Downy Mildew and Angular Leaf Spot of Cucurbits

Downy mildew and angular leaf spot are both damaging foliar diseases of cucurbits, especially in cucumbers. These diseases can look very similar in the field, but require different management tactics for effective control. Because of this, it is critical to correctly identify which disease you are dealing with. This blog discusses the the two diseases and how to differentiate them. 

Downy Mildew: 

Downy mildew of cucurbits (Pseudoperonospora cubensis) was not considered a major threat in North America until 2004 when the disease reemerged and caused significant damage to cucumber varieties previously thought to be resistant to the disease. Downy mildew of cucurbits was first detected in Nova Scotia in 2021, and has appeared every year since. The disease does not overwinter in Nova Scotia or the North Eastern United States, and is spread from the Southern United States each summer by  storms. Cucurbit downy mildew can be tracked at this site (https://cdm.ipmpipe.org/), as of July 19, 2024 the disease has only progressed as far North as Pennsylvania and New York, and has not been detected in Nova Scotia yet this season. The disease can significantly damage cucurbit crops if there are no management techniques in place.

The signs of downy mildew include lesions on the leaves (Figure 1). Angular, vein-delimited lesions that may initially appear slightly chlorotic are typical disease symptoms on cucumbers, and pathogen sporulation is easily visible on the lower leaf surface. Under humid and moist conditions, early infection lesions on cucumbers may appear water-soaked. The bottom leaf surface may appear "dirty" due to the sporangial masses' grey to purplish coloration when they are present in large numbers. These dark sporangial masses on the underside of the leaf are unique to downy mildew of cucurbits, and the underside of the leaf should always be examined to distinguish between downy mildew of cucurbits and angular leaf spot. Lesions become more chlorotic and necrotic as the disease worsens, leaves begin to die and the plant is unable to support fruit production. It is possible that both the quality (misshaped fruit) and quantity of marketable yield will decrease.

Figure 1. Downy mildew on cucumber leaves. Note the dark, spongy masses on the back of the leaf.

The pathogen was found to be resistant to the strobilurin fungicides (FRAC class 11) when it reappeared in 2004. While reports of decreased performance of particular fungicides demonstrates the need for resistance management and the development of new and unique active ingredients, newer downy mildew fungicides have been useful in containing the disease. The use of resistant cultivars and fungicide treatments should be paired with cultural practices to decrease downy mildew incidence. Increased row and plant spacing, drip watering and elevated plant beds with plastic mulch can all assist in limiting the pathogen by reducing leaf wetness, boosting airflow, and lowering the relative humidity.

Angular Leaf Spot:

The most common bacterial disease of cucurbits is angular leaf spot, caused by the bacterium Pseudomonas syringae pv. lachrymans. Disease severity is greatest in cucumber cultivated in warm, humid and semi-humid climates, but it affects a wide variety of cucurbit crops worldwide. Initially infecting cotyledons and leaves, the disease later spreads to fruits and contaminates seed.

Small, water soaked lesions first emerge on leaves as the disease spreads (Figure 2). The lesions typically grow until they are surrounded by substantial secondary veins in the leaves, which give them an angular appearance. A clear to milky exudate that gathers in a tear on the lower surface of the lesion occurs in conjunction with water-soaking at high relative humidity levels. On or near the lesion, the exudate dries to produce a thin, white crust. The blemishes on the leaves grow dry, tan-brown, and may even drop out. Lesions on cultivars that are sensitive frequently have yellow edges. In areas between lesions, heavily diseased leaves may turn yellow. Later, they may appear frayed or ragged. Petioles, stems and fruits may also experience lesions, showing a white, crusty discharge. This white, milky exudate is the defining characteristic of angular leaf spot and can be used to distinguish the disease from the very similar-looking downy mildew of cucurbits.

Figure 2. Angular leaf spot on cucumber leaves. Note the lack of dark, spongy masses on the back of the leaf.

Pseudomonas syringae pv. lachrymans is seed-borne, and infestation occurs beneath the seed coat, so the cotyledons are infected upon germination. The bacterium grows and colonizes leaf surfaces in the intercellular spaces of leaves. Raindrops, insects, human field workers and farm equipment can spread the inoculum from leaf to leaf and from plant to plant. The bacterium enters stomata and tiny abrasion wounds. The bacterium can survive for up to 2.5 years in dry leaves and overwinters in crop debris that has been infected.

