Watch for white mold in soybeans
Diane Brown-Rytlewski
Plant Pathology

Soybean canopies have grown very lush from the recent hot weather and rain.  Now that the weather has cooled off, particularly if you are in the areas that received heavy rainfall, be on the lookout for white mold.
White mold is caused by the fungus Sclerotinia sclerotiorum. Cool temperatures (less than 85°F), rainy weather, moist soil and high humidity in the crop canopy, particularly as plants are flowering provide a favorable environment for the disease.  Foliar symptoms of white mold are not very distinct; foliage wilts and the leaf tissue between the veins turns a faded, grayish green. Leaves eventually turn yellow and drop, but stems remain attached.  Stems develop white, bleached lesions in the lower part of the canopy.  Infections may spread up and down the stem from a node where a flower was infected. Cottony, white mycelium may be present on the stem or other infected plant parts.  Sclerotia develop on or in infected stems and pods.

The fungus survives in crop residue as hard, black lumps of dormant mycelium (sclerotia) or on infected seed. In spring and summer, the sclerotia germinate and form mushroom-like fruiting bodies that produce large numbers of spores, which spread by wind and splashing rain.  Infection takes place mainly through soybean flowers. The spores germinate using dead and dying soybean flowers as a food source to grow mycelium. The mycelium infects the stem near the node and spreads to other plant parts. White mold also infects dry and snap beans, peas, potatoes, alfalfa, cabbage, canola, carrots and others, including many broadleaf weeds. Corn, sugar beets and small grains are not susceptible. This disease is difficult to manage.  Even if you are rotating to a non-susceptible crop, this fungus can survive for years in the absence of a susceptible host. Control broadleaf weeds during the non-host crop rotation – many are hosts for this disease.  Plant partially resistant varieties. See MSU soybean variety trials web site at:  http://www.css.msu.edu/varietytrials/soybean/whitemold.htm 

Use planting rates and row widths that promote air circulation and rapid drying of plants and soil surface. Irrigate only as required for optimum plant growth.  Using fungicides successfully is difficult, as soybeans often re-flower low in the canopy, providing additional entry points for the fungus later in the season.  Fungicides labeled for white mold control in soybean include Topsin and Thiophanate methyl.  We are well past the flowering stage where application is generally recommended (R1-R2 and 7-14 days later), and fungicides are likely to be of limited value at this stage of development.

The University of Wisconsin had developed an excellent guide to managing white mold based on field history and the susceptibility of the soybean variety you are planting.  This management table should be useful for planning white mold management for the future.

Soybean sudden death syndrome
Diane Brown-Rytlewski
Plant Pathology

For many parts of the state, soybeans are at the stage of development (R4-R6) when symptoms of sudden death syndrome (caused by the fungus Fusarium solani f.sp. glycines) start to appear in infected soybeans. Early symptoms include small, round, light green to yellow spots on leaves between the veins. Later, the areas between the veins turn brown to tan with chlorotic margins, while the veins remain green. Stem pith remains white (compared with brown pith in brown stem rot). Plants have smaller root systems and some degree of decay to the roots. Discoloration takes place on the lower part of the taproot first.  Sometimes, but not always, dark blue to blue-green areas on the root surface are visible where the pathogen has produced spores.

This fungus produces a thick-walled survival structure within soybean root tissue and overwinters as a resting spore where it can survive for several years in the soil. Yield reductions due to sudden death syndrome are dependent on when infections begin. Typically, infections that occur after flowering will not have a significant impact on yield. Infections that occur early will result in pod abortion, reduced seed number and size.

The severity of sudden death syndrome tends to be greater under no-till than conventional tillage systems. Research on the relationship between sudden death syndrome and soybean cyst nematode suggests that soybean cyst nematode increases the severity of sudden death syndrome but isn’t required for the development of the disease.

Management practices for sudden death syndrome include the use of resistant cultivars.  Cultivars resistant to soybean cyst nematode tend to show fewer symptoms of sudden death syndrome than susceptible cultivars. Avoid early planting.  Sudden death syndrome is often less severe in delayed plantings and in early maturing cultivars, as the onset of the disease doesn’t occur until later reproductive stages.  

