Nebraska's climate this summer was favorable for increased development of Sclerotinia stem rot, also known as white mold, in soybeans.

September 24, 2004

Climate conducive to Sclerotinia stem rot and Cercospora blight

Many producers and commercial agriculture clientele are reporting Sclerotinia stem rot (white mold) in soybeans. In some cases fields are being severely affected with over 25% of the field being lost.

Cercospora blight and purple seed stain develop from the same fungus Cercospora kikuchii. Climatic conditions in Nebraska this summer were excellent for the development of both diseases. Leaves on plants with Cercospora blight with be discolored and have a leathery appearance. Purple seed stain, which was widely found this year, does not affect yields but does affect seed quality if planted the following year.

More commonly, there are isolated pockets in the fields dying from Sclerotinina. Symptoms of this disease became evident about one month ago, but conditions which favored development of the disease occurred earlier, during the flowering period for soybeans. For Sclerotinia to develop we must have cool, wet conditions which we had in July over most of the state. Many fields in Nebraska have at one time or another had Sclerotinia present in the field and the fungus is just waiting for a year like this to start disease development.

Fields with a history of continual Sclerotinia stem rot problems should be planted to soybean varieties rated with higher tolerance to the disease. The use of narrow rows is also not recommended in these fields and it has also been shown that higher plant populations can increase the amount of Sclerotinia stem rot in a field. As this year was not typical for most in Nebraska, I would not recommend significant changes to your variety selection if you observed only an isolated pocket of this disease in your field.

The other disease problem we have observed this year is Cercospora blight. Symptoms of Cercospora blight occur on the upper leaves which are exposed to the sun. Light to dark purple areas of discoloration occur and leaves will have a leathery appearance. This develops into angular to irregular lesions on both the upper and lower leaf surfaces. Veinal necrosis can also be observed as the disease progresses. Green leaves will be present below the area being affected. Reddish purples lesions also will occur on petioles and pods.

Cercospora kikuchii -- the fungus that causes Cercospora blight -- is the same fungus that causes purple seed stain. This disease is widely distributed in Nebraska and occurs every year at low levels. However, this year we have had excellent conditions for its development. While this disease generally does not reduce yield at the levels observed in Nebraska, it will reduce seed quality and can impact seedling quality if planted next year.

Fields with severe Cercospora blight should be harvested among the first. Conditions that favor purple seed stain are when wet weather delays the harvest or when warm, wet weather hits when plants have begun to reach maturity (growth stages R7 and R8) or when pods are completely brown. Most of the fields I have seen with severe Cercospora blight are in the earlier maturity groups around 2.5. Symptoms of purple seed stain are purple to pink streaks on the seed coat. Discoloration can range from streaks to large blotches. The fungus grows into the pod and spreads though the hilum, resulting in seed discoloration being centered on the hilum. In some cases the entire seed may be discolored.

Seed lots with a high percentage of purple seed stain are not recommended for planting since they may produce weakened seedlings. Rapid dry-down prevents seed infection and recent cool weather slows the rate of fungus growth, but if moisture continues into harvest I expect there to be an abundance of this discolored seed.

In varieties showing severe Cercospora blight, I would not recommend eliminating them from potential varieties for next year, as this was such an atypical year for Nebraska production and most likely, this disease will not be as severe next year.

Free activities and tours will begin at 10:30 a.m. and continue to 2:30 p.m. Hayrack tours will pass through woodlands and tree research plantations and the walking tours will help participants develop basic tree identification skills. Added attractions include educational exhibits, sawmill and post peeler demonstrations, tree grafting demonstrations, and master wood turners.

Event sponsors include University of Nebraska Cooperative Extension, Nebraska Forest Service, Nebraska Statewide Arboretum, and the Lower Platte South Natural Resources District.

The coldest pocket of air associated with this strong trough remained west of Nebraska and thus freezing temperatures did not develop across the western third of the state, as had been expected. It appears that the next significant chance for freezing temperatures will not occur before October 8. As this trough moves northeast of Nebraska, high pressure will build back into the central United States. If models are correct, an active weather pattern with occasional shots of moisture will continue for the next few weeks.

