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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2010-10

Dates Covered: 
April 26, 2010 - May 3, 2010
Steve Prochaska

Wheat Approaching Flag Leaf Emergence: Foliar Disease and Cold Temperature Injury Concerns

SCOUT FOR FOLIAR DISEASE: The wheat crop is already at Feekes 8, flag leaf emergence, in some parts of southern and central Ohio and will reach this growth stage within the next 7 to 10 days in northern counties. Foliar diseases such as powdery mildew and Septoria leaf blotch are beginning to show up and Feekes 8 is an important growth stage for making fungicide use decisions to manage these diseases. Scout wheat fields to determine which disease is present and at what level before making a decision to apply a fungicide. Although several fungicides are available to control foliar diseases in Ohio, the decision to use these products should be based on the susceptibility of the variety planted, the level of disease in the field, weather conditions, the yield potential of the field, fungicide cost, and the market price of wheat. 

Powdery mildew is important during the month of May and early June in mild seasons with high relative humidity. There are many varieties grown in Ohio that are susceptible to powdery mildew, so under mild conditions with temperatures in the 60's and low 70's and high humidity the disease can develop rapidly. Plan to scout those fields planted to susceptible varieties because these are the fields most likely to sustain yield loss. Research has shown that if disease affects the upper two leaves by heading, yield losses can be as high as 25% on susceptible varieties. Scout fields by pulling about 50 individual tillers randomly from throughout the field and look for the small white pustules on the lower leaves and leaf sheaths. Evaluate individual tillers by looking at the top (flag) leaf, then the second leaf. One percent of the leaf area (about 2-3 mildew pustules) on the second leaf between growth stage 8 (flag leaf emergence) and 10 (boot) is the threshold level for applying a fungicide. By the time the second leaf becomes infected, the lower leaves generally have a lot of mildew on them. Fields that needs a fungicide application will have lots of powdery mildew in the lower canopy, but mildew becomes an economic problem only if the disease advances to the upper leaves before flowering. Yield responses to fungicide application are generally dependent on the amount of disease on each plant, how early disease attacks the upper leaves and the level of susceptibility of the variety to the disease. If powdery mildew is present in a field planted to a susceptible variety you should watch its development over the next week or so and decide whether fungicides should be applied. 

Stagonospora leaf and glume blotch is most severe when frequent rains occur during the months of May and June. Scout fields between growth stages 8 (flag leaf emergence) and 10.5 (full head emergence) and if 1 to 2 lesions are detected on the leaf below the flag leaf on a susceptible variety, fungicide should be applied. 

Remember, for foliar disease management (powdery mildew, Septoria, Stagonospora and Rust) fungicides are usually not needed when resistant varieties are grown. An updated list of fungicides registered for wheat disease management can be found on the field crops disease web site at . 

COLD TEMPERATURE CONCERNS: Colder weather is forecasted for later this week and this has prompted some concerns about possible injury to the wheat crop. Once it warms up in the spring and the wheat starts to grow, it loses its cold-temperature hardiness, becoming more prone to injury from freezes. At the current growth stage (between Feekes 6 and 8), the growing point is no longer protected by the soil, however, it is somewhat protected by the vegetation and its nearness to the soil surface. Wheat is a cool season crop and can tolerate temperatures well below freezing. At this growth stage, wheat can tolerate cold temperatures down to about 24 to 26 degrees F. 

Whether or not the crop is damaged by cold spring temperatures and the extent of the damage depend on three main conditions: 1) how cold it gets, 2) the length of time the crop is exposed to the cold temperatures and 3) the growth stage of the crop at the time of exposure. Freezing temperatures are most damaging when the crop is at more advanced stages of development. Injuries are most severe when freezing temperatures occur during boot and heading growth stages. 

Based on information coming out of a Kansas State University publication , temperatures below 12 F are injurious during tillering, whereas, during jointing, 2 hours of exposure to 24 F may be injurious. At these growth stages, injuries tend to be greatest if the wheat is lush and actively growing (especially after spring nitrogen application) and are more common in low areas of the field. 