Canola: An oilseed for organic and sustainable crop rotations?
Sieg Snapp and Russell Freed
Crop and Soil Sciences

There has been new interest recently in an old oilseed crop, canola. Canola was developed by Canadian plant breeders that made selections from rapeseed that had low erucic acid and glucosinolate levels – less than 2% erucic acid and less than 30 micro-moles of glucosinolate in the meal. As a member of the Brassica family, canola could be an important crop to help diversify our region’s agriculture, complement our cropping systems, and maintain a vibrant rural sector. Canola has tremendous potential to have an impact on our economic, health, environment and agricultural systems. Some of canola’s attributes are:

• High yield of value-added products (over 3000 lbs/acre).
• High quality oil: Lowest saturated fat of vegetable oils (7%) and high levels of healthy monounsaturated fats (61%) and alpha-linolenic (omega-3) acid (11%).
• New uses such as environmentally friendly bio-based oils and fuels.
• Niche market opportunities (organic/specialty oil) for non-GMO.
• Excellent soil building properties and an alternative crop that provides winter ground cover.
• Flexibility in planting time and diversification for sustainable production.

One of the challenges of producing alternative crops is identifying a secure market. There is a small and volatile organic canola market and increasing interest in growing canola as a potential component of biodiesel (In Europe there are biodiesel plants that process canola oil, but this market is not yet developed in the United States). The export and domestic demand for canola is not consistent and attention to marketing is important.

Canola will provide diversity in terms of flowers, plant residues with unique biochemical compounds and reduced host potential for many plant parasitic nematodes. Another attribute of Brassica family plants often discussed is the potential for bio-fumigation. Many Brassica species such as mustards produce chemical compounds in the roots and leaves, which have biocide effects that inhibit soil-borne diseases. If managed as a green manure crop, where green residues are chopped and incorporated, then a mustard or oilseed radish may improve the root health of subsequently grown cash crops. For more information, see the recent MSU Extension bulletin: Snapp, S.S. K. Date, K. Cichy and K. ONeil. 2006. Mustards: A Brassica Cover Crop for Michigan. Michigan State University Extension Bulletin E2956.

It is important to realize that canola grown in a crop rotation is not expected to have the same effects as a mustard grown as a green manure or cover crop. The glucosinolates have been bred out of the canola varieties; these are the plant biochemical compounds that have biofumigation effects. Also, growing a crop to maturity and removing the seed will leave older residues and roots that may have minimal effects on soil organisms compared to incorporating a fresh, green vegetative cover crop. However, canola will provide very different types of root inputs than other plant families such as legumes (soybean, dry bean) and grasses (corn, wheat, oats), and crop diversification promotes a healthy soil community.

Canola production
Canola has exacting production requirements. Soils must be well drained, and soil fertility is important in order to supply the considerable nitrogen, phosphorus and sulfur requirements of this crop. The biochemical compounds that are unique to the brassica family are a key reason why these plants require high sulfur availability. Organic sources of sulfur include elemental sulfur and gypsum. Soils will also have good sulfur supplying capacity if they are high in soil organic matter through long-term attention to following soil-building practices such as growing cover crops and adding judicial amounts of manure.

There are winter and spring varieties of canola. Generally, both can be considered to fit into diverse cropping systems throughout the Upper Midwest as these are widely adaptable to this region. Winter canola is often grown in locations where winter barley does well, and winter-seeded canola will usually produce moderately higher yields than spring canola. See information summarized by the Great Lakes Canola Association on requirements for of spring and winter canola production, below and www.agry.purdue.edu/ext/canola/varieties.htm

See map

Wet and poorly drained soils are not suitable for production of canola and this is a primary consideration in choosing a field for canola – there should be no standing water problems. It is also important to have no wild mustard weed infestation problems.
For the seeding rate of a specific canola variety, check with the seed source. A general recommendation is to plant 5 to 7 lbs per acre with a drill used for planting small grains.

Canola has a small seed and produces a small seedling that initially may be susceptible to weed competition, so a management strategy for pre-plant and pre-emerge control of weeds is important. Once canola is established, it has a broad leaf and will suppress many weeds. Pest problems are generally minimal although there are some potential disease and insect issues that are summarized by the Great Lakes Canola Association, at http://www.agry.purdue.edu/ext/canola/. A potential problem is Western Beet Yellows virus, which has the potential to be transferred between sugar beets and canola, so do not produce canola in sugar beet-producing areas.

Canola can be combined directly by a small grain combine, at about 9 to 10 percent seed moisture. Generally, about 95 percent of the pods will have turned brown and seed in the pods will be black at maturity. Slow combine speed should be used to enhance seed cleanliness. To maintain high seed oil quality is important, and processors and market outlets should be consulted to learn of specific harvest or post-harvest storage recommendations.

