By Jan Suszkiw
"Field intelligence" gathered by an Agricultural Research Service
(ARS) scientist could give sweet corn growers a new edge in their war on
weeds.
Based on field studies he has conducted near Urbana, Ill., since 2004,
ARS 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
ARS' Invasive Weed Management Research Unit at Urbana.

In Illinois, one of several Corn Belt states, growers plant sweet corn
between April and early July, depending on the market they're targeting. 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
corn's 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 percent, versus 15 percent for June-planted corn. Moreover, the May
corn'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 north-central United States, planting in
June or later could mean savings on herbicides, tillage or time spent
hand-pulling weeds, such as might be practiced by organic farmers.


[www.ars.usda.gov]