Utilizing a thorough set of control measures, angular leaf spot can be reduced. Using seed free of pathogens is the first step in primary control. The number of bacteria in the cucurbit seed can also be  reduced but not eliminated after 20 minutes of treatment with water at 50^oC containing different acidic organic compounds. Repeated applications of copper sprays as a foliar protection can be beneficial in warm, humid locations where the bacterium is endemic.

Summary:

It is essential to determine which of these diseases you are dealing with as, with one being a fungus-like oomycete and the other a bacterium, the control options available (such as fungicides) differ drastically, and one control measure may have no effect on the other disease. By looking at the key differences in these two pathogens, as described above, one can differentiate between these diseases that cause similar symptoms on cucurbits.  In 2023 the Perennia Plant Health Lab opened its doors to accepting disease plant samples in addition to its virus testing services. At this time the focus is on meeting the needs of the Nova Scotia agriculture industry, however if you are interested in learning more about what diagnostic services provided, please follow https://www.perennia.ca/agriculture/plant-health-lab/. Our team of plant disease diagnosticians and specialists, with the aid of conventional and molecular diagnostic tools, can accurately identify what disease you are dealing with and provide tailored recommendations for your unique growing operation.

 

July Newsletter

 Upcoming Events/Perennia Updates

Below is a summary of some of the industry events that are coming up in the next few weeks! The events listed below are primarily hosted by Perennia, and more information on each of them can be found here.

• TunnelTalk (virtual Series)
• July 10 - Implementing Commercially Available Bio-Control Agents
• August 14 - Expert Panel Discusses Greenhouse Structures
• Understanding Alternative Nutrient Amendments (Virtual Series)
• July 2 @ 6:30 pm - Management and Considerations with Compost
• July 9 @ 6:30 pm - Nutrient Amendments and Soil Interactions 
• July 16 @ 6:30 pm - Conversion and Creation of Raw Material to Nutrient Amendments
• July 23 @ 6:30 pm - Biostimulants in our Systems

• Nova Scotia Young Farmers Summer Event
• July 27 @ 2 pm
• ACORN: Gathering at Abundant Acres
• July 28 @10 am 

New Service Launched!

The Plant Health Lab is now offering plant parasitic nematode analysis, following a two year study of nematode presence and distribution across Nova Scotia! 

Check out our website for more information about nematodes, sampling, and general submission guidelines.

Weather Updates

Growing degree days (GDD) are important for anticipating key dates for crop growth stages, as well as pest emergence and flights. Consider some of the most persistent critters on your farm, and when they typically start to show up. Even if we are still early in the season for your biggest headache, its a good reminder to revisit our target GDDs, and think about what needs to happen to prepare for them on your farm. We are still tracking ahead of the 5 and 10 year averages, with comparable recent accumulations recorded in 2017 and 2021.

Based on reports out of the North Eastern United States...tarnished plant bug is alive and well! Be sure to familiarize yourself with this pest, and expect it'll be coming around the corner in no time!

Figure 1. Degree day accumulation as of June 24, 2024. All data are taken from the Environment and Climate Change Canada weather station located at the Kentville Research and Development Centre, provided by Jeff Franklin. 

Table 1. Degree day accumulations as of June 24, 2024. All data are taken from the Environment and Climate Change Canada weather station located at the Kentville Research and Development Centre. Calculations are based on a start date of March 1, and calculated using the single-sine method. Provided by Jeff Franklin.

Seasonal Considerations: Humidity and Vapour Pressure Deficit

When it comes to managing humidity in protected spaces, it is (unfortunately) more complicated than setting a target value (ex. 60%), and walking away. The target humidity for any cash crop is dependent on the temperature of the air, meaning that number is going to change depending on what is happening with the air temperature. For anyone who has monitored greenhouse/tunnel temperatures throughout the span of a spring, summer, or fall day, you know that number changes a lot from sun up to sun down. 

Vapour pressure deficit (measured in kPa) is a metric which takes the relationship between temperature and humidity into account. It is the driving force for transpiration and water movement through the plant, starting at the roots and ending at the stomata. The plant can be likened to a straw: the more pull you exert at the top of the straw, the more liquid is pulled from the cup (in our case, the growing media), through the straw (the plant) and out (the surrounding air).