Resources
The Great Lakes Canola Association has a website with excellent conventional canola production information, see http://www.agry.purdue.edu/ext/canola/

A recent guide on organic production of canola was produced in Australia. For a copy of this review, type ‘Canola’ into the search engine at: www.dpi.vic.gov.au/dpi/nreninf.nsf. Note that the organic production method described is somewhat ‘substitution’ oriented, as organic mined sources of nutrients are described and limited information is provided on building soil fertility with cover crops. It was also developed for a drier climate than the upper Midwest as the annual rainfall is about 15 inches in the region of Australia where organic canola is primarily produced.

Regional reports
1 -- Southeast
Ned Birkey

Weather
It has been hot and somewhat dry over the past two weeks.  Crops are not under moisture stress as we had above normal precipitation for May, June and July.  Since last week was fair week, we did get one storm of up to 1.5 inches of rain, though this was not widespread.

Commodity reports
Alfalfa is suffering from potato leafhoppers.  Third cutting has started.  Prices for small, square and green bales have held up better than normal for this time of the season.

Corn is finally having a great growing “mid” season with advanced fields in the dent stage.  Second generation European corn borer numbers are increasing, though not at economic levels to field corn.  Corn rootworm root feeding and pruning has been very heavy is occasional fields.  No leaf rolling was noted last week during last week’s hot (90s) temperatures.  The early season plant growth variability has been “masked” with the tall plants along the road.  There could be substantial corn borer egg laying in these late-planted fields.

Soybeans are showing various symptoms of problems, ranging from yellow, stunted plants or brown spots on leaves.  Japanese beetles, bean leaf beetles, corn rootworms, potato leafhoppers and a few soybean aphids can be found, though none are at economic levels.  No Western bean cutworms have been found in a trap at the soybean cyst nematode plot.  The second report of sudden death syndrome has come in this week and soybean cyst nematodes can be found in several fields.  I anticipate more Sclerotinia white mold this year than in recent years.

Wheat fields have a great growth of common ragweed with mowing and spraying going on in most fields.

Miscellaneous    
The demand for wheat has been relatively weak.  Toledo’s Nabisco (Kraft) flour plant is booked up with wheat into next year.  ADM Grain Company at Ottawa Lake started moving wheat onto outside ground storage this week anticipating a big corn crop.  ADM has also been shipping wheat to Oklahoma for storage as the Plains states had a poor wheat crop.  As of now, they have loaded more boats with corn than they did all of last year, with most corn going to Algeria.

The Andersons’ Cargill Port of Toledo facility is expected to be up and running by fall harvest after the July 1, 2005, fire.  Now that the Detroit Red Wing’s goalie situation has been resolved, attention can shift to the Tigers and their playoff hopes.

2 -- Southwest
Bruce MacKellar

Weather
Parts of southwest Michigan were once again blessed with generous amounts of rainfall this morning.  Soils were just beginning to dry out in St. Joseph and surrounding counties earlier this week, and irrigation systems were just beginning to run again on some area soybean fields.  Rainfall amounts, although variable, should help the crops to progress relatively moisture stress-free for the next week or so.  

Commodity reports
Commercial corn generally looks very good.  Corn is in various stages of grain fill in the region.  There are beginning to be signs that corn fields in pollination during the extreme heat may have issues with incomplete ear development.  Dan Rajzer reports seeing fields where the outer one to two inches of the ear tips are not producing kernels.  Some areas west of US-131 showed signs of moderate to severe drought stress in the later vegetative growth stages, which may have reduced the potential girth and ear length and may mean lower yield potentials.  We have also seen a significant eastward expansion of root feeding damage from the “rotation resistant” western corn rootworm beetles which laid their eggs in soybean fields last season.  Fields in northwestern St. Joseph County have suffered significant feeding damage in first year corn following soybeans.  One of these fields was blown nearly flat in thunderstorm winds last week.  In transect sampling completed on August 9, we found signs of rootworm larval feeding in first year corn about halfway through St. Joseph County from west to east.  We are planning to place four yellow sticky traps in the four compass points in several soybean fields to help determine the eastward movement of the western corn rootworm variant this summer.  Dr. Chris DiFonzo is planning on writing a grant to complete a rootworm damage survey next season to help quantify the movement of this pest.  The movement of the variant will expand area where MSU will recommend the use of rootworm protection in first year corn following soybean if scouting is not being conducted.  The best way to determine if rootworm protection is warranted is to place sticky traps in soybean fields and monitor the activity of western corn rootworm beetles in soybeans this fall.  Threshold is reached if you have five beetles per trap per day for about a week, or 35 beetles per trap during a week period.  If you do not want to use sticky traps, you can make an estimate of the potential for damage by looking for rootworm beetles in fields by visual examination.  If you are observing what Chris calls a “shocking” number beetles in soybean fields, the variant is likely to be in your area.  Another indication that the variant is in the area is if the beetles are a dark green color.  This indicates that they have been feeding on soybean leaf tissue.  If you have questions on how to scout your fields, give me a call at the St. Joseph County MSUE office at (269)-467-5511.

