C.O.R.N. Newsletter 2009-26

Dates Covered: 
August 10, 2009 - August 17, 2009
Editor: 
Andy Kleinschmidt

Soybean Aphid Update

Authors: Bruce Eisley, Andy Michel, Ron Hammond

Soybean aphids remain a concern in Ohio, especially in the northeast part of the state. Although not a lot of fields are at threshold, some are reaching that level. However, there also are reports that some fields are holding steady, while some are having their aphid populations go down in numbers. Remember that the threshold for treatment is an average of 250 aphids per plant with the population rising. Economic damage will not occur until you reach 700-800 aphids per plant. The level of 250 aphids per plant is a very conservative threshold. See the images on our website (http://entomology.osu.edu/ag) for photos of what 250 aphids per plant might look like. It is a lot of aphids! And this should be the average for all plants, not just a few.

Also, being mid-August, this is the time when numerous natural factors can often help begin limiting population growth including beneficial insects, pathogens, weather conditions, and host-plant suitability. Thus, we urge growers to wait until the threshold of 250 aphids per plant is reached, with a RISING population, before pulling the trigger and making an insecticide application. Having a noticeable, but lower population at this time is not a guarantee that the threshold will ever be reached.

Soybean Diseases Making Appearance

Authors: Anne Dorrance

Sclerotinia stem rot, early season sudden death syndrome, Phytophthora, and Diaporthe stem canker are all making early appearances throughout Ohio. Late season diseases, those that typically occur when soybeans reach R5 growth stage (seed is 1/8 in long in pods at one of the top four nodes of the plant) are making some early appearances this year due to the substantial rains and cool weather conditions in the state. The following is a list of key symptoms, when infection occurs and courses of action that can be taken by producers.

Sclerotinia stem rot – right now the fluffy white growth which is also called mycelium can be seen on the stems. Soon, affected plants will die. This fungus survives in soil as hard black bodies which look like rat droppings except they are pink on the inside. When canopy forms early and cool moist conditions persist, then form small mushroom like structures. They are the size of a pencil eraser. These shoot spores onto dying blossoms and from there, the fungus gets a head start and begins to colonize the plant. The primary time of infection is when the plant is in full flower and the most important nodes are those on the main stem. Fungicides can be effective when they are applied when the plant is flowering but not later. In addition, there is only one fungicide, Topsin M, that has the best data to show a clear reduction in disease at this time. Disease incidence needs to be 10% or higher for yield losses to occur for this disease. http://www.planthealth.info/whitemold_basics.htm

Sudden Death Syndrome and Brown Stem Rot – There are some early foliar symptoms showing up on isolated plants in some fields. Yellow, irregular shaped to circular spots are forming between the veins and these are already turning necrotic. One key factor that separates these two diseases is the color of the pith – for brown stem rot, the pith turns a chocolaty colored brown while for sudden death syndrome it remains white, but the internal tissues of the tap root are gray colored. I have recovered both pathogens from the same plant so it is possible to have both. Infections for sudden death syndrome and most likely brown stem rot were favored by our cool wet spring. For sudden death syndrome, symptoms are worse when Soybean cyst nematode is present and it is just as important to manage cysts as it is to plant resistant varieties. For brown stem rot, soil pH can play a big role in how severe the symptoms are, soybeans grown in soils with a pH < 6.0 have greater symptom severity and yield loss compared to those grown in soils where the pH is greater than 7.0.

Phytophthora root and stem rot – if you are in an area that has received biweekly heavy rains you will continue to see losses due to Phytophthora stem rot. I was in a field last week where several acres were affected. Plants were short and there were big holes in the field. From the roadside, the plant growth looked uneven as each plant was a different height. In reality, this should not be happening. If the partial resistance or field resistance levels are high (better or equal to a score of 5.0) then we rarely see the stem rot phase. The symptoms include yellowing and wilting plants with the classic brown stem canker moving up the stem. In a few rare cases the canker is found only on one side of the plant but in most cases – these were ‘gonners’. The best time to see symptoms is approximately 1 to 2 weeks after a heavy rain and as the season continues, each time it rains more plants will continue to die and all that is left is the crunchy skeleton of a soybean plant.

Diaporthe stem canker – this also is a bit early and is another fungal disease. Foliage will begin to yellow as the stem is girdled at the third or fourth node. On the surface of the canker will be raised black dots, which are the fungal bodies that will overwinter for next season.

For all of these diseases soil drainage is playing a role in how severe the disease is but also choosing varieties with high levels of resistance will greatly reduce losses.

Soybean Rust Update for Ohio

Authors: Anne Dorrance

As of today, soybean rust is still limited to the gulf coast states with the latest find in commercial soybeans in mid-central Mississippi. According to colleagues in Mississippi, weather is predicted to be hot over the next few days and much of their crop is past the time to be affected. They will be monitoring over the next few days.

For Ohio, all of the plots are negative for soybean rust including slides collected from spore traps. We continue to be at low risk for soybean rust.

