C.O.R.N. Newsletter 2010-18

Dates Covered: 
June 21, 2010 - June 29, 2010
Editor: 
Jon Rausch
Is this a year for white mold?  White Mold on soy stem

Is this a year for white mold?

There are no tried and true solid prediction systems, currently for white mold development on soybeans.  However, conditions exist in the state similar to last year – with one key difference, it is hotter this year and moisture levels have been exceedingly higher in some parts of the state. White mold infections are favored by consistently damp conditions (not flooded) from the time of canopy closure through flowering. These conditions favor the development of the fruiting structures, called apothecia, which form from those overwintering or survival structures called sclerotia. Sclerotia are the hard, black, irregular shaped fruiting bodies that form on and in the soybean plant. IN many cases they look just like rat and mouse droppings but the difference is they are pink or white on the inside. Once these very small sclerotia germinate, the spores are deposited on the dying blossoms and from there they can infect the plants.

apothecia Western

 Not all fields in Ohio have inoculum for white mold.  IN general, there are some fields that have a consistent history of the disease and it tends to be in pockets – fields that have poor air drainage, high yielding, and high plant populations.

For those high yielding, high value soybeans, in areas of the state where this is a constant issue, this is the time to consider a fungicide. Applications should be made at the R1-R2 phase. At this time, only Topsin M is labeled for control of this disease. We have seen this work, when conditions are favorable at the early flowering stages. If the following conditions occur through flowering a second application is necessary at the R3 stage: weather pattern of cool nights, light rains, and heavy dews. However, if temperatures hit the high 80’s and dews do not form, these conditions are not favorable for disease to develop and the fungus will just sit there.

There are several other management measures that have been touted for Sclerotinia stem rot and white mold of soybean.  Some have secondary effects that contribute to yield loss due to the late application time (Cobra) while others only reduce disease levels slightly based on some data from other states.  The best disease management strategies for this disease are resistant varieties, reduced plant populations (<160,000 plants/acre) and 15” row widths. Putting some numbers on paper and calculating out the cost of application based on how the field looks, reduced yield due to application will help you make these types of decisions. Late planted fields that have been hit repeatedly with rains and have poor root development are probably best left alone. Putting more money into these fields is like keeping that old truck going – with all of the repair costs you could have bought a newer better truck!

sclerotinia apothecium

Micronutrient Availability Issues with Increasing Soil pH

Micronutrients are those plant-essential elements that are needed in relatively small quantities, and include a lot of the trace metals we hear about, like manganese, zinc, and iron.  As with other nutrients, the availability of these nutrients in soil solution is  dependent on pH of the soil (moisture level, organic matter, soil texture, drainage, and plant development are other factors).  Growers who over-apply lime or frequently use poultry litter (from layer operations specifically) year after year may see soil pH levels creeping up to 7.0 or higher.  Though molybdenum, calcium, and magnesium are abundantly available at pH 7.0-7.5, the availability of iron, manganese, copper, and zinc decreases.  Iron deficiencies are relatively rare in Ohio, but do occur on occasion (usually with very high pH soils), and we do see manganese deficiencies in soybeans (primarily on high organic matter soils), copper deficiencies in wheat (coarse textured soils with high organic matter), and zinc deficiencies in corn. 

Tissue sampling is a method to determine content of these elements in the plants, and will guide the necessity of foliar fertilizers to remediate deficiencies (since only small quantities of the nutrient are needed).  One can take samples from non-symptomatic parts of the field as well as those where deficiencies appear to make a comparison.  Soil testing both areas will yield more information as well.  For the relatively low price of lab analysis, one will be much better equipped with information to make decisions on the land, and OSU recommends soil testing each field every three years.  If high pH is noted in fields, it may make sense to cut back on land application of materials that raise pH above recommended levels (> 6.8 in mineral soils).

For more information:

Ohio Agronomy Guide section on nutrient availability and pH: http://ohioline.osu.edu/b472/0004.html

Western Bean Cutworm Flight Has BegunDefiance Western bean cutworm

Western Bean Cutworm Flight Has Begun

Last Friday morning, June 18th, a single western bean cutworm moth was caught in a milk jug trap in Defiance Co.  Last year, our first moth was collected on June 19th, so we have seen a relatively consistent start of western bean cutworm flight in Ohio for the past 2 years.  There is still time to place traps in your cornfields, see our article on June 8 for instructions.  Normally, we recommend scouting corn for eggs and larvae when moths are collected on consecutive nights.  Based on previous years, egg and larvae scouting usually begins in early July or mid July during peak western bean cutworm flight.  Stay tuned to this newsletter, as well as our website (http://entomology.osu.edu/ag/), where we will upload catch maps weekly.  As our trap counts increase during the course of the summer, we will provide updates on when and where egg and larvae scouting should begin.

