In This Issue:
- What Soybean Diseases to Scout for Next
- Corn Growth and Yield Potential: Impact of Recent Cool Weather
- Weather Outlook: Drier and Warmer
- Soybean Reproductive Stages
- Late Season Soybean Insects
- Changes to Insecticide Labels Coming Related to Bees
- Keep Scab Resistance at the Top of Your List as You Select Wheat Varieties This Fall
What Soybean Diseases to Scout for Next
Downy mildew. A few samples came in over the week that had very high levels of downy mildew in the upper canopy. This disease is common at the end of the season. It has a small yellow to brown spot on the top of the leaf, while the bottom of the leaf has white “fuzz” which are the sporangia or spores. The high levels of infection this year are due to highly susceptible varieties and the heavy dews, and cool nights we have been experiencing over the last several weeks. The conditions could not be more perfect for this disease. Recorded losses have been hard to estimate for this disease. Most consider this disease a very minor nuisance, but if severe it may cause early defoliation. This is what will have to be monitored for in those fields that have large numbers of spots. Downy mildew can infect seed. If conditions continue to be favorable in those fields, the fungus will infect the pods and grow over the seed. It forms a crust on the outside of the seed coat.
Sclerotinia. We talked earlier this season that conditions were favorable for white mold, and I scouted some fields and the stem cankers have started. By the end of the week, the plants that are affected will be dying and may be seen from the edge of the roads. What we observed was fluffy white growth on the bottom of the stems of the plants. The seeds will not fill out on these plants and this will be lost. On some of the plants, the hard black sclerotia were forming, so these fields will get a fresh covering of sclerotia to serve as inoculum for the next few years. Monitor fields. First, make note of the variety that was planted, if infections are above 20% incidence (more than 20 plants out of 100 are infected), then drop this variety from your lineup. Second, harvest these fields after all of the other fields are harvested. We will repeat this again later, but the approach here is to prevent contaminating additional fields.
Sudden Death Syndrome. This disease is already present in some of my research plots. Symptoms are continuing to develop. This is a root pathogen which is caused by a fungus. This fungus produces a toxin which travels up the stem and causes the bright yellow and brown discoloration in the leaves. The key to this is, first make sure it is SDS and not brown stem rot. The first thing to do is to split the stems open and examine the pith. If it is a chocolate brown color – it is brown stem rot. If it is clear and there are blue spores on the tap root, then it is SDS. Soybean plants can be infected by both. With SDS, in Ohio, I have found this to be more severe in fields with high soybean cyst nematode populations. These are good fields to target in the fall for SCN sampling.
Soybean Rust. We have not detected soybean rust in any fields in Ohio to date. Lots of talk last week with my colleagues to the south as rust has been found on the Tennessee/Alabama border. We are monitoring and the concern will be for those soybeans that are between flowering and R4 (pods are 3/4 inch long in one of four uppermost nodes on the main stem). In Ohio, we are sandwiched between the soybeans that were planted really late and how long before the first frost. Soybean rust will take several cycles to get to damaging levels depending on how much arrives in the storm fronts. Our southern colleagues in Alabama and Mississippi are going to be really challenged this year as they were still planting late into July and very high levels of inoculum are present.
Editor’s note: Photos of various soybean disease symptoms are available on the OSU Extension field crop disease web site at: soybeandiseaseimages
Corn Growth and Yield Potential: Impact of Recent Cool Weather
Have recent below average temperatures adversely affected corn growth and yield potential? No, corn actually yields best with moderate temperatures (and adequate soil moisture). Temperatures that occur in Ohio in July and August (especially at night) are often warmer than optimum for corn. The ideal daytime temperatures for corn are about 80 to 86 degrees F (and higher if moisture is plentiful at all times). Although some believe that corn grows best when nights are hot, past research shows that warm temperatures adversely affect yield potential. While temperatures in the 40’s may impair photosynthesis, high night temperatures (in the 70s or 80s) result in wasteful respiration and a lower amount of dry matter accumulation in plants. With high night temperatures, more of the sugars produced by photosynthesis during the day are lost; less is available to fill developing kernels, thereby lowering potential grain yield. Research conducted at the University of the Illinois indicated that corn grown at night temperatures in the mid - 60s outyielded corn grown at temperatures in the mid- 80s. High night time temperatures result in faster heat unit (GDD) accumulation that can lead to earlier corn maturation, whereas cool night temperatures result in slower GDD accumulation that can lengthen grain filling and promote greater dry matter accumulation and grain yields.
