Air pollution injury to vegetables

Figure 1 air pollution injury on watermelo

Diagnosing crop problems can often be difficult. Identifying disease, insect or nematode problems is not always straightforward. And what about nutrient problems -- herbicide injury, soil compaction, and physiological problems? And then there's air pollution.

Air pollution injury can manifest itself in many ways, depending on the pollutant, its concentration, crop species, crop growth stage, weather conditions, soil moisture, and more. Often, leaves of a certain age are affected, or just portions of those leaves that happened to be in the most susceptible stage at the time peak levels occurred.

Ozone is a common cause of plant damage. Plants can be damaged by long-term exposure to ozone concentrations of 50-80 parts per billion. In Chatham, for example, ozone levels have reached a peak between 50 and 70 parts per billion for 18 of the first 26 days of June. You can find these readings at

Cucumbers, onions, peas, tomatoes and watermelons are some of the vegetable crops most sensitive to ozone. White beans are particularly sensitive and are often used as an indicator crop.Sulfur dioxide and nitrogen oxides can also damage plants, but more significantly, combinations of these pollutants with ozone can cause higher levels of injury. Some cruciferous crops and cucurbit crops are quite sensitive to sulfur dioxide. Other sensitive vegetable crops include onions, peas, lettuce, peppers, and tomatoes.

Another pollutant, peroxyacetyl nitrate, known as PAN, is known to affect tomatoes in Ontario. It causes a distinctive bronzing or glazed appearance of the underside of the leaves. PAN also injures spinach, Swiss chard and certain varieties of lettuce and beans. PAN is not emitted directly from pollution sources, but is formed by a chemical reaction between nitrogen oxides and other pollutants.

OMAFRA has a factsheet on the effects of air pollution on agricultural crops. Search for it online or visit for more information.

Janice LeBoeuf is vegetable crops specialist for OMAFRA, Ridgetown, Ontario.

If latest news: 
Check if it is latest news (for "Latest News" page)
Publish date: 
Wednesday, August 3, 2016

Click to leave a comment

For security purposes, please confirm you are not a robot!


The future of IPM: something old, something new

Dr. Mary Ruth McDonald has mentored dozens of students as professor of plant agriculture, University of Guelph. Equally at home in the field, she’s working with Master’s student Alexandra Dacey, documenting carrot weevil found in carrot trials at the Muck Crops Research Station in Bradford, Ontario. 

How to tell and sell the origin story

Seedless watermelon is only one of the specialties carried at Howe Family Farm Market near Aylmer, Ontario. Kevin Howe says ground cherries and canary melons also pique the interest of consumers. The on-farm market has been so successful that the family has opened another location south of London Ontario. 

Showing face in the midst of trade wars

Bill George Jr. and his son Will have tasted the promise of Icewine exports to China. With geopolitical tensions in 2019, the risks of diversifying into markets abroad have been amplified. It’s too early to know if the recent U.S-China deal will help or hinder.    

Soil fitness – just do it!

Fourth-generation grower Kyle Horlings is questioning the way things have always been done. Since 2015, he’s taken about 10 acres of carrots and onions out of production every year for restorative cover plantings. His experiments near King, Ontario garnered him the Healthy Soil Award from the Lake Simcoe Region Conservation Authority in November. 

Frequent flyer earns bonus points for good taste

Oleen Smethurst is known for her quest for flavour. As assistant vice-president, general merchandise manager for produce, Costco Canada, she jets all over the world from Berlin to Bogotá, meeting with growers and seed suppliers. While touring southern Ontario in late August 2019, she visited Martin’s Family Fruit Farm near Waterloo, Ontario.