It does appear that a weak El Nino is beginning to form in the Pacific Ocean and is forecast to slowly strengthen over the next few months. Typically an El Nino would begin forming in July-August, so this event is unusually late. At present, models project a weak event with impacts expected in December-March. If this event becomes a player in our weather pattern, expectations are for above normal temperatures for December-March, with an increased likelihood for late season snow in the central Rockies and western High Plains.

If the present weather pattern continues through fall, temperatures should remain below normal across the northern and central plains, with normal to above normal precipitation in response to southward movement of the northern jet. As El Nino strengthens, the northern jet will weaken and give way to a strong southern (tropical) jet stream pattern. Instead of cold dry snowstorms, wet snow and warmer than normal temperatures should occur as storm systems traverse the southern third of the United States in late winter.

Nebraska farmer Chuck Myers heads to a field south of Lyons to harvest corn in a combine equipped with a yield monitor. (File photo)

A yield monitor consists of several sensors and a small computer to integrate, display, and save the information. On most yield monitors, the grain flow through the combine is estimated by measuring the force the grain exerts on a sensor at the top of the clean grain elevator. The greater the grain flow, the greater the force or displacement measured. The area harvested is determined from the measured travel speed and the known width of cut. Grain moisture content is also measured so that the grain yield can be corrected to a standard moisture content.

Safety risks for children vary depending on age, but for those 15 and under, the biggest risk is being run over by farm equipment, said Dave Morgan, extension safety engineer in the University’s Institute of Agriculture and Natural Resources.

”Since 1969, farm equipment has been the leading cause of injury for kids,” he said.However, taking on-the-job precautions can minimize physical risks for both children and farmers, he said.

”Teach kids that machinery and equipment are not places to be playing, and neither are grain bins, especially if you have automatic unloading equipment,” he said.Farmers should develop “no play areas” to park machinery in and never park in a play area, Morgan said. Fenced play areas increase safety, especially for younger children.

Following farm equipment accidents, tractor overturns, harm from animals, suffocation and falling off vehicles are the most common on-farm lethal incidents, according to the Department of Biological Systems Engineering statistics. Children being carried along as extra riders on farm and lawn care equipment continues to be a concern, Morgan said. It is difficult for operators to have full attention to the operation of the machine if they have a child on their lap or riding along or on a fender, he said.

Unless there is an extra seat and a seatbelt, children should not be allowed to ride along. When children are helping care for farm animals, they also need to be aware of potential dangers, he said.

”It’s easy for a small child to get crushed between a fence and a cow,” he said. “Kids have got to understand that animals outweigh people, are unpredictable and aren’t always controllable.”

He also recommends keeping farm chemicals and treated seeds well out of children’s reach.To help children look out for each other, hazardous occupation training courses are available through local Cooperative Extension offices, which help make kids aware of safety issues about operating tractors and other machinery.”With the right education, kids can be a great help on the farm and still be safe,” Morgan said.

Suzanna Adam
IANR News

The combine cab offers an excellent vantage point to note where channels have developed in the field from the concentration of runoff water. These rills generally develop in the same places each year. They get filled in by tillage in the spring, redevelop during the growing season, get bounced over by the combine during harvest, and the cycle is repeated the following year. Consider installing grassed waterways in these areas. Erosion will be reduced and the possibility of equipment damage lessened.

Grassed field borders can provide a convenient location for unloading combines into trucks or grain carts, or for turning planters and other equipment around. Controlling field traffic in this manner can greatly reduce the likelihood of developing a compaction problem within the field. Often field borders can be used to eliminate crop rows that would otherwise be planted up-and-down hill, further reducing soil erosion.

Water and sediment control basins generally are used where gully erosion is a problem and a grassed waterway cannot be installed or maintained because of large volumes of runoff water. They also are used when runoff and sediment from up-slope areas cannot be managed and damage to down-slope areas or other practices will occur. Basins must be cleaned periodically to remain effective.