Average corn yields are generally much higher with irrigation in western states, which have low humidity and limited rainfall. While these areas are characterized by hot sunny days, night temperatures are often cooler than in the Eastern Corn Belt. Low night temperatures during grain fill are associated with some of our highest corn yields in Ohio – 143, 158, and 174 bu/A in 1992, 2004, and 2009, respectively (the highest state yields recorded to date at that time).
Although much of Ohio has received above average rainfall during grain fill, some localized areas are experiencing rainfall deficits. In these areas, cooler than average temperatures have minimized what could been severe drought stress if we’d had higher temperatures. The cool temperatures may have also slowed the development of foliar diseases and insect problems.
So what’s the “downside” to these lower than average temperatures? Cooler temperatures (if they continue) could delay grain harvest and result in higher grain moisture. Growers may want to consider this possibility when they estimate fuel costs for drying grain. Moreover, the cool wet growing season of 2009 was associated with ear rots and mycotoxins. The corn harvest in 2009 was delayed by frequent rains which allowed molds to grow resulting in major mycotoxin problems for many farmers.
This article contains information I’ve adapted and cited from the “Climate and Corn” section in Modern Corn and Soybean Production by R.G. Hoeft, E. D. Nafziger, R.R. Johnson, and S.R. Aldrich. (Published 2000. MCSP Publications, Champaign, IL).
Weather Outlook: Drier and Warmer
The weather pattern has changed some and it looks like the rain will remain mainly limited for the rest of August and temperatures will be on the rise. The wet pattern is gone for August and possibly September before returning in October.
Above normal temperatures will persist the rest of August. Temperatures the week of August 19 will see highs mainly in the 80s and lows in the 60s. High temperatures will grow to 85 to 93 the week of August 26.
Rainfall is forecast for the rest of August to average 0 to 0.25 inches in the northwest third of Ohio to 0.25 to 0.75 inches in southern and eastern sections which is below normal. The best chances of rain the rest of August will come Wednesday and Thursday August 21/22.
This could begin to stress some crops as topsoil continues to dry. Subsoil moisture remains in good condition.
Soybean Reproductive Stages
Properly staging soybeans is important as many management decisions are stage-dependent. Currently, soybeans are in the ‘R’ (reproductive) stages with most fields in the R4 to R5 growth stages. (Vegetative stages are considered the ‘V’ stages.) The reproductive stages for soybean are listed below. It is important to note that vegetative growth, flowering, pod development, and seed fill can occur simultaneously. Each specific growth stage is defined only when 50% or more of the plants in the field are in or beyond that stage.
R1 – Beginning flowering. The R1 growth stage is defined as one open flower at any node on the main stem. In Ohio, soybeans generally enter the R1 stage during the first two weeks of July. Flowering is triggered by daylength as nights get longer after the summer solstice (June 21). Generally the first flower is found at the third to sixth node.
R2 – Full flowering. At the R2 stage, there is an open flower at one of the two uppermost nodes on the main stem with a fully developed trifoliolate leaf node (a fully developed leaf node must have a leaf above it without any leaflet margins touching). Flowering generally begins lower on the plant and moves upward.
R3 – Beginning pod. At R3, there is a 3/16th inch long pod at one of the four uppermost nodes on the main stem with a fully developed trifoliolate leaf node. Similar to flowering, pod development begins lower on the plant (where flowers first developed) and moves upward. Soybeans will often abort 60 to 75 percent of the flowers or pods.
R4 – Full pod. The R4 growth stage is defined as the plant having a pod 3/4th inches long at one of the four uppermost nodes on the main stem with a fully developed trifoliolate leaf node. Soybean plants are entering the most critical time for yield from about mid R4 to mid R5.
R5 – Beginning seed. At the R5 stage, the seed is 1/8th inches long in the pod at one of the four uppermost nodes on the main stem with a fully developed trifoliolate leaf node. Plants at this stage will have reached maximum height, peak nitrogen fixation and maximum nutrient accumulation by leaves.