Seed corn is progressing well.  Male row destruction is nearing completion.  Folks are working on preparing harvesters.  It is anticipated that there will be a relatively early harvest this year because of the heat.  There also will likely be a break in the harvest due to planting delays in May because of wet weather.    

Soybeans continue to look generally good.  There was substantial vegetative growth in most fields because of the rainfall.  Closer observation of soybean plants tends to reveal larger spaces between nodes than normal.  Some of these fields look to be susceptible to lodging as the season progresses.  Plants are at R-4 and R-5 in many fields.  The sentinel plots are showing some signs of downy mildew and Septoria, but no soybean aphids at this point.  There are some soybean aphids being found in fields in the southwest region.  Winged aphids are on the increase following the thunderstorm activity on August 3.  Levels remain low.

We have seen a fair amount of white mold in irrigated soybean east of US-131.  Fields that have a production history of snap beans seem to have higher levels of the disease.  White mold requires a substantial period of soil saturation (two to three days) for the sclerotia (overwintering structures) to germinate and produce spores.  The disease organism does not infect living tissue, but can gain a foothold into soybean plants from flowers that senesce after pollination.  This provides a conduit for the disease to spread into the plants vascular tissue and for the tell tale white mycelia growth on the stems.  Infected plants produce sclerotia, which can then fall back to the soil or be transported to other fields via combines.  Look for plants in the field that are showing signs of rapid decline, broad yellowing of the leaves following by necrosis.  Closer observation will usually reveal the white mycelia on the stems.  The sclerotia can remain viable in the soil for many years before conditions are right for release of spores.  Fields with high levels of white mold may require longer crop rotations away from soybeans and wider row spacings to help improve airflow to keep leaves drier.  Soybean varieties have varying levels of susceptibility to white mold.        

Growers have faced challenges putting up alfalfa this season because of the showers.  Recent conditions have opened narrow windows of opportunity.  Productivity has been below normal.  Potato leafhopper numbers have been heavy all season long and many growers have had to make multiple applications of insecticides to protect against this pest. 

The heat wave of 2006: An epilogue
Jeff Andresen and Aaron Pollyea
Geography

Unusually hot and humid weather impacted nearly all continental United States during the last two weeks of July and the first week of August. Nationally, more than 2,300 individual daily records for high temperatures were broken as well as 50 new records for the hottest July temperature ever. More than 200 fatalities were associated with the stressful conditions, the majority occurring in California during the initial week of the event. The unusually hot temperatures also led to record or near record warm mean temperatures for the month of July across the country. July 2006 will go down in the record books as the second warmest on record nationally (since 1895) at 77.2oF, following only July of 1936 at 77.5oF. The heat wave was associated with meteorologically with a broad upper air ridge over a massive subtropical air mass that moved slowly from west to east across the country.

While maximum air temperatures near or above 100oF were common during the event, one of the most important aspects of the heat wave was extremely high dew point temperatures. The dew point temperature is the temperature at which water vapor in the air would begin to condense out at liquid if the air were cooled at constant pressure. It is a direct measurement of how much water vapor is in the air at a given time. The greater the dew point temperature, the greater the water vapor content of the air. The more water vapor in the air, the lower the rate of evaporation of perspiration and the lower the rate of cooling. This is why humans and other animals that perspire become increasingly uncomfortable as the dew point temperature rises (for most individuals, discomfort begins at dew points around 60oF or higher). During the heat wave, dew point temperatures at or above 70oF were common over widespread areas with some approaching 80oF, which is near the absolute climatological limits for most regions of the United States, including Michigan.