Cereal Leaf Beetle Adults in Corn

Previously, we discussed the cereal leaf beetle concern on cereal grain including wheat and oats this past spring.  On those crops, it was the larvae which caused the damage.  However, with their adults emerging soon, we will begin seeing adult cereal leaf beetles feeding on corn leaves.   Adults (http://entomology.osu.edu/ag/images/cereal_leaf_beetle_adult.pdf) will feed on available crops, most notable corn, before they go into a type of hibernation for the remainder of the summer and then winter.  This feeding will often be heaviest along the edges, especially in those fields that are across the road or adjacent to wheat or oat fields where the population had built up.  We would remind growers and scouts that this feeding is usually superficial unless the injury is extremely heavy.  Recommendations for treatment are only when feeding is greater than 50% over the entire plant, the corn is under stress, and beetle populations are extremely large. Because this seldom if ever happens, nothing should usually be done. The feeding will then end shortly.Cereal Leaf Beetle

True Armyworm in Corn armyworm feeding

True Armyworm in Corn

A question came up this past winter as to transgenic corn’s ability to control the true armyworm, whether if the corn is planted adjacent to wheat and armyworms migrate into it, or when corn is planted into a rye cover crop which is the most common situation where we see heavy armyworm damage in Ohio.  We currently have studies examining this.  We would like to hear from extension educators, crop consultants, growers, and others about what they are seeing in the fields.  If you are aware of or have a true armyworm problem in corn, please contact us at hammond.5@osu.edu and let us know what type of corn hybrid was planted.  We would like to know whether it is a Bt corn hybrid or not, and if so, the type of Bt trait.  This information will allow us to match up what is happening in the field with what we are seeing in our tests.

Harvesting Wheat from Scabby Fields

Care should be taken when harvesting wheat from scab-infected fields to reduce the amount of scabby kernels and level of vomitoxin in the harvested grain and avoid potential health problems for combine operators and grain handlers. Scabby wheat is heavily contaminated with mycotoxins, especially vomitoxin, that are harmful to humans. Here are a few harvest tips to minimize problems and losses:      

1-      Avoid breathing in dust from scabby wheat fields by using a dust mask. The harvest operation usually produces huge dust clouds. In the cloud coming from scabby wheat fields are spores of the scab fungus (Fusarium graminearum) and small pieces if scab-infected and vomitoxin-contaminated plant parts. Inhaling these particles may cause health problems.    

2-      Turn up the air on the combine to blow out scabby kernels. These kernels are usually lighter in weight than non-infected or healthy kernels and as such will be blown out of the back of the combine if the air is turned up, reducing the amount of scabby kernels and vomitoxin in the grain lot.

3-      Harvest areas or fields with the most scab first and keep that grain separate from the rest. Since the level of vomitoxin in infected grain may increase if the grain is exposed to wet conditions leading up to harvest, if rain is in the forecast, it may be better to harvest scabby fields at a slightly higher moisture content than to wait for grain to dry down completely in the field. However, this grain still needs to be dried down and maintained below 15% moisture after harvest to prevent fungal growth and vomitoxin buildup in storage.         

4-      Get grain from scabby fields tested for vomitoxin before feeding, before making a decision to discard suspect grain, or before blending.

Sampling and Testing for Vomitoxin

Wheat harvest is about to begin and since we have had fairly high levels of scab in some fields this year, elevators will be testing grain for vomitoxin (deoxynivalenol or DON). Because of the negative effects of this toxin on humans and livestock, the U.S. Food and Drug Administration (FDA) has set strict advisory limits for DON to insure the safety of the food and feed supply. Based on these limits, grain may be priced down or rejected completely at elevators if DON levels exceed 2 ppm. For bran, flour, and germ intended for human consumption the limit is 1 ppm; for grain and grain by-products destined for consumption by ruminating beef and feedlot cattle older than four months, and chickens the limit is 10 ppm, with the added recommendation that ingredients with 10 ppm DON should not exceed 50% of the diet for cattle or chicken; for grain and grain by-products destined for swine, and all others animals the limit is 5 ppm, with the added recommendation that ingredients with 5 ppm DON should not exceed 20% of the diet for swine and 40% of the diet for other animals.  