R6 – Full seed. At the R6 stage, there is a pod containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem with a fully developed trifoliolate leaf node. Root growth will decline and stop at this stage.
R7 – Beginning maturity. The R7 stage occurs when one normal pod on the main stem has reached its mature pod color. Mature pod color depends on variety, but is normally brown or tan (some have a grayish color).
R8 – Full maturity. At full maturity, 95% of the pods have reached their mature pod color. When looking at soybean plants, make sure only pod color is taken into account. Sometimes soybean stems will remain green and can influence staging, but green stems should not be taken into account when staging.
Reference: Pedersen, P. 2009. Soybean growth and development. Iowa State University Extension. PM 1945.
Late Season Soybean Insects
As the season winds down, soybean growers need to continue scouting their fields, especially those later planted fields that will remain green well into September. As other fields in the area begin maturing and turning yellow, some insects will migrate to soybeans that are still green and continue their feeding. Two of those insects, with one being a complex, are second generation bean leaf beetles and the stink bug complex consisting of the green, the red shouldered, and perhaps the brown marmorated stink bug. These insects feed on the pods and seeds of the plant, causing direct damage to the harvestable part of the soybean. We calculate that losing only 1-2 seeds per plant will cost growers an economic loss because of the high price of soybeans and the relatively low cost of making an insecticide application. Indeed, based on observations over the past few years, Ohio growers are probably losing yield and thus money to these insects in late maturing soybeans.
Treatment to prevent pod damage from bean leaf beetle is based on the level of insect injury observed on the pods. Evaluation of pod injury should be based on inspection of all pods on 10 randomly selected plants. On each plant sampled, count the number of total pods and the number of pods exhibiting pod scar injury, and then determine the percent pod injury based on the 10 plants inspected. It is important to estimate percent pod injury on inspection of the entire plant. Treatment is justified if the percent pod injury is approaching 10-15%, and BLB adults are still present and still active. More information can be found at http://ohioline.osu.edu/ent-fact/pdf/0023.pdf .
Scouting for stink bugs should be done by walking into the field at least 100 ft from the field’s edge. Sampling should be taken as sets of 10 sweeps at 3 to 5 locations in a field. Both adults and nymphs should be counted together. Experience suggests that the brown marmorated stink bug is difficult to sample using sweep nets, so you might need to walk slowly through the soybeans and attempt to count the bugs directly on the plants. Insecticide treatments should be considered when an average of 4 or more adults or nymphs of all species are collected per 10 sweeps in regular soybeans. When grown for seed or are food grade soybeans, we suggest lowering the threshold to only 2 adult or nymphs per sample. For brown marmorated stink bug, control is suggested if you see 1-2 per row ft through at least the R4 stage. More information on stink bugs can be found at
When the decision to make a rescue treatment is made to prevent pod and seed injury to later maturing soybeans, there are numerous foliar insecticides to use for bean leaf beetle and stink bug control. Growers should also be aware of pre-harvest intervals for the insecticides, which range from 14 days to 60 days. The time period left before anticipated harvesting of a field might dictate the insecticide chosen. See Bulletin 545 for all insecticides labeled on soybean (http://entomology.osu.edu/ag/545/soy545.pdf ).
Changes to Insecticide Labels Coming Related to Bees
In an ongoing effort to protect bees and other pollinators, the U.S. Environmental Protection Agency (EPA) announced last week that they have developed new pesticide labels that prohibit use of some neonicotinoid pesticide products where bees are present. However, because few products containing these insecticides are used in field crops for foliar spraying especially during flowering or pollination (mainly on soybeans), any label changes should not have major impacts for field crops. Currently, most neonicotinoids in field crops are used as seed treatments. On the other hand, because almost all insecticides have caution statements about bees, we might see additional changes in future years. As new labels come out, we will continue to educate growers on how changes might affect production practices. For more information on EPA’s efforts to protect pollinators, see http://www.epa.gov/opp00001/ecosystem/pollinator/index.html. Information on the new bee-advisory labels can be found at http://yosemite.epa.gov/opa/admpress.nsf/d0cf6618525a9efb85257359003fb69d/c186766df22b37d485257bc8005b0e64!OpenDocument. To illustrate the conversation currently going on over potential problems with honey bees and other pollinators, especially with neonicotinoids, we would call attention to last week’s issue of Time Magazine, where the problem with honey bees is the cover story!