To put this in another perspective, I remember when working as a young meteorological intern with the National Weather Service, the operational dew point sensor used at that time (late 1970s) had a maximum of 80oF on the readout dial (Technology has advanced since then!). Readings at a few locations during the recent event actually exceeded 80oF, which would have necessitated old, manual observations (most likely a sling psychrometer) given the limitations of the earlier technology. Finally, it is also important to remember that the dew point temperature serves as a general base for minimum air temperatures during the nighttime hours. Thus, overnight readings with this event were also at near record warm levels, with little or no relief for humans without climate control.

In Figure 1, representative hourly temperatures and relative humidity levels are plotted vs. time (dates are labeled just below the times) during the peak of the heat wave event in the Great Lakes region. The data were taken from the MAWN automated weather station near Bath, Michigan. The diurnal cycles are clearly evident with air temperatures reaching 90oF or higher on three consecutive days. Heat index values are also plotted, which depict the temperature which humans “feel” due to the combined effects of high air temperature and high humidity. The peak heat index value of 105oF at this location was reached early afternoon on August 1. Note from the graphs the symmetrically opposite diurnal patterns of air temperature (thick solid line) and relative humidity (thin dotted line). As air temperature rises, the relative humidity value falls (since warmer air can hold more water vapor) and vice versa.

The dew point temperature is a more straightforward indicator of how much water vapor is actually in the air. It reaches the mid-70s during the peak of the event and basically remains there until another air mass moves into the region on August 3. Note also that there is some diurnal change in the dew point: it tends to drop off a few degrees during the overnight hours and rise by about the same amount during the mid and late morning. This is due (no pun intended!) to the daily dew cycle and is a result of moisture leaving the atmosphere from vapor to liquid as dewfall/dew accretion during the overnight hours and going back into the atmosphere again the next morning as solar radiation and daily heating evaporate the dew back into vapor.

If you are wondering about the decreases in dew point during the early afternoon hours of July 31 and August 1, this is actually the addition of some relatively drier air from aloft being brought down to the surface during the peak turbulence and vertical mixing of the day in the planetary boundary layer. It did not occur on August 2, most likely because the lower-middle layers of the atmosphere were moistening as a cool front approached from the west (Note air temperatures on August 3 behind the front). Finally, from a climatological perspective in Michigan, the recent heat wave was noteworthy. Considering the number of hours the heat index temperature was at or above 90oF, this event (with approximately 50 hours above 90oF) would generally rank as the most significant since the heat wave of August 10-16, 1995 (The same event that claimed more than 500 lives in the Chicago area alone.).

Weather news
Jeff Andresen
Agricultural Meteorology
Geography

Northwesterly flow aloft and high pressure in place across the Great Lakes region has resulted in the recent spell of fair and dry weather across Michigan since last weekend. A cool front will move across the state Thursday (August 10), bringing a chance for a few isolated showers. Precipitation totals should remain less than 0.1 inches where rain falls (best chances will be across eastern sections of the state) with the vast majority of the state remaining dry. Fair weather will return statewide on Friday and continue through at least the first half of the upcoming weekend.  High temperatures during the next couple of days will generally range from the low to mid-70s far north to the upper 70s to near 80 far south with lows falling to the upper 40s north to the 50s elsewhere. High temperatures will slowly increase once again this weekend to the upper 70s to mid-80s statewide by Sunday. Another cool front is expected to move across the region by late Sunday into next Monday, bringing the next chance for significant precipitation.

Recent medium range forecast guidance is currently suggesting a number of possible scenarios for the next one to two weeks, which translates into low overall confidence in the outlooks. The official forecast pattern calls for upper air troughing features along the west and east coasts of the United States during the first week of the period gradually becoming more west to east or zonal during the second week.

The 6-10 day outlook from the NOAA Climate Prediction Center (covering August 15-19) calls for above normal temperatures statewide. Precipitation is forecast to range from below normal levels in southeastern sections of the state to near normal levels in the northwest. During the 8-14 day time frame (covering August 17-23), mean temperatures are forecast to remain at above normal levels with precipitation totals expected to increase to a range from near normal levels in southeastern sections of the state to above normal levels in the northwest. Further ahead, the latest 30-day outlook for the month of August calls for increased odds of above normal temperatures across the state, with near equal odds of above-, near-, and below-normal levels of precipitation.