Conservation buffers placed along the edges of streams or other water bodies can serve as a last line of defense for sediment and other pollutants that might enter the water. They are very effective at trapping sediment and enhance the infiltration of runoff water. Buffers also provide excellent habitat for pheasants, songbirds, and other wildlife and can enhance safety by keeping equipment away from the edge of the stream. When planted to trees, a buffer may provide income for future generations.

For more information, see . . . Conservation Buffers, a UNL Web site with information on the many types of riparian buffers, including grass filter strips and riparian forest buffers. The USDA Natural Resources Conservation Service site The Natural Resource District Web site for your area

A number of programs such as the Continuous Conservation Reserve Program are available to help landowners with the adoption and maintenance of conservation practices. Check with the local Natural Resources Conservation Service or Natural Resources District office to determine what programs are available for your land.

Conservation is a good investment, and this fall is an excellent time to begin or increase that investment.

1. Alfalfa makes an outstanding weaning pasture for spring calves.
2. Yearlings continue to gain weight rapidly on fall alfalfa even after summer grass starts to die off.
3. Cows can gain excellent condition before winter.
4. Ewes and lambs perform very well on fall alfalfa.

Also be careful not to damage your alfalfa stand. Only graze when fields are dry and firm. Reserve a small sacrifice area to graze and for feeding when soils are wet to avoid damaging the entire field.

How we graze our pastures, though, does not affect the basic growth processes of our grasses. If we severely graze a pasture, and then graze it again before plants have recovered, they will be injured. This is true regardless of whether the plants are grazed continuously or in rotation. Recovery time is particularly important as we approach winter. With the drought conditions prevalent in many areas this year, plants and especially warm-season grasses did not begin to recover until they received rain. Severe grazing now, before they have fully recovered from their summer stress, will weaken plants as they go into winter. Most plants probably will survive, but next spring they will green-up later, early growth will be slow, and they'll compete poorly with weeds. Cool-season grasses aren't quite as sensitive, but they too will be affected.

So as we approach winter, "take half and leave half" still is a good management technique. It helps assure that your pastures will be healthy and grow vigorously again next year.

Gary Zoubek, Extension Educator in York County: Things have really changed the past week. Soybeans have dried down rapidly and soybean harvest is in full swing! Yields have been variable with some better than expected dryland yields. I’ve had reports of 25-50+ dryland yields. Some irrigated yields, however, have been less than expected. I’ve had reports of 50-75 bushel per acre irrigated yields. The problem with green stems varies greatly depending upon field, varieties and other factors.

Gary Lesoing, Extension Educator based in Nemaha County: Harvest began last week and is in full swing. Soybeans are dry, 10-13% moisture, although there are some green beans coming in. Soybean yield reports are generally good, ranging from 45 to 60 bushels per acre. Corn harvest also has begun with moistures of 14-19%. I have heard one dryland corn yield report of about 150 bushels per acre.

Following is an update on crop conditions as of September 19, as provided by NASS:

Corn rated 3% very poor, 6% poor, 20% fair, 46% good, and 25% excellent, above last year and average. Irrigated fields rated 80% good and excellent while dryland fields rated 58%. This compares to 75 and 12, respectively, a year ago. Harvest was 4% complete.

Soybean condition rated 4% very poor, 12% poor, 29% fair, 43% good, and 12% excellent, still well above last year and average. Leaves had dropped on 57% of the acreage. Harvest was 6% complete.

Sorghum condition rated 4% very poor, 12% poor, 43% fair, 35% good, and 6% excellent, still well above last year and average. About 82% of the fields were showing color, and 15% were mature.

Dry bean condition rated 6% very poor, 16% poor, 26% fair, 44% good, and 8% excellent. Seventy-nine percent had turned color, well behind last year at 94%. Harvest was 8% complete.

Proso millet harvest progressed and was 30% complete.

Wheat seeding progressed to 48%, ahead of average at 50%. Fourteen percent had emerged.

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Copyright 2004 by the University of Nebraska

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