C.O.R.N. Newsletter: 2015-13
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Early Insect and Slug Concerns
For a couple of weeks we have been warning about the possibility of black cutworms based on adult catches reported by surrounding states. We have begun to observe some minor feeding on corn, suggesting that the larvae are there and the worst of the damage is yet to come. We have also received some reports of slug feeding—this is no surprise given the amount of early season rain as well as the more recent precipitation over the weekend. As our crops are starting to emerge, these are prime sources of food for hungry cutworms and slugs. Now is the time to scout your fields for the presence of damage from these pests. Although all fields should be scouted, focus on those with a history of these pests, where weed control was less than effective, or with a lot of residue left on the field. The past few weeks and warmer temperatures have really gotten crops off to a good start, but with the milder temperatures predicted for this week and most of our soybean having been planted more recently (which is perhaps a greater concern for slug feeding), crops are still vulnerable and may not keep pace with feeding from these two pests. For more information on slug management, see these two videos from the Plant Management Network developed by our recently retired Extension Entomologist, Dr. Ron Hammond:https://www.plantmanagementnetwork.org/edcenter/seminars/soybean/SlugManagementSoybean/
http://www.plantmanagementnetwork.org/edcenter/seminars/corn/slugmanagementcorn/
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Wheat Disease Update: The Week of May 18 2015
The wheat crop progressed considerably over the last week and is now heading-out in some fields. In fact, some fields in southern Ohio and even fields planted early or with early-maturing varieties in the central and northern parts of the state are at the flowering growth stage or will be flowering by the end of this week. The forecast is for cool conditions and rain over the next few days, which could potentially slow down the development of the crop. Scab and vomitoxin become our biggest concerns at this time of the wheat season. Keep your eyes on the weather and the scab forecasting (http://www.wheatscab.psu.edu) and alert systems, and be prepared to apply a fungicide (Prosaro or Caramba at full label-recommended rates) at flowering. For those early-flowering fields planted with varieties that are very susceptible to scab, the risk for head scab is currently low-moderate and will likely remain low as conditions become cooler over the next three days.
So far this season, conditions have not been very favorable for the development of early-season diseases such as powdery mildew and Septoria. However, the extended cool weather and recent rainfall and high relative humidity could cause that to change. Septoria usually spreads from the lower to the upper leaves during rainy weather and develops best as temperatures between 50 to 68oC. Powdery mildew also develops well under cool conditions with high relative humidity. So monitor fields for powdery mildew and Septoria over the next week, and if lesions are seen on the leaf below the flag leaf, particularly if the variety is susceptible, a fungicide may be needed to prevent the diseases from reaching the flag leaf (the upper-most leaf of the plant) before grain-fill is complete. However, remember, applications made prior to flowering will control leaf diseases, but will not adequately control head scab.
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Updated Scab Forecasting System 2015
The Wheat Scab forecasting system (www.wheatscab.psu.edu) is up and running and is now available for use in Ohio. This is an excellent tool to help guide fungicide application decisions. Based on the flowering date of your crop and the weather conditions leading up to flowering, you can estimate the risk of scab occurring and make a timely fungicide application to reduce scab and vomitoxin. This year, the forecasting tool looks a little different, but it still works in essentially the same way. Now in addition to selecting your flowering date (day when anthers are first seen sticking out of the heads) and wheat type (winter wheat in Ohio), you can also selected the scab susceptibility of your variety. This is an interesting new feature that allows you to assess the risk of scab for varieties of different levels of susceptibility. Once you select your flowering date, wheat type, and cultivar susceptibility, color patterns across Ohio (and neighboring states) will then indicate the level of risk in the region for the flowering date you select: Red = High Risk; Yellow = Moderate Risk; and Green = Low Risk. You can then use the zoom tool to take a closer look at the risk in your area.
