregistrations.com
to register!

Coffee and muffins at 8:15 AM at the Kentville Research Station - bus leaves at 8:30 AM sharp!

Insect and Floating Row Covers

Insect covers provide an alternative pest control option for growers.  Insect covers come in different sizes and are suitable for control of a whole host of insects such as carrot rust fly, cabbage maggot, and flea beetles.   Insect covers will create a physical barrier between the crop and flying insects.  It has to be applied tightly so insects are unable to get under the netting.

 

Insect cover on rutabaga

 

Insect covers do not trap heat and therefore are used on cole crops, carrots etc where extra heat might be undesirable.  On the other hand crops such as cucurbits, lettuce and peppers may benefit from extra heat, so floating row covers are more beneficial.

 

Floating row cover on lettuce

 

Cabbage Maggot Control

Cabbage maggot is one of the most destructive pests of cole crops in the Maritimes. The first generation is the most important to control because plants are small and very susceptible to damage.

The best control method consists of preventing the flies from laying eggs. Physical barriers such as row covers or netting of fine screening can be used for this purpose. The research shows that these can be as effective as insecticide application as long as it is placed over the crop immediately after the seeding (rutabaga) or transplanting (cabbage, cauliflower and broccoli).  In order to be effective, there must be no gaps or tears in the material, the material must be placed over the crop before or immediately upon crop emergence or transplanting, and no hosts of the pests should have been grown on that site the previous year. It is also important to bury the edges of the netting so that  cabbage maggot flies cannot get under the edges, and to allow the cover to be a little loose so the plants have room to grow.

Large commercial planting will have to be treated with insecticide for cabbage maggot. For more information please visit: http://www.agrapoint.ca/Pest%20Management%20Guides/Vegetables/2012/Cole%20Crops%202012.pdf

Given that the first generation of cabbage maggot was strong in 2012 it is fair to expect that the second generation which is less severe might be significant.

Rutabaga grown under netting.