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Corn Newsletter : 2018-23
No Pigweed Left Behind - Late-Season Scouting for Palmer Amaranth and WaterhempAuthor(s): Mark Loux
If you don’t already have to deal with waterhemp or Palmer amaranth, you don’t want it. Ask anyone who does. Neither one of these weeds is easy to manage, and both can cause substantial increases in the cost of herbicide programs, which have to be constantly changed to account for the multiple resistance that will develop over time (not “can”, “will”). The trend across the country is for them to develop resistance to any new herbicide sites of action that are used in POST treatments. Preventing new infestations of these weeds should be of high priority for Ohio growers. When not adequately controlled, Palmer amaranth can take over a field faster than any other annual weed we deal with, and waterhemp is a close second. Taking the time to remove any Palmer and waterhemp plants from fields in late-season before they produce seed will go a long way toward maintaining the profitability of Ohio farm operations. There is information on Palmer amaranth and waterhemp identification on most university websites, including ours – u.osu.edu/osuweeds/ (go to “weeds” and then “Palmer amaranth”). An excellent brief video on identification can be found there, along with a fact sheet. The dead giveaway for Palmer amaranth as we move into late summer is the long seedhead, and those on female seed-bearing plants are extremely rough to the touch. We recommend the following as we progress from now through crop harvest:
- Take some time now into late summer to scout fields, even if it’s from the road or field edge with a pair of binoculars. This would be a good time to have a friend with a drone that provides real-time video, or your own personal satellite. Scouting from the road is applicable mostly to soybean fields, since corn will often hide weed infestations.
- Walk into the field to check out any weeds that could be Palmer amaranth, waterhemp, or are otherwise mysterious. If you need help with identification, send photos to us or pull plants and take them to someone who can identify them. Palmer and waterhemp are considerably different in appearance than giant ragweed and marestail, the most common late-season offenders.
- Where the presence of Palmer amaranth or waterhemp is confirmed, check to see whether plants have mature seed (in Palmer infestations these are the rough female seedheads), by shaking/crushing parts of the seedhead into your hand or other surface that will provide contrast. Mature seed will be small and very dark.
- Plants without mature seed should be cut off just below the soil surface, and ideally removed from the field and burned or composted. Plants with mature seed should be cut off and bagged (at least the seedheads) and removed from the field, or removed via any other method that prevents seed dispersal through the field.
- If the Palmer amaranth or waterhemp population is too dense to remove from the field, some decisions need to be made about whether or how to mow or harvest. Harvesting through patches or infested fields will result in further spread throughout the field and also contamination of the combine with weed seed that can then be dispersed in other fields. So consider: 1) not harvesting areas of the field infested with Palmer amaranth or waterhemp, and instead mowing several times to prevent seed production, and 2) harvesting the infested field(s) after all other fields have been harvested, and cleaning the combine thoroughly before further use. This also applies to any infestations that are discovered while harvesting.
- Scout field borders and adjacent roadsides, areas that flood or receive manure application, and also CREP/wildlife area seedings. The latter can become infested due to contaminated seed produced in states where Palmer amaranth and waterhemp are endemic and not considered noxious. Reminder - ODA will test any seed used for these purposes for the presence of Palmer amaranth.
What is the R3 Growth Stage?Author(s): Laura Lindsey
A few weeks ago, Dr. Anne Dorrance wrote an article about foliar fungicide application to soybean for control of frogeye leaf spot disease. She recommended spraying at the R3 growth stage. (Her entire article is here: https://agcrops.osu.edu/newsletter/corn-newsletter/2018-19/we-have-found-some-whiskers-spores-cercospora-sojina).
What is the R3 growth stage? And has it already passed?
A soybean plant is at the R3 growth stage when there is a pod at least 3/16 inch long (but less than 3/4 inch long) at one of the four uppermost nodes on the main stem with a fully developed leaf. (A leaf is fully developed and the node is counted when the leaf at the node immediately above it is open.) The soybean plant pictured is at the R3 growth stage.
In our research trials in Clark County (planted the first week of May), Group 2 and 3 soybeans entered the R3 growth stage during the first two weeks of July. They are now at the R4 to R5 growth stage. Don’t rely on plant height, calendar date, or your neighbor’s field…Walk your own fields (each year) to assess growth stage.
Keep in mind:
- Soybean plants within a field may be at different growth stages. Over half of the plants need to be at a certain growth stage for the whole field to be considered that growth stage.
- An individual soybean plant may have flowers, pods, and seeds filling all at the same time. The soybean plant develops from bottom to top.
For more information on soybean staging, see A Visual Guide to Soybean Growth Stage by Dr. Shawn Conley (University of Wisconsin-Madison) available here: https://coolbean.info/library/documents/2017_Soybean_GrowthDev_Guide_FINAL.pdf
Japanese Beetles in Corn and Soybean
We have been hearing reports of Japanese beetles in corn and soybean. These beetles are large with a shiny copper and green color. Foliage feeding in corn is almost never economic, though economic damage from silk clipping is possible (though rare). Consider a rescue treatment when silks are clipped to less than ½ inch and, fewer than 50% of the plants have been pollinated, and the beetles are still numerous and feeding in the field.
Japanese beetles will also feed on soybean foliage. While the damage might look startling, it is very rare that this reaches economic levels from Japanese beetle. A rescue treatment is advised when defoliation levels reach 30% in pre-bloom stages, and 20% in bloom to pod fill. These defoliation levels apply to the plant as a whole, not just certain leaves, and can also be used for general defoliation from more than one kind of leaf-feeding insect in soybean. A visual guide to defoliation is useful because it is very easy to over-estimate defoliation in soybean. If there are other foliage-feeding insects present in soybean the same percent defoliation guidelines can be used for all of them collectively.
