Tag Archives: Cucurbits

Time to Start Scouting for Powdery Mildew

Powdery mildew typically arrives in Southern Ontario in mid-to-late July. Plants are most susceptible to infection during the fruit sizing and development. Poor control results in decreased yield and poor fruit quality at harvest. The threshold for treatment is 1 lesions/50 plants. Optimum powdery mildew control is a combination of variety selection, fungicide timing and fungicide selection.

Powdery Mildew Lesion on the Lower Leaf Surface
Powdery Mildew Lesion on the Lower Leaf Surface

Cheryl Trueman, a vegetable pest management researcher at the University of Guelph’s Ridgetown Campus, has been conducting powdery mildew efficacy trials since 2009. In these trials, several products consistently provided good control of powdery mildew. These products are powdery mildew targeted, and have a single site mode of action. To prevent the development of resistance, it is essential to always rotate between different fungicide groups and/or tank mix with a broad spectrum fungicide.

Powdery Mildew Targeted Fungicides Showing Consistent Control in the Ridgetown Field Trials:

Group 13: Quintec (quinoxyfen)
Quintec was the most consistent powdery mildew product tested in Ridgetown. It provided excellent control in 4/5 years and good control in 1/5 years tested.

Group U8: Vivando (metrafenone)
Vivando provided excellent control in 1/3 years and good control in 2/3 years and tested.

Group 7: Fontelis (penthiopyrad), Aprovia (benzovindiflupyr), Sercadis (fluapyroxad) and Pristine (boscalid/pyraclostrobin).
Fontellis was somewhat less consistent. Control with this produce ranged from excellent to poor, depending on the year. It provided excellent control in 1/5 years, good control in 2/5 years and poor control in 2/5 years. Note: Aprovia, Sercadis and Pristine were not tested in the Ridgetown Campus trials.

Group 3: Inspire (difenoconazole), Proline (prothioconazole) and Quadris Top (azoxystrobin/difenoconazole)
Inspire provided a level of control similar to Fontelis; good control in 3/5 years, and poor control in 2/5 years. Proline and Quadris Top were only tested for one year in the Ridgetown trials, in which they both provided good control.

Fungicides containing chlorothalonil (Bravo ZN and Echo) provided a lower level of powdery mildew control, but are still better than the untreated checks. They also control a broad range of other foliar diseases including scab and alternaria.

Research in Ontario and other jurisdictions indicates that the group 11 (QoI) fungicides, Cabrio (pyraclostrobin) and azoxystrobin (a component of Quadris Top) no longer control powdery mildew. However, they may provide control of other cucurbit diseases such as anthracnose and alternaria.

Additional reading: http://www.omafra.gov.on.ca/IPM/english/cucurbits/diseases-and-disorders/powdery-mildew.html#advanced

Cucumber Downy Mildew Confirmed in Kent County, Ontario

July 5th, 2016: cucurbit downy mildew was identified today in a processing cucumber field in Kent County, Ontario.  Now that the disease is present in the great lakes region, growers should immediately move to a targeted downy mildew spray program.

See the 2016 Downy Mildew Control Strategy for Cucumber Crops for an up-to-date list of registered control products.

Use only the downy mildew targeted products listed in the strategy. Research trials in Ridgetown, Simcoe and in the neighbouring states have shown these products to be the most consistent from year-to-year.

Rotate between all three of the targeted downy mildew products, starting with the most effective product, Orondis Ultra, and then rotate to either Zampro or Torrent within 7-days.

If you have any questions about the cucumber downy mildew control strategy, please call 519 674 1616 or email elaine.roddy@ontario.ca

Cucumber Downy Mildew Update – June 14th, 2016

Do date there have been no confirmed reports of downy mildew in the Great Lakes region.  However, activity does continue in the Southern US.  The ipmPIPE website tracks the epidemic (figure 1) and also forecasts the potential spread of the disease.

Cucurbit Downy Mildew Epidemic Status Map, 2016-06-14

Historically, downy mildew has arrived in this area in late-June to early July. We have found that using an early broad spectrum preventative fungicide program, staring at vine development, will result in better season long control of the disease. This is especially important if weather conditions turn wet and overcast, with storm originating in the Southern US.

