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)

Leek Moth Monitoring Update

 

2020 marked the third season of collaboration between Perennia and Agriculture and Agri Food Canada (AAFC), with support from NSDA in monitored for Leek Moth (Acrolepiopsis assectella) in across Nova Scotia. Leek Moth is an invasive pest native to Europe and was first identified in Canada (near Ottawa) in 1993. Leek Moth has expanded its range in Eastern North America and was first identified in Kings County, Nova Scotia in 2017. It has established itself here and we have confirmed its presence in both Annapolis and Kings Counties in all 3 seasons of the monitoring program (2018 – 2020). If you are a small scale or commercial grower of Allium crops, particularly garlic or leeks, it may be wise to take some time to familiarize yourself with this pest. For more information on leek moth, Cornell and OMAFRA have great resources pertaining to identification, life cycle and management.  

Adult leek moth. Photo: David Fuller, University of Maine Extension.

Larval feeding damage on garlic. Photo: Agriculture and Agri-Food Canada.

Monitoring in 2020 took place at six sites across Annapolis and Kings Counties. Pheromone traps were set out in early April to try and catch the first flight of overwintering adults, which typically occurs when temperatures reach 9.5^oC. Throughout the entire season (April – October) trap liners (sticky paper in bottom) were changed weekly and inspected for adult leek moths. Frequent liner/sticky changes allowed us to have a detailed look at flight patterns of the insect at each location. Trap lures were changed monthly.

Pheromone (Delta) traps used for monitoring leek moth. Photo: Agriculture and Agri-Food Canada.

In 2020 we observed up to 3 flights or 2 generations of leek moth in some locations. The first flight of leek moths was caught as early as the end of April at a couple sites and as late as mid-May in others. A second flight of insects was observed at some sites the end of June into early July. There were traps that experienced a third and final flight later in the summer (late July – late August). Interestingly, some locations did not catch any moths until the end of July. Trap data can be seen in the ‘2020 Leek Moth Catches’ graph pictured below.

Leek moth catches observed on a given date for each trap. Each line corresponds to a separate trapping site. 

Overall, data from the pheromone traps are showing similar trends to what has been observed in Ontario. Studies out of Ontario have determined that there are 3 flights or 2 generations of leek moth each season in Eastern Ontario:

    - Overwintering adults emerging in late April to mid-May

    - An early summer flight of 1st generation adults beginning in mid to late June through mid-July

    - A late summer flight of 2nd generation adults beginning in late-July to August.

Focused monitoring continues for the 2021 season and will follow the same trapping procedure as 2020. The goal for this year is to compare the trap data to previous years’ and to validate an insect development model used in other regions.

If you think you are seeing leek moths or feeding damage in your alliums, feel free to reach out to Perennia or check out our Pest Management Guides for Allium crops for products registered for use on leek moths.

Garlic scape removal

If you haven’t signed up for it before, OMAFRA has a fantastic vegetable blog.  A couple of years ago, Travis Cranmer, OMAFRA’s Allium Specialist, wrote a great piece about the benefits of removing garlic scapes.

Figure 1. Yield and bulb weight in response to scape removal timing of
garlic cv. ‘Music’. (Zandstra, 2006)

John Zandstra did some research on scape removal and the influences it has on yield.  Scapes should be removed sooner rather than later to preserve yield and bulb size (Figure 1). The longer you leave the scapes growing in the field, the more energy the plant will divert to creating a flower and bulbils - to the detriment of bulb size and yield.

Figure 2. Influence of leaf removal on yields and bulb weights of
garlic cv ‘Music’. (Zandstra, 2000)

Best practices also suggest that the scapes should be removed by hand (Figure 2).  Using a sickle bar mower, or other mechanical means to remove the scape often damages leaves.  Damage to the leaves reduces the photosynthetic potential of the plant, resulting in less energy to be poured into bulb development.  In short, even a small percentage of leaf damage will reduce bulb weight and total yield so be careful when removing scapes!

Scape removal is also a good time to be on the lookout for leek moth damage in your crop. Leek moth is a new pest to Nova Scotia and has been found in Kings and Annapolis Counties.  Cornell has an excellent site devoted to providing further leek moth information.  If you grow garlic, leeks, or onions, I strongly suggest you make yourself familiar with this pest.

Leek moth damage on garlic, photo credit Amy Ivy, Cornell

Leek moth damage on garlic leaves, photo Amy Ivy, Cornell

Leek moth damage on garlic scapes, photo Scott Lewins, UVM

Pest Update - Leek Moth

Perennia in association with NSDA and AAFC has been monitoring for leek moth across Nova Scotia since early May this year. Leek moth is an invasive insect pest from Europe that feeds on Allium species (onions, garlic, leeks,etc), and can cause significant damage to these crops. Previous to 2018, leek moth had been identified in Kings County in 2017. In 2016 gardeners reported damage on garlic which could have been due to leek moth but no specimens were ever recovered to verify these observations. In response to this a provincial leek moth monitoring project was established, to determine how widespread the pest is in Nova Scotia. As of this week we have confirmed leek moth in both Kings and Annapolis County. Currently we have not found the pest in large scale commercial fields, and all the leek moth samples we have identified have been from garlic. Leek moth favours garlic and leeks primarily; we are currently unsure of its effects in onion production.

Leek moth can be monitored using commercially available pheromone traps, which attract adult males. The adult leek moth is a small (5-7 mm in length) brown moth with a distinctive white triangle in middle of its wings when they are folded at rest. Additionally allium crops can be scouted for feeding damage from leek moth larvae. On alliums with flat leaves (garlics, leeks) the larvae feeds on the tops and inside of the leaves, as well as bores into the center of the plant leaving noticeable frass. In alliums with hollow leaves (onions, chives) the larvae will feed internally producing translucent areas on the leaf known as "windowing". The larvae will also occasionally bore into bulbs.

There are several chemical controls registered for leek moth in garlic, leeks, and onions that can be found in the Perennia's Garlic Management Schedule, Leek Management Schedule, and Onion Management Schedule. These pesticides are most effective when eggs are present and leek moth larvae are small, so monitoring is crucial to ensure proper timing of applications. Row cover is also an effective means of protecting allium crops against leek moth, without using chemical controls.

For additional information on leek moth identification and management please consult AAFC's An Integrated Approach to Management of Leek Moth . If you think you have leek moth please contact Matt Peill, horticultural specialist with Perennia (email: mpeill@perennia.ca, cellphone: 902-300-4710).