The commentary section at the top of the forecasting website, provides up-to-date information to help producers assess the risk of scab and decide if a fungicide should be applied. You can also gain access to these commentaries directly on your cell phone or via email. Commentaries will be updated regularly and sent directly to the emails or cell phones of those who sign up to receive the alerts. Once there is cell phone coverage and email access, you will receive the alerts anywhere in the country. You can then visit the website to see whether your crop is at risk and contact your state specialist for more information. To sign up, click on this link: http://scabusa.org/fhb_alert.php and complete the form with your name, email address, cell phone number and other requested information. You can choose whether you want to receive the scab alert via email, text message (on your cell phone), or both. You can also choose whether you want to receive alerts from all regions covered by the system or only from the Mid-West / Mid-South Soft Winter Wheat region.
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Wheat Heading Growth Stage
After seemingly being behind throughout the month of April, the wheat crop in Ohio “changed gears” over the last week and is now heading-out in some areas – do not be deceived by the fact that plants still look short in some fields. Heading will continue over the next week to 10 days across the state. This is a very important growth stage from the standpoint of disease management, since it is critical to maintain healthy heads and leaves during grain fill to enhance yield.
1- Examine primary tillers at multiple locations in the field – remove them if it makes it easier for you to examine;
2- Identify the flag leaf, which is the fourth leaf above the lowest node on the stem, and look at the position of the head in the leaf sheath of the flag leaf;
3- If the flag leaf is fully emerged with the sheath fully extended and the head is still encased and swollen in the leaf sheath, then you are still at Feekes 10, the boot stage;
4- If the first few spikelets are out of the leaf sheath then you are at Feekes 10.1;
5- If about 25% of the head is out of the leaf sheath then you are at Feekes 10.2;
6- If about 50% of the head is out of the leaf sheath then you are at Feekes 10.3;
7- If about 75% of the head is out of the leaf sheath then you are at Feekes 10.4; and
8- If the head is fully emerged (the entire head is out of the leaf sheath) then you are at Feekes 10.5;
Click on the links below for information on management practices that are recommended (or not recommended) at these growth stages: http://ohioline.osu.edu/agf-fact/pdf/0126.pdf
Video: https://youtu.be/Q6Da1HRlmV8
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How is that stand?
Some soybeans have been planted and issues have already been reported. The most common symptom is spotty areas around the field with large skips or limited emergence. Take a garden trowel and dig up a few places and try to find the seed that was placed there. Here is a review of the seedling disease issues that are common most years in Ohio.
1. The Watermolds, Pythium and Phytophthora, are very common on poorly drained, high clay soils. These pathogens love wet soil conditions. The few places in the state where saturated soil conditions have occurred are the very typical. Look for any shade of brown or tan on the seedling root or hypocotyl, the area right behind the deep green cotyledon.
2. Rhizoctonia is another foe of seedlings. Fluctuating conditions, dry to wet can sometimes favor this pathogen. This is a brick corky red color, close to a brick house on the lower stem and the roots can range from light brown to dark brown in color.
3. Fusarium graminearum or other Fusarium spp. – Fusarium tends to be bright pinkish-red and fluffy. We have found this most often in fields with a high level of corn residue.
There are other pests that will feed on the seeds and seedlings. Seed corn maggot is one, slug damage is another. Missing plants or plants with holes in leaves, cotyledons will appear differently than the sunken, rotting tissue of diseases.
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Evaluating Soybean Stand
Soybean planting is well underway throughout Ohio. The USDA National Agricultural Statistics Service reported 23% of the soybean acres were planted by May 10 (and many more acres were planted between May 10 and 18) up from 13% at the same time last year.
As soybeans are emerging, consider evaluating your stand this spring. Most are reporting good stands; however, there have been some reports of damping-off. To quickly estimate stand, count the number of plants in 69’8” of row for 7.5 inch row spacing, 34’10” for 15 inch row spacing, or 17’5” of row for 30 inch row spacing. These counts represent 1/1000th of an acre (i.e., 120 plants in 69’8” of row in 7.5 inch row spacing = 120,000 plants/acre). During the past ten years, the AgCrops Team has conducted several seeding rate trials. When planting in May, soybean yield is maximized when there is at least 116,000 plants/acre at harvest.
Keep in mind that soybean stand may look a little uneven especially in areas of Ohio that are dry. If there are gaps where soybeans have not yet emerged, dig around in the area where there are no plants. If the seed that is healthy and germinated, but just not broken through, with moisture, the soybeans should continue to emerge.
