Tag Archives: seed quality

Timely harvest will minimize seed quality problems

The map below shows the amount of rainfall received in Virginia over the last 14 days.  And the weather forecast is calling for more.  While this rain may still help our double-crop soybean, early-planted early-maturing varieties will run the risk of seed quality problems if they are not harvested soon after maturity.Precip Analysis 092716For details of the main diseases that cause these problems, I refer to you to a blog from last fall (Oct 16) when seed quality problems were horrendous –  Soybean Seed Quality Continues to Deteriorate. 

But to review, the seed decaying diseases are worse when wet weather is combined with relatively warm conditions, like we are having now.  Early-maturing varieties, especially those planted in April and early-May will have the worst seed quality because they are maturing during a warmer time of the year.  I’m most concerned about maturity group (MG) III and IV soybeans; MG V’s are not yet mature.  Last year, later-maturing varieties fared better than early varieties, as shown in the 2015 variety test data below.  We rate seed on a scale of 1 to 5, with 1 being a perfect seed and 5 being an unsaleable product.  Usually, anything averaging 2.5 or less is pretty good seed.  Double-crop soybean seed quality is always better since they are maturing during a cooler time of the year.Seed Quality 2015

What can you do to minimize these disease?  Harvest as soon as possible.  Phomopsis seed decay will only get worse the longer that you leave mature plants in the field.  And pray for cooler and dryer conditions in October and November.

Avoid Seedling Disease with Quality Seed, Proper Seed Placement, & Good Soil-To-Seed Contact

We were hoping to be about half way finished with our soybean plantings by now, but we haven’t put a planter in the field in two weeks.  The rain continues to delay us, but I hope that we will get back into the field next week.

The rain and cooler weather has lowered soil temperatures somewhat and this means that we need to take a few extra precautions, especially pertaining to seedling disease.  I wrote a detailed blog a few years ago on seedling disease; little has changed and, for more details, you can view that blog here:

Fungal Seedling Disease in Soybean

Planting soybean in cool soil will lead to delayed emergence and increased chance of seedling disease that can reduce stands, weaken emerged plants, and inhibit early-season growth. I stress that the greater time required for emergence, the greater probability that the seed will become infected with soil-borne disease.  If you are planting into cool soils, I strongly suggest using fungicide-treated seed as an insurance against seedling disease. These treatments will protect the seed and seedling if emergence is delayed.

But, seed treatments should not be a substitute for other practices that encourage rapid seedling emergence.  Here is my checklist for insuring a good stand free of seedling disease:

  • Know the germination and vigor of your seed; adjust the seeding rate accordingly.
  • Insure good soil-to-seed contact by properly setting your planter to cut through the residue and penetrate to the proper depth.
  • Plant soybean seed ¾ to 1 inch deep into good soil moisture.  Planting deeper will delay emergence
  • Consider fungicide seed treatments if planting into cool soils.

Soybean Seed Quality Continues to Deteriorate

The warm and wet September combined with early planting of early-maturing varieties have led to some rather severe seed quality problems in soybean this year.  Our harvest to date indicates that seed quality in our Northern Piedmont is pretty good, but declines as one moves south.  There also seems to be a good correlation with lack of rotation, earlier maturity groups, and earlier planting showing most of the problems.  The issues can usually be attributed to the diseases phomopsis seed decay and purple seed stain, which I’ll describe in more detail below.  Other diseases such as Alternaria, anthracnose, and frogeye leaf spot can also cause seed discoloration and quality issues, but are less common.  The bottom of the plant usually has more seed decay than the top.  But if harvest is delayed, the entire plant will be infected.

Phomopsis Seed Decay.  When soybeans mature during warm and wet conditions, we can expect seed quality to deteriorate.  Because this disease develops more rapidly on plants that are maturing under warm and wet conditions, we usually have more problems with early-maturing varieties.  We can however have seed decay on our later- maturing varieties if October is warm.  Although pods can be infected earlier, seed decay does not usually begin until after physiological maturity (R7).

Infected seed are shriveled, elongated, and cracked.  Severely infected seed may appear white and chalky.  The fungus secretes enzymes that degrade the seed coat proteins.  Test weight can be lower.  High occurrence of these seed can lead to discounts or rejection.