Keep Scab Resistance at the Top of Your List as You Select Wheat Varieties This Fall
Even though we did not have high levels of scab and vomitoxin this year, we still need to keep this disease in our minds as we select varieties to plant this fall. In the past, there were very few Ohio-grown winter wheat varieties with decent scab resistance, and some of those varieties yielded poorly or did not grow well under our conditions. Today we have far more varieties with very good scab resistance in combination with very good yield potential. So, as you prepare to plant wheat this fall, scab resistance should be a top priority on your list when selecting a variety. However, remember, no variety is completely resistant or immune to scab, so if conditions are wet and humid during flowering, even varieties considered resistant will develop scab and become contaminated with vomitoxin, but, disease and toxin levels will likely be lower in resistant varieties than in susceptible varieties. When conditions are favorable for scab, producers who plant resistant wheat varieties and applied a fungicide at flowering usually see lower levels of scab and vomitoxin than those who planted susceptible varieties. With a scab resistant variety, growers tend to see greater benefit from the use of fungicides if scab develops. In general, compared to the most susceptible varieties, scab and vomitoxin reductions may be as high as 70% when fungicides (Prosaro or Caramba) are applied to resistant varieties, and only about 50% when susceptible varieties are treated.
This table shows the most scab resistance varieties in this year’s wheat performance trials. There were 59 varieties rated as either R or MR. R = resistance, indicating that a variety has resistance comparable to Truman, one of the most scab resistant soft red winter wheat varieties. MR = moderately resistant, indicating that a variety has resistance comparable to Freedom. Other rating include MS = moderately susceptible, and S = susceptible. More information about the varieties shown in the table will be published in the 2013 Wheat Performance Trial:
NOTE: R does not mean that the variety will not become infected; it means that it is among the most resistant we have at this time, based on multiple years of testing. You will still need to treat a variety rated R or MR with a fungicide to control scab if it becomes wet and humid next spring.
The Most Scab Resistant Cultivars in the 2013 Wheat Performance Trial
|Brand||Cultivar||2013 Head Scab Rating|
|Certified - Proprietary||Bravo||MR|
|Certified - Public||Bromfield||MR|
|Certified - Public||Freedom||MR|
|Certified - Public||Malabar||MR|
|Dyna - Gro||9171||MR|
|FS Wheat||FS 602||MR|
|Great Lakes CG||GLCG 1229||MR|
|Limagrain - LCS||LCS 34969||MR|
|Limagrain -LCS||LCS 38686||MR|
|Seed Consultants||SC 1302||MR|
|Seed Consultants||SC 1321||MR|
|Seed Consultants||SC 1341||MR|
|Seed Consultants||SC 1342||MR|
|Shur Grow||SG 1542||MR|
|Shur Grow||SG 1549||MR|
|Sunstar||S - 1100||MR|
- Glen Arnold (Nutrient Management Field Specialist),
- Mark Badertscher (Hardin),
- Debbie Brown (Shelby),
- Sam Custer (Darke),
- Amanda Douridas (Champaign),
- Nathan Douridas (FSR Farm Manager),
- David Dugan (Adams, Brown, Highland),
- Mike Gastier (Huron),
- Jason Hartschuh (Crawford),
- Mark Koenig (Sandusky),
- Rob Leeds (Delaware),
- Mark Loux (Weed Science),
- Les Ober (Geauga),
- Steve Prochaska (Agronomy Field Specialist),
- Eric Richer (Fulton),
- Adam Shepard (Fayette),
- Harold Watters, CPAg/CCA (Agronomy Field Specialist)
- Anne Dorrance (Plant Pathologist-Soybeans),
- Peter Thomison (Corn Production),
- Jim Noel (NOAA/NWS),
- Laura Lindsey (Soybeans and Small Grains),
- Ed Lentz (Hancock),
- Ron Hammond (Entomology),
- Andy Michel (Entomology),
- Pierce Paul (Plant Pathology),
- Clay Sneller (Horticulture & Crop Science),
- Rich Minyo (Corn & Wheat Performance Trials)