Bob Hartzler

Dr. Bob Hartzler is a professor of agronomy and an extension weed specialist. He conducts research on weed biology and how it impacts the efficacy of weed management programs in corn and soybean. Dr. Hartzler also teaches undergraduate classes in weed science and weed identification.

Bob Hartzler image
December 13, 2018 12:36 PM

While herbicide resistance is not a new issue, the rapid increase in multiple resistant biotypes in waterhemp, giant ragweed, and horseweed (marestail) is limiting herbicidal options. A waterhemp biotype resistant to six herbicide groups (2, 4, 5, 9, 14, and 27) was recently identified in...

December 11, 2018 12:47 PM

This is part three of a four-part series originally posted in 2016 on using multiple, effective herbicide sites of action (herbicide groups) at effective rates as part of a long-term weed management system. Read ...

Herbicide Resistance
December 4, 2018 8:25 AM

This is part two of a four-part series originally posted in 2016 on using multiple, effective herbicide sites of action (herbicide groups) at effective rates as part of a long-term weed management system. Read...

Herbicide Resistance
November 27, 2018 12:56 PM

This is part one of a four-part series originally posted in 2016 on using multiple, effective herbicide sites of action (herbicide groups) at effective rates as part of a long-term weed management system.

With the stagnant development of new herbicides and weeds seemingly...

Herbicide Resistance
November 1, 2018 7:31 AM

Updated on November 2, 2018

I feel obligated to write something about EPA’s dicamba announcement, but will confess at this time I still have several questions...

October 31, 2018 1:05 PM

While the monarch butterfly is a globally distributed species, the eastern United States population is renowned for its annual migration from the breeding range in the northeastern United States (and Canada) to overwintering sites in central Mexico.  Overwintering populations of this cohort have...

Crop Production
September 3, 2018 8:53 AM

It's Labor Day weekend, that means it's time for me to see what's happening at the first three Palmer amaranth infestations in western Iowa. The infestations (Harrison, Fremont, and Page Counties) were first reported in 2013.  Harrison County had two fields (approximately 50 acres) with...

August 25, 2018 10:10 AM

The finding of mile-a-minute weed near Knoxville, and the subsequent request for reports of additional infestations, has led to a flurry of calls regarding potential findings. Fortunately, none of the reports have been positive, but we appreciate people paying attention to plants in the...

August 15, 2018 12:40 PM

Another contest is in the books, and once again we provided a sufficient challenge to prevent anyone from earning a perfect score.  In the Professional Division, two-time defending champion Cindy Recker was narrowly edged out by Karen Stiles, last year’s winner in the General Division. Both...

July 23, 2018 3:36 PM

Mile-a-minute weed (Persicaria perfoliata) is an invasive species in the Polygonaceae (smartweed) family that is native to Asia.  It is believed to have been introduced to the United States in the late 1800’s and early 1900’s, but the initial introductions failed to form permanent...

July 9, 2018 9:35 AM

Off-target injury associated with dicamba application in dicamba-resistant soybean was a significant problem in the Cornbelt during 2017 (A final report on dicamba-injured soybean acres).  The increase in...

May 18, 2018 8:31 AM

Cool conditions during planting season increase the potential for herbicide injury to seedlings due to slow emergence and reduced ability of the crop to metabolize herbicides. While herbicides may be responsible for emergence issues, most problems that have been brought to our attention seem to...

March 4, 2018 10:40 AM

The Center for Biological Diversity (CBD) recently released a report (A menace to monarchs) describing the threat to monarch butterflies posed by an increased use of dicamba. ...

December 27, 2017 3:37 PM

Dicamba has been an important component of Iowa weed management systems for more than 40 years.  The history of its use is somewhat unique in that its popularity has ebbed and flowed over time.  The increase in herbicide resistant weeds combined with the introduction of dicamba-resistant soybean...

December 19, 2017 8:30 AM

At the recent North Central Weed Science Society annual meeting I was asked to provide the opening presentation (A historical perspective on dicamba) in a symposium focusing on issues with dicamba.  Following are the slides and the abstract of my presentation.


September 18, 2017 11:59 AM

My colleagues at Purdue recently compiled weather data to determine how many hours would be available to apply the new dicamba products (e.g. Xtendimax with VaporGrip Technology, FeXapan with VaporGrip Technology, and Engenia...

September 5, 2017 10:56 AM

For the past four years (maybe five) I’ve visited the first three known infestations of Palmer amaranth in western Iowa to track the status of the populations in these fields.  Following is a brief summary of  my visits to Harrison, Fremont and Page Counties on September 3.

August 16, 2017 7:47 AM

The following article originally appeared on the ISU Weed Science Online website.  Current research is showing that the new formulations of dicamba (Xtendimax with Vapor Grip Technology and Engenia) have not solved the volatility problem associated with dicamba.  Since the fundamentals of...

August 15, 2017 12:49 PM

For the first time in recent history, a contestant successfully defended their title in the Professional Division at the State Fair Weed ID Contest.  Cindy Recker of Peosta repeated as champion of the Professional Division, Karen Stiles of Des Moines won the General Division, and Henric Krause...

July 19, 2017 8:13 AM

The 2017 State Fair Weed Identification Contest will be held on Friday, August 11, from 9:00 AM to 11:30 AM.  Contestants can show up anytime during this period and complete the task at their own pace.  

The contest is held outside of the John Deere Agriculture Building, but moves indoors...

July 13, 2017 8:38 AM

While off-target movement of pesticides is not a new problem, the growth regulator herbicides create a unique situation due to their ability to induce easily observed symptoms at very low doses. Large scale drift problems were experienced when the phenoxy herbicides were introduced in the 1950s...

June 22, 2017 11:04 AM

The introduction and spread of Palmer amaranth in Iowa undoubtedly will have a significant impact on crop production and weed management in the future.  However, since the first infestations were identified I've been intrigued by what seemed odd behavior for a plant with Palmer amaranth's...

June 21, 2017 12:33 PM

The six weedy Amaranthus species at the weed garden have grown quite a bit, but I'm not sure how much easier it is to differentiate a few of the species. The six pigweeds are Palmer, Powell's and spiny amaranth, waterhemp, and redroot and tumble pigweed (not in that order!!). The...

June 13, 2017 7:55 AM

This year at the ISU FEEL weed garden I've established a plot with nine weedy members of the Amaranthaceae family, including six pigweeds .  The pigweeds were transplanted on June 9 and pictures taken on June 11. Species include redroot pigweed, tumble pigweed, Palmer amaranth, spiny amaranth,...

June 8, 2017 2:19 PM

While searching for Palmer amaranth in a pollinator habitat planting I encountered a few musk thistles.  As I always do when I see this weed, I examined flower heads for the presence of the musk thistle weevil.  This insect was imported to North America as a biocontrol agent for musk thistle.  ...