C.O.R.N. Newsletter 2008-14

Dates Covered: 
May 20, 2008 - May 27, 2008
Editor: 
Todd Mangen

Low Wheat Head Scab Risk

Authors: Pierce Paul, Dennis Mills

For wheat flowering on May 19, the head scab prediction tool is indicating a low risk of head scab across the state (http://www.wheatscab.psu.edu). This prediction is probably due to the fact that temperatures have been relatively low. The head scab fungus (Fusarium graminearum) can produce spores and infect across a wide range of temperature conditions, once moisture is available. However, the development of this fungus is much slower at lower temperatures and more extended periods of wetness is needed for infection to occur at lower temperatures than at higher temperatures. Most of the wheat is either at growth stage Feeke’s 9 (full flag leaf emergence; Northern Ohio), Feeke’s 10.1 (early heading; central Ohio) or Feeke’s 10.5 (full head emergence in southern Ohio), and should be flowering over the next 3 to 7 days. As the wheat gets closer to flowering and the weather changes, check the risk tool at regular intervals over the next few days to assess the risk of scab occurring in your area. This is important to help guide fungicide application decisions. Even if it is not raining on the day that your crop flowers, it may still be at risk for scab because of wet, humid conditions that occurred during the days before flowering. Remember, scab develops best when wet, humid conditions occur during the seven days before flowering, so even if it is dry at flowering, any three to six days of extended rainfall during the seven days before flowering would be enough to increase the risk of scab.

Now that we have fungicides labeled for head scab suppression, the risk tool would be of great value to help guide fungicide application decisions. Proper timing of fungicide application is critical for head scab suppression. It is extremely important to apply the fungicide at anthesis (when fresh male floral parts are seen sticking out of the heads), well before visual symptoms are seen on the heads. Symptoms usually develop about three weeks after anthesis (depending on the weather), so the risk tool can be used as a predictor of the risk of scab occurring to help guide fungicide decisions. In general, fungicides provide about 45 to 55% reduction in scab and vomitoxin, if applied at anthesis. Applications made 3 days before or 3 days after anthesis will reduce the level of suppression. For foliar disease management, the presence of lesions on the lower leaves often is used as an indication of the risk of foliar diseases spreading up the plant. Application decisions are based on the presence of lesions on the flag leaf and the leaf below the flag leaf. For head scab management, however, disease thresholds cannot be used as indicators of scab risk. In fact, by the time scab symptoms are observed, it is too late to apply a fungicide - grain DON content may already be high and all fungicides will be off label.

If applying a fungicide for head scab management, remember to leave an untreated strip in your field for comparison. This would be useful for determining how well the fungicide performs under conditions in your field.

Seedcorn Maggot in Late Planted Field Crops

Authors: Ron Hammond, Andy Michel, Bruce Eisley

We have already received reports of corn and soybean fields having stand reductions because of seedcorn maggots. These have come from fields that either had a cover crop or manure tilled into the soil. Being that there are no curative treatments at this time, many growers are considering replanting. Additionally, because of the wet and cool conditions in some parts of Ohio that have prevented planting, we are reaching a situation in many unplanted fields where weeds are becoming larger. Last week in the C.O.R.N. newsletter (http://corn.osu.edu/index.php?setissueID=228), Mark Loux discussed this latter situation and the need to apply herbicides in addition to tilling the soil. Tilling heavy weed growth can be similar to tilling a cover crop or manure in its ability to attract seedcorn maggot flies. Thus, the potential in these fields for seedcorn maggot problems is higher than if they had been tilled and planted earlier when weeds were small.

In these situations, growers should consider an insecticide seed treatment if not already on their seed. Whereas both Poncho (clothianidin; corn only) and Cruiser (thiamethoxam; both corn and soybean) do an excellent job at controlling seedcorn maggot, our studies have suggested that Gaucho (imidacloprid) does not offer acceptable seedcorn maggot control on soybean.

Bean Leaf Beetle on Soybean

Authors: Ron Hammond, Andy Michel, Bruce Eisley

With soybeans either emerging or finally getting planted, growers should plan on monitoring their emerging fields for bean leaf beetles during the rest of May through early June. Growers should realize that early season problems are unusually. If early defoliation reaches 50% or cotyledons are being destroyed, and plants appear stunted, an insecticide treatment would be recommended. Because of the limited amount of soybeans planted in some areas, there might be locations where only a few soybean fields are emerging. Remember that bean leaf beetles will tend to be most numerous in these early-planted fields. If populations are deemed sufficient to warrant treatment, a list of labeled insecticides is available at http://entomology.osu.edu/ag/545/siblb.pdf.