High VPD is defined by:

•      low moisture content in the ambient air (aka a dry day)
•      high moisture content surrounding the stomata (assuming 100% humidity)

This results in a large difference in moisture content between the air and the plant cells, and therefore we see the mass movement of water from areas of high concentration (the stomata) to areas of low concentration (the surrounding air). Water is rapidly pulled from the plant leaves, and due to the 'stickiness' of water molecules in the plant, causes a chain reaction all the way down to the roots. 

When this happens too quickly, there are going to be some sacrifices to water, and water-transported nutrients, to the 'extremities'. That is usually leaf/tip margins, but we can also see an impact of that on the tips of fruits and vegetables as well. The plant is unable to cycle water to where it needs to go, at the rate it is being extracted into the surrounding air. 

Figure 2. A bean crop showing leaf margins that have lost their turgor pressure. 

Figure 3. A tomato crop with leaf tips/margins that were subject to high VPD a few days prior. The soft tissue will then turn brown and die off after being subject to these conditions. 

Figure 4. A lettuce plant with leaf margins that were subject to a low humidity environment on a high temperature day. 

Low VPD is defined by:

•        high moisture content in the ambient air (aka a very muggy day)
•        high moisture content surrounding the stomata (assuming 100% humidity)

This smaller difference in moisture content between the air and the plant significantly slows down the movement of water out of the soil, up the plant, and into the surrounding air. With less water movement through the plant, the rate of photosynthesis (which converts carbon dioxide and water into sugars) slows down. This one is a bit harder to notice, but is typically characterized by much slower growth compared to a plant growing in a more balanced growing environment. 

Figure 5. These young radishes had been planted many weeks prior to the photo being taken. Their development was significantly delayed compared to what you would expect this many days post germination.

How Do I Measure VPD?

There are sensors which will measure VPD directly, and then it is just a matter of staying in the ideal range. The optimal range of values is 7.5-10 mb, or 0.75 - 1.0 kPa

For those who don't have the specific sensor, the use of temperature and humidity information collected inside the tunnel will do just fine. The following has been re-designed by our team, but pulled from a chart provided from Delphy UK. It showcases the ideal VPD values for long cane raspberry, though in general, these numbers are going to be good ones to aim for. We can see that the 'danger' zone exists on either side of the green band, either for being too low, or too high for that temperature. Yellow is mellow, but ideally we are able to exist in the green range of values as much as possible. 

Figure 6. A vapour pressure deficit guide for deciphering where we stand in terms of temperature and humidity relationships! Green represents a good dynamic between temperature and humidity, and red shows that there is an imbalance happening (either too much is moving out of the plant, or not enough depending on which side of the scale you are on). 

A great place to start when thinking about managing the relationship between humidity and temperature is to purchase sensors for your greenhouse. Keep an eye on those values over time, and what region your readings are putting you in for the VPD chart in Figure 6. Seeing a pattern you don't like? Let's chat!

How can I change my VPD?

This can be done by either altering the temperature or humidity in the greenhouse. Typically this time of year, we are going to be talking about changing the humidity. Humidity can be added a few ways depending on the setup: spray bottles, buckets/containers of water left to sit out, or under-trough sprinklers can be used to add moisture into the system. For a more targeted infrastructure option, high pressure fogging systems can be installed to help regulate our humidity. 

BEWARE OF INTRODUCING LEAF WETNESS AND ADDING TOO MUCH WATER. 

This will result in increased disease pressure/spread in the greenhouse. We don't want the plants to be wet, its more about introducing moisture to the space than giving it to the above-ground tissue. This is definitely a slow practice to get acquainted with to make sure we aren't tipping the scales to far in either direction. 

If our humidity is too high, that's when we talk about air movement. 'Wind' does a great job of drying up excessive moisture in a tunnel, and the use of fans or ventilation can help to pull some of that water through the plant when the humidity is not allowing for that process to happen on its own.

If you have any questions about this, please don't hesitate to reach out to Talia, Perennia's Protected Crop Specialist. We can come up with a plan of action that makes sense for you and your setup. 

Production Tidbits: Diagnosing Deficiencies vs Disease

Distinguishing between plant disease and nutrient deficiency is no easy task, especially once the season goes on and we could be looking at multiple factors overlaying each other, making that diagnosis even harder to put our fingers on. 

Here is some helpful information to help get to the bottom of it:

Are we observing signs or symptoms?