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Corn Replant Considerations
Although corn stands are looking remarkably good across the state according to most observers, there are some localized reports of growers considering replanting. Most of these replant issues appear related to the consequences of planting in wet soils.
Replant decisions in corn should be based on strong evidence that the returns to replanting will not only cover replant costs but also net enough to make it worth the effort. Don’t make a final assessment on the extent of damage and stand loss too quickly. The following are some guidelines to consider when making a replant decision.
If the crop damage assessment indicates that a replant decision is called for, some specific information will be needed, including:
Original target plant population/Intended plant stand
Plant stand after damage
Uniformity of plant stand after damage
Original planting date
Possible replanting date
Likely replanting pest control and seed costs
To estimate after damage plant population per acre, count the number of viable plants in a length of row that equals 1/1000 of an acre and multiply by 1000. Make several counts in different rows in different parts of the field. Six to eight counts per 20 acres should be sufficient. Table 4-12 in the OSU Agronomy Guide (https://agcrops.osu.edu/specialists/fertility/fertility-fact-sheets-and-bulletins/agron_guide.pdf) shows row lengths required to equal 1/1000 acre when corn is planted at various row widths.
A major consideration in making a replant decision is the potential yield at the new planting date and possibly different planting rate; this can vary depending on the hybrid used, soil fertility and moisture availability. Table 4-15 in the OSU Agronomy Guide is a chart developed by Dr. Emerson Nafziger at the University of Illinois that show effects of planting date and plant population on final grain yield for the central Corn Belt. Dr. Bob Nielsen modified this table to provide estimates of potential yield losses for planting dates in early June (on-line athttp://www.agry.purdue.edu/ext/corn/news/articles.08/delayedpltupdate-0523.html). Grain yields for varying dates and populations in both tables are expressed as a percentage of the yield obtained at the optimum planting date and population.
Here’s how these tables might be used to arrive at a replant decision (Table 4-15 from the OSU Agronomy Guide will be used in this example). Let’s assume that a farmer planted on May 9 at a seeding rate sufficient to attain a harvest population of 30,000 plants per acre. The farmer determined on May 28 that his stand was reduced to 15,000 plants per acre as a result of saturated soil conditions and ponding. According to Table 4-15, the expected yield for the existing stand would be 79% of the optimum. If the corn crop was planted the next day on May 29 and produced a full stand of 30,000 plants per acre, the expected yield would be 81% of the optimum. The difference expected from replanting is 81 minus 79, or 2 percentage points. At a yield level of 175 bushels per acre, this increase would amount to a gain of about 3.5 bu per acre.
It’s also important to note plant distribution within the row. Remember that values in replant charts like Table 4-15 from the OSU Agronomy Guide are based on a uniform distribution of plants within the row. Add a 5% yield loss penalty if the field assessment reveals several gaps of 4 6 feet within rows and a 2% penalty for gaps of 1 3 feet. Yield loss due to stand reduction results not only from the outright loss of plants but also from an uneven distribution of the remaining ones. The more numerous and longer the gaps between plants within the row, the greater the yield reduction. It’s also important to consider the condition of the existing corn.
When making the replant decision, seed and pest control costs must not be overlooked. Depending on the seed company and the cause of stand loss, expense for seed can range from none to full cost. As for the correct hybrid maturity to use in a late planting situation, continue to use adapted hybrids switching to early/mid maturities, if necessary, depending on your location in Ohio.
You also need to review herbicide and insecticide programs under late planting conditions. For instance, it may be necessary to reapply herbicides, especially if deep tillage is used. However, try to avoid such tillage depending instead on postemergence chemicals or cultivation for weed control. Concerning insect control, if soil insecticides were applied in the row at initial planting, check insecticide label restrictions before re application. Also remember that later May and June planting dates generally increase the possibility of damage from European corn borer (ECB) so planting ECB Bt hybrids is often beneficial.
The cost of replanting will differ depending on the need for tillage and chemical application. The cost and availability of acceptable seed will also be considerations. These factors must be weighed against expected replanting yield gains. If after considering all the factors, there is still doubt as to whether or not a field should be replanted, you will perhaps be correct more often if the field is left as is.
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.
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