We know that some growers also have a concern with the beetle's ability to vector bean pod mottle virus. This concern tends to be greatest on food grade soybeans and those being grown for seed where seed quality is an important issue. The bean leaf beetle transmits this virus, especially in early season during feeding by the over-wintering beetle. If growers choose to treat the bean leaf beetle for virus control, they should spray the bean leaf beetle during the VC-V1 stage after the soybeans emerge from the soil and when beetles begin to appear in the field. Recommendations also suggest that a second spray be made in July at the beginning of the first beetle generation.
 

Insect Update

Authors: Ron Hammond, Andy Michel, Bruce Eisley

We are getting reports on numerous insect pests on field crops, including black cutworms and flea beetles on corn, aphids and cereal leaf beetle on wheat, alfalfa weevil on alfalfa, and slugs on corn and soybean. None are major problems at this time, but all require watching. With the rain and cooler temperatures this past week, neither corn or soybeans have not been growing well. If not already started, growers should begin sampling their crops to prevent unnecessary early season injury by using appropriate management tactics.

Concerning aphids on wheat, there appears to be a major push to treat for these pests. Growers should be aware that infestations great enough to cause economic damage are rare in Ohio. At the current stage of wheat growth, treatment threshold for aphids is 50-100 aphids per linear foot or row. As aphid numbers increase, we would also expect to see aphid predators and parasites in the wheat, helping to hold the aphid population below economic levels. Only if fields reach these high numbers should an insecticide become necessary. The following web site list recommended materials for field crops including small grains: http://ohioline.osu.edu/b545/pdf/b545.pdf. In terms of aphids transmitting barley yellow dwarf virus, remember that this virus is generally transmitted to the wheat in the fall or early spring before Feekes Growth Stage 4, and we are well past that growth stage. We urge growers to use IPM principles, which mean scouting and treating ONLY when necessary.
 

Should Seeding Rates be Changed for Delayed Corn Plantings?

Authors: Peter Thomison

Past university research indicates that optimal plant populations for early (mid to late April) and late planted (late May to early June) corn are similar. Based on results of these studies, most extension agronomists recommend that final plant populations should not be changed as planting date is delayed. One of the questions I’ve been asked recently is whether seeding rates should be increased for late planted corn. I’m not aware of studies in the Corn Belt that show consistent yield benefits from increasing plant population in late plantings. If planting is delayed until early June, some Ohio data suggests that certain hybrids are more susceptible to stalk lodging at high populations. In a recent OSU study, effects of early (late April) and late plantings (early to mid June planting dates) on corn response to population (24,000, 30,000, 36,000 and 42,000 plants/A) were investigated at three locations. Results suggested that final stands of 30,000 to 36,000 plants/A were required for optimal yield for the late April plantings. However, for the early to mid June planting dates, the results indicated little benefit from increasing seeding rate and a significant yield loss at plant populations above 30,000 plants/A. For corn planted late, grain yields, averaged across the three locations, were 159, 161, 133, and 138 bu/A at 24,000, 30,000, 36,000 and 42,000 plants/A, respectively. The lack of response to plant population was related to stalk lodging which ranged from 59% at 24,000 plants/A to 97% at 42,000 plants/A.

In delayed planting situations, use the optimal seeding rates for the yield potential of each field. Recommended seeding rates for early planting dates are often 10% higher than the desired harvest population. However, soil temperatures are usually warmer in late planted fields, and as a result germination and emergence should be more rapid and uniform. So, as planting is delayed, seeding rates may be lowered (decreased to 3 to 5% higher than the desired harvest population) in anticipation of a higher percentage of seed emerging.

References

Nafziger, E.D. 1994. Corn planting date and plant population. J. Prod. Agric. 7:59-62.

Nielsen, R.L. and P.R. Thomison. 2002 .Late Planted Corn & Seeding Rates. OSU Crop Observation and Reporting Network Newsletter. May 13 - 20, 2002 C.O.R.N. 2002-13
http://corn.osu.edu/archive/2002/may/02-13.html [URL verified 5/15/08].

Presidedress Soil Nitrate Test

Authors: Robert Mullen, Edwin Lentz

The presidedress soil nitrate test (PSNT) or late spring nitrate test (LSNT) is often promoted as a soil testing tool that can be used to aid in nitrogen management decisions. Soil samples are generally collected between mid-May to mid-June whenever sidedress applications of nitrogen are being made. The question is when should I use the PSNT and what does the PSNT tell me as a crop manager?

