Know your enemy: MU website helps ID common weeds

When weeds invade your field, pasture, garden or lawn, you want to use the right weapon for fighting back.

 

“Proper identification of weeds is important so that you choose an appropriate and cost-effective method of control,” said Kevin Bradley, University of Missouri Extension weed scientist.

 

There are hundreds of common weed species in Missouri, but an online tool from the MU Weed Science program can help you narrow your list of suspects.

 

The MU Weed ID Guide—available in desktop and mobile versions at weedID.missouri.edu and weedID.missouri.edu/mobile—has information on more than 400 plant species that can show up as weeds of field and horticultural crops, pastures, lawns, gardens, and noncrop or aquatic areas in Missouri and surrounding states, Bradley said.

 

“The website has a keying system that allows users to identify an unknown plant after they have selected the appropriate characteristics from a series of drop-down boxes,” he said.

 

Pop-up illustrations help the user identify more obscure characteristics such as the presence of ligules, auricles and petioles.

 

“If you have some idea as to what your weed species might be, you can simply type all or part of the common or scientific name into the appropriate text box,” Bradley said.

 

Once you’ve narrowed the possibilities to a reasonable number of candidates, the site will display the names and photos of weeds that match the characteristics you selected, with links to more information about each plant.

 

Bradley said an improved mobile version of the website is in the works that will better match the usability of apps for smartphones and tablet computers.

 

MU Extension publications on weed management

Lawn and garden: www.extension.missouri.edu/main/DisplayCategory.aspx?C=70.

Farms and fields: www.extension.missouri.edu/main/DisplayCategory.aspx?C=57.

 

MU Extension Plant Protection Programs: ppp.missouri.edu.

MU Weed Science: weedscience.missouri.edu.

 

Planning for Critical Weed Control

Each year, we are busy managing our crops. Sometimes we delay post-emergence weed control trying to get the most weed control during a spray application. However the cost of delaying weed control costs yield.
There are critical stages in the growth of corn and soybean where weeds do not significant hurt yield before or after these time periods. Critical timing in corn is often at high nitrogen rates, between the 6th and 9th leaf stage of corn. If you are using lower nitrogen rates, then the leaf stage may be lowered so it is from the 4th to 9th leaf stage.
As for soybean, the critical weed stage is the first trifoliate stage in 30-inch rows whereas in 15-inch rows it was the second trifoliate. This implies that weed control should begin earlier in wide rows than narrow rows.
Delaying weed control beyond the start of the identified period for weed control will cost the grower an average of 2 percent yield loss for everyone leaf stage delay in corn and also in soybean according to University Nebraska weed research data.
As you make your spring herbicide plans, don’t forget to apply pre-emergence products to manage glyphosate weed resistance and be sure to apply your post-emergence products at the proper time to prevent yield loss.
For more information, contact Wayne Flanary at 660-446-3724 or Heather Benedict at 660-425-6434, Regional Agronomists, University of Missouri Extension.

Big Weeds Showing in Soybeans

Some soybean fields have large weeds and these are already out of labeled height with most products. Most post-emergence products work best when weeds are small say 4 to 6 inches tall.

By controlling weeds when small, you are avoiding yield losses by competition from the larger weeds. Smaller weeds are also easier to control.


For those hard to control weeds, you may want to include a tank-mix partner that is specific to that weed species. This will increase control for weeds that may have developed resistance.

Be sure to consider the crop stage when applying when applying weed control products. Injury may occur if applications are to crops outside the labeled height or growth stage. Corn is especially sensitive to late applications compared to soybean.

For more information, contact Wayne Flanary at 660-0446-3724 or Heather Benedict at 660-425-6434, Regional Agronomists, University of Missouri Extension.

Proactive Weed Management

For adequate weed control in soybean, growers need to take a proactive approach using an appropriate pre-emergence herbicide program, said a University of Missouri Extension agronomist.

“Pre-emergence programs have increased in importance within the past several years as the number of glyphosate-resistant weed species has increased,” said Julie Abendroth.

Currently, there are five species confirmed to be glyphosate-resistant in Missouri: common ragweed, giant ragweed, horseweed (marestail), waterhemp and Palmer amaranth.