With a fungal or bacterial disease, there will often be signs of the actual organism on the impacted plant tissue. 

• angular leaf spot typically presents with a wet spot/cloudy ooze emerging from lesions on the underside of the leaf
• bacterial wilt will show a stream of bacterial ooze if a piece of tissue is submitted in water, or if you make a cut in the stem and slowly pull those two pieces apart from one another
• powdery mildew and botrytis are examples of fungal infections with very obvious growth, where the white and grey masses are the physical forms of the infection

Figure 7. Late blight of tomato photographed by Dr. Lina Quesada (https://content.ces.ncsu.edu/tomato-late-blight). Notice the white growth on the underside of the leaf

• fungal fruiting bodies may also be present on the plant tissue

• A point of infection can help to differentiate between a disease and a nutrient deficiency as well. Concentric circles around a singular point can be an indication that a pathogen is the culprit for the symptoms observed. This is disease dependent, so lacking concentric circles or obvious 'targets' does not mean that you are free of disease. 

Figure 8. Late blight of tomato photographed by Inga Meadows (https://content.ces.ncsu.edu/tomato-late-blight). Notice the obvious concentric circles through the leaf lesion, which indicates the presence of an organism as the cause of the symptom. 

The exception to this rule is viruses, which don't present as obviously as some of the above indicators (ex fruiting bodies, ooze, physical fungal growth). If you suspect you have a viral infection in the crop, reach out to your extension specialist immediately to verify. 

What are some other things we should pay attention to when the crop starts to look off?

1) Where on the plant are the symptoms located? 

Are you seeing it primarily on the new growth of the plant, or the older leaves? Have the symptoms spread to the stem? Are flowers and fruits impacted? 

2) What is the distribution of the observed plant symptoms? 

Are you seeing it throughout the greenhouse or just in one patch? Is it concentrated on one side versus the other? Down the middle or along the edge? Concentrated in low patches in the production space? 

3) How quickly did it show up? 

Are you seeing quick spread or is it staying contained within the first few impacted plants?

4) Are the symptoms uniform across the leaf or irregularly scattered?

Typically a highly regular/uniform distribution of discolouration/necrosis can be attributed to abiotic factors (sprays gone wrong, growing environment stress, nutrient deficiency) as opposed to biotic factors (disease and/or pest pressure). 

The earlier we can identify and address the issue, the better! 

Additional Resources:

• Perennia's Nutrient Deficiency Guide
• Perennia's Plant Health Lab is always available to give an official diagnosis on the weird and wacky. 

Feature Pest/Disease: Fungus Gnats

The following information is a summary of session 5 of the BugBites Series: Fungus Gnats and Shorefly Suppression with Beneficial Organisms. To watch the full session, click here! 

Adult fungus gnats are mosquito-like insects with long legs, and a characteristic y-shaped wing vein. Adults can be found hanging around or near the soil, mostly under plant canopy. The fungus gnat larvae are white with a shiny black head. Larvae spend most of their time underground and will feed on the roots. 

Figure 9. A photo of an adult fungus gnat stuck to a yellow sticky card. Below it is an image of the fungus gnat larvae. If you look closely, you can see the characteristic black head at the end of the larva. Image taken from the BugBites! Session 5 presentation. 

Monitoring and Scouting: 

Adults are not strong fliers, meaning that sticky cards will only be effective when placed close to the soil line. If placed correctly, traditional sticky cards are a great tool to monitor population sizes.

As an attractant, some growers will use half a potato, or a potato slice, placed in a pot to draw larvae up from the soil. As the larvae are accustomed to feeding on roots, the use of a tuber is a big draw.

For the adults there are various traps available. These traps typically involve the use of an attractant (ex. UV bulb) and a way to capture the insects (sticky cards, soapy water solution etc.). This is useful for general scouting purposes as well as mass trapping.

Biological Control Options: 

As with any biological control program, prevention is the first line of defense in controlling population sizes. By conducting regular scouting checks of the crop, and maintaining populations of biological control agents, you can limit the degree of pest infestation.