The goal is to provide better nitrogen recommendations for crop producers. Nitrogen transformations that occur in the soil are dynamic and strongly influenced by environmental conditions because it is the result of soil biological activity. The transformation we are primarily concerned with in agriculture is the mineralization of organic nitrogen to inorganic forms (initially ammonium and eventually nitrate). If mineralization rates for soils could be predicted for a given growing season nitrogen recommendation strategies could be improved. Because accurate models do not exist to quantify this phenomenon we must rely on a snapshot in time of what has occurred in the soil (i.e. the PSNT/LSNT) or some other alternative method (reference/nitrogen rich strips). The PSNT/LSNT conducted on soils that do not have a manure history or previous forage legume crop rarely return levels high enough to prompt a decision. The PSNT/LSNT is almost exclusively promoted for fields that have received recent manure applications or where corn is following a forage legume crop. Presidedress soil nitrate tests should not be taken when preplant commercial fertilizer nitrogen was applied. This can result in an elevated PSNT level indicating a low probability of nitrogen response.

Depending upon the PSNT/LSNT level we get an estimate of the likelihood of seeing a response to additional nitrogen fertilizer, but we do not get an actual nitrogen recommendation. PSNT/LSNT values near 25-30 ppm are unlikely to benefit from additional nitrogen fertilizer, and the higher the value the less likely the need for supplemental nitrogen. The problem arises when PSNT/LSNT values are less than 25 ppm. PSNT/LSNT values below this level may or may not respond to additional nitrogen fertilizer, but the stock recommendation would be that they do require more nitrogen. There can be sites that have a low PSNT/LSNT value but show no response to nitrogen fertilization. This is a major limitation of the PSNT/LSNT. Bottomline: if the PSNT values are above 25 ppm, adequate nitrogen should be available for this year’s corn crop. If it is less than 15 ppm, the normal nitrogen rate should be applied. Between 15 and 25 ppm, other factors should be considered before reduction of the normal nitrogen rate.

Weather Update

Authors: Jim Noel

Over the past week we saw 0.50 to 1.00 inch of rain in the north, 1.00 to 1.50 in central Ohio and 1.5-3.0 inches south of I-70. You can use this link to look at rainfall totals, it is updated daily http://water.weather.gov/ . You can select length of time and zoom in to an area.

What is interesting (with little rain this week) is by this weekend, Columbus will be below average rainfall for May, Dayton average and Cleveland and Cincinnati above average showing the range of rainfall this month and how wet our subsoil is from winter and early spring rains.
There will be a weak system with some showers mainly in the south late today into early Tuesday. Otherwise, mainly dry weather is on tap this week. This week can be summed up with a cool and dry week. Next week looks to be warmer with a few rain chances, but there is uncertainty in timing and amounts. Some indications are we may not see that much either, but the milder weather is a given.

The bottom line, with the high sun angle, low relative humidity and cool temperatures slowly moderating, conditions will be slowly improving.

The North American Ensemble Forecasting System calls for a 60-80% chance of 1 inch of rain through June 3rd with most of that falling after May 30th with a 20-50% chance of 2 inches through June 3rd with most falling after May 30th. The lowest chances are in the north and highest in the south.

http://www.weatheroffice.gc.ca/ensemble/produits_e.html

The future seems to have become clouded. I think it will be important to see how the next few weeks evolve. If you base your outlook on the last few weeks, you would go with persistence. However, if you base it off La Nina and current model trends, you would go with earlier thoughts of a drier June and then near normal July/August rainfall. Here is a link to the latest CPC outlooks. http://www.cpc.noaa.gov/index.php

Summary:
This week: Cool and drier
Next week: Warmer with only a few rains.
Summer Outlook: Average temperatures and rainfall from June through August with a risk of going below average on rainfall.

Distorted Wheat Leaves and Stems

Authors: Pierce Paul, Jim Beuerlein, Mark Loux, Dennis Mills

Some wheat fields in northwest Ohio are showing severely distorted leaves and stems. Flag leaves are deformed, stems are twisted with huge loops below the node, and some partially emerged heads are trapped in the sheath of the flag leaf. The problem is widespread in some fields and non-existent in others. The damage appears to be severe on some varieties, but mild or absent on others. Questions relative to this situation include the following: What is causing this problem? Why is it occurring in some fields and not in others and on some varieties but not on others? How will this affect yields?

