Spring 2016 field crop weeds update for southwest Michigan

Cool, wet weather has made weed control challenging this spring as farmers feel the pressure to get crops planted under less than ideal conditions.

Incomplete burndown of a cover crop. Photo: Bruce MacKellar, MSU Extension.
Incomplete burndown of a cover crop. Photo: Bruce MacKellar, MSU Extension.

As with most agronomic considerations in southwest Michigan in 2016, weed control issues have revolved around the relatively cool, wet weather we’ve had since late April. Wet conditions have kept farmers out of fields, so spring tillage and burndown applications have been delayed. Michigan State University Extension weeds specialist Christy Sprague presented best weed control practices and answered participants’ questions at a recent field crops integrated pest management (IPM) meeting in St. Joseph County. Sprague addressed the challenges associated with weed control under these weather conditions and offered suggestions moving forward as fields dry and temperatures return to normal.

Herbicides applied during cool temperatures (less than 50 degrees Fahrenheit) have diminished efficacy as weeds are not actively growing and taking up the active ingredients. Weed control with burndown applications that would normally take seven to 14 days have often taken 14–21 days this spring. Similarly, cover crop termination in some fields was relatively late while in others control was incomplete.

Another challenge brought on by cooler temperatures is the crop’s weakened ability to metabolize herbicides, resulting in increased crop injury. Differences exist among varieties or hybrids, and inbreds in the case of seed corn, in their tolerance to various herbicides, and growers are encouraged to consult with their seed dealers on which herbicides are safe.

Sprague also addressed the lack of organic matter in sandier soils as another consideration with herbicide selection in southwest Michigan. Certain herbicides can cause greater levels of crop injury under these cool, wet conditions and are not recommended or they should be applied at the lowest recommended rate for the particular soil-type to avoid this injury.

Although farmers feel the pressure to get into fields to plant as soon as possible, Sprague stressed the importance of starting with a clean field where there has been a history of herbicide-resistant weeds. Several populations of weeds such as horseweed (marestail) and pigweeds like common waterhemp and Palmer amaranth have developed resistance to glyphosate and acetolactate synthase (ALS) herbicides, both of which remain staples in many weed control programs in corn and soybean. Soybean in particular can be challenging as no post-emergence herbicides are available for control of glyphosate- and ALS-resistant weeds in glyphosate-resistant soybean, so applying pre-emergence herbicides with residual activity (e.g., products including flumioxazin, sulfentrazone or metribuzin) is strongly encouraged.

Since pigweeds thrive in warm temperatures, Sprague said farmers should begin scouting in late May or early June this year, and control is best when weeds are less than 4 inches tall. MSU Extension’s 2016 Weed Control Guide for Field Crops is an excellent resource for choosing herbicides that effectively control weeds commonly found in fields in Michigan. Meeting participants were also encouraged to attend the 2016 MSU Weed Tour on June 29 in East Lansing, Michigan, for a first-hand look at the efficacy of numerous weed control programs.

The St. Joseph County IPM Breakfast Series is organized by the MSU Extension field crops team in southwest Michigan. The meetings run through the end of June and are held on Tuesdays at the Royal Café in Centreville, Michigan, beginning at 7 a.m. Each meeting includes an update of the major field crops grown in the region, including a crop and pest report, followed by a presentation from a guest speaker on a topic important to crop production. Participants can order breakfast and eat during the meeting.

The speaker for May 24 will be Kurt Steinke, MSU assistant professor of soil fertility and nutrient management, addressing the topic, “Field Crop Nitrogen Management Concerns and Technologies.” The meeting will be sponsored by Tony Belcher with Koviack Irrigation and Farm Services in Three Rivers, Michigan, and CEU and RUP credits will be available. Meetings are open to the public.

For more information on the IPM Breakfast Series, contact Eric Anderson at the MSU Extension St. Joseph County office at 269-467-5511.

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