Waterhemp’s Big, Bad Brother is Back This Spring

Palmer amaranth has been confirmed in five Iowa counties over the last two summers. The only (known) infestation in Muscatine County is on a very sandy soil near the Cedar River, and most emerged seedlings had at least four true leaves on May 4, 2015. This particular infestation has been intensively managed for just over a year, resulting in a significant decrease in its presence at the farm. This is very encouraging that with early discovery and good management, eradication may be possible

Palmer amaranth: It’s here, now what?

Palmer amaranth and waterhemp are two dioecious pigweed species native to North America. Waterhemp’s original range was the western Corn Belt, including Iowa, whereas Palmer amaranth originally inhabited the southwestern United States. Palmer amaranth began to spread to the southeastern United States early in the 20th century but was not listed among the most troublesome weeds of the Southeast until the late 1980s. Interestingly, this is the same time frame that waterhemp emerged as a serious management issue in Iowa and surrounding states. This paper will review the history of Palmer amaranth in Iowa, factors that contribute to its weediness, and management considerations

Interactions between cover crops and weed management in Iowa\u27s conventional cropping systems

The effect of different levels of cereal rye (Secale cereale L.) residue on common waterhemp (Amaranthus rudis Sauer) and common lambsquarters (Chenopodium album L.) emergence was determined. Cereal rye seeding date had a greater effect on rye biomass accumulation and percent cover than seeding rate. Common waterhemp emergence was equal to or increased in the presence of cereal rye residue in both 2013 and 2014 compared to the control. Common lambsquarters emergence was increased in two treatments in 2014 but was otherwise unaffected by cereal rye. The presence of cereal rye residue increased the time to 10% and 50% emergence of common waterhemp in both years but had less effect on common lambsquarters. The lack of weed emergence suppression seen in these experiments is a concern for cover crop use in Iowa\u27s conventional cropping systems, while the delay in weed emergence associated with cereal rye residue may be beneficial or detrimental to weed management. Greenhouse trials determined the soil activity of low rates of eleven corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] herbicides on five cover crops: cereal rye (Secale cereale L.), oat (Avena sativa L.), hairy vetch (Vicia villosa Roth), lentil (Lens culinaris Medik.), and radish (Raphanus sativus L.). Cereal rye was the most tolerant cover crop, whereas radish was the most sensitive species. Dry weight of radish was severely reduced by nearly all herbicides, whereas other cover crop species had smaller reductions due to herbicide injury. Root growth of oat was inhibited more by pendimethalin than the other species. Flumetsulam + clopyralid, atrazine, and herbicides containing isoxaflutole caused significant injury to most species studied. Though it is difficult to make direct comparisons between these experiments and the potential for injury in the field, these studies provide guidelines for growers wanting to include cover crops within their current rotation

Crop Injury Associated with Growth Regulator Herbicides

While off-target dicamba injury to soybean has dominated the news the past year, it is important to recognize that dicamba is not the only Group 4 herbicide (HG4) capable of injuring soybean. These herbicides mimic the activity of indole acetic acid (IAA), a hormone that regulates the activity of numerous genes involved in plant growth. IAA also is referred to as auxin. HG4 products can induce plant responses at lower doses than most other herbicide groups, thus off-target injury has been a problem since their introduction in the 1940’s. This article will discuss some of the problems observed this growing season. All HG4 cause malformed leaves, and distinguishing symptoms between products is difficult (Figure 1). Timing of symptom development and patterns of injury are important in identifying the source of injury

Fall Marestail (Horseweed) Management

Marestail (Conyza canadensis) is one of the most difficult weeds to manage in no-till soybean. While classified as a winter annual, the plant has significant emergence in both late summer/early fall and in the spring. This extended emergence period greatly complicates management since the success of postemergence products is closely tied to plant size. Attempting to control populations at the time of planting often results in control failures as fall-emerged plants are too large for acceptable control

Achieving Full-season Waterhemp Control in Soybean

Although there are many ways weeds escape control in crop fields, one of the leading causes of waterhemp control failures is emergence of plants following postemergence herbicide (POST) treatments. Waterhemp requires more than twice as many growing degree days to reach 50% emergence as giant foxtail or velvetleaf (Figure 1), resulting in much of the population emerging after mid-June

Effect of Residual Herbicides on Cover Crop Establishment

The interest in cover crops has increased recently due to the benefits they can provide to the corn-soybean cropping system. The use of residual herbicides has increased at the same time, and the potential impact these herbicides may have on establishing cover crops is an important consideration

ANALYSIS AND RECOMMENDATION OF POLICIES TO SUPPORT THE ENERGY TRANSITION OF WEST TEXAS ENERGY COMMUNITIES

Declarations of emission reduction goals have left an uncertain future for oil and gas markets. During a transition to increased use of clean energy resources, areas known as energy communities which economically depend on the success of the fossil fuel industry may experience more negative impacts than other areas of the nation. This includes the Permian Basin of West Texas, one of the largest areas of oil and natural gas production in the United States. The following analysis investigates policy solutions which could provide support for the communities in this area and avoid such trends as those seen in coal energy communities which have experienced economic hardship due to a changing energy landscape. For the investigation, review of past policy efforts as well as qualitative data analysis is used to determine a set of policy criteria and two policy alternatives to investigate. The first policy suggests the development of new education and retraining programs through community colleges and vocational schools. A second policy alternative considers support for emerging and developing industries of the area, including wind, solar, geothermal, hydrogen, and aerospace. After contrasting both cases against a “business-as-usual” control scenario, the first policy alternative was determined to be a more likely candidate for success in the area, but certain elements of a policy to develop industry outside the oil and gas energy sector may also be appropriate for policy makers to consider

Fomesafen Carryover to Corn

ISU Extension and Outreach Field Agronomists continue to receive calls regarding fomesafen carryover injury to rotational corn. There are several factors resulting in this injury: 1) continued problems with waterhemp result in late-season applications, 2) fomesafen is relatively persistent, and 3) many areas of Iowa received less than average late-season rainfall in 2017. In most cases, this carryover injury has been limited to relatively small sprayer overlap areas, though some fields are showing injury on a more widespread area

Managing Wet Soybeans in a Late Harvest

As of October 14, 2018, Iowa soybean harvest was only about 20% complete, making it the latest soybean harvest on record. This was caused by the prolonged heavy rains in September and early October. As a result, field losses, abnormally high harvest moisture content and moldy/weathered soybeans are all issues this year