C.O.R.N. Newsletter: 2014-17
Principles of Pokeweed ManagementAuthor(s): Mark Loux
Penn State recently completed a two-year study on pokeweed management in corn and soybeans that provides some useful information. Some of the highlights:
- pokeweed is a perennial that regrows from a large taproot, and individuals may live a year or two, or for several years, depending on their environment. Harsh winters such as the last one can reduce plant survival.
- seed production and dispersal are essential for pokeweed success. A pokeweed berry contains 9 or 10 seeds. Pokeweed plants that emerged in May or June grew into perennial plants that first season, and produced up to about 2500 seeds. Preventing berry/seed production is an important management tactic for this weed, much like for annual species.
- systemic postemergence corn herbicides (glyphosate, 2,4-D, dicamba, Status, Callisto + atrazine, etc) can provide at least 80% control by the end of the season. None of the herbicides provided complete control, indicating the potential for recovery and regrowth the following year, and the need for a multi-year management approach.
- similar results occurred with postemergence soybean herbicides, but effective options were fewer. Research showed the value of Roundup Ready and glyphosate as a foundation herbicide for managing common pokeweed in soybean; the non-glyphosate treatments (Classic, Harmony, Synchrony, FirstRate, and Raptor) provided only 39 to 62% control.
- application in late June through the rest of the summer provided good control of pokeweed, while late spring application was less effective. At least 90% control occurred when glyphosate was applied at 600 to 800 GDD (48 F base temperature) or later. The late June and later applications coincide with pokeweed flowering, and herbicide translocation to below ground vegetative structures is probably much greater with the later applications.
- results are summarized in a Penn State newsletter article -http://extension.psu.edu/plants/crops/news/2014/05/pokeweed-management-update.
Asiatic Garden Beetles Continue to be an Issue in NW Ohio
Grubs of the Asiatic Garden Beetle (Maladera castanea) have been making their presence known in Northwest Ohio corn fields since 2012. For a long time this grub has been a pest in the lawn and turf industry, but in past few years it has severely damaged corn. This beetle is similar to most in its life cycle having four stages of egg, larva (or grub), pupa and adult. Currently, the third instar larva are feeding on root systems, specifically the mesocotyl. Damaged fields often have gaps in rows, and affected corn often appears wilted and stressed (see picture).
In Ohio, damage appears to be most prevalent in sandier soils, which are concentrated in NW Ohio, but can also be found in isolated areas near sandy river beds. This year we have been seeing them since approximately the 3rd week of May, and now is the time to scout for this pest. Look for corn in sandy soils that appear to have uneven growth stages, are wilting, or with gaps in the row. Dig around the plant and look for the presence of white grubs (see the video here:http://www.oardc.ohio-state.edu/ag/pageview3.asp?id=3787 ) Asiatic garden beetles are typically smaller and more active than other grubs and also have a white “bubble” near the head. If uncovered from the soil surface, the grubs try to move quickly back underneath the soil. At this point in time, the grubs can be found within the first 1-2 inches of soil and often create tunnels around the root system of the corn—you may also find them in between rows. In the mid June we anticipate the larva to pupate and by July, adult beetles will begin emerging to lay eggs all over again.
While the turf and ornamental industry has dealt with these insects for some time, we have much to learn about this insect, its management and the thresholds for economic damage as they relate to growing corn. While there are some ways to trap for Asiatic Garden Beetle larva, at this point in time, it is just necessary to get out into your corn fields and dig for the larva in those sandier soils. We suggest starting with your no-tilled fields and fields without soil applied insecticide first. We are still making observations and at this time there doesn’t seem to be any “silver bullets” for controlling this pest. Many things are part of the discussion and research plots including tillage, seed treatments, insecticide, rotational programs and more. There are also no rescue treatments available besides replanting. Please conduct a stand count before considering replanting. It is suggested to use the re-plant calculator (http://web.extension.illinois.edu/csrec/eb260/entry_6903/), written by Emerson Nafziger and Bob Nielson, from Illinois and Purdue, respectively. If you have questions on this new pest, please contact Eric Richer (email@example.com) or Andy Michel (Michel.firstname.lastname@example.org).