Adequate sampling and testing of grain are critical to determine whether vomitoxin is below advisory levels before using or feeding grain. The number of scabby heads in a field and number of scabby spikelets per head are highly variable. As a result, scabby kernels and vomitoxin levels vary considerably within the grain lot, leading to highly variable test results. Careful attention should be given to sampling in order to accurately quantify vomitoxin levels. Before pulling samples to test for toxins, grain handlers should first protect themselves from dust and toxin exposure by wearing a mask, goggles and gloves. Sampling and testing guidelines are available at the United States Department of Agriculture Grain Inspection, Packers and Stockyards website at http://www.gipsa.usda.gov/GIPSA/documents/GIPSA_Documents/don.pdf.

 To collect a representative sample from the bin or truckload of grain, 5-10 subsamples should be randomly collected from multiple locations. Samples taken only from the central or outer portions of the load or from the beginning and end of the grain stream will not provide an accurate estimate of toxin contamination. For end-gate sampling, sample from the entire width and depth of the stream. For probe sampling, use hand or mechanical probes to sample from the entire load, in an “X”-shaped pattern, for example. The use of suction or air probes is not recommended when sampling grain for mycotoxins. Scabby kernels are lighter in weight than healthy kernels and usually contain high levels of vomitoxin. Air probes will pull these kernels and overestimate the overall vomitoxin level in the lot. Once subsamples are obtained, bulked, and cleaned, the grain must be ground uniformly, in a clean grinding apparatus, to resemble flour. Finer particle size increases surface area of the grain and allows for more efficient extraction of vomitoxin. 

The most common test for vomitoxin is an ELISA test. ELISA-based tests are generally qualitative, providing a yes/no answer for the presence of DON, or semi-quantitative, giving an estimate of DON above certain levels or within a given range. However, quantitative estimates can also be obtained using some ELISA-based test. ELISA’s are easy, quick and affordable, but must be performed carefully to ensure quantifiable and accurate results. Due to the test’s specificity, you must use an ELISA kit specifically designed to detect vomitoxin.

Poor sampling and/or testing technique may lead to incorrect estimation of vomitoxin in the grain. If you have doubts as to whether your grain was sampled and tested correctly, you may request that a second sample be drawn and sent for testing at a certified laboratory. Following vomitoxin testing, producers/agents have the right to reject the commodity testers’ results and order the handler to send the sample to a federally licensed grain inspector for a re-test. Refer to Ohio Code 926.31 for details.

A listing of toxin testing laboratories can be found at: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/mycotoxin%20text2.htm

Shrivels, lightweight Wheat Grain: Stagonospora or Scab?

This year we have seen quite a bit of Fusarium head blight (head scab) and Stagonospora leaf and blume blotch in our wheat fields. Some fields have scab, some have Stagonospora, while others have both diseases. At high levels, both scab and Stagonospora are capable of causing substantial losses, reducing grain yield and test weight. For Stagonospora, the earlier the disease occurs during grain fill, the greater the yield and test weight reductions. Late occurrence of Stagonospora glume blotch will have less effect on yield, but may still reduce test weight if infection levels are high.

Losses to scab and Stagonospora are due largely to the fact that kernels from heavily infected fields are usually small, shriveled, and lightweight. The easiest way to tell whether kernel damage was caused by scab or Stagonospora is to know whether the field was infected with scab alone or Stagonospora alone. However, based on the appearance of the kernels, it is fairly easy to tell the difference between kernel damage caused by scab and Stagonospora. 

The telltale symptom of scab damage is the white, chalky color of the kernels with tinges of pink. This is usually referred to tombstone kernels. Scabby wheat kernels

For Stagonospora, the kernels are usually small and shriveled without the white chalky or pinkish appearance. While both diseases may lead to price discounts due to low test weights, scabby grain may also be discounted or rejected at elevators because of high levels of vomitoxin. So, it is important to know the difference as you harvest your fields. Stagonospora kernels

Healthy kernels are usually plump, without discoloration.

healthy kernels

Weather Update

The outlook in the coming weeks into July is for continued above normal temperatures. June is already running about 4 degrees above normal and I see no change in that area. With all the rain this spring and early summer, it is holding up minimum temperatures. Expect high temperatures to be only slightly above normal but nighttime lows well above normal. This translate into lots of highs between 85-95 and lows 65-75.

As we talked about in the past weeks and months, rainfall is the tough call this summer. It looks like the trend is for near normal to slightly above normal rainfall, but the above normal rainfall will be in streaks and not uniform. The favored areas to heaviest rain will be across northern and western Ohio. The bottom line is at least near normal rainfall is expected in the next 2-4 weeks but we will continue to watch for any shutdown in the rainfall pattern. I do not really see that in the next 2-3 weeks though.

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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.