Tag Archives: Herbicides

Herbicide injury symptoms in tomatoes

Darren Robinson, University of Guelph, Ridgetown Campus; Janice LeBoeuf, OMAFRA, Ridgetown

Introduction

Herbicides are useful tools for the management of weeds.  The herbicides registered for use in tomatoes are selective in their activity, injuring or killing weeds while being safe to use on the crop. Crop injury may occur, generally when a crop is stressed beyond its ability to adequately deal with a herbicide application.  Injury due to herbicides can arise as a result of several factors, including weather-related stress, soil factors such as light soil texture and low soil organic matter, shallow planting and sensitive crop varieties.  The pages in this section contain information on herbicide injury for several products registered on tomatoes in Canada. Continue reading Herbicide injury symptoms in tomatoes

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.

66th Annual Muck Vegetable Growers Conference

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

Continue reading 66th Annual Muck Vegetable Growers Conference

How sensitive is your crop to dicamba and 2,4-D?

Are soybeans or tomatoes more sensitive to dicamba? Are sweet potatoes or watermelon more likely to be hurt by 2,4-D? Could crops show visual injury at 1/800th of the rate of one of these products?

In a recent article in Southeast Farm Press, Dr. Stanley Culpepper, University of Georgia Extension weed specialist, shared his data on crop sensitivity (visual injury) to dicamba and 2,4-D. Note that most of this data is from trials in Georgia (and some of the crops on the list reflect that). Continue reading How sensitive is your crop to dicamba and 2,4-D?

Seasonal topics – May 2, 2016

Weed escapes

May 2, 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 – May 2, 2016

Annual rye-grass and clover sensitivity to soil applied corn herbicides

Annual rye-grass and clover sensitivity to soil applied corn herbicidesVegetable growers using cover crops in rotation with corn will be interested in a new article on the tolerance of cover crops to various soil applied corn herbicides. The article, by Dr. Darren Robinson (University of Guelph, Ridgetown Campus) and Mike Cowbrough (OMAFRA), is found on fieldcropnews.com.

2016-17 Guide to Weed Control (Pub. 75) pdf now available for download

OMAFRA's 2016-17 Guide to Weed Control

Updated March 9, 2016 with print publication ordering information.

The 2016-17 edition of OMAFRA’s popular and informative Guide to Weed Control (Pub. 75) is now available for free download (6 MB).

It is also available in French.

The printed publication can be ordered through Service Ontario Publications (order number 109113) for $20 + tax + shipping.