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Scientist pinpoints when sweet corn weeds are most meddlesome

So-called “field intelligence” gathered by an U.S.-based scientist could give sweet corn growers a new edge in their war on weeds.

So-called “field intelligence” gathered by an U.S.-based scientist could give sweet corn growers a new edge in their war on weeds.

Based on field studies he has conducted in the state of Illinois since 2004, ecologist Marty Williams has identified specific timeframes during the sweet corn growing season when competition from weeds will inflict yield losses. Moreover, this so-called critical period for weed control is influenced by the sweet corn planting date, notes Williams, who works in an invasive weed research unit at Urbana, Ill.

In Illinois, one of several Corn Belt states, growers plant sweet corn between April and early July, depending on their target market. May and June are peak months of planting for both fresh and processing markets.
A few years ago, Williams decided to determine the critical weed-control period and, for good measure, find out whether planting dates affect a crop’s susceptibility to weeds. His experimental design called for planting sweet corn in either early May or late June and allowing weeds to grow to various heights (e.g., ankle, knee or shoulder high) before killing them off.

In other plots, Williams let the weeds – including common lambsquarters, redroot pigweed and green foxtail – grow throughout the crop growing season, about 83 days. This enabled him to measure and compare each weed treatment’s effect on the crop’s yield of marketable ears.

In general, the May-planted crop suffered the greatest yield losses – up to 85 per cent, versus 15 per cent for June-planted corn. Moreover, the May planting’s critical weed-control period began earlier, on day 18, when the corn had reached its four-leaf stage.

For the June-planted corn, the critical weed-control period didn’t begin until day 53, which was beyond the 12-leaf stage and only a few weeks before harvest. Williams attributed the difference to sweet corn’s excellent growth in late-season conditions, which gave the crop an edge over weeds.

For sweet corn growers in the northern U.S. and southern parts of Canada, planting in June or later could mean savings on herbicides, tillage or time spent hand-pulling weeds, such as might be practised by organic farmers. It could also mean a loss in revenue from early season sales.