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The Virginia soybean crop harvest is just beginning as I write this newsletter, with less than 5% harvested at this time. Most of the crop was recently rated in the fair to good categories and the predicted statewide average yield is now up to 26 bu/A. I would have to say that this is about right. Coastal Plain growing areas north of the James River is generally looking good; rains from the recent Hurricanes benefited growth and raised potential yield. I would expect our best double-crop yields since 1996. We have seen some detrimental side effects of the Hurricanes in the southeastern portion of the state however. Although some serious flooding of entire fields (water standing for more than 48 hours) in Southampton County and in the Cities of Suffolk and Chesapeake took place, widespread damage was minimal. On the other hand, we have noticed small seed size in our variety trials in Chesapeake and Suffolk (3500-4000 seed/lb.) and we are getting reports of the same phenomenon in northeastern N. C. This is occurring mainly on the low-lying, generally wet soils. I believe that the lack of sunlight and saturated soils, which restricted oxygen to the roots, is the primary cause of the small seed. Remember any stress during seed filling and after the final pod set has occurred will result in small seed. In this case it was primarily the lack of adequate oxygen in the soil and low light conditions. Severe lodging may also play a role due to inefficient use of the light that is intercepted. Keep this in mind as harvest proceeds throughout the rest of Virginia. Although it may look as if the yield potential is high considering the number of pods on the plant, seed size may be lacking.
The soybean price outlook hasn't improved that much. The best news came earlier this month when USDA announced that total production estimates for the U. S. had been reduced to 2.7 billion bushels (down from 2.8 in Sept.). Average national yield predictions dropped to 37 bu/A with a little over half of the U. S. crop harvested. The most significant number was that predicted ending stocks dropped to 385 million bushels. Although this is still a lot of carryover, itıs only about 10% higher than a year ago, which is much better than what was predicted earlier in the year. Still, donıt expect average prices to go much higher than $5.00/bu. On the bright side, exports are still stronger than ever and the improving economies of Asia should help in the future.
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Seek Quality/Discolored or Damaged Soybean Seed
Every year, we get reports of poor seed quality due to disease, insects, or environmental conditions. The excess rainfall and humid conditions that followed may increase the incidence of certain diseases. Other pests such as stinkbug can also result in discolored and shriveled seed. Below is a list of some of the causes of poor seed quality and suggestions for prevention.
Purple seed stain. Infected seed will exhibit a pink or pale to dark purple color of the seedcoat. Diseased seed are often dull, cracked, or rough. Prolonged periods of wet weather during pod set to harvest will result in increased incidence of the disease. Although oil content may be slightly reduced, yields are not usually affected. The real problem comes with saving and planting the infected seed next year. Infected seed may result in reduced stands or infected seedlings. Therefore, do not save seed for planting if this disease is present. There is some varietal resistance to the disease; results of the Official Variety Test will list our ratings of this disease in the 1999 publication. Prevention of the disease can also be achieved through crop rotation, use of seed treatment fungicides, and foliar-applied fungicides at early podset.
Phomopsis Seed Decay. This disease is caused by Phomopsis longicolla, which is a fungus that also contributes to the disease, Pod and Stem Blight. Severely infected seed are small, shriveled, elongated, cracked, and appear white and chalky. The pods and stem is usually covered with speck-sized black structures called pycnidia. Soybean pods can become infected anytime after they are formed, but most infection occurs after physiological maturity. Infection increases dramatically during warm, humid conditions (August, September). This disease can cause serious yield and quality loss if the crop matures early and harvest is delayed. We regularly see the disease on early-maturing varieties (MG III or early IV) planted in full-season production systems. This year, we are seeing a higher incidence of the disease, likely due to the excessive rainfall from the hurricanes. Therefore, do not delay harvest of full-season early maturity groups. Seed may also be infected even if they do not visually show the symptoms described and will result in pre- and postemergence damping off if re-planted. The fungi can over-winter in soybean debris in the soil. Prevention can be accomplished through crop rotation, seed treatment fungicides, and a foliar application of fungicide at podset.
Phomopsis Seed Decay
Phomopsis Seed Decay: Pycnidia on stem and pod.
Soybean mosaic virus. Infected seed will be smaller and lighter than normal and have a black to brown mottling that seems to "bleed" from the hilum. Yield can be substantially reduced. If infected seed germinate, they will produce diseased seedlings and plants that are usually somewhat stunted with crinkled, puckered, and mottled leaves. The virus is then spread to non-infected plants by aphid feeding. Prevention can be achieved by planting non-infected seed and through the selection of resistant varieties.
Anthracnose. This is another disease that occurs during warm, humid conditions after prolonged rainfall. All plant parts can be infected, but a characteristic feature is the small, spiny, black fungal fruiting bodies (resembling tiny pincushions) on the stem. The disease may lead to premature defoliation. When it attacks developing pods, pods may be empty or the seed may be shriveled, moldy, and dark brown in color. The fungi survive in crop debris and seed. Seed treatments at planting or a foliar fungicide at early podset will lower the disease incidence.
Stinkbug. This damage is caused by the mouthparts of the insect piercing the developing pods and seed. If damage occurs early, pods may fall off. But if the injury occurs later, seed size is reduced, the seed may be discolored and shriveled, or the seed may have a flat appearance. If infestation occurs after the seed has reached its normal size, injury will appear as splotches on the seed coat. Scouting and treating if the pest exceeds economic thresholds accomplish control.
While seed quality reduction from the above diseases and insects are not all that common in Virginia (probably due to the large acreage of double-crop soybean that mature later in the year), we could see a higher incidence in the areas most affected by the recent hurricanes. Most of the concern should be directed towards early maturing varieties that are planted full-season. Even in these cases, yield may not suffer. However, if considering producing seed for use in planting next year, one should consider the use of a foliar fungicide on that portion of the crop for next fall.
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Harvest season is once again upon us. I will not go into the detail of setting the combine to avoid harvest loss, but this can be found in the Soybean Production Guide as well as last year's Soybean Update, vol. 1 no. 5. Generally, harvest needs to begin as soon as the moisture content drops below 15% if drying facilities are available in order to avoid field losses. If one waits until moisture drops below 13%, begin as soon as possible. Wetting and drying of soybeans after seed moisture reaches 13% will increase the likelihood of shattering. Remember that four soybean seed per square foot of ground equals approximately 1 bu/A yield loss. Appropriate adjustments to the combine can minimize these losses.
One final word regarding safety needs to be repeated. Harvest can be one of the rewarding times of the year. This is what one has worked hard all season for. Harvest is also one of the most hectic and dangerous times due to long hours, moving equipment along the roads, loading and unloading grain bins, and the general stress of the season. Let's be careful and take our time to insure a safe and bountiful harvest.
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Sincerely,
David L. Holshouser
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