C.O.R.N. Newsletter 2010-24

Dates Covered: 
August 3, 2010 - August 10, 2010
Editor: 
Greg LaBarge

Late Season Diseases: Making an Early Appearance in Soybeans

Early reports of several late season diseases are common in Ohio this year.  The following is a list of key characters to help in diagnosis.

  1. Patch of stunted plants - leaves normal in size -  just the plants are shorter – SCN.  This is the time of year where the pockets within a field can be found that have very high SCN levels.  If you are walking through waist-high soybeans and all of sudden the beans are knee high it is time to dig some up and take a look at the roots to look for those SCN females. 
  2. Brown Canker on the stem – early wilting  - and early death.  There are 2 possibilities here Phytophthora stem canker or Diaporthe stem canker. Phytophthora is very prevalent this year, especially in fields which have high levels of clay and have been receiving weekly rains.  The roots are often rotted and the canker goes from the roots up to 6 or 7 nodes of the plant.  In some cases, the canker may only be visible on one side of the plant.  Diaporthe stem canker has a much different life cycle, in this case the infection starts at the 3 or 4th node, and is restricted.  It is a darker brown and below the canker the plant is alive and green.  This results in top dieback.PhytothoraDiaporthe Stem Canker
  3. Chlorosis (yellowing) and necrosis (brown) in between the veins on the leaves and early dying of the soybean plants.  There are 2 possibilities for this as well:  SDS or Brown stem rot.  Both have already been identified in Ohio this year and in one case both were found on the same plant. The key difference is that the SDS fungus colonizes the crown and produces a toxin that causes the foliar symptoms.  In this case the pith is white, but the crown is gray/discolored. For brown stem rot, the fungus that causes brown stem rot, colonizes the vascular system and causes the pith to turn a chocolate brown color.  This color does not always occur the entire the length of the plant, but will sometimes be in patches.  Low soil pH (<6) can favor the expression of this disease.Sudden Death SyndromeBrown Stem Rot
  4. White fluffy growth or bleaching of the main stem and early dieback.  There is only one possibility for this and that is Sclerotinia stem rot also known as white mold.  When the infections are found early, and there is a lot of humidity the mycelium of the fungus is the white “fluff” on the stems.  As the infections mature and the stem dries out the stem takes on a bleached appearance and the stem is hollow.  When you crack it open you can often find the hard black “rat-turd” like sclerotia.Sclerotinia stages
  5. Early dying plants, we have identified charcoal rot here in Ohio in a few fields.  In this case the plants die early, in one field it looked like similar yellow as SDS, but the crown of the roots looked like they had grains of pepper scattered throughout.  In general, this tends to be in southern Ohio and is often associated with drought-like conditions.Charcoal Rot

In all of these cases, they all look the same at 60 mph from the truck.  They actually look the same from the stopped truck along the side of the road.  So to really know what is causing early dying of soybean plants, you need to get out of the truck – and walk the fields.  Take a shovel with you if you need to dig up some plants to look for SCN females.    For all of these diseases, choosing varieties with resistance will solve most of these issues.  So having a correct diagnosis is the  key to better management in the future.

Gibberella Ear Rot in Corn: Post Pollination Update

About a month ago, before the corn crop reached pollination, we responded to questions about the risk of Gibberella ear rot (GER), after this year’s scab problems in wheat (remember the same fungus that causes scab also causes Gibberella ear rot). At that time we indicated that planting corn after scabby wheat or close to a scabby wheat field increases the risk of GER. We also indicated that hybrid susceptibility to GER and weather conditions were also very important for the development of this disease. Now that most of the early-planted corn is well past pollination, it is time to reevaluate the risk of GER.

The fungus enters the ear mainly through the silk and may damage large sections of the ear if infection occurs early and weather conditions are cool and humid just after silking. However, infections can also occur at the base of the ear if frequent rainfall occurs late in the season, especially in those hybrids where the ears do not turn down at maturity. Let us compare last season with this season to see where we stand in term of GER. Like last July, thus July was wet and humid. Based on data from the OARDC weather stations at Ashtabula, Columbus, Wooster, Hoytville, South Charleston and Caldwell, average July rainfall was 4.6 inches in 2010 compared to 3.5 inches in 2009. So we did have a wetter July this year than last year. However, last July was much cooler than this July, with an average temperature of 69 F compared to 75 F this year. So, although we had more rain during silking, compared to last year, temperatures during the weeks after pollination have been on average 6 F warmer. Warmer conditions are less favorable for Gibberella ear rot.

