C.O.R.N. Newsletter 2009-07

Dates Covered: 
March 30, 2009 - April 7, 2009
Harold Watters

Correction for Last Issue on the Foliar Use of Fungicides in Ohio

Authors: Harold Watters

Correction to an article in the last newsletter on fungicide use in Ohio: http://corn.osu.edu/story.php?setissueID=283&storyID=1688. We inadvertently left out one word that changes the meaning of one sentence significantly.
“Across the Midwest and in Ohio specifically, in replicated trials (both on-farm and in research plots) we have not been able to show large increases in yield due to the control of disease ("not" added for correction March 18, hdw). For soybeans brown spot and frogeye leaf spot severity was reduced when Headline® and other strobilurin type compounds were used on HIGHLY susceptible soybean varieties. Only 3 out of 31 on-farm trials from 2004 to 2008 were able to recoup the costs of the fungicide, let alone see any profit. In all three cases, foliar diseases had reached the mid to upper canopy, the key leaves for yield in soybeans.”

Wheat Heaving and Root Diseases in Ohio in 2009

Authors: Dennis Mills, Pierce Paul, Jim Beuerlein

Wheat in Ohio is at the "green-up" stage, and it is time for growers to evaluate plant stands for adequate yield potential. We look for a minimum stand of 12 tillers per foot of row, but we like to see 20 or more per foot of row. This time of year marks the start of possible stand losses from heaving -- a situation where ground freezing and thawing pushes the plant crowns and roots to the surface. The result of heaving is the desiccation and eventual death of the plants.

Plants generally do not show stress until the temperatures warm and they begin to grow. By late March, growers begin to see these plants turn color and report that the wheat is 'going backwards. This is because it generally takes several weeks for heaved plants to show water stress and die.

Plants with the crown heaved out of the soil, have almost no chance of survival. Heaved plants with the crown still in the soil have the potential to develop new roots and produce some grain. Depending on soil type, soil moisture and degree of heaving, there is a slight chance that rolling the field may save much of the stand, but a good outcome is still a long shot at best. While no-till doesn’t guarantee the elimination of heaving, no-till seeding to the proper depth of 1.0 – 1.5 inches, will reduce heaving by more than 90 percent.

While observing fields for heaving, it would be a good time to look for root and seedling disease problems. If there are low-lying areas in the field or areas with unhealthy-looking plants, remove a few plants from those areas and observe the roots and crowns for discoloration. Gently remove (preferentially by washing) the dirt from the roots, and look for darkish areas or lesions. Healthy roots and crowns typically have a milky-white color, compared to the dark discoloration usually seen on infected roots. Remember, it is not uncommon for the older, lower leaves of the plant to die at this time of the year. If these plants are not completely heaved out of the ground and the root systems are healthy they will likely recover to produce grain.

Importance of Knowing the Growth-Stage of Wheat

Authors: Pierce Paul, Dennis Mills, Mark Loux, Edwin Lentz

Adequate timing of nitrogen, herbicide, and fungicide applications is important for a successful wheat crop and depends on correct growth stage identification. Failure to correctly identify these growth stages may lead to inadequate timing of applications, which may result in violation of pesticide label restrictions (products being applied off label), inferior efficacy, and injury to the crop.

Growth staging wheat in early spring involves identifying and counting leaf and nodes on the main tiller. Coming out of the winter, the crop is usually between Feekes growth stage 3 and 4. Warmer temperatures and precipitation in the spring will favor rapid growth and development. Wheat in northern Ohio is currently at, or will soon be at, Feekes' growth stage 4 to 5 when the leaf sheaths begin to become erect. Early planted fields in southern Ohio are at Feekes’ GS 5. Each wheat plant now consists of a number of tillers and will continue to develop new tillers until the stems begin to elongate (growth stage 6) or day length exceeds 14 hours. Tillers with at least three leaves have the potential to develop heads, but the actual number of heads produced per plant will depend on weather conditions in late April and early May and the level of fertility.

