C.O.R.N. Newsletter 2009-15

Dates Covered: 
May 26, 2009 - June 2, 2009
Editor: 
Tim Fine

Wheat Scab Update May 26, 2009

Authors: Pierce Paul

Wheat has already flowered in southern and parts of central Ohio and began flowering in more northern counties late last week. For some counties in the northern-most third of the state, the crop should be flowering during this week. For those areas where wheat reached the flowering growth stage during the last two weeks, the risk of having scab and vomitoxin problems may be very low. Thankfully, the week on May 18th was very dry, so although it rained during the weeks of May 4th and May 11th, those rain events did not coincide with flowering in most fields, and even when they did, they were not followed by consecutive days of rainfall during and after flowering. Remember, scab develops best when frequent rainfall occurs shortly before, during, and shortly after flowering.

Rainfall during the first half of the month may not have contributed to infection and scab development in most fields, however, those events certainly contributed to the production and spread of spores of the scab fungus (Fusarium graminearum). This could be important for scab in fields flowering over the next two weeks, especially if it rains during flowering. So, while most of the state may have escaped a scab epidemic in 2009. Counties in northern Ohio may still be at risk. Rain is forecasted for tonight, tomorrow, and Thursday. A single rain event may not cause a problem, but multiple days of heavy rain could lead to infection, scab, and vomitoxin contamination. Pay attention to the forecasting system (http://www.wheatscab.psu.edu) during the next week to see if the risk of scab increases in your area.

Troubleshooting Miscellaneous Emergence Problems in Corn

Authors: Ron Hammond, Pierce Paul, Peter Thomison

Some of this information has been adapted from a newsletter article by Dr. Greg Roth at Penn State University.

Due to favorable field conditions during the past week, corn planting is nearing completion in Ohio. Across the state and within localized areas, corn is at a range of growth stages. Corn planted in late April is showing several leaf collars but in many fields, corn is just emerging.

Troubleshooting emergence problems early is critical in identifying solutions and developing successful replant plans, if needed. Here's a list of a few common things to look for if you encounter an emergence problem in corn this spring.


-No seed present. May be due to planter malfunction or bird or rodent damage. The latter often will leave some evidence such as digging or seed or plant parts on the ground.

-Coleoptile (shoot) unfurled, leafing-out underground. Could be due to premature exposure to light in cloddy soil, planting too deep, compaction or soil crusting, extended exposure to acetanilide herbicides under cool wet conditions, combinations of several of these factors, or may be due to extended cool wet conditions alone.

-Seed with poorly developed radicle (root) or coleoptile. Coleoptile tip brown or yellow. Could be seed rots or seed with low vigor. Although corn has just started to emerge or has not yet emerged, growers should carefully inspect seedlings for symptoms of disease, especially in lower lying areas of fields where ponding and saturated soils were more likely. Seeds and seedlings that are brown in color, are soft and fall apart easily while digging are obviously dead or dying. Seeds and seedling roots or shoots that have a weft of white to pinkish mold growing on them are likely victims of fungal attack and will likely die. Pythium and Fusarium are common fungi that attack plants and cause these damping-off or seedling blight symptoms under wet, cool conditions. It is more difficult to diagnose disease damage on plants that also show abnormal growth caused by cold soil conditions or by crusting of the soil surface. However, dark, discolored roots and crowns, instead of a healthy creamish-white appearance, are typical symptoms of seedling diseases problems. So, it is best to check these seedlings very closely for dark brown or soft areas on seedling roots and shoots. Any discoloration will indicate a problem that could worsen if the soils remain cold or wet.

- Seed has swelled but not sprouted. Often poor seed-to-soil contact or shallow planting- seed swelled then dried out. Check seed furrow closure in no-till. Seed may also not be viable.

-Skips associated with discolored and malformed seedlings. May be herbicide damage. Note depth of planting and herbicides applied compared with injury symptoms such as twisted roots, club roots, or purple plants.

-Seeds hollowed out. Seed corn maggot or wireworm. Look for evidence of the pest to confirm.

-Uneven emergence. May be due to soil moisture and temperature variability within the seed zone. Poor seed to soil contact caused by cloddy soils. Soil crusting. Other conditions that result in uneven emergence already noted above, including feeding by various grub species.

Note patterns of poor emergence. At times they are associated with a particular row, spray width, hybrid, field or residue that may provide some additional clues to the cause. Often two or more stress factors interact to reduce emergence where the crop would have emerged well with just one present. Also, note the population and the variability of the seed spacing. This information will be valuable in the future.

Don’t forget that corn may take up to 3 to 4 weeks to emerge when soil conditions are not favorable (e.g. temperatures below 55 degrees F, inadequate soil moisture). This was widely observed in many fields in 2005 when corn planted in mid April did not emerge until the first or second week of May. As long as stands are not seriously reduced, delayed emergence usually does not have a major negative impact on yield. However, when delayed emergence is associated with uneven plant development, yield potential can be reduced.

Black Cutworm and Bean Leaf Beetle Becoming More Common

Authors: Ron Hammond, Andy Michel, Bruce Eisley

Over this past week, we have received many calls about black cutworms causing significant injury in corn, already above the threshold of 3% or more plants being cut. One report was about a field having over 10% plants being cut. Growers should be monitoring their small corn that is up or that will be emerging shortly, especially in those fields that have or had winter annuals such as chickweed present. Growers should read our new fact sheet on cutworm at http://ohioline.osu.edu/ent-fact/pdf/0035.pdf , and see http://entomology.osu.edu/ag/images/cicw.pdf for a list of insecticides for cutworm control.

