Herbicides – Gardening at Last

2023 April: Chemicals

In this post, I’ll explore some recent stories about pesticides beginning with an update on Ontario’s pesticide regulations.

Ontario Pesticide Ban

Since 2008, Ontario has had a ban on cosmetic use of pesticides, meaning most pesticides are no longer allowed in home gardens. The Act and associated regulations were amended in 2019-2020 so Ontario’s rules are more closely aligned with the federal laws. Before a pesticide (pest control product) can be sold or used in Ontario, it must be registered under the federal Pest Control Products Act (PCP Act). The Pest Management Regulatory Agency (PMRA) of Health Canada registers pesticides for use in Canada following an evaluation of scientific data to ensure that any human health and environmental risks associated with its proposed uses are acceptable, and that the products have value. (From OMAFRA page on Using Pesticides in Ontario.)

With the alignment of Ontario regulations to those at the federal level, the way in which Ontario now categorizes pesticides has been streamlined. The new classification system reduces Ontario’s former Classes 1 through 7 to four classes – Class A (manufacturing), Class B (restricted), Class C (commercial) and Class D (domestic). The former Class 12 will be changed to Class E in the Pesticides Regulation, a stand-alone class specific to neonicotinoid-treated seeds. Also, Ontario’s Pesticides Advisory Committee, which used to provide advice to support classification, has been eliminated.

Training, licensing and permitting requirements are established for the new classes of product to help educate farmers and vendors. Previous exemptions to the general cosmetic pesticides ban have been retained, including exemptions for golf courses, forestry, health and safety, etc. However, the former classes 7-11, which were previously used to manage the ban, have been replaced by a single list of allowed pesticides. Cemeteries were added as an excepted use to the cosmetic pesticides ban, but with conditions such as training in Integrated Pest Management and producing an annual report of pesticide use. (Source: Ontario introduces significant amendments to the Pesticides Act and the Pesticides Regulation.)

Ontario Ministry of Energy and Environment offers information Natural ways to manage pests in home gardens, which includes a list of allowable products for homeowners’ use. Incidentally, I came across one wonderful expression of free (but crazy) speech. Pesticide Truths appears to be the brainchild of someone who goes by the handle “UncleAdolph”. I’m sure it’s pure coincidence that Adolph was Hitler’s first name. The site argues forcefully for ending all pesticide bans and features downloadable posters of chubby babies happily playing on pesticide-laced lawns. Great for parents who want their children to suffer developmental delays and risk getting cancer.

So-called ‘safe’ pesticides not so safe

Health Canada is currently reviewing regulations for pesticides in Canada, and three UBC researchers say regulators might want to consider what happened in Japan. A lake in Shimane Prefecture has seen its commercial fishery collapse by more than 90% since 1993, when insecticides known as neonicotinoids were first introduced to the area. It just so happens that zooplankton—the tiny creatures in the water that fish feed on—declined by 83% during the same period. That’s just one example of the unanticipated ripple effects of pesticides uncovered by UBC ecologists Dr. Risa Sargent, Dr. Juli Carrillo and Dr. Claire Kremen in their review of recent science.

They also found concerning research about glyphosates. Use of this weed-killer has increased 100-fold in recent decades. Because it targets an enzyme that exists only in plants, it was thought to be perfectly safe for animals. However, a study last year showed that it alters the mix of bacteria and microbes in bees’ intestines, while also disrupting their ability to keep hives at the optimum temperature.

A third study showed that the use of neonicotinoid in a cornfield produced no increase in corn yields but did depress yields and profits in nearby watermelon fields by 21%. The paper is published in the journal Trends in Ecology & Evolution.

Bland strawberries could be due to pesticides

Organic strawberries from Rebecca’s community garden. Photo by R. Last.

Have you ever bitten into a plump, red strawberry, only to find it bland and watery? Certain pesticides might be responsible. A team reporting in the Journal of Agricultural and Food Chemistry has found that two common strawberry fungicides can impact cellular mechanisms, creating berries with subdued flavor and sweetness, as well as a lower nutritional value.

Bees’ pesticide risk varies

A researcher carefully collects a pollen sample from a bee. Credit: Daphne Wong.

In a new study, ecologists have shown that bees’ pesticide exposure depends upon their interaction with the environment, meaning different species face different risks in any given environment. According to the ecologists, increased agricultural land surrounding bees increases pesticide-related risk, but only for the solitary bee and bumble bee—species that forage over smaller areas than the honeybee. (Note, honeybees are not native to North America.) In broad terms, these findings support the capacity of semi-natural areas to reduce pesticide risk for wild bees.

Pesticide risk assessment is evolving to capture the ecological complexity of things like species’ different foraging ranges. However, greater understanding is required. This newly published study evidences this at a landscape scale as the ecologists measured pesticide concentrations in different food sources for different bee species in multiple cropping systems. The study was published in Nature Ecology and Evolution.

Pesticides in pollen and nectar may be hazardous for pollinators

Graphical abstract. Credit: *Science of The Total Environment* (2023). DOI: 10.1016/j.scitotenv.2023.162971

In another study from Trinity College, Dublin, researchers found pesticides in flowers not targeted with the chemicals, which could be an additional, underestimated threat to pollinators. “This is the first time that a multi-field survey of pollen and nectar from crops and wild plants has been undertaken in Ireland and is critical to our understanding of pesticide residues in the Irish context,” says Prof. Jane Stout, School of Natural Sciences, Trinity, who co-led the research with Prof. Blánaid White, School of Chemical Sciences, DCU.