Dalotia coriaria; Rove beetle

•  Predator to both shoreflies and fungus gnats
•  Both adults and larvae are predators
• Orange larvae will be noticeable in your soil
• Adults readily move around via flight

• Establish readily in greenhouses and work well in hydroponic systems
  
  

Figure 10. A photo of a rove beetle in the adult (left) and larval (right) stages. stuck to a yellow sticky card.  Image taken from the BugBites! Session 5 presentation

The use of rearing boxes allows for a slow-release approach and will help maintain beetle populations through the season. Rearing boxes can be as basic as media (ex. peat, vermiculite) set inside a Tupperware container, and supplemented with food (ex dog or fish food, artemia). It is crucial to keep this moist, but not wet. These can be placed under benches.

Bacillus thuringeniensis israeleinsis 

•  Functions as a stomach toxin for fungus gnats
•  Best applied via soil drench or chemigation. Irrigation is not ideal as the soil needs to get very wet to allow for good establishment of the biopesticide

Stratiolaelaps scimitus; predatory mite

• Target fungus gnat larvae
•  Well suited for greenhouse environments: optimum development temperature of 25^oC (77^oF)
• Ideal range is 15-30^oC (59-86^oF)
• Live in the top half inch of the soil: best applied to the substrate surface after transplant
• Want to avoid burying too deep in the growing media
• Does not establish well in rockwool
• Persistent control agents, and can provide season-long protection

                                               

Figure 11. An image of an adult predatory mite. Image taken from the BugBites! Session 5 presentation

S. scimitus can be mixed with Dalotia, but it is not recommended to introduce them before adding into the crop. They will feed on each other, so make sure they are spread evenly throughout the canopy when distributed.

Steinernema feltiae; entemopathogenic nematode

• Target fungus gnats, shoreflies, thrips pupae and many others
• Forage in the top inch or two of the soil
• Water into your growing media lightly- if they get too far in, they will not work
• Not highly mobile
• Well suited for greenhouse environments with an ideal temperature range of 10-25^oC (50-78^oF)

• Susceptible to being washed away in rockwool
• When growing in rockwool, apply after the last irrigation of the day to give them a chance to establish

Recent Uploads

• Nova Scotia Soil Newsletter - June issue
  
• Tunneltalk - Venting Greenhouse Environments
  

_______________________________________________________________________

That's all for now! If you have any questions, feel free to reach out to your extension specialist.

Happy growing everyone!

-Talia

June Newsletter

Upcoming Events/Perennia Updates

Below is a summary of some of the industry events that are coming up in the next few weeks! The events listed below are primarily hosted by Perennia, and more information on each of them can be found here.

• TunnelTalk (virtual Series)
• June 13 - Greenhouse Ventilation w Matthew Kleinhenz
• July 10 - Implementing Commercially Available Bio-Control Agents
• August 14 - Expert Panel Discusses Greenhouse Structures
• David Vantage Pro 2 Weather Station Maintenance Workshop - Murray Siding
• June 7
• Understanding Alternative Nutrient Amendments (Virtual Series)
• June 25 @6:30 pm - Introduction to Nutrient Amendments 
• July 2 @ 6:30 pm - Management and Considerations with Compost
• July 9 @ 6:30 pm - Nutrient Amendments and Soil Interactions 

New Service Launched!

The Plant Health Lab is now offering plant parasitic nematode analysis, following a two year study of nematode presence and distribution across Nova Scotia! 

Check out our website for more information about nematodes, sampling, and general submission guidelines.

Weather Updates

Cucumber beetles have been observed across the Northeastern States! Check back to last month's newsletter about management options

Lets take a look at the weather data collected for this year, and how it compares to our historical records. Growing degree days (GDD) are important for anticipating key dates for crop growth stages, as well as pest emergence and flights. Consider some of the most persistent critters on your farm, and when they typically start to show up. Even if we are still early in the season, its a good reminder to revisit those dates, and think about what needs to happen to prepare for them to limit the impact they have on your farm. 

Figure 1. Degree day accumulation as of May 28, 2024. All data are taken from the Environment and Climate Change Canada weather station located at the Kentville Research and Development Centre, provided by Jeff Franklin. 

Table 1. Degree day accumulations as of May 28, 2024. All data are taken from the Environment and Climate Change Canada weather station located at the Kentville Research and Development Centre. Calculations are based on a start date of March 1, and calculated using the single-sine method. Provided by Jeff Franklin.

Seasonal Considerations: Irrigation

In 2021, the focus of Perennia's annual 'Getting Into the Weeds' series was Irrigation. As precipitation levels remain significantly lower than what typically falls through the month of May, it may be worth revisiting the resources available for those who are looking to fine-tune their irrigation systems. 