Glyphosate-resistant waterhemp populations are becoming more common in Missouri, Abendroth said. An MU weed science team conducted a survey in 2008 and 2009 inviting people to submit waterhemp samples suspected to be glyphosate-resistant. Of the 144 waterhemp samples submitted, 58 percent were confirmed glyphosate-resistant. Thirty-nine counties in Missouri are now known to have glyphosate-resistant waterhemp, although the actual number of counties is likely higher.

From 2007 through 2010, MU has investigated the influence of pre-emergence herbicide treatments on waterhemp control. MU plant pathologist Kevin Bradley’s research has shown that there are numerous pre-emerge herbicide options that will provide excellent waterhemp control.

These herbicides all provided excellent control in the three-year study: Valor (2 ozs./acre), Valor XLT (3 ozs./acre), Prefix (2 pints/acre), Boundary (1.5 pints/acre), Gangster (1.8 ozs./acre), Fierce (3 ozs./acre), Enlite (2.8 ozs./acre), Envive (3.5 ozs./acre), and the Authority line of products, which includes Authority First (3.2 ozs./acre), Authority MTZ (10 ozs./acre) and Authority Assist (5 ozs./acre).Other pre-emerge options, including INTRRO, Dual, Outlook and Prowl, were not as effective but did provide some early season waterhemp control. (Mention of trade names within this article does not imply endorsement by the University of Missouri.)

For those growers struggling with giant ragweed control, a proactive approach is very important, Abendroth said.

“It is difficult to achieve adequate control of giant ragweed once plants have emerged, and research data indicates that if ragweed is allowed to compete with the soybean crop for at least four weeks, a 25 percent yield loss can occur,” she said.

From the two-year weed survey, 44 percent of the 27 giant ragweed samples submitted to MU were confirmed glyphosate-resistant.

“In addition to controlling glyphosate-resistant weed populations, the residual control offered from a pre-emerge herbicide will also provide growers with greater flexibility with their postemergence applications,” Abendroth said.

MU Extension’s 2011 Missouri Pest Management Guide (M171) is available for purchase or free download at http://extension.missouri.edu/publications/DisplayPub.aspx?P=M171. The guide provides weed, insect and disease control recommendations for corn, cotton, soybean, grain sorghum, rice and winter wheat.

For more information, contact your local MU Extension center or see extension.missouri.edu.

Spring Brings a Purple Haze

Spring Brings a Purple Haze

By Heather Benedict, Agronomy Specialist

The weather is finally cooperating. People all over Missouri are spending more time outdoors in their fields, yards or gardens. Something you may have noticed is a purple haze over parts of the landscape. This is due to one or several different weeds. Purple deadnettle (Lamium purpureum) and henbit (Lamium amplexicaule) are both low growing plants with tiny purple flowers.

Purple deadnettle, and henbit are winter annual type plants. This means they germinate in the fall or late winter. They generally bloom in the spring, produce seed and then the plants die. Both Purple deadnettle and henbit are in the mint family, so when crushed or mowed, they produce a slightly minty scent. Both types of weed have square stems. The difference between them is in the shape of the leaves. Henbit has rounded leaves and darker purple flowers. Purple deadnettle has pointed leaves and pale flowers. The top leaves of purple deadnettle can also be a purplish color.

In crop fields, these types of weeds are not very competitive for moisture or for nutrients. The crop that may be most affected by henbit is wheat. Researchers in Missouri have found that henbit in densities of 82 plants per square foot can result in yield reductions. However, densities of 18 plants per square foot do not show any yield reduction. The fact that henbit dies off quickly in the spring, has led researchers to look into using it as a ground cover for row crops. However, there is some concern with using henbit as a ground cover for soybeans as it is a host for the soybean cyst nematode. In order to decrease the damage to yield from the nematodes, a good rotation system should be used. In the rotation system, henbit is not a good option.

In pastures henbit is surprisingly digestible with relatively high protein values. Henbit has been shown to have protein values comparable to tall fescue. Henbit is also palatable for animals and can be used for grazing until later maturing species come on. The drawback to using henbit or even chickweed in a pasture system is that they are not high producing.

For home owners, these weeds can be a nuisance. They spread quickly and easily. Also, they are most noticeable in the spring when they are difficult to control. 2,4-D herbicides may be used to help control purple deadnettle and henbit, however that type of herbicide is volatile and can easily injure or kill, tomatoes, flowers, grapes, and other garden vegetables. Another option for control is to use a pre-emergent herbicide on the lawn in the fall.