Onion smut

Tuesday, August 20, 2019

Fig. 1. Infected leaves can become
bloated and split open, releasing spores
and contaminating the surrounding
soil.  Photo taken early August, 2019.
Onion smut only infects Alliums, and is a disease that can lie dormant in the soil for 15+ years, even in the absence of a host crop.  A cold spring such as we had this year results in the onion flag leaf emerging slowly, increasing the likelihood of smut infecting the onion.  The smut fungi can only penetrate and infect young seedlings - if the cotyledon escapes infection until it is mature, no further infection can occur despite high disease pressure. For this reason, healthy transplanted onions or onion sets typically avoid being infected by smut since they do not emerge in infected soils.  The infection period is from two or three days after the seed germinates until the first leaf is about three inches tall (about 10-21 days, depending on the year.)

Fig. 2. Black streaking on the onion bulb, August.
Early infections can result in seedling death, and plants that do survive will have characteristic black spots, blisters, and/or streaking (Fig. 1, 2).  Some infected plants will shed their outer leaves in the second month of growth, and continue growing, free of infection.  However, this year I'm seeing many infected plants that have survived the first few weeks of infection, and the smut fungus has continued to grow, systematically colonizing the plant.  These plants are are usually stunted.  Black pustules can infect as deep as the third or fourth scale (Figure 3).  Many infected plants will dry up, wither, and die by harvest.  Infected bulbs that do make it into storage shrink more rapidly, and are more prone to bacterial rots which can contaminate other bulbs in storage.

The causal fungi, Urocystis magica (synonym: U. cepulae) and U. colchici, can be transmitted from one field to another by surface drainage water, wind-blown soil, tools and farm equipment, soil in your shoe or truck treads, or any other method that transports soil.  Have you read Perennia's fact sheet about biosecurity in horticulture crops?

Fig. 3.  Smut infections penetrating several scales deep.

Long crop rotations are an important tool to limit the build up of disease in the soil.  Conventional growers that are planting into a known infected field should use seed treatments or an in-furrow fungicide application.  If organic or small-scale growers have a field history of onion smut, it is recommended to transplant onions into the field, rather than plant from seed in the infected soil.  Growers with smaller plantings should also remove and destroy diseased seedlings and plants to avoid building disease levels in the soil.



Hailstorms and crop impact

Tuesday, August 13, 2019

The hail storm over the weekend caused scattered damage in the Annapolis Valley, as well as in Hants, Colchester, and Cumberland Counties.  The degree of damage depends a lot on location and crop type, as well as on wind velocity, the size and shape of the hailstones, and how long the hail lasted.  The warm, wet weather that followed the storm can exacerbate disease problems, especially bacterial infections.

Crops with large leaves such as Cucurbits will typically look pretty destroyed, but, depending on the severity of the damage to the leaves, and how well the fruit were protected, might pull out of it with minimal yield loss.  If the Cucurbits are on a drip system, a little extra nitrogen will encourage the regeneration of leafy growth.  Damaged zucchinis and summer squash should be removed.  Leaving damaged fruits on the plant, which are unlikely to be marketable, will be a drain on the plant's resources and could result in more prolonged yield losses.

Bacterial infection spreading down an onion leaf
Other crops that are susceptible to bacterial rots such as onions will have long-lasting damage - crop injury opens the door for bacterial infection, which quickly spreads down the leaves into the bulbs.  Dead tissue is prime for stemphylium infection.  Growers are encouraged to continue with preventative stemphylium sprays.  Copper may help with bacterial infection, but results have been poor on onions in the past.

Leaf loss in crops close to harvest such as sweet corn or root crops should have minimal effects on yield.  However, direct impact on sweet corn ears can render them unmarketable, depending on the degree of damage.

Fruiting vegetables such as peppers will be more prone to sunburn if protective foliage has been badly damaged.  Fruits that have taken a direct hit, depending on the size of the hail stone and the velocity of the strike, can be unmarketable.

Losses of flowers and small fruit will reduce yield and delay harvest in crops such as green beans.