One of the most important growth stages for early management decision making is the end of tillering and the beginning of stem elongation or jointing (Feekes' growth stage 6). Depending on spring temperatures, growth stage 6 generally occurs around April 20 in southern Ohio and the end of April in northern Ohio. This growth stage is identified by examining the larger tillers in the fields for the first node. Dig up plants from multiple locations in the field, remove secondary (smaller) tillers, and observe the main stem. Strip down the lower leaves and leaf sheaths to check for the presence of the first node at the base of the stem. The node typically appears as a small, slightly swollen region, of a slightly different shade of green from the rest of the stem, at about an inch or so above the soil line. It can be felt by gently running the fingers up and down the base of the stem. If the first node is found, then the crop is at Feekes 6. All top dressed nitrogen should be applied by this time in order to maximize yield. This is also the growth stage at which dicamba herbicide can no longer be applied.

Weed control in wheat

Authors: Mark Loux

Herbicides should be applied soon to minimize the impact of winter annual weeds on wheat growth and development. Herbicides will be most effective where it is readily apparent that plants have resumed active growth. Winter annual grasses, such as downy brome, cheat, annual bluegrass, and annual ryegrass, should be controlled as soon as an inch of new growth has occurred. The wheat herbicides available for control of grasses, Axial, Maverick, Osprey, and Olympus, are most effective when applied in the fall, and effective spring activity is dependent upon the weeds being small. Winter annual grasses are not nearly as prevalent as winter annual broadleaf weeds, though, and the major problems in many fields consist of chickweed, purple deadnettle, henbit, marestail, etc. While several herbicides are available for control of winter annuals, Harmony Extra, Nimble, or TNT Broadleaf should be included where control of chickweed is desired, since these are the only herbicides that control this weed. Nimble and TNT Broadleaf are 75%DF generic equivalents of Harmony Extra TotalSol, which is a 50%DF.

Most effective control of dandelions will occur when they have resumed active growth, and it is still too early for control of Canada thistle and early-season summer annual weeds. Control of dandelion is generally variable in spring. We have had the best results with combinations of Express and 2,4-D, but this may not result in more than about 70% control. Fields treated at this time for winter annual control should be scouted again later in April to determine if later-emerging populations of summer annual weeds, Canada thistle, wild garlic, or other weeds require another herbicide treatment. In fields without many winter annuals or dandelions, the best advice may be to delay herbicide application until later in spring, and select herbicides based on scouting.

Be sure to follow label guidelines to minimize risk of crop injury and yield loss. Labels for some products specify the number of tillers or leaves that wheat should have before treatment is allowed. All labeled wheat herbicides can be applied prior to jointing, but the number of herbicide options decreases as wheat progresses through jointing and more advanced growth stages. Wheat should be dissected to determine growth stage, because size is not a good indicator of stage. Weather and soil conditions can affect the risk of crop injury from certain herbicides. Injury from ALS inhibitors (Harmony Extra, Express, etc) is more likely when wet soils and cold temperatures are inhibiting wheat growth.

Most herbicides can be applied using 28% UAN as the spray carrier, although some labels do not provide much guidance on this. Results of OSU research indicate that wheat should tolerate application of herbicide in 28% UAN well into April, as long as the restrictions on herbicide labels relative to wheat growth stage are followed. For products that are applied with surfactant, consult labels about the surfactant rate when applying in water vs 28%, since surfactant rates may be reduced to minimize the risk of injury when applying in 28%. Guidelines and effectiveness ratings for wheat herbicides can be found in the 2009 Weed Control Guide for Ohio and Indiana.

Considerations for Selecting Phosphorus and Potash Rates

Authors: Robert Mullen, David Henry, Keith Diedrick

On calling your fertilizer dealer for the latest prices, you may experience sticker shock and think about cutting rates of these pricey inputs. What should you think about when making rate decisions?

First of all, what does your less-than-three-year-old soil test show? The best (and rather inexpensive) tool we have for making input decisions is a recent soil test report from a reputable lab. If you are well above the critical levels of P and K (30 pounds P2O5, 225 pounds K20), or have applied manure in the recent past, you are unlikely to benefit from additional P and K inputs. If you are right at those critical levels, consider an application of some P and K (see Tri-State Fertilizer Recommendations), since your soil test report is an average; some parts of the field are above that test level and some are below. We want to make sure that the lower-testing soils in the field are getting sufficient P and K nutrition. These additional materials in the higher testing areas are not lost and are available for future crops.

