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North Central Illinois | This is not in the upper Midwest, but still some good information.
https://www.frontiersin.org/journals/agronomy/articles/10.3389/fagro...
I will note that there is adaptation if the same management is used repeatedly. On my home farm giant ragweed is almost exclusively an April and early May emerging species (and I am very diligent about hand pulling late emerged escapes to keep it that way). I know of other organic producers who relied on delayed planting to manage it without rouging the cultivator escapes and now the emergence peak is in June. | |
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Weed growing degree days
