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In This Issue:
A) Spider Mites Still Feeding
B) Current Bean Leaf Beetle Populations Concern For Later In Soybeans
C) Green Clover-Worm On Soybeans
D) Blackened Wheat Heads Caused By Sooty Mold Not Smut
E) Gray Leaf Spot Off To An Early Start
F) "Beer Can" Ear Syndrome
G) Recovery And Yield Potential Of Root Lodged Corn
H) Salvaging Drought Stressed Corn
Hot temperature along with little moisture continues in some areas of the State. A tour into the south central region of the State - especially Fayette County compares to the spider mite outbreak of 1988. Where drought conditions continue in infested areas, growers are wonder whether full field treatments are needed or a field treated earlier may need to be treated again. Fields with long duration infestations and remaining untreated are exhibiting a bronze appearance that can be readily seen while driving by at 50 miles per hour. Some fields are still green but close inspection will identify widespread infestations that may need attention in the next week or two.
In spider mite infested areas growers should recognize that infestation has likely spread throughout the field. Spots of heavy infestation in the field interior are likely where mites ballooned from the field perimeter a few generations before. The presence eggs and small mites along with foliar discoloration need continued monitoring to determine whether the situation is improving or deteriorating.
A few good rains plus some cooler evening temperatures could reduce mite activity and improve soybean development. When monitoring spider mite presence, the most important tool is a good hand lens, which will enable inspection for mite eggs. If eggs can be readily found, a new generation of mites is forthcoming. If eggs cannot be found, weather conditions may be having a negative effect on mite reproduction and their numbers may be declining.
A couple days after release of last week's CORN issue, I received a report from Curtis Young that BLB sweep net collections in some northwest Ohio sites were running 8 to 10 BLB adults per sweep. In addition, Ron Hammond (OARDC) reported some high activity from sites in the Scioto River valley where 1st generation BLB adult activity appears to have peaked.
Observations of BLB activity in Ohio during past years have demonstrated that the potential for pod injury can be linked to the population levels and development of 1st generation adult BLB. Pod feeding may occur with late 1st and early 2nd generation beetles. Significant pod injury problems occurred in 1988 and 1991, when 1st generation BLB occurred 3 to 4 weeks earlier than in years where pod injury was minimal. Pod injury problems were observed in 1994, but a dry late summer resulted in minimal development of moldy beans.
Where BLB populations are currently being collected at a rate of 6 or more beetles per sweep, defoliation resulting from foliar feeding may warrant a rescue treatment. Where BLB abundance is at about 1 to 3 beetles per sweep, defoliation will likely remain below 10 or 15%. However, when BLB abundance increases to 6 or more BLB per sweep, defoliation may exceed the threshold of 15% during bloom to pod-fill.
A report has been received from R. Hammond that 1st generation moths of green clover-worm (GCW) are now flying and abundant in some fields. Thus, second generation GCW larvae should appear within the next few weeks. In general, pathogens and other natural controls tend to lessen the impact of GCW on soybeans.
Since wheat harvest we have received a number of samples and phone calls concerned with blackened wheat heads associated with low yielding wheat fields. In every situation no smut was found on the wheat heads. Instead we identified ‘sooty mold’ caused by a saprophytic mold growing on dead wheat heads. The heads remain intact, but there is a black mold growing on the glumes and awns surface. It does not reduce yield or affect the plant in any way. The mold begins the decomposition process organic matter naturally goes through.
There are two different smut diseases that can be found in Ohio, but they are uncommon because nearly all the wheat seed planted is treated with fungicides that effectively control smuts. Loose smut causes the glumes to be replaced by smut spores so that by a few days after head emergence only a bare spike is at the top of the stem is seen instead of a wheat head. Common bunt (stinking smut) is more difficult to recognize because there is no obvious discoloration of the head. Instead the kernels are converted into ‘bunt balls’ that break open during combining and spread spores to healthy kernels. Grain contaminated with common bunt also has a very distinct rotten fish odor.
Sooty mold appears on wheat heads because the plants have been prematurely killed. There were several different problems in wheat this year that could have caused the plants to die prematurely. Most commonly premature death can be associated with root diseases.
We have identified affected plants with take-all root rot and sharp eyespot. Both of these diseases affect plants in the spring of the year and when drought conditions occur after head emergence plants die early in the grain filling period causing small shriveled kernels. If plants with sooty mold heads occurred in patches or large oval areas, root disease may have been the cause.
Besides root diseases, several virus diseases were present in the crop that could cause premature death. Most common was barley yellow dwarf, a virus disease carried by aphids. If individual heads scattered throughout the field had sooty mold, then the plants may have been killed prematurely by barley yellow dwarf.
The third major problem was late application of herbicides. Wheat advanced through its growth stages early this year due to warm weather in March and April. Unfortunately, a number of fields were sprayed for weeds at too late a growth stage. Banvel was the most common culprit causing this damage. Most wheat varieties are damaged when Banvel is applied at or after jointing growth stage (Feekes growth stage 6). The combination of these disease/herbicide problems in association with late season drought stress probably made sooty mold a more common occurrence this year than in the recent past.
Gray leaf spot is now common in most corn growing areas of the state that have had a history of this disease. In no-till, continuous corn fields near Wooster, OH, plants have gray leaf spot lesions up to the ear leaf. These fields first started pollinating last week, so plenty of time exist for significant leaf damage and yield loss.
