Fomesafen Carryover Injury to Corn

We have received several calls regarding suspected fomesafen carryover injury to corn. Fomesafen is a group 14 herbicide (PPO inhibitor), and the active ingredient in Reflex, Flexstar, Prefix, Marvel and other products. Carryover is typically associated with applications made after late June and/or when the season turns dry following application. Labels of most products containing fomesafen specify a 10-month rotation interval for planting corn. The primary symptom of fomesafen injury is striped leaves due to chlorotic or necrotic veins on the leaves. Other factors can cause striping on leaves, but fomesafen is unique in that the veins are affected rather than interveinal tissue. Some of the leaves may fold over midway due to loss of integrity of the leaf midvein

Weed Ecology Field Day is August 16, 2004

A field day focusing on the impacts of crop rotation on weed population dynamics will be held Monday, August 16, near Boone, Iowa. The event will be held at the site of a 21-acre experiment involving 3 crop rotations (corn - soybean; corn - soybean - small grain/red clover; corn - soybean - small grain/alfalfa - alfalfa). Information on why weeds respond differently to the rotation systems will be presented. Speakers include Matt Liebman, Bob Hartzler, and Andy Heggenstaller from the Iowa State University Department of Agronomy; weed management practitioners; and others. Refreshments will be served after the field day

Critical periods of competition in corn

The critical period of competition defines how long weeds can compete with crops before affecting yields. Two critical periods are defined. The first involves weeds that emerge at the same time as the crop and compete until a postemergence strategy is applied. These weeds have the greatest potential to affect crop yields and are the focus of this article. The second critical period involves weeds that emerge after crop emergence. As the interval between crop and weed emergence increases there is less likelihood that the weeds will impact yields

Do CRP Acres Converted to Soybean Require Inoculation?

Nitrogen fixation is the process of converting atmospheric nitrogen into a usable form for the plant and is critical for producing higher yields in soybean. For nitrogen-fixation to occur, the nitrogen-fixing bacteria known asBradyrhizobia japonicum need to be readily available in the soil or must be applied to the seed to form nodules on the soybean root. Because of the widespread production of soybean across Iowa, most Iowa fields have sufficient infestations of these bacteria to fully nodulate soybean without the use of supplemental inoculants. However, questions frequently arise concerning the need for seed inoculation when planting soybean in fields without a recent history of soybean production, such as fields in the Conservation Reserve Program (CRP)

Factors leading to inconsistent waterhemp control

Waterhemp continues to be one of the most problematic weeds for Iowa farmers. A higher frequency of waterhemp escapes was observed in Roundup Ready soybean fields during 2001 than in previous years. Control failures may be caused by unfavorable weather, tolerant/resistant biotypes, improper application timing, poor spray coverage, and late emergence. Sorting through these variables can be difficult, but is important in adjusting management programs to avoid repeat problems

Evaluation of a biological control agent for musk thistle

Musk thistle (Carduus nutans L.) is a serious weed found in pastures, roadsides, conserva­ tion reserve acres, and other noncultivated areas across Iowa. This weed infests more than three million acres in the state. Because the state of Iowa classifies musk thistle as a noxious weed, landowners must control any plants of this species present on their property. It is estimated that Iowa farmers spend more than $5 million annually to control musk thistle. Currently, the primary control method for musk thistle involves the use of herbicides

It’s Time to Scout for Winter Annuals

In addition to wet fields and localized flooding, this winter’s record snow cover is likely to contribute to abundant winter annual weed infestations in no-till fields. In most years, winter annual infestations suffer significant mortality due to cold temperatures and freeze/thaw cycles, but the snow provided a blanket of protection. Thus, winter annual infestations will likely be more abundant and vigorous than in typical years

Online Review Course for Iowa Certified Crop Adviser Exam Now Available

Iowa State University Extension and Outreach, with support from the Iowa Certified Crop Advisers Board, has developed an online review course for individuals taking the Iowa Certified Crop Advisor (CCA) examination. The course consists of four modules included in the exam: crop management pest management nutrient management soil and water management

A History Lesson in Herbicide Resistance

The evolution and spread of glyphosate resistant weeds has increased people’s awareness of the threat of herbicide resistance. Participants at a recent series of meetings were asked their perspective of the prevalence of resistance to several herbicide classes in fields they managed. In the survey, 60 percent of farmers reported that waterhemp resistant to Group 2 herbicides (ALS inhibitors) was not present in their fields or they were unsure of its presence. Industry representatives were somewhat more aware of Group 2 resistance, with 38 percent saying resistance was widespread and 42 percent reporting it was isolated in their territories. Both groups reported that glyphosate (Group 9) resistance was more common than Group 2 resistance