2009 Ohio Wheat Performance Results and Improving Wheat Profits Bulletin Available

Authors: Jim Beuerlein, Edwin Lentz

The purpose of the Ohio Wheat Performance Trial is to evaluate wheat varieties, blends, brands, and breeding lines for yield, grain quality and other important performance characteristics. This information gives wheat producers comparative information for selecting the varieties best suited for their production system and market. Varieties differ in yield potential, winter hardiness, maturity, standability, disease and insect resistance, and other agronomic characteristics. Selection should be based on performance from multiple test sites and years. Results of the 2009 wheat performance evaluation are available at: http://www.oardc.ohio-state.edu/wheattrials/

When we have one of those rare dry springs with low disease levels followed by a cool June with a long grain-filling period, the yields of some fields have reached 120 bushels per acre or more (most varieties have yield potentials over 180 bushels per acre). But attempting to produce ultra-high wheat yields by using extra inputs is usually not profitable for most Ohio wheat producers. That is because the climate of Ohio limits maximum wheat productivity. Guidelines to help minimize the factors limiting wheat yields and to lower production costs are presented in the publication, “Improving Wheat Profits in Ohio”. The bulletin is available at: http://ohioline.osu.edu/b938/pdf/b938.pdf

Volunteer Corn Helps Rootworms Beat Insecticides

Authors: Julie Douglas

The following article originally appeared in the August 6, 2009 Ag Answers http://www.agriculture.purdue.edu/AgAnswers/index.asp.

Volunteer corn can act as a safe harbor for some pests by expressing lower doses of the insecticide found in newly planted corn, according to Purdue University researchers.

Christian Krupke, an assistant professor of entomology, said western corn rootworm larvae feed on volunteer corn, unwanted plants that grow from seed dropped during the previous year's harvest. Volunteer corn doesn't have a full dose of the insecticide Bt, which can help the rootworms build up resistance.

"Now they're exposed to a sublethal source of Bt that didn't exist before," Krupke said. "That becomes problematic."

In field tests, Krupke and Bill Johnson, a professor of weed science, found that more than half of the volunteer plants expressed some amount of Bt and, of those, some had severe rootworm damage. The concern is that the rootworms could build a tolerance that, if passed to offspring, could allow the pests to eventually survive a full dose of the insecticide in commercial corn hybrids. Their results were published in a recent edition of Agronomy Journal.

Volunteer corn in soybeans is easy to spot as it towers above the other plants. But killing it can be costly since the corn is resistant to the popular herbicide Roundup.

"A grower has to add a new herbicide to control a volunteer crop. They use Roundup to kill a dozen weeds, but this adds a big expense for a grower to control just one," Johnson said. "It's essentially developing a new weed problem."

In continuous corn rotations, the problem is worse because volunteer corn is visibly indistinguishable from the wanted plants. And since the volunteers carry the same genes, there isn't a herbicide that would only kill those unwanted plants.

Johnson suggested scouting before planting to eliminate volunteers as early as possible and making sure combines are set properly to ensure little corn escapes and becomes volunteers in the next growing season.

Krupke and Johnson said this line of research would focus in the future on how to determine which plants are volunteers in continuous corn rotations and how many rootworms survive and build tolerance. The Indiana Soybean Alliance funded the research.

2009 FSR CCA College – Registration Now Open

Authors: Harold Watters

The Ohio State University Agronomic Crops Team in cooperation with Purdue University will be presenting a Certified Crop Adviser program at the Farm Science Review, the FSR CCA College. While we call this the CCA College, anyone who makes recommendations for growers is encouraged to attend.

Crops are very good this year at the FSR demonstration area. We planted in mid-May and suffered through the same dry period you all did and then got much needed rainfall in July that continued until the present. We expect very good yields off our plots.

Planned program:

  • This is a corn year for the demonstration area. We will have the Bob & Peter team running through our crop physiology plots. These two always bring good information and encourage great discussion. If you want to talk corn in the eastern corn-belt, then these two are the two to get to know. Bob Nielsen from Purdue University and Peter Thomison from OSU are our corn production specialists for a two-hour segment of the program.
  • Also on the program will be corn disease expert Pierce Paul, OSU Extension Plant Pathology Specialist. Pierce will be discussing the impact of corn foliar diseases in our fungicide demonstration plots this year. Think we didn't have diseases this year? - then why did we spray fungicides?
  • The third and final segment will center around fertility issues. There has been a lot of discussion at least in northern Ohio about phosphorous movement into Lake Erie. Robert Mullen, OSU's state soil fertility specialist will discuss in the Vice President's tent the research on winter P transport.
  • The program will start with breakfast on Thursday of the Farm Science Review, September 24th, and end at noon with a lunch catered by the OSU Crops & Soils Club.
  • Registration is $75
  • please register now through September 11th

To register this year you may download a registration form and the program details from: http://champaign.osu.edu/ag/ag.htm, or call Harold Watters or Sheila Callicoat at the Champaign County Extension office 937-484-1526 or email watters.35@osu.edu
Archive Issue Contributors: 

State Specialists: Dennis Mills and Anne Dorrance (Plant Pathology), Ron Hammond, Andy Michel, Bruce Eisley (Entomology), Peter Thomison (Horticulture and Crop Sciences). Extension Educators and Associates: Glen Arnold (Putnam) Roger Bender (Shelby), Bruce Clevenger (Defiance), Tim Fine (Miami), Mike Gastier (Huron), Wes Haun (Logan), Jonah Johnson (Clark), Ed Lentz (Seneca), Les Ober (Geauga), Alan Sundermeier (Wood), Harold Watters (Champaign), Mark Koenig (Ottawa/Sandusky), Steve Prochaska (Crawford)

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.