Ted van der Gulik, President at the Partnership for Water Sustainability in BC, lays the foundation for planning and design of a drip irrigation system, as well as operating and managing it. These session are focused on implementation outdoors, compared to protected production, but the key considerations for either setup are the same. Concepts such as the importance of considering the amount of water 'lost' to the environment are crucial when calculating the maximum system capacity required, and how much water should be applied on a regular basis. Wind, solar radiation, temperature and relative humidity impact evapotranspiration, which is water lost from the soil surface. The use of plastic mulch, or growing a crop in a container that quickly becomes shaded by the canopy overhead, significantly reduces the amount of water that is lost from the rootzone through evapotranspiration.

Lets consider vegetables that are not mulched in raised beds, and are not grown in a container. Farmwest's Evapotranspiration calculator is a great tool to estimate how much water is lost from the soil through normal environmental conditions. Adjustments can be made seasonally to figure out how much is estimated to be lost different times of the year, however for the most protective strategy, choosing a date range of about a week where evapotranspiration is at its peak (ex. August) allows for you to establish your system at maximum capacity, and scale back when it is not needed. 

•     Looking to maximize the use of this tool? Check the peak dates over a few years to establish a more reliable value. It's been a wild few years, and we don't want to make assumptions based on one scenario!

Check out the source material on Perennia's Youtube channel for an in-depth refresher!

• Planning and Design of a Drip Irrigation System
• Operating and Managing a Drip Irrigation System
  
• Pivot and Guns: Irrigation System Management

Production Tidbits: Tank Mixing Made Easy:

As we move towards peak spraying season, growers should be reminded that many tank-mix compatibility problems can be avoided by adhering to the proper tank mix order. The WALES method has been put together to help remind folks of the ideal mixing order. Prior to creating any complex mixes, it is recommended to perform a small-scale test known as a jar test to assess chemical compatibility. This is a good time to remember that the sprayer should be thoroughly cleaned out between uses so that residues from previous applications do not interfere with mixability and application. 

By following the Wales method below growers can generally, mix products in the tank without incident. 

W

• fill the tank about ½ full with WATER and start the agitation
• add WATER CONDITIONERS at this time, if needed, for hard water or pH adjustment
• add WATER SOLUBLE BAGS (WSB) to the clean water in the tank.  Allow the bags to completely dissolve before adding any other products
• add WETTABLE POWDERS (WP)
• add DRY FLOWABLES (DF)
• add SOLUBLE GRANULE (SG)
• add WATER DISPERSIBLE GRANULES (WDG)

These products may have to be pre dissolved or slowly added to the tank so that they will be dissolved before beginning sucked into the sump, collecting in the filters and plugging the sprayer. Be sure dry products are thoroughly dissolved prior to adding other products. 

A

• continue AGITATION and allow the dry products to mix entirely to ensure uniform dispersion.

L

• add LIQUID FLOWABLES like SUSPENSION CONCENTRATED (SC)
• add LIQUIDS (L)
• add FLOWABLE liquids(F)

E

• add EMULSIFIABLE CONCENTRATES (EC) and MICROEMULSION CONCENTRATES (MC)

S

• Add SOLUTIONS (S) or SOLUBLE LIQUIDS (SL)
• Add SURFACTANTS and ADJUVANTS
• Finish by completely filling the spray tank with water and continue to agitate until the spray application is complete. 
•  Test and adjust water pH if needed before heading to the field

 If boron fertilizers are required in the spray mixture make sure that water soluble bags are completely dissolved before adding the boron fertilizer to the tank. 

For products that quickly degrade at high pH’s be sure to measure the pH of the tank solution before and after mixing is complete as multiple pesticide and fertilizer products can change the overall solution pH. 

There are new rules beginning December 20, 2024, outlining what will be allowable for tank mixes which will be stated on each of the product labels.  To find out more about these new regulations please follow this link.  CLICK HERE. For a summary article on the subject please follow this link: CLICK HERE. 

 Article has been adapted from https://www.syngenta.ca/agronomy/wales-mixing-order.

Feature Pest/Disease: Squash Bug

It will soon be time to start scouting for squash bug, a pest of cucurbits with a particular preference for pumpkins and squash. They feed with their piercing sucking mouth parts and cause leaf necrosis, rapdi plant wilt and scarred fruit. Crop injury from feeding damage can result in reduced yields, delayed plant growth, and poor fruit storability. Squash bugs can also vector bacterial diseases such as angular leaf spot. 