The researchers looked for pesticide residues in the nectar and pollen of crop and non-target hedgerow plants. They evaluated a variety of herbicides and fungicides that are commonly used, as well as neonicotinoids that are no longer being used but of which residues may remain for some time. “The research takes place in the context of Ireland reaching the ambitious European Commission target in the Farm to Fork Strategy of reducing the use and risk of chemical pesticides by 50%,” says Prof. White.

Doctoral student Elena Zioga, who was jointly supervised by Prof. White and Prof. Stout, collected thousands of flowers from agricultural fields across Ireland, and carried out her chemical analysis work at the DCU Water Institute. Finding traces of certain neonicotinoids, which are known to threaten pollinators, still lingering despite a 2018 ban by the European Commission “is a worry” said Ms. Zioga, who would like to know the extent of their presence in the environment, and at what concentrations. The researchers also found mixtures of pesticides more often than single compound detections, and this means it is important to understand the impact of these mixes on pollinators and other non-target organisms.

“We need to understand how different compounds move through the environment, and the rate at which these compounds degrade, so that we can understand the extent of their persistence,” said Prof. White. “And we need to know what their long-term effects are on pollinators and other organisms” added Prof. Stout. The paper was published in Science of The Total Environment (2023).

2023 February Weeds

Why dandelion seeds are so good at spreading widely

On any given dandelion, some seeds are destined to go north, while others are fated to fly east, south or west, and every direction in between. In effect, each dandelion seed is programmed to release for a wind coming from one direction and resists winds from other directions, according to research presented at the American Physical Society’s Division of Fluid Dynamics. Dandelion seeds are susceptible to different wind directions depending on where they are on the seed head, says Jena Shields, a biophysicist at Cornell University. The feathery seeds on the side facing a breeze will let go most easily; the others hold on tens to hundreds of times tighter — until the wind shifts. Shields measured the force it takes to pluck dandelion seeds by supergluing a fine wire to the tufted ends and pulling them from the seed heads at various angles. This seed-by-seed study mimicked what happens when wind, or a child’s breath, pushes them over. Because each seed is most susceptible to winds from distinct directions, it helps prevent seeds from all going the same way, Shields says, and may explain why the plants are so successful at spreading. Once blown off a dandelion, the umbrella-like tuft on a seed carries it on the breeze that pulled it away. In fact, it turns out the movement of air around dandelion seeds is teaching us a new way of moving through air, which also helps the seeds stay aloft much longer than would otherwise be the case!

Why we should all learn to love stinging nettles

Stinging nettles are food for peacock butterfly caterpillars. Keith Hider/Shutterstock

I still remember the itch and burn of stinging nettles (Urtica dioica) encountered while exploring wasteland areas as a child. We always used to rub the stinged skin with dock leaves (Rumex obtusifolius) to relieve the pain. Although there is no scientific evidence this actually works, it always made me feel better. Aside from their sting, which is their defense against being eaten, nettles offer a host of benefits. Permaculturalists love them because their fibrous roots, which make them such a pain to remove as weeds, help draw nutrients up from the subsoil and make them available to other plants. They are amazing at colonizing disturbed areas and bare soil – a useful trait at a time when human activity has disturbed so much nature. In addition to those persistent roots, Charles Darwin was right when he theorized that nettle seeds could withstand a long soak in salty water. This ability may have allowed the humble nettle to become a world traveller, colonizing areas across oceans. Those same seeds can lie dormant in soil for up to five years. Nettles are good for wildlife. They are larval host plants for Question Mark, Milbert’s Tortoiseshell, Red Admiral butterflies

Ouch! The silica hairs (trichomes) act as needles, injecting irritants into skin. Floki/Shutterstock

In the UK, nettles spreading to gardens and cultivated areas have allowed several species of butterflies to expand their range. Ladybugs often lay their eggs on nettles, and when those eggs hatch, the ladybug larvae are voracious eaters of aphids – one of the more persistent garden pests. Nettles are good food for humans, too. They are highly nutritious, full of vitamin A and C along with calcium and iron. Nettles have a long history in folk medicine and there is scientific evidence that extracts from nettle leaves, roots and stems can treat high blood pressure and diabetes.

Nettle fibers were used in Europe when the two world wars caused shortages. Indeed, there is evidence that people in cool climates have used nettles since the Bronze Age to create textile fibres until sheep breeding gave rise to more effective wool-producing sheep. So this is another “weed” with potential super powers.

Study explores control options for black swallowwort

Otherwise known as dog-strangling vine (Vincetoxicum nigrum), this nasty invasive plant has super powers that include rapid spread through wind-dispersed seeds and the ability to outcompete and strangle native species, including small trees. It also fools monarch butterflies into laying their eggs on it, but the monarch larvae can’t eat this nasty weed, so they starve.

I haven’t seen any information about potential beneficial properties and to date, no scientific studies have been conducted to determine how the weed responds to common controls, such as mowing and broad-spectrum herbicides. However, an article featured in Invasive Plant Science and Management, begins to fill this information gap. Over three years, the team explored how black swallowwort responded to two glyphosate products and one triclopyr product. The weeds were either sprayed annually with a two percent solution of one the herbicides at flowering in early July—or were mowed in early July and then treated in late August. The study showed the two glyphosate formulations were effective in reducing aboveground black swallowwort biomass, but they were less effective in reducing cover and stem densities. Researchers also determined that mowing failed to enhance the efficacy of the glyphosate applications on a consistent basis. With or without moving, Triclopyr was generally ineffective.