This spring’s warm temperatures should speed crop emergence. The bad news is that if your fields or parts of your fields are infested with the winter annual purple deadnettle, you may notice your fields have a purple tinge to them. Although that may be pretty to see, it’s ugly from a weed management point of view.

“Winter annuals have really gotten ahead of us,” says Meaghan Anderson, Iowa State University Extension field agronomist. “Based on our forecast, we’re likely to have continued above-normal temperatures.”

This not only means that faster development and flowering will continue for purple deadnettle, but also for other winter annuals such as henbit and chickweed. Besides winter annuals, many biennial and perennial weeds took advantage of an unusually warm February and early March to resume growth earlier than usual.

“Purple deadnettle, henbit and chickweed are already flowering,” Anderson says. “I’ve seen pennycress flowering, but it is not widespread in fields.”

Once winter annuals begin flowering, managing them becomes challenging.

“We are getting behind the eight-ball on controlling these weed species,” Anderson says. “A lot of people are making their burndown applications and getting [preemergence] herbicides out there. If they're [winter annuals] not flowering yet, we can still get really good control of them as long as they haven't bolted too much.

“Field pennycress is probably marginal as far as our ability to control them. If it is flowering, a burndown application may still reduce their seed production. However, we aren’t going to burn these weeds down and make them all disappear at this point. It's unlikely we'd get good enough coverage to eliminate the presence of those plants from the field. We need to keep in mind that once these weeds are flowering, they are producing seed and will be back this fall.”

That’s why it’s paramount to mark down these fields or areas of fields for winter annual herbicide treatments this fall. “It’s a lot easier to get ahead of them in October and November than it is to go out in March and kill them before they flower,” Anderson says.

This year’s weather also will be pushing the timetable ahead for the emergence of summer annuals, namely waterhemp. “If we have applied [burndown and preemergence] herbicide earlier and planted our crops earlier, we need to be scouting for when to apply post-applications by the time mid-May rolls around,” Anderson says.