In addition, corn is further along this year than last year. Warmer conditions have also led to the rapid development of this year’s crop. This will also reduce the risk of early infection. However, another major difference between last year’s corn crop and this year’s is the fact that we have more late-planted fields this year. Some of those fields are now approaching or going through pollination, and as such, may still be at risk for early infection and Gibberella ear rot, especially if it rains in August like it did in July and conditions become cooler in August than they were in July.

So it seems like we are on track to avoid a major Gibberella ear rot problem this year, but we are not yet out of the woods. Let us now hope that dry conditions occur during harvest so that we can get this year’s crop off early, at an acceptable moisture level to minimize the chance of late infections. Part of last year’s problems resulted from the facts that, in addition to cool, wet conditions during the weeks after silking, which favored early infection, we also had wet conditions during harvest, which resulted in late infections. So, again, weather conditions during harvest will have the final say, with susceptible hybrids that dry down with the ear in an upright position at the greatest risk for Gibberella ear rot, if it does rain during harvest.

Green Cloverworm on Soybean Greenclover Worm

Green Cloverworm on Soybean

We mentioned last week in the C.O.R.N. newsletter about other states reporting significant defoliation in soybean caused by numerous lepidopteran caterpillars.  Last week while sweeping numerous fields, we noticed many with green cloverworm larvae, many more than usually seen.  These caterpillars were mainly small and medium size ones, meaning that their heavier feeding will occur over the next one to two weeks.  We suggest that growers might want to check their soybeans for defoliation and presence of green cloverworms.  When sampling for the caterpillars, remember that they are light green in color with multiple white stripes, with their main characteristic being violent shaking and wiggling when disturbed or held in your hand.   This movement is a defensive mechanism against predators. 

Although some states are having economic populations, we do not necessarily think that this will occur in Ohio.  Many of the soybeans where we found green cloverworm are quite tall and very lush, with a large amount of leaf area.   Having higher amounts of leaf area before defoliation means that there will still be a lot of leaf area left after insect feeding stops.   Thus, these lush fields have an inherent capacity to withstand more feeding.   While we still recommend using a defoliation threshold of 15-20%, remember the amount of defoliation should be estimated over the entire plant, not just the top portions of the canopy.  If only the upper leaves are defoliated, remember that sunlight will still be intercepted by the leaves in the middle portion of the canopy.   As long as 95-100% of the light is being intercepted, yields should not be affected.  See our Soybean Defoliator fact sheet at http://ohioline.osu.edu/ent-fact/pdf/0039.pdf for more information on dealing with soybean leaf feeders.

Western Bean Cutworm UpdateWestern Bean Cutworm Larvae

Western Bean Cutworm Update

Western bean cutworm adults have been tough to catch this past week signifying that the flight will be ending soon.  Our total for last week only reached 45 moths (to view a western bean cutworm distribution in Ohio go to: (http://entomology.osu.edu/ag/pageview3.asp?id=1390).  Given this sharp decrease in numbers, oviposition is about over.  At this point, scouting must concentrate for larvae which can be found on We have already been notified of ear damage in some scattered spots of Ohio, mainly Northwest OH. 

To scout for larvae in corn, look in 10 corn plants in 10 locations and inspect the leaves, leaf axils, silk and the ear itself (see lead picture, courtesy of Bruce Clevenger, Defiance County).  See our webpage for a western bean cutworm scouting video (http://entomology.osu.edu/ag/pageview3.asp?id=1465).

If larvae have not entered the ear yet, there may yet be a chance that pesticide application could provide a slight benefit (remember the 5% of infected corn economic threshold still applies), but in most cases that we’ve seen larvae are already feeding in the ear zone. 

