Category Archives: Cucurbits

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)
Timing:
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: 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.

2016-06-16_CDMepidemicstatus
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

 

Research Update – Fungicide Efficacy on Downy Mildew in Cucumbers

Cheryl Trueman, College Professor, University of Guelph – Ridgetown Campus
Rachel Riddle, Research Technician, University of Guelph – Simcoe
Elaine Roddy, Vegetable Crops Specialist, OMAFRA

Over the past two years, there have been several changes in the efficacy of fungicides commonly used to control downy mildew in cucumbers. The results from field trials conducted by the University of Guelph reflect trends also observed in Michigan and North Carolina.

Figure 1 and Figure 2 show the results of the Ontario 2015 downy mildew fungicide trials conducted at Ridgetown and Simcoe. Note that in both trials, a significant decline was observed in the efficacy of both Presido 4SC and Tattoo C. Presidio preformed no better than the untreated control, while the results from Tattoo C were no different than chlorothalonil (Bravo Zn).

The Canadian Pest Management Regulatory Agency (PMRA) is currently evaluating a new active ingredient called oxathiapiprolin (Orondis Ultra). In both of the University of Guelph studies, oxathiapiprolin demonstrated good control against cucumber downy mildew. If approved, this product will provide a good option for rotation with currently registered downy mildew fungicides.

Figure 1. AUDPC (area under the disease progress curve) for leaf area affected by cucurbit downy mildew in cucumber cv. Vlasstar, Ridgetown, ON, 2015. Fungicides were applied on a 7-day interval July 7-Aug 4. Columns with the same letter are not significantly different from each other.
Figure 1. AUDPC (area under the disease progress curve) for leaf area affected by cucurbit downy mildew in cucumber cv. Vlasstar, Ridgetown, ON, 2015. Fungicides were applied on a 7-day interval July 7-Aug 4. Columns with the same letter are not significantly different from each other.

 

Figure 2. AUDPC (area under the disease progress curve) for leaf area affected by cucurbit downy mildew in cucumber cv. Vlaspik, Simcoe, ON, 2015. Fungicides were applied on a 7-day interval July 16-Aug 6. Columns with the same letter are not significantly different from each other.
Figure 2. AUDPC (area under the disease progress curve) for leaf area affected by cucurbit downy mildew in cucumber cv. Vlaspik, Simcoe, ON, 2015. Fungicides were applied on a 7-day interval July 16-Aug 6. Columns with the same letter are not significantly different from each other.