The hot, humid conditions that have occurred over the state for the past month have provided the conditions that favor disease spread. This disease does not require a lot of rainfall; in fact rainfall is probably detrimental to spread of the spores. Research has shown that spores are produced on old corn residues during the night when relative humidity rises and spores are spread by wind currents as residues and leaves dry during early afternoon. Infection occurs when leaves are wet during the early morning; especially when dew and fog extend the time of leaf wetness to 13 or more hours per day.
At this time it is very difficult to predict the extent of gray leaf spot this year. In past years we have seen high disease levels at the end of July, but cooler conditions in August restricted further spread. The year 1995 was an exception where hot humid weather in August provided conditions for GLS to spread so that by September many fields were prematurely killed. Yield losses were as high as 50% in some fields that year. Now is a good time to scout start scouting your fields to see if a problem may be starting and how hybrids are performing.
I have received several reports during the past week of an abnormal corn ear condition in which ear length is markedly shortened. This abnormal ear stunting has been referred to as "beer can ear," or "pinched ear" syndrome.
The two key visual symptoms associated with ear stunting are ears that are much shorter than normal and a considerable section of the ear tip that has not produced kernels. This latter symptom appears to be related to poor pollination, perhaps the result of tight husks preventing and/or delaying normal silk emergence. These husks tightly cover stunted ears and may not provide adequate space for silks to emerge normally.
Corn plants with stunted ears have generally appeared healthy with normal husk formation and growth. However, husks appear somewhat pointed, probably because husks were more tightly wrapped around the much smaller ear enclosed. Ear stunting is often localized within fields (e.g. in head rows and border rows) with only a small percentage of plants (<5%) affected.
Corn ear stunting was widely observed across the Corn Belt in 1992 but has been reported on a more limited geographical since. Little is known concerning possible causes of this abnormal ear development. The problem may be related to a low temperature stress or shock during ear development (between the 6-leaf stage and 12-leaf stage). In 1992 the only common factor shared by fields exhibiting ear stunting problems was low temperature (down to near freezing) in late June during ear size determination. In 1992 no consistent relationships between soil fertility levels, herbicide programs or corn diseases were evident. Some have suggested micronutrient deficiencies associated with high pH effects may play a role. Hybrids also appear to differ in susceptibility to the problem.
Strong winds and heavy rains associated with severe thunderstorms can lodge or knock corn plants over, especially if the nodal root system is not fully developed. Recent hot, dry weather conditions and soil compaction may have inhibited good nodal root formation and predisposed plants to such wind injury. Strong winds can pull corn roots part way out of the soil; a condition referred to as root lodging. The problem is more pronounced when soil are saturated by heavy rains accompanying winds. If root lodging occurs before mid-grain fill, plants usually recover at least partly by "kneeing up." This results in the characteristic gooseneck bend in the lower stalk with brace roots providing above ground support. If this stalk bending takes place before pollination, there may be little effect on yield. When lodging occurs later in the season some yield decrease due to partial loss of root activity and reduced light interception may occur. If root lodging occurs shortly before or during pollen shed and pollination, it may interfere with effective fertilization thereby reducing kernel set. Hybrids differ in their ability to resist root lodging.
In a University of Wisconsin study, root lodging was simulated by saturating soil with water and manually pushing corn plants over at the base, perpendicular to row direction. Wind damage was simulated at various vegetative stages through silking (V10 to R1). Compared to hand harvested grain yields of control plants, grain yield decreased by 2 to 6%, 5 to 15% and 13 to 31% when the lodging occurred at early (V10-V12), medium (V13-V15) and late (V17-R1) stages.
Many questions regarding the use of corn for silage in drought-stressed areas of the state have been asked. Listed below is some information that you may find helpful.
OPTION 1. Grazing Stunted Corn certainly can be done; however, greater yield will occur by letting the plant become more mature and harvesting it as corn silage. Nitrates could be a problem but is not likely unless the animals eat the lower 1/3 of the stalk. Nitrates may actually be more of a problem if the corn is harvested as green chop or silage - IN ANY CASE, IF SUSPICIOUS OF HIGH CONCENTRATIONS OF NITRATES, USE A NITRATE ANALYTICAL PROCEDURE. Feeds can be tested for nitrate-nitrogen by most feed testing labs. The following labs, among others, can conduct the nitrate test:
Field-testing kits are available from different suppliers including
OPTION 2. Harvesting Immature Corn for Silage
| Maturity | DM | CP | NEL |
| (%) | (%) | (Mcal/lb) | |
--------- DM basis ------- |
|||
| Pre-silk | 10 | 12.4 | .65 |
| Silk | 15 | 11.3 | .65 |
| Milk | 21 | 9.0 | .69 |
| 1/2 Milk | 35 | 8.0 | .72 |
| Few ears, stunted | 25 | 9.9 | .62 |
| Non-pollinated, growth mature | 27 | 7.6 | .67 |
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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.
Contributors to C.O.R.N. this week include:
Contributors to C.O.R.N. this week include: State Specialists: Pat Lipps & Anne Dorrance (Plant Pathology), Hal Willson (Entomology), Peter Thomison (Corn Production), Jay Johnson (Fertility), Maurice Eastridge (Animal Science), Bill Weiss (Animal Science) and Mark Sulc (Forages); District Specialists: District Specialists: Ed Lentz (Agronomy), Bruce Eisley (IPM); Extension Agents: Roger Bender (Shelby), Barry Ward (Champaign), Dennis Baker (Darke), and Greg La Barge (Fulton).
Editor: Greg La Barge Web Editor: Steve Lichtensteiger
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