Deformed plants at this growth stage, between Feeke’s 9 and Feeke’s 10, could be the result of several factors acting together or in isolation. In particular, low temperatures can cause leaves to be distorted and heads to be trapped in the boot. The extent of this damage depends on the variety, the growth stage of the crop, and the time of exposure to the cold temperatures. Over the past three weeks we have had relatively low temperatures across most of the state, with nighttime averages in the lower 30s in some areas. Under such conditions, varieties that are more sensitive to cold injury may show symptoms, especially in low lying areas of the field. However, in most of the fields with the reported problem, symptoms are not restricted to low lying areas, and entire fields or huge sections of fields are affected. It is possible that low lying areas were not affected differentially from other parts of the field.

Such widespread damage may be due to injuries caused by herbicides or the interaction among herbicides, and this appears to be the cause in some fields where multiple herbicides have been applied. It is highly likely that the unusual cool temperatures in May have amplified the impact of herbicides on plant growth, which is almost always present in very low levels and usually not observed. Wheat varieties are also part of the equation since they are variable in response to low temperatures and also herbicides. Because we have not experienced cold May temperatures for many years, most of our currently used varieties were not exposed to these conditions during their development so that weakness was not detected.

Many of the fields that were most severely affected were treated with a combination of Peak and 2,4-D last fall, and the use of 2,4-D in these treatments may be a primary cause of the injury. Peak is labeled for postemergence application to wheat in fall or spring, from emergence until the second node is detectable in stem elongation (Feeke’s Growth Stage 7). Labels for 2,4-D products vary in their wording on the use of 2,4-D in wheat. The more conservative labels state that 2,4-D should be applied in the spring after wheat has fully tillered, while others (including some products used in the affected fields) state that application can be made after tiller initiation with no mention of fall versus spring application. We take the more conservative approach in the “Weed Control Guide for Ohio and Indiana”, stating in the 2,4-D description that it should be applied in the spring. The reason for the more restrictive statements on some labels and in the Weed Control Guide is that there is potential for injury and yield loss from application of 2,4-D in the fall. This has been demonstrated in research conducted by OSU and at Ridgetown College in Ontario. Several products containing a mixture of 2,4-D and dicamba (e.g. WeedMaster, Brash) are labeled for postemergence application to wheat in the fall, but these labels state that there is risk of injury from fall application. Dicamba is labeled for postemergence application to wheat in the fall, and can generally be substituted for 2,4-D, especially in mixtures with Harmony Extra or Peak to improve control of dandelions and other weeds in the fall. We have not observed injury or yield loss in wheat from fall applications of dicamba.

It is difficult to say how much yield loss may occur in the affected fields. Yield loss will depend on the extent of the damage to the primary and secondary tillers. Most of the damaged tillers will probably not recover. Where the primary tillers are severely affected, yield losses could be very high, since they are responsible for 40% to 70% of the yield. Where only a few secondary tillers are damaged, losses will still occur, but they should be low. If crop damage is severe enough to warrant crop destruction, be sure to check on the crop insurance aspects. At the time of head emergence, wheat plants have taken up about half of the nitrogen to be removed, and only about 20% of the nitrogen in the wheat tissue will be available for a substitute corn crop.

Peak has residual activity in soil, and fairly long rotation restrictions for some crops. Where Peak was applied last fall and soil pH is less than 7.8, field corn or oats can be planted at this time. For any other crop or where soil pH is 7.8 or greater, a bioassay must be conducted before planting the entire field. To conduct the bioassay, take soil samples to a depth of 6 inches from treated areas at several locations within the field, and also in untreated areas (to compare plant response). Plant the intended crop into this soil, and allow plants to grow for 3 weeks. If there is no difference in growth between treated and untreated soil, the entire field can be planted.

Archive Issue Contributors: 

Pierce Paul, Anne Dorrance, and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel and Bruce Eisley (Entomology), Jim Beuerlein (Soybean & Small Grain Production), Peter Thomison (Corn Production), Robert Mullen (Soil Fertility), Mark Loux (Weed Science), Ed Lentz (Agronomist) and Jim Noel (NOAA). Extension Agents and Associates: Roger Bender (Shelby), Howard Siegrist (Licking), Glen Arnold (Putnam), Greg LaBarge (Fulton), Harold Watters (Champaign), Mike Gastier (Huron), Mark Koenig (Sandusky), Wes Haun (Logan), Marissa Mullett (Coshocton), Jonah Johnson (Clark), Ed Lentz (Seneca), Bruce Clevenger (Defiance), Les Ober (Geauga), Steve Bartels (Butler), Steve Prochaska (Crawford), Alan Sundermeier (Wood), Gary Wilson (Hancock), Todd Mangen (Mercer) and Tim Fine (Miami)

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.