Adults overwinter in plant debris stones, or clods  of soil. They can also be found in nearby wood piles and around building foundations. Adults begin emerging in early to mid-June when they mate and lay bronze coloured eggs on the undersides of leaves. After one or two weeks, the first nymphal instars (immature squash bugs) will emerge. The adults aren't affected by pesticides, and the youngest instars are the must susceptible, so its best to flag a few egg clusters and check back regularly to time your sprays. Be mindful of pollinator presence and only apply spray when bees are not active. 

If you have multiple types of squash in the field, squash bugs seem to prefer pumpkins, blue hubbard, buttercup and kabocah types, so make sure those are getting extra attention during your scouting walks. For more information please refer to Perennia's factsheets on Squash Bug and Cucurbit Angular Leaf Spot. 

Recent Uploads

• TunnelTalk - Biological Spray Programs
• Nova Scotia Soil Newsletter
• Getting Into the Weeds: Tank Mixing

_________________________________________________________________________

That's all for now! If you have any questions, feel free to reach out to your extension specialist.

Happy growing everyone!

-Talia

Updated 2024 Emergency Use Registrations for Cabbage Maggot in Brassica Crops

 

To address the loss of chlorpyrifos (Lorsban, last use date: December 10 2023) in Brassica crops for control of cabbage maggot, emergency use registrations (EUR) were recently approved for Success and Cimegra in Rutabaga and Cimegra in Head and Stem Brassicas (broccoli, Brussel sprouts, cabbage, cabbage (Chinese, Napa), and cauliflower) for cabbage maggot. Application instructions from the EUR labels of each product can be found below. 

	Success Insecticide	Cimegra	Cimegra
Active ingredient	Spinoad	Broflanilide	Broflanilide
Registration period	May 17, 2024-May 16, 2025	May 21, 2024-May 20, 2025	May 17, 2024-December 31, 2024
Group	5	30	30
Crop(s)	Rutabaga	Rutabaga	Broccoli, Brussels Sprouts, Cabbage, Cabbage (Chinese, Napa), and Cauliflower
Insect	Cabbage Maggot	Cabbage Maggot	Cabbage Maggot
Application Instructions	Soil drench at the rate of 273 mL/ha to 546 mL/ha (131 g/ha to 262 g/ha a.i,). For 76 cm (30-inch) plant row spacing apply Success at 6 mL to 12 mL per 300 linear metres (1000 linear feet).	Apply 250 mL/ha1 of Cimegra insecticide post-planting as a drench banded spray, 10 cm on each side of the plant targeting the soil and base of plant to control cabbage maggot.  Use a minimum water volume of 1000 L/ha.	Apply 187.5 – 250 mL/ha1 of Cimegra insecticide post-planting as a drench banded spray, 10 cm on each side of the plant targeting the soil and base of plant to control cabbage maggot.  Use a minimum water volume of 1000 L/ha.
Application Timing	Begin applications when adult activity is observed in or near the field.	Apply at peak egg laying and before the build-up of heavy pressure.	Apply at peak egg laying and before the build-up of heavy pressure.
Application Rate	273 - 546 mL/ha	250 ml/ha1	187.5 - 250 ml/ha1
Applications Per Season	2 (Max 1.1L/ha of Success per year)	2 (Max 500ml/ha of Cimegra per year)	2 (Max 500ml/ha of Cimegra per year)
Application Interval	4 days	10 days	10 days
REI	12 hr	12 hr	12 hr
PHI	3 days	40 days	1 day

¹ 1.9 mL/100 m of row for 76 cm (30”) row spacing.  For a different row spacing, adjust the product rate using the following equation: (row spacing (cm) / 90) x 2.3 mL = mL per 100 m of row.

To reiterate, Success can ONLY be used on Rutabaga for Cabbage maggot. Cimegra has been approved for use in both Rutabaga and Head and Stem Brassicas (broccoli, Brussel sprouts, cabbage, cabbage (Chinese, Napa), and cauliflower) for cabbage maggot but the application rates are different for each crop type.  Full product labels can be found at the Pest Management Regulatory Agency (PMRA) Pesticide Label Search website, always read product labels before applying pesticides.