Soybean Aphid Populations Not Being Found on Buckthornaphids on buckthorn

Soybean Aphid Populations Not Being Found on Buckthorn

In C.O.R.N. newsletters last fall, we mentioned that soybean aphids, while in large densities on buckthorn in late summer and early fall, were decimated by what appeared to be a fungal pathogen. This disease outbreak appeared to have occurred before egg laying, mainly based on our inability to find aphid eggs in October and November. To confirm this lack of eggs, we have been sampling buckthorn in Ohio the past few weeks for the presence of aphids that would be present if eggs had been there. After many hours of sampling we have found only a single aphid colony in our sampling, which appears to confirm the relative lack of eggs last fall. 

Although we still will not offer any prediction as to aphid problems this coming summer, we are leaning towards low populations. However, we do advise growers to remain vigilant as to potential problems because aphid populations might surprise us and build to large numbers. We will be scouting for soybean aphids this summer, and if numbers do begin to increase, we will inform growers through this C.O.R.N. newsletter. 

Cereal Leaf Beetle on WheatCereal leaf beetle egg

Cereal Leaf Beetle on Wheat

Last week while scouting wheat plots at the OARDC in Wooster, OH, we saw numerous adult cereal leaf beetles along with eggs already laid on leaves. We have also received reports of cereal leaf beetle eggs from other locations in Ohio. This image shows an adult Cereal leaf beetle.

Cereal leaf beetle closeup

As wheat continues to grow and flag leaves emerge, and as spring-planted oats begin their growth, growers should keep an eye on these and other cereal grains for the presence of cereal leaf beetle larval feeding. See the following fact sheet for more information on the cereal leaf beetle . We will continue to watch for this insect and report additional observations in later C.O.R.N. newsletters.

Armyworm and Black Cutworm Moths Arriving in Ohiocutworm injury to corn

Armyworm and Black Cutworm Moths Arriving in Ohio

Reports from neighboring states suggest that moths of the true armyworm and black cutworm are now flying in the Midwest. While the black cutworm is a concern in corn, both wheat and corn are often attacked by the true armyworm. Corn is especially at risk from true armyworms when planted into rye cover crops. Armyworm is of most concern on wheat when feeding on the flag leaf. 

A fact sheet on armyworms on wheat is available at . 

Black cutworms will begin cutting corn in May, especially when the corn is planted into weedy fields, with chickweed being a preferred weed species; a fact sheet on black cutworm is at . 

Because the larvae of both these pests potentially could become concerns over the next month or two, growers should remain vigilant with both pests. Presently, none of the neighboring states are seeing large numbers of either insect; however, we will keep Ohio growers up-to-date on future happenings and need to sample.

Is Soybean Rust Gone?PIPEE website shot April 27, 2010

Is Soybean Rust Gone?

This past winter was very cold across much of Ohio, we had “great snow” finally for us skiing enthusiasts – even enough for “skinny ski’s or cross country”. What it also did was kill back the kudzu and the rust that was sitting on it. The kudzu is now leafing out and regaining quickly, but to date no rust pustules have been identified. On the Soybean Rust website: where the calendar is, you can go back and look at every April 25th, from 2005 to today. In each of these previous years, soybean rust was already identified. That is not the case this year. In Alabama, there were a few kudzu vines inside a building that had rust that were protected from the weather. This was destroyed in March – so at this point, there is no known rust in the US. Based on the Alabama situation, I would expect that there was some kudzu someplace in the south that still harbored some rust. But it is going to take quite a while to build up and begin to move in the south during 2010. 

As many of you now know the sentinel plot system is continuing only in the Southern States. They will continue to monitor for rust throughout the season. In Ohio, we are going to move to more mobile scouting on an “as-needed basis”. When rust begins to appear in the south, we will sample based on projected and predicted spore movements. We won’t be collecting leaves weekly. Based on the last few years and all we have learned, I think this is the right response. We will collect leaves from research plots and other areas around the state as double check, but I don’t see the need at this time to examine 4,000 leaves a week when the rust is at undetectable levels in the Southern US. We can focus on other areas and sample and incubate leaves on an as needed basis. I will continue to add commentary and updates via the soybean rust website and C.O.R.N. newsletter throughout the season.

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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.