Wounds in plant tissue open the door for diseases to come in.  It is recommended that a protectant such as copper or Bravo be applied (if labeled) for your damaged crop, which will help guard against infection while the plant heals.  Always read and follow the label, the most up to date labels can be found on the Health Canada website.

If you have Crop Insurance, it is recommended that you reach out so that they can document the damage.  Should a claim be necessary down the road, they will have a record of how extensive the damage was, which will make filing a claim easier.  The days just after a hail storm are often the worse.  Apply a protectant, maybe give your crop a bit of extra fertility, if appropriate, and then come back in a week to see how things look.  If the crop pulls out of the damage, then no insurance claim needs to be filed.  Registered farms in Nova Scotia shouldn't hesitate to contact Perennia if you are unsure of best management practices in crops that have been affected by adverse weather.


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Garlic harvest!

Friday, August 2, 2019

Wrapper leaves snug around cloves.
Garlic harvest is upon us, and if you haven't already started harvesting your garlic, now would be the time to start planning it.  Different varieties will mature at different times, so it's always good to check on bulb development of few bulbs of each variety.  One way to determine harvest-readiness is by looking at the number of green leaves.  Each leaf corresponds to a wrapper leaf around the bulbs.  Wrapper leaves protect the cloves from light, moisture, heat, etc.  For best storability, it is suggested to harvest with five to six green leaves.  That way, if a wrapper leaf or three is lost in harvesting and cleaning, there will still be two to three wrapper leaves around the bulb to protect it from storage rots, desiccation, etc.

Stem and bulb nematode damage
Green leaves should be used as a guideline, but not a rule.  Sometimes on a particularly healthy plant, the leaves can remain green despite harvest-readiness.  Alternatively, if there is heavy thrip damage, high stem and bulb nematode populations, etc. the leaves can brown prematurely.  It is always best to pull a few bulbs and check to see how the cloves are filling the wrapper leaves.  Give the bulb a squeeze, and if there is any give, then the garlic isn't quite ready yet.  You should also cut the bulbs in half perpendicularly to the stem.  Each clove should be tight in the wrapper leaves.  If the wrapper leaves seem a little loose around the cloves, then wait a little longer to harvest.  The cloves in harvest-ready garlic will also start to pull slightly away from the stem, especially in hardneck varieties. 

Cloves starting to pull away from stem.
Hardneck varieties (Allium sativum var. ophioscorodon) produce scapes.  Hardneck types, as a general rule of thumb, produce larger cloves, but have a shorter storage life, which can be greatly influenced by harvest timing.  If you leave harvest for too long, the wrapper leaves will start to decay, and the cloves will continue to grow and pull away from the stem and the bulb will split open, rendering the bulb unmarketable.  Softneck varieties (A. sativum var. sativum) do not produce a scape, and typically have a longer storage life.

Garlic harvested too early might not have fully developed its yield potential or flavour profile, and will tend to shrivel when cured.  Late-harvested garlic is more likely to have poor storability, particularly the hardneck varieties, as the wrapper leaves start to deteriorate, exposing cloves.  It is often better to harvest a little early than a little late.

Target harvest for early in the morning on a dry day for best results.  Do not leave garlic in the sun for long as it can scald, and the cloves will quickly deteriorate.  Handle garlic gently as it is sensitive to bruising.  The higher the moisture or relative humidity when you are drying your garlic, the slower the garlic will dry down and cure, resulting in high disease potential.

Post-harvest handling can dramatically affect garlic quality and storability.  Recent research from Cornell University suggests that root trimming does not have any impact on bulb quality, weight, or disease incidence.  Washing garlic post-harvest, while resulting in good looking bulbs initially, ultimately resulted in more discolouration after drying and curing.  For more details about post-harvest handling of garlic, check out Cornell's Garlic Post-Harvest Study.



Tortoise beetles on sweet potatoes

Tuesday, July 9, 2019

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.



Growing degree days and crop and pest development

Monday, July 8, 2019


I was talking to Michelle Cortens, Perennia's Tree Fruit Specialist, this morning and she mentioned something interesting...  By June 5th, 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.


Garlic scape removal

Sunday, June 30, 2019


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

Thursday, July 5, 2018

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).