Secondly, if funds are limited, purchase inputs for the nutrients that are most limiting. More benefit per pound of fertilizer is realized at the lower soil test levels than those with higher test levels, that is, 50 pounds of P from MAP or DAP will have a greater benefit to the crop in terms of yield at soil P levels of 8 pounds versus 30 pounds per acre. For example, if P is cheaper per pound than K, spending the same amount for fewer pounds of K may produce more of a positive crop response than supplying P if initial P levels are closer to the critical soil test level.

Thirdly, shop around and consider all sources of the inputs in terms of cost per pound. The actual form of P or K is not terribly important, as most commercial fertilizers become plant available in the soil quickly. See our article on phosphorus forms and formulations (http://corn.osu.edu/story.php?setissueID=280&storyID=1665) for more information on this topic. Please note, that even though rock phosphate is inexpensive compared to MAP and DAP, it is not a recommended P source for land application as it is not water soluble, thus, unusable by plants.

Ten Proven Practices for Increasing Corn Yields

Authors: Peter Thomison

Shooting for high corn yields is a topic of perennial interest to corn growers. It’s received even greater attention in recent years as more new technologies have been introduced. According to some agronomists we’ve entered a new era characterized by a higher annual rate of yield improvement that can be largely attributed to higher yielding genetics that withstand various crop stresses better and transgenic traits that enhance crop tolerance to stress conditions. However in order to exploit the yield potential that the new technologies offer, growers need to follow proven cultural practices that are the foundation for successful corn production. The following are ten proven practices for increasing corn yields.

1. Know the yield potential of your fields, their yield history, and the soil type and its productivity.
2. Choose high yielding, adapted hybrids. Pick hybrids that have produced consistently high yields across a number of locations or years. Select hybrids with high ratings for foliar and stalk rot diseases when planting no-till or with reduced tillage, especially after corn. Select high yielding Bt rootworm resistant hybrids when planting after corn or where the first-year western corn rootworm variant is present.
3. Follow pest management practices that will provide effective, timely pest control – especially weed control.
4. Aim to complete planting by May 10. If soil conditions are dry, begin planting before the optimum date but avoid early planting or poorly drained soils. If planting late (after May 25 in central Ohio) plant corn borer resistant Bt hybrids.
5. Adjust seeding depth according to soil conditions. Plant 1 1/2 to 2 inches deep. Monitor planting depth periodically during the planting operation and adjust for varying soil conditions. Make sure the planter is in good working order. Inspect and adjust the planter to improve stand establishment. Slow down (4 1/2 to 5 mph) to optimize seed placement. Uneven emergence affects crop performance because of competition from larger, early emerging plants.
6. Adjust seeding rates on a field by field basis. On productive soils, which average 175 bu/A or more, final stands of 30- 32,000 plants/acre or more may be required to maximize yields.
7. Supply the most economical rate of nitrogen. Use an application method that will minimize the potential loss of N (incorporation/injection, consider stabilizers under high risk applications, etc.).
8. Utilize soil testing to adjust pH and guide P and K fertilization. Avoid unnecessary P and K application. High soil tests do not require additional inputs.
9. Perform tillage operations only when necessary and under proper soil conditions. Deep tillage should only be performed when a compacted zone is detected and soil conditions are dry (usually late summer).
10. Take advantage of crop rotation - corn grown after soybeans will typically yield 10-15% more than corn grown after corn.

These are by no means the only management practices with which growers need to be concerned but they are keys to achieving high corn yields.

New Ohio Nitrogen Recommendations Available Online

Authors: Robert Mullen

Ohio State University has recently updated the Economic Nitrogen Recommendations and they are now currently available online at https://agcrops.osu.edu/fertility/. Use of the Excel spreadsheet has not changed over the last few versions, all you have to enter as a user is the current corn price and nitrogen cost. For more information on how to use the spreadsheet, there is a pdf document (https://agcrops.osu.edu/fertility/documents/Users_guide_03_06.pdf) available online to provide you directions.

Soybeans: When to use a fungicide seed treatment and which seed treatment should you use?