“Rootless” and “Floppy Corn” Make an AppearanceAuthor(s): Peter Thomison
Last week I received several reports of “rootless” and “floppy corn” in Paulding County (Figure 1). Rootless corn (or rootless corn syndrome) occurs when there is limited or no nodal root development. Plants exhibiting rootless corn symptoms are often leaning or lodged. Affected corn plants may only be anchored in the soil by seminal roots or by a single nodal root. This condition is generally observed in plants from about the three leaf stage to the eight leaf stage of development. The problem often becomes evident when corn is subjected to strong winds, which result in plants falling over because there is a limited number or no nodal roots supporting them. The force of winds can also break off nodal roots and inhibit establishment of a permanent root system. Leaning and lodged plants (sometimes referred to as "floppy corn”) may also be wilted. When affected plants are examined, the nodal roots appear stubby, blunt, and unanchored to the soil.
Rootless corn problems are usually caused by weather related conditions that coincide with development of the permanent (or nodal) root system and various environmental factors. These include shallow plantings, hot, dry surface soils, compacted soils, and loose or cloddy soil conditions. Excessive rainfall and shallow plantings may cause erosion and soil removal around the crown region that can result in rootless corn.
“High crown syndrome” has been associated with rootless corn problems (http://bulletin.ipm.illinois.edu/article.php?id=1650). One of the causes of high-crown syndrome is subsidence of the soil due to rainfall after planting, when planting occurs in dry soils fluffed by tillage. If the planting furrow opens as soils dry after planting (this is most common in no-till), coleoptile growth stops and the crown can be set near the seed, essentially placing the seed and seedling above the soil (Nafziger, 2012).
The nodal roots develop above the seed and comprise the permanent root system of corn. The nodal roots, not the seminal roots (associated with the seed), are important in providing the water and the mineral nutrients that the corn plant needs for normal growth and development. If corn seed is planted 11/2 to 2 inches deep, then the nodal (or crown) roots begin develop at about 3/4 inches below the soil surface. However, if seed are planted shallower (1 inch or less), then the nodal roots may form near or at the surface where they are more exposed to fluctuations in soil moisture and temperature. Nodal root growth is very sensitive to high temperatures (w/ root growth slowing or stopping at soil temperatures exceeding 86 degree F). When unshaded surface soil temperatures reach the mid 90's or higher on hot days, the nodal root growth of shallow planted corn may stop. Plants are forced to rely on the seed root system or limited nodal root growth until more favorable temperatures and moisture conditions allow nodal root growth to resume.
Certain types of herbicide injury (e.g. 2,4-D, Banvel) and insect feeding (e.g. corn rootworm) may also cause lodging to occur in corn plants during vegetative development. Generally they are not the major causes of the rootless corn problems. However, there may be situations where insect feeding and/or herbicides may be a contributing factor.
Can rootless corn recover? Yes, after plants lodge, adequate rainfall will promote crown root development and plants can recover. Cultivation to throw soil around exposed roots may aid the corn's recovery. Of course, this is difficult to do in a no-till situation or when the soil is hard and dry. Since affected corn is likely to be vulnerable to potential lodging
problems at maturity, it should be harvested as soon as grain moisture conditions permit.
Nafziger, E.. 2012. Root Problems in Corn Plants. The Bulletin, Univ. of Illinois.http://bulletin.ipm.illinois.edu/article.php?id=1650 [URL accessed June 2014].
Nielsen, RL (Bob). 2010. "Rootless" or "Floppy" Corn Syndrome. Corny News Network, Purdue Univ. http://www.kingcorn.org/news/timeless/FloppyCorn.html [URL accessed June 2014].
When to Spray Soybeans Field DayAuthor(s): Amanda Douridas
Assessing soybean diseases and insect pressure can be difficult without proper training and experience. On July 8, 2014 farmers and crop consultants are invited to attend a 2 hour in-field session with Drs. Anne Dorrance and Andy Michel. Anne Dorrance is OSU Extension’s state specialist in soybean diseases and Andy Michel is the OSU Extension entomologist for agronomic pests. They will work with participants to identify insects and diseases and discuss when spray applications should be made.
The Union County session will be from 10 am until noon and the Champaign County session will take place from 2 pm to 4 pm. The field locations will be decided the week before the event and registrants will be notified at that time of the location. There is no cost to attend and the event is sponsored by the Ohio Soybean Council. Participation is limited to 25 at each location so register early if interested. Register by calling (937) 644-8117 or emailing Douridas.email@example.com. The event flyer with a mail-in registration form can be found at: go.osu.edu/agevents.
Crop Observation and Recommendation Network
C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.
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