Kristen Obeid, OMAFRA Weed Specialist – Horticulture
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
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
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
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.
 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.
Kristen Obeid, Weed Management Specialist – Horticulture, OMAFRA
Published by the Grain Farmers of Ontario, the resource features over 120 species commonly found in and around agricultural fields. The Weed ID Guide for Ontario Crops is now available in the following formats:
- ePub format (124 MB file for Kindle, iBooks and other e-reader apps)
- pdf format (8 MB file)
- print ready pdf (141 MB file)
These can be downloaded from the following website: http://fieldcropnews.com/2016/09/weed-id-guide-for-ontario-crops/
- Print Copy (printing and shipping costs apply, volume discounts available) can be ordered from the following website: http://www.blurb.ca/b/7797011-weed-id-guide-for-ontario-crops
- The price is $37.51 for one copy
- 10% discount if you order 10 or more
The publication was funded through Growing Forward 2, a federal-provincial-territorial initiative.
The 66th Annual Muck Vegetable Growers Conference will be held April 12-13 at the Bradford and District Memorial Community located at 125 Simcoe St., Bradford, ON. The conference is free and registration starts at 8:30. For more details please see: http://www.uoguelph.ca/muckcrop/muckconference.html
The website, Ontario CropIPM, contains the full range of pest management information from many vegetable crops, including asparagus. Many users do not realize that it is also home to weed galleries, herbicide injury information and critical weed control period information. The following three problem weeds for asparagus are excerpts from the weeds and herbicides section of Ontario CropIPM. Continue scrolling for the best control options for each of the problem weeds. Continue reading Three Problem Weeds for Asparagus
June 6, 2016 — Some topics are relevant year after year, but you might not always take the time to filter through previous posts to find them. I’ve highlighted some here that might be of interest this week. Click on the preview images below to jump to the articles. Continue reading Seasonal Topics – June 6, 2016