Category Archives: Pumpkins

Tips for Broadleaf Weed Control in Pumpkins and Winter Squash

Originally published in ONvegetables in The Grower, April 2017

Even with the use of herbicides, broadleaf weed control in pumpkins and squash can be problematic. Product selection is key but timing and weather conditions are also important to the success or failure of a weed control program. Each of the broadleaf herbicides comes with its own strengths, weaknesses and risks.

As a general rule, the spectrum of weeds controlled can be increased by using tank-mixes. But, for pumpkins and squash, it is wise to limit the tank-mix to two products.  A three-way tank mix is risky from a crop safety standpoint; root damage, stunting, yellowing and/or burning may occur, especially under certain soil conditions.

All of the pre-emergence herbicides require soil moisture. The active ingredient is carried by the soil water into the germinating weed seedlings, causing them to die.  Under dry soil conditions, it is tempting to use overhead irrigation to “activate” the herbicides.  This is an inexact science.  Too much water can quickly move the herbicide band into the zone of the germinating crop roots, causing injury to the pumpkins or squash. Too little water may be insufficient to move the herbicide into the germinating weeds.

It becomes a gamble between loosing crop to herbicide damage or loosing yield to weed competition. Fortunately, both Dual II Magnum and Sandea can be used for early post emergence weed control.  Unfortunately, control of weeds such as lamb’s-quarters and pigweed is less effective with a post emergence spray.

Product: Command 360 ME (clomazone)
Timing:  after seeding but before crop and weed emergence.
Rate: 0.78-1.17 L/ha (0.31-0.47 L/acre) use the low rate on light, sandy loam soils; use the high rate on heavy soils.
Strengths: lamb’s-quarters, nightshades, ragweed, velvetleaf
Weaknesses: pigweeds.
Cautions: very sandy soils and/or certain varieties may be prone to crop injury, see label for details. Also refer to the label for rotational crop restrictions.

Product: Sandea (halosulfuron)
Timing(s): after planting and before soil cracking (direct seeded), before transplanting; do not transplant sooner than 7-days after application, OR post-emergence between the 3-5 true leaf stage or 14-days after transplanting[1]
Rate: 35-70 g/ha (14-28 g/acre). See the product label for specific rate information for direct seeded, transplanted, processing and fresh market pumpkins and squash.
Strengths: pigweeds, lady’s thumb, mustards
Weaknesses: lamb’s-quarters
Cautions: Under adverse growing conditions (dry or excessive moisture, cool weather, etc.) the maturity of the treated crop may be delayed which can influence harvest date, yield, and quality. Under dry soil conditions, apply 3 – 5 cm of sprinkler irrigation to settle the soil after planting and prior to application. Do not make a post emergence application if female blossoms are present on the plant; crop damage may occur to developing fruit.

[1] If using pre-emergence and post emergence applications of Sandea, allow for a minimum of 21 days between the two applications.

Product: Dual II Magnum (s-metolachlor/benxacor)
pre-emergence or at the 1-2 leaf stage (direct seeded crops). Prior to transplanting or within 48 hours after transplanting (transplanted crops).
Rate: 1.15 L/ha (0.47 L/acre)
Strengths: annual grasses, nightshades, pigweeds
Weaknesses: lady’s-thumb, ragweed, velvetleaf
Cautions: risk of crop injury increases with cool and wet conditions. Foliar contact can increase the potential of crop injury. Note: research in Ontario has shown high levels of phytotoxicity when using Dual II Magnum on cucumber crops.  Use on cucumber crops is not recommended.

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:

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

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.

Watch for Increased Insect Activity in Sweet Corn and Pumpkins

By: Elaine Roddy, Vegetable Crops Specialist
OMAFRA – Ridgetown

In general, insect pressure has been relatively low this year.  However, over the past week we have noticed an increase in insect activity.

Sweet Corn
Start scouting for European corn borer at the mid-whorl stage, before the tassel begins to emerge from the plant.  Look for flattened, white egg masses on the under surface of the leaves. Newly hatched larvae often hide in the developing tassel during the heat of the day.  Window panes, pin-hole feeding and small amounts of saw dust-like frass are all signs of feeding. Optimal control occurs during the early stages of insect development, before the larvae enter the stalk. Young larvae range in colour from almost translucent to yellow to brownish, with a black head.

The website, reports scattered flights of corn earworm into the great lakes region. Corn is susceptible to earworm infestation during the silking period. The best way to monitor for the presence of corn earworm is with a pheremone trap. Continue reading Watch for Increased Insect Activity in Sweet Corn and Pumpkins