We also have heard of bean leaf beetles causing heavy injury to seedling soybeans that were planted early. Remember that the earliest soybean fields in an area receive the majority of beetles. With the late planting that is occurring, many of the emerged soybean fields might fit into this scenario. See the bean leaf beetle fact sheet at http://ohioline.osu.edu/ent-fact/pdf/0023.pdf for more information and http://entomology.osu.edu/ag/images/siblb.pdf for a list of insecticides labeled for bean leaf beetle on soybeans.

Fungicides will not Control Diseases Caused by Viruses

Authors: Pierce Paul

Trace to moderate levels of wheat spindle streak mosaic and barley yellow dwarf are present in some fields across the state and there is concern that some growers might be of the impression that fungicides will control these diseases.

Both diseases are caused by viruses and viral disease will not be controlled with a fungicide. Wheat spindle streak is transmitted by a fungus in the soil and generally develops best when cool, wet conditions in the spring extend through May. Typical symptoms of this disease are discontinuous yellow streaks with tapered ends parallel with the veins of the leaves.

Barley yellow dwarf causes stunting and yellowing of plants, yellowish or reddish leaf tips, and also develops best under cool moist conditions. There are several different strains of this virus which is transmitted by more than 20 species of aphids.

Resistance is the best means of control for both diseases. Fungicides will not work!!

Potato Leafhopper in Alfalfa

Authors: Ron Hammond, Andy Michel, Bruce Eisley

We have begun finding potato leafhoppers in alfalfa in the state, and thus, growers should plan on scouting the regrowth for the leafhopper as soon as alfalfa reaches sufficient height for sweep-net sampling. Sampling is done using a sweep net and taking 10 samples throughout the field. Each sample should consist of 10 sweeps with the net. Count all potato leafhopper adults and nymphs, though over the coming weeks, mostly adults will be seen. When the average number of leafhoppers in a single sample (10 sweeps) is equal to or greater than the average height of the alfalfa stand, insecticide treatment is warranted for varieties not resistant to the potato leafhopper. For example, if the alfalfa is 6 inches tall and the average number of leafhoppers per 10-sweep sample is 6 or higher, insecticide treatment is warranted. If the average is lower, the grower should re-sample in a few days to check for populations above threshold.

For potato leafhopper-resistant varieties of alfalfa, the economic threshold established from research is three leafhoppers per inch of growth (30 leafhoppers for 10” tall alfalfa, for example). If the resistant alfalfa is a new planting this spring, growers might want to use thresholds meant for regular alfalfa, at least during the very first growth from seeding. Resistance improves as the seedling stand develops. After the first cutting of the stand, the threshold for a highly resistant variety can be increased to 3 times the normal level for susceptible varieties.

A new fact sheet on potato leafhopper with a lot more information is available at http://ohioline.osu.edu/ent-fact/pdf/0033.pdf . A list of insecticides labeled for leafhopper is at http://entomology.osu.edu/ag/images/aiplh.pdf . As we mentioned last week, it would also be worthwhile to keep an eye out for alfalfa weevil larvae that might be limiting alfalfa regrowth. Weevil larvae are quite common in many fields that are being cut. Although weevil injury to regrowth is rare, it does require mentioning at this time.

Get Current Agronomic Information Specific to your Area of Ohio

Authors: Tim Fine, Harold Watters

As a supplement to the CORN newsletter, producers are encouraged to view the sites listed below for the latest and greatest information on crop progress, pest problems, weather and more.

If you live in West Central Ohio (the counties of Darke, Auglaize, Miami.
Mercer, Champaign, Clark, Logan and Shelby) you will want to visit http://westohcropweather.blogspot.com

Producers in the counties of Fulton, Williams, Defiance and Paulding in Northwest Ohio are encouraged to go to http://nwohcropweather.blogspot.com/

Van Wert County has it's onw site, located at http://agvanwert.wordpress.com/

In Northeast Ohio, or, more speficially Ashtabula and Trumbull Counties, please visit http://neohiocropweather.blogspot.com/

Coshocton County and east central Ohio producers are encouraged to go to http://eastohiocrop.blogspot.com/

And in the counties of Fayette, Pickaway and Ross South Central Ohio, your blog can be found at http://southcentralohioagnewsblog.blogspot.com/
 

Weather

Authors: Jim Noel

The forecast is slightly wetter and cooler than normal. Overall, June-August looks to have near normal temps and precipitation to me right now.

 

Archive Issue Contributors: 

State Specialists: Pierce Paul and Anne Dorrance (Plant Pathology), Ron Hammond, Andy Michel, and Bruce Eisley (Entomology), Peter Thomison (Corn Specialist), Jim Noel (NOAA). County Professionals: Suzanne Mills-Wasniak (Montgomery), Tim Fine (Miami), Jonah Johnson (Clark), Harold Watters (Champaign), Roger Bender (Shelby), Wesley Haun (Logan), Glen Arnold (Putnam), Bruce Clevenger (Defiance), Alan Sundermeier (Wood), Gary Wilson (Hancock), Mark Koenig (Sandusky), Mike Gastier (Huron), Howard Siegrist (Licking), Les Ober (Geauga)

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.