For more information about Japanese beetle and other defoliating inseces visit our factsheet at:
Japanese beetle adult (photo by John Obermeyer)
Visual Guide to Soybean Defoliation
Western Bean Cutworm: Adult Moth Catches Increase (Scouting Video Included)Author(s): Amy Raudenbush, John Schoenhals, CCA, Mark Badertscher, Lee Beers, CCA, Amanda Bennett, JD Bethel, Bruce Clevenger, CCA, Sam Custer, Tom Dehaas, Mike Gastier, CCA, Jason Hartschuh, CCA, Ed Lentz, CCA, Rory Lewandowski, CCA, Cecilia Lokai-Minnich, David Marrison, Sarah Noggle, Les Ober, CCA, Eric Richer, CCA, Garth Ruff, Jeff Stachler, Alan Sundermeier, CCA, Curtis Young, CCA, Chris Zoller, Andy Michel, Kelley Tilmon
Western bean cutworm (WBC) adult moth catches in our trapping network continue to increase. For week ending July 21, 23 counties monitored 89 traps (Figure 1). Overall, there was an average of 25.4 moths per trap (1928 total captured). This is an increase from an average of 14.3 moths/trap (1116 total captured) the previous week. It is important to note that not all counties are seeing an increase in WBC adult moths. Counties where WBC adult moth catches decreased included Paulding, Van Wert, Darke, Auglaize, Miami, Hancock, Hardin, Champaign, Clark, Crawford, and Tuscarawas.
Figure 1. Average Western bean cutworm adult per trap in Ohio counties, followed in parentheses by total number of traps monitored in each county for the week ending July 21, 2018. Legend in the bottom left describes the color coding on map for the average WBC per county.
Life cycle and feeding. Adult moths (what we monitor in the traps) will be making their way into corn fields where females will lay eggs on the uppermost portion of the flag leaf. Eggs are laid in unevenly distributed clusters of 5–200, but averaging about 50 per cluster, and hatch within 5–7 days (Figure 2). Eggs first appear white, then tan and then a dark purple. Once eggs turn purple, they will hatch within 24 to 48 hours (Figure 3). In pre-tassel corn, caterpillars will move to the whorl to feed on the flag leaf and unemerged tassel. Once the tassel emerges, larvae then move to the ear, while feeding on corn pollen, leaf tissue, and silks. Later they will enter the ear through the tip, or by chewing through the side of the husk. Damage occurs from both direct feeding and from mold problems at feeding sites.
Figure 2. WBC egg mass. Figure 3. WBC larvae hatching from egg mass.
Scouting and management. You can view our scouting video here.
Female moths prefer to lay eggs in pre-tassel corn approaching tassel, so check such fields first. To scout for eggs or larvae, choose at least 20 consecutive plants in 5 random locations and inspect the uppermost 3–4 leaves for eggs, as well as the silks for larvae if tassel has emerged. Be sure to inspect different areas of the field that may be in different growth stages. For field corn, if 8% or more of the plants inspected have eggs or larvae, consider treatment. For sweet corn, consider treatment if eggs or larvae are found on >4% of plants for the processing market or on >1% of plants for fresh-market. Bt corn with the Cry1F trait can no longer be relied upon for good western bean cutworm control, so these fields should be scouted too. These include Herculex I, Herculex Xtra, SmartStax, and others.
If infestations exceed threshold, many insecticides are available to adequately control western bean cutworm, especially those containing a pyrethroid. However, as with any ear-burrowing caterpillar pest, timing is critical. Insecticide applications must occur after egg hatch, or after tassel emergence, but before caterpillars enter the ear. If eggs have hatched, applications should be made after 95% of the field has tassel. If eggs have not hatched, monitor for the color change. Hatch will occur within 24–48 hours once eggs turn purple. To search for larval injury after it has occurred, search the corn for ears having feeding holes on the outside of the husks.
Cover Crop Survey - Quick and PainlessAuthor(s): Mark Loux
OSU weed scientists are in the process of planning cover crop research, and could use your input. Cover crop use has been on the rise in recent years, most commonly for the preservation of soil, reduction in nutrient loss, and suppression of weeds they can provide. Feedback from this survey will allow us to perform trials that are in line with practices common in the state of Ohio and thus generate more impactful results. Thank you!
Please take our five second survey!
Manure Management and Cover Crops Field DayAuthor(s): Jeff Stachler
Want to learn more about sidedressing corn with liquid manure, latest on water quality, and how to make cover crops work? Attend the Manure Management and Cover Crops Field Day in Auglaize County. The field day is on August 8, 2018 from 9:00 AM to 3:30 PM. The Field day will take place at the southwest intersection of Main Street and Doering Roads with the field entrance to the west at the woods. The nearest address to the field is 09244 Doering Road.
Topics presented at the field day include Basics of Cover Crops, How to Make Cover Crops Work, No-Tillage and The Smoking Tile, Water Quality Update, Best Management Practices, Manure Research, and Manure Sidedress Demonstration.
Register for the field day before July 25 by contacting the Ohio State University Extension Auglaize County office at 419-739-6580 or e-mail Jeff Stachler at firstname.lastname@example.org. There is no charge for the field day.
See you at the field day.
About the C.O.R.N. Newsletter
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.
The information presented here, along with any trade names used, is supplied with the understanding that no discrimination is intended and no endorsement is made by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.
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