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Herbicides Can Negatively Affect Seed Performance in Native Plants

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Abstract

Herbicides are widely used to control invasive non-native plants in wildlands, yet there is little information on their non-target effects, including on native plants that are intended to benefit from the treatment. Effects at the seed stage have been particularly understudied, despite the fact that managers commonly seed native plants immediately after herbicide application. We conducted a greenhouse experiment to explore the effects of two broadleaf-specific herbicides (aminopyralid and picloram) on seedling emergence and biomass for 14 species that grow in dry grasslands of NW North America. For each species, we placed 50 seeds in soil-filled pots that were sprayed with a water control or one of the herbicides at one of two rates (1× and 0.01× of the recommended rate). After 5 weeks, we assessed seedling emergence and dry aboveground biomass per pot. At the recommended rate (1×), both her bicides significantly suppressed seedling emergence and lowered biomass. At the diluted rate (0.01×), the effect of picloram was comparable to the effect at the recommended rate, whereas aminopyralid had no effect. There was no difference in effects of herbicides on native versus non-native species. Although both herbicides are considered to be broadleaf-specific, monocots were just as vulnerable as dicots at the recommended rate. Our results show that herbicides can harm non-native and native plants at the seed stage, alike. Land managers should avoid spraying if recruitment of native species from the seedbank is a goal and should not seed directly after spraying.

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