Researchers discovered that low doses of a common herbicide can increase flowering in weeds, with unexpected consequences for visiting insects.<\/p>\n
Weedkiller is meant to stop weeds from growing. But what happens when only a little of it reaches a plant?<\/p>\n
For yellow wood sorrel, a weed found in lawns and fields, the answer is complicated. <\/p>\n
In a two-year experiment, plants exposed to a small amount of the herbicide dicamba produced more flowers than plants that weren\u2019t sprayed. Their flowers were smaller, though, and insects visited each one less often.<\/p>\n
The findings suggest that herbicide drift doesn\u2019t always have the effect people expect. Even when it doesn\u2019t kill a plant, it can change how that plant grows, flowers and attracts insects.<\/p>\n
Regina Baucom is the senior author of the study and a professor at the University of Michigan<\/a>.<\/p>\n \u201cThe general public uses herbicides in their lawn to kill weeds. They\u2019re not using herbicides to make the weeds do better,\u201d said Baucom.<\/p>\n \u201cThey probably don\u2019t even know this is a potential side effect or something that can happen.\u201d<\/p>\n When a small dose has a different effect<\/p>\n Dicamba is commonly used to control broadleaf weeds. It works by imitating auxin, a natural plant hormone that helps regulate growth. At a high enough dose, it disrupts development so badly that susceptible plants die.<\/p>\n But dicamba can also move beyond the area where it\u2019s sprayed, carried in droplets or vapor. The U.S. Environmental Protection Agency<\/a> identifies damage to nearby plants as a major ecological concern.<\/p>\n A tiny dose may do something quite different from a full-strength spray. Scientists call this\u00a0hormesis: a low level of something harmful produces a boost in growth or another trait.<\/p>\n Researchers have seen similar effects with other herbicides, including glyphosate. Some studies have reported increases in plant growth or reproductive traits after low-dose exposure.<\/p>\n Anah Soble Botran and colleagues wanted to know whether that kind of response could also influence flowering and the insects that visit flowers.<\/p>\n Their subject was yellow wood sorrel<\/a> (Oxalis stricta), a hardy plant that often survives attempts to remove it. <\/p>\n Earlier greenhouse research had already suggested that drift-level dicamba could extend its flowering season.<\/p>\n More flowers, but not necessarily more seeds<\/p>\n The researchers collected seeds from wild wood sorrel growing in Kentucky and Tennessee. <\/p>\n In 2022, they planted nearly 500 seeds representing 31 maternal families at the Matthaei Botanical Gardens<\/a> in Ann Arbor, Michigan.<\/p>\n Half were sprayed with dicamba at roughly 0.7% of the recommended field dose. The rest received the same spray mixture without the herbicide.<\/p>\n The difference appeared quickly. Over three weeks, treated plants added leaves 44% faster.<\/p>\n They also flowered more. By the first hard frost in November, sprayed plants had produced an average of 139 flowers each, compared with 95 on the other plants.<\/p>\n In 2023, the team repeated the experiment with nearly 700 plants from 16 of the same families.<\/p>\n There was no clear growth boost in the second year. But the flowering effect returned. <\/p>\n During the first month after spraying, treated plants produced about 180 flowers on average, compared with 140 on untreated plants \u2013 roughly 29% more.<\/p>\n Across both summers, extra flowering was the clearest response to low-dose dicamba.<\/p>\n More flowers, however, don\u2019t automatically mean more offspring.<\/p>\n In 2022, sprayed plants produced around 18% more seeds. Yet the counts varied so widely that the difference alone wasn\u2019t statistically convincing. <\/p>\n Further analysis suggested the herbicide influenced seed production indirectly, by increasing the number of flowers.<\/p>\n In 2023, the extra flowers didn\u2019t lead to an increase in fruit.<\/p>\n One possible explanation is timing. In 2022, only 17% of the plants had started flowering when they were sprayed. In 2023, 78% had already begun. <\/p>\n Plants exposed earlier in their development may respond differently, and weather conditions could also have played a role.<\/p>\n How did pollinators respond?<\/p>\n The researchers found another trade-off: sprayed plants grew more flowers, but those flowers were slightly smaller.<\/p>\n Measurements of 3,430 flowers in 2023 showed that treated flowers averaged 8.09 millimeters across, compared with 8.73 millimeters on untreated plants.<\/p>\n The team observed plants during September and October, recording insects entering flowers during 20-minute sessions. <\/p>\n Wood sorrel can largely pollinate itself, but hoverflies<\/a>, honeybees<\/a> and other insects still visit for pollen and nectar.<\/p>\n Insects\u00a0visit\u00a0flowers\u00a0less<\/p>\n Individual flowers on treated plants received about one-third fewer visits than those on untreated plants. <\/p>\n Honeybees visited flowers on treated plants less frequently, while bumblebees<\/a> visited them slightly more often. Hoverfly visits showed no meaningful difference.<\/p>\n But looking at visits per plant told a different story. <\/p>\n Plants with more flowers attracted more visits overall. In other words, insects weren\u2019t necessarily avoiding treated plants; their attention was spread across a larger number of blooms.<\/p>\n That could affect pollen movement, although the study didn\u2019t test whether it did.<\/p>\n Does this make weeds harder to control?<\/p>\n The results raise a question: could repeated exposure to drifting herbicides eventually help certain weeds thrive?<\/p>\n The study doesn\u2019t establish that. The researchers found no evidence that families differed genetically in how much dicamba increased flower numbers. <\/p>\n Without that kind of inherited variation, there\u2019s no clear basis for this particular response to become stronger through natural selection.<\/p>\n \u201cWe found no evidence of genetic variation,\u201d Baucom said, describing the flowering increase as a response within one generation rather than evidence of evolution.<\/p>\n There was one exception: the amount by which flowers shrank differed across families, suggesting a genetic component to that trait.<\/p>\n The experiment also tested just one weed species and one low dose in a research garden. It doesn\u2019t show that herbicide drift is increasing weed populations on farms.<\/p>\n Long-term\u00a0effects\u00a0remain\u00a0unknown<\/p>\n Future research will need to examine other doses, plants and growing conditions, as well as whether smaller flowers provide enough food for visiting insects. <\/p>\n Tracking seedlings over several generations could also reveal whether extra flowers eventually translate into more weeds.<\/p>\n For now, the takeaway is simple but unexpected: a weedkiller doesn\u2019t need to kill a plant to change its life. <\/p>\n Sometimes, at the edges of a sprayed field, it may even leave that plant with more flowers.<\/p>\n The study was published in\u00a0New Phytologist<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"Researchers discovered that low doses of a common herbicide can increase flowering in weeds, with unexpected consequences for…\n","protected":false},"author":2,"featured_media":932222,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[64,63,128],"class_list":["post-932221","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-au","tag-australia","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/932221","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/comments?post=932221"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/932221\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media\/932222"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media?parent=932221"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/categories?post=932221"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/tags?post=932221"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}