Once larvae enter the ear, chemicals have a more difficult time to come into contact with larvae, dramatically decreasing the effectiveness of control.  However, estimating the extent of damage in corn will provide information as to where we are likely to have overwintering of western bean cutworm, and where managing this pest will become a priority.  If you find suspected western bean cutworm damage, please contact your local extension educator or entomology specialists.

NOW is the Right Time for Summer Seeding of Forages

We are now in the prime time frame for late summer seeding of forage crops.  This is true whether you are establishing new stands or need to seed in bare or thin spots in stands established earlier this year.  The following highlights key management steps toward successful establishment of forages this summer.

1. Apply lime and fertilizer according to a soil test. Since the stand will be used for several years, ideally the soil test should have been taken within the past year.

2. Control problem perennial weeds ahead of seeding. Be careful with herbicide selection because some have residual soil activity and will harm new forage seedings if proper waiting periods are not observed. Be sure to read the labels of any herbicides being considered.

3. Plant new perennial forage stands as soon as possible in August. Seedlings require at least 6 to 8 weeks of growth after emergence to have adequate vigor for winter survival. In northern Ohio, plant during the first two weeks of August. In southern Ohio, plant by August 30. Later planting may work, but there is greater risk for failure and the stand may have lower yield potential next year. The new stand should have six to eight inches of growth before a killing frost. Slow establishing species should be planted as early as possible. Fast establishing species like red clover, alfalfa, and orchardgrass can be seeded up to the dates listed above if moisture is present. Kentucky bluegrass and timothy can actually be seeded 15 days later than the dates listed above.

4. It is risky to place seeds into dry soil – there may be just enough moisture to germinate the seed but not enough to get the seeding established. Either plant soon after a rain when soil moisture is adequate, or when a good rain system is in the forecast.

5. No-till seedings conserve moisture and can be very successful provided weeds are controlled prior to seeding. Remove all straw from fields previously planted to small grains. Any remaining stubble should either be left standing, or clipped and removed. Do not leave clipped stubble in fields because it will form a dense mat that prevents good emergence.

5. If you are going to use tillage, don’t over-till and be sure to prepare a firm seedbed. Loose seedbeds dry out very quickly. Deep tillage is not ideal for late summer seedings. A cultipacker or cultimulcher is an excellent last-pass tillage tool. The soil should be firm enough that the your boot leaves a print no deeper than 3/8 inch (you can bounce a basketball on it).

6. Plant the seed shallow (1/4 to 1/2 inch deep) and in firm contact with the soil. Carefully check seeding depth, especially when using a no-till drill. A drill with press wheels provides the greatest success with summer seeding. Broadcasting seed on the surface without good soil coverage and without firm packing is usually a recipe for failure in the summer.

7. Use high quality seed of known forage-type varieties from reputable dealers. Cheap seed often results in lower yield and shorter stand life. Check out our variety performance trials and those of neighboring states at the following websites:

Ohio: http://oardc.osu.edu/forage2009/
Kentucky: http://www.uky.edu/Ag/Forage/ForageVarietyTrials2.htm
Pennsylvania: http://cropsoil.psu.edu/pdf/2009_forage_trials_report.pdf
Michigan: http://web1.msue.msu.edu/fis/

8. Make sure legume seed has fresh inoculum of the proper rhizobium to ensure nitrogen fixation. If the seed is pre-inoculated, check with the seed supplier to ensure the seed was stored under conditions that guarantees viable inoculant.

9. If planting alfalfa, don’t plant new alfalfa immediately after an older established alfalfa stand. Autotoxic compounds are released by old alfalfa plants, which inhibit growth and productivity of new alfalfa seedlings. You can seed in alfalfa in late summer to thicken up a new alfalfa seeding that was made this spring. The autotoxic compounds are not present in young alfalfa plants. They are released from older, established alfalfa plants.

10.  As the stand develops this fall, do not be tempted to harvest it. No matter how much growth accumulates, it is usually best to let the cover protect the new crowns during the winter. The only exception to the no fall harvest rule for late summer seedings is perennial ryegrass. If perennial ryegrass has tillered and has more than six inches of growth in late fall, clip it back to 3 to 4 inches in November or early December. Finally, scout new seedings for winter annual weeds in October. Apply herbicides as needed. Winter annual weeds are much easier to control in late fall than they will be next spring.