Authors: Anne Dorrance

Unlike many areas of the Midwest, seed treatments have routinely returned money on the investment under Ohio soil conditions. Our soils are heavy, drain poorly, and are easily compacted. These 3 factors all favor soil borne pathogens that attack seeds and seedlings. The key culprits for soybeans are the water molds which are Phytophthora sojae and Pythium irregulare, Py. ultimum var ultimum, Py. ultimum var sporangiferum, Py. dissoticum along with 15 other species. In addition to these watermolds, Fusarium graminearum (the wheat head scab fungus) and Rhizoctonia solani are the two next most prevalent. In regions of the state that have suffered from drought, Macrophomina phaseoli which causes charcoal rot may also be impacting seedlings. Charcoal rot is very common in areas like Kansas, southern Indiana, and southern Illinois. Symptoms for many of these are the typical dying seedling that is lying croaked on the soil surface. The identification of many of these pathogens has to come as the seedling is dying or the symptom is just a lesion on the roots or hypocotyl. For clear cut identification we plate these out on agar in the lab as many symptoms are the same for all of these pathogens.

Are seed treatments necessary? For those fields which have had a difficult time establishing a stand the answer is an unequivocal YES! If planting has become an annual ritual of replanting 2 to 3 times, then the seed should be treated. This is an indication that the pathogens have built up in population and are present and ready to go. Fields that are no-till and are in a continuous soybean rotation – the seed for these fields should also be treated with fungicide as they are production practices that favor survival of these pathogens. Fields with a history of Phytophthora sojae, in particular, require treatment with mefenoxam or metalaxyl at the high rate of the fungicide. Fields that are well drained and have never had to replant, the answer is probably no and there are a few areas of the state that we don’t recommend treating seed with fungicide prior to planting.

There are fewer seed treatment fungicides readily available for seed treatments than there were five years ago. In addition, any one active ingredient will only manage a small segment of the total seedling pathogen profile that may exist in a given field. Therefore it is important to select a fungicide seed treatment that is comprised of one or more of the following products. Metalaxyl (Allegiance) and mefenoxam (ApronXL) are effective at controlling Phytophthora sojae and some of the Pythium spp. Stobilurin compounds that are labeled for soybeans are effective at controlling more of the Pythium spp.. Fludioxinil (Maxim) controls both Fusarium graminearum and Rhizoctonia solani. There are older fungicides like Captan and Thiram that also control a number of pathogens but these also have additional issues with regards to the treatment process. We are currently in the process of evaluating the efficacy of several newer materials across this broad range of soybean seedling pathogens. The good news is that there are a number of newer materials coming down the pike that look exciting but these will not be labeled for a few years.

Don’t forget the inoculant! For a number of years, Dr. Jim Beuerlein has evaluated these and they have provided a return on investment. If you are applying inoculant at the same time as the seed treatment be sure that it is a safe combination.

Planting soybeans in Ohio is tough, especially when it is one of those years when there are only 5 good days to plant between April and the end of May. Our soils are a bit more challenging and take some special care and they do favor the pathogens. A good seed treatment package that covers the bases and is applied correctly at the correct rates will go a long way to alleviating replant issues later on.

Revised soybean disease fact sheets now available

Authors: Dennis Mills

The following soybean disease fact sheets have just been revised and are now available as PDF files on Ohioline http://ohioline.osu.edu/ac-fact/index.html

Phytophthora Damping Off and Root Rot of Soybean AC-17-09
Brown Stem Rot of Soybean AC-35-08
Phomopsis Seed Rot of Soybeans AC-36-09
Sclerotinia Stem Rot (White Mold) of Soybean AC-45-08
Soybean Cyst Nematode AC-39-08
Charcoal Rot of Soybeans AC-47-09

Archive Issue Contributors: 

State Specialists: Peter Thomison (Corn Production), Jim Beuerlein (Small Grain & Soybean Production), Anne Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Ron Hammond and Andy Michel (Entomology), Mark Loux (Weed Science), Robert Mullen, Keith Diedrick and David Henry (Soil Fertility). County Extension professionals: Mark Koenig (Sandusky), Jonah Johnson (Clark), Roger Bender (Shelby), Harold Watters (Champaign), Les Ober (Geauga), Steve Foster (Darke), Greg LaBarge (Fulton), Glen Arnold (Putnam), Tim Fine (Miami), Flo Chirra (Williams), Wesley Haun (Logan), Bruce Clevenger (Defiance), Howard Siegrist (Licking), Ed Lentz (Seneca), and Mike Gastier (Huron).

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.