For complete details see the 2016 Downy Mildew Control Strategy for Cucumber Crops.

If you suspect downy mildew in your cucurbit crop, please notify OMAFRA, your agri-business supplier or your grading station.  Downy mildew is a community disease and open communication is vital to ensuring a healthy crop.

2016 Downy Mildew Control Strategy for Cucumber Crops

The 2016 Downy Mildew Control Strategy for Cucumber Crops contains an updated list of fungicides, including the newly registered Orondis Ultra. The restricted entry interval for Bravo has also been updated to reflect the new Bravo ZN label.

Due to the development of resistance and concerns about efficacy, Tattoo C and Presidio have been removed from the 2016 strategy. These products may provide  suppression under low risk conditions, however research results indicate that they are not sufficient controls under higher disease pressure.

For more reading:

Research Update – Fungicide Efficacy on Downy Mildew in Cucumbers

Ontario CropIPM – Downy Mildew

Angular, tan-to-brown lesions caused by cucurbit downy mildew
Cucurbit Downy Mildew


Pumpkins and Squash Disease Update: 15-Aug-2105

Downy Mildew – While downy mildew is a common occurrence in cucumbers, it is less so in pumpkins and squash.  However, growing regions across eastern North American are experiencing unusually high pressure from downy mildew in all cucurbit crops this year.  Symptoms and spores were recently identified in a pumpkin field in Norfolk county.  While the disease is typically less aggressive in pumpkins and squash than it is in cucumbers, it is still a good idea to scout fields regularly for symptoms.  If the scouting results show that the levels of disease are increasing, downy mildew targeted sprays may be warranted to keep later-maturing crops healthy.  Keep in mind that fungicides commonly used for powdery mildew control will not control downy mildew.

Powdery Mildew – powdery mildew is active in most pumpkin fields by now.  Fungicides must be applied at the very early stages of this disease in order to be truly effective.  Once symptoms are readily visible on the upper-leaf surface, it is usually too late to really benefit from control measures.  When scouting, look for white, powdery spores on the lower surface of the leaf.  There may be a corresponding light-green or yellow lesion on the top surface.  Symptoms usually first appear on the mid-portion of the plant, or even the petioles.

Powdery Mildew Lesion on the Lower Leaf Surface
Figure 1. Powdery Mildew Lesion on the Lower Leaf Surface

The Squash Bee; Essential Native Pollinator

By Ian Seifried, Summer Research Technician, OMAFRA.

Squash bees are native pollinators. They are directly associated with the cucurbita family of crops (squash, pumpkin, gourd, zucchini, marrow and courgette). This means that the squash bee populations depend solely on the production of these crops to establish their broods as well as feed their larvae.

Cucurbita flowers are synchronized to open just as the sun comes up and to close as soon as the temperature heats up, approximately 3-hours later. Squash bees are similarly synchronized to start collecting pollen as the sun comes up and to stop once the flowers begin to wilt. You can find both solitary male and unmated females in the flowers; you can even touch them, as they are stinger less.

Figure 1. Squash Bee - Hairy Thorax
Figure 1. Squash Bee – Hairy Thorax

Squash bees are medium sized with a very hairy thorax and black and white horizontal stripes running down the abdomen ending with a smooth point, without a stinger. The specialized hairs on the squash bees’ thorax and legs enable the bees to pick up cucurbita pollen which is larger, stickier and coarser than the other types of pollen (Figure 1). This makes them more efficient than other pollinators such as the bumblebee and honeybee.

The squash bee constructs ground burrows that are a series of lateral tunnels ending in individual brood cells. The cells are connected to a central vertical tunnel (which can be up to 45cm deep) leading to the surface hole. The surface hole is approximately the width of a pencil and can be found either in the field that is home to cucurbita crops or around the edges of fields.

The squash bee burrows are directly affected when tillage is used. Tillage can fill in these burrows, destroying the central tunnel along with several brood cells, and even kill the squash bees trapped inside.

During a recent field survey of squash bee activity in commercial pumpkin fields, the number of bees varied considerably. Total bees observed in 10 minutes (1 minute intervals at each of 10 locations across the field) ranged from 11 to 170, depending on the location.