By following these guidelines, and with a little cooperation from the weather, I trust you will have a vigorous and productive new forage stand next year that should yield the same as if it had been planted this past spring.

Effect of Wheat Growth Habit, Seeding Rate and Row Spacing on Yield

Recent questions have centered around planting wheat in 15 rows. A more comprehensive wheat planting article will be included in next weeks newsletter. The following study shows the interaction of row spacing and population.

In the fall of 2008 we established a study at two locations, the Northwest branch of the OARDC and at Wooster, to evaluate the effect and interactions of variety growth habit, seeding rate and row spacing on wheat yield. The two locations were chosen because wheat plant height at the NW Branch is typically about 80 percent of the height at Wooster. We chose the Sunburst variety for its very erect growth habit, Porter Hybrids PH-47 for its intermediate growth habit and AgriPro W-1377 because of its defuse growth habit.

All three varieties are of mid-season maturity, but Sunburst is about six inches shorter than the other varieties which are relatively tall. Four seeding rates, 15, 20, 25, and 30 seeds per foot of row were planted in rows spaced either 7.5 or 15 inches apart. Both test sites were planted within eight days after the fly-safe date and winter survival was excellent at both test sites. The following table shows the effects of variety growth habit, seeding rate and row spacing on grain yield when the data from both locations are combined for analysis.

Variety

Row Spacing

Seeding Rate (seeds/ft of row)

 

 

15

20

25

30

Average

Sunburst

7.5

89.6

90.0

95.8

94.6

92.5

 

15

79.7

86.6

89.6

89.6

86.4

 

Avg

84.6

88.3

92.7

92.1

89.4

 

 

 

 

 

 

 

W-1377

7.5

83.0

88.7

88.5

90.2

87.6

 

15

75.5

80.8

81.9

82.8

80.3

 

Avg

79.3

84.8

85.2

86.5

83.9

 

 

 

 

 

 

 

PH-47

7.5

88.8

93.1

96.0

95.5

93.3

 

15

81.6

87.2

90.0

88.6

86.8

 

Avg

85.2

90.1

93.0

92.0

90.1

 

 

 

 

 

 

 

3 Variety Summary

7.5

87.1

90.6

93.4

93.4

91.1

 

15

78.9

84.9

87.2

87.0

84.5

 

Avg

83.0

87.7

90.3

90.2

87.8

 The LSD 0.10 for variety was 2.86 bu/ac indicating that W-1377 produced less yield than the other varieties. The 7.5 inch row spacing produced a significantly higher yield than 15 inch row spacing, and the two highest seeding rates produced significantly higher yields than the two lowest seeding rates. Based on this data, the most profitable seeding rate regardless of variety and row spacing was between 20 and 25 seeds per foot of row or 1,578,000 and 789,000 seeds per acre in 7.5 inch and 15 inch rows respectively. Variety, row spacing, and seeding rate would each likely have a larger effect on yield in growing seasons when yields are lower.

Unwanted Farm Pesticide Disposal Collection

The Ohio Department of Agriculture will be conducting the Clean Sweep Program at three locations in Ohio to collect old or unwanted farm pesticides.

The collections are for only farm pesticides. No paint, antifreeze, solvents, household pesticides or other non-farm pesticides will be accepted. Farmers and landowners with old, unwanted pesticides (insecticides, fungicides, insecticides, rodenticides and herbicides) are encouraged to dispose of them.

The three sites for collecting pesticides are:

Hardin County
August 5, 10:30 a.m. - 2:30 p.m.

Hardin County Fairgrounds
14134 Fairground Road
County Road 40
Kenton, OH  43326

Putnam County
August 12, 10:30 a.m. - 2:30 p.m.

OSU Extension Office, Putnam County
124 Putnam Parkway
Ottawa, OH 45875

Licking County
August 26, 10:30 a.m. - 2:30 p.m.

Ohio Department of Agriculture
8995 E. Main St.
Reynoldsburg, OH  43068

No pre-registration is required for farmers to bring farm chemicals for disposal and there is no charge. For more information, contact the Ohio Department of Agriculture, Pesticide Regulation Section, at (614) 728-6987.

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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.