There are a few things that can be done to reduce the disease incidence.  It resides in the soil and on infected residue.  So, rotation is very important.  More decay will occur in a crop deficient in potassium, infected with viruses, and heavily attacked by insects.  Later-maturing varieties and later planting dates that delay maturity into the cooler parts of the year will reduce the incidence.  Still, timely harvest is the best management strategy.  The longer you leave the soybeans in the field, the worse the disease.  So, only plant as many early varieties as you can harvest in a timely manner.  Foliar fungicides will decrease the incidence of seed decay if applied from pod development (R3-R4) to early seed filling stages (R5).  My experience is that a single R3 will do little to prevent seed decay; it will usually take a second application at R5.

Purple Seed Stain.  Purple seed stain is caused by the organism Cercospora kikuchii, the same organism that causes Cercospora blight.  Before maturity, fields with Cercospora blight can be recognized by reddish leaves and reddish purple blotches on the stem and leaf petioles.  When severe, defoliation of the upper leaves of the plant will take place.  In many cases, the blotching progressed up the stem and to the pods.  Dark, nearly black pods may appear on some varieties.  Once it progresses to the pods, there is a higher likelihood that the seed will be stained.

Purple seed stain is very noticeable.  The seed will contain pink to pale purple to dark purple splotches, which can cover the entire seed coat.  The purple stain itself does not reduce yield, but seed with nearly 100% discoloration may be lower in oil and higher in protein.  A lot of staining can result in discounts.  Germination of seed with 50% or more staining will likely be delayed.

Usually, the disease first appears on the plant during early seed development.  If conditions are right (average temperatures over 80o for several days), then the disease will build up rapidly.  Other weather factors do not generally affect seed infection.  Severity of the infection is largely related to amount of infected leaf debris and residue.  Therefore, rotation with a non-legume crop is critical for control.

Other control measures include variety selection, planting high quality seed free of visual staining, and fungicides.  Varieties differ in their susceptibility of Cercospora kikuchii, but that information is rarely available in seed catalogs.  We routinely evaluate purple seed stain in our variety tests.  Fungicides will give some control if applied during pod or seed formation.

Wet Conditions May Lead to Soybean Seed Sprouting

One of the most disturbing late-season issues can be pod splitting and/or seed sprouting in the pod.  Pod splitting is most common when pods develop and seed begin to grown (R4 to R6 stages) during dry conditions and seed finish filling under wet conditions.  Sound familiar.  This is more-or-less what we experienced this year.  Seed sprouting is usually caused by extremely wet conditions after the crop is mature and seed moisture has dropped below 50%.

What causes pod splitting?  The reason is not clear, but here are my observations.  Generally pod splitting happens when the crop is under severe stress, usually drought conditions up until the full-seed stage (R6).  Pods are generally small due to the drought.  Then rains set in between R6 (full seed) and R7 (physiological maturity).  The seed grow and grow, and seem to outgrow the pods, causing them to split.  Obviously, this splitting can then lead to seed quality issues.  It can also open the plant up to seed sprouting,

Even if the crop does not experience the above conditions and pods do not split due to rapid seed enlargement, wet conditions after the crop is mature can lead to sprouting seed.  Sprouting seed is not always directly related to the pod splitting; pods may not split until seed sprout.  I’ve seen up to 30% of pods with sprouted seed when conditions are perfect for this.  Although an unusual occurrence, seed sprouting can occur if soybean seed drop below 50% moisture, then increase to 50% or more moisture.

In addition, I have seen more sprouting in pods showing Cercospora blight (very dark pods).  I do not understand why and could not definitively relate the sprouting to this disease.  But, there appeared to be a relationship. Sprouting occurred primarily at the top of the plant where the dark pods were located.  In contrast when pods were not dark, I have observed most sprouting at the bottom of the plant where the relative humidity is greater.

Usually, the number of split pods and sprouting seed is low and yield and seed quality effects are minimal.  After a week of drying conditions, the sprouted seed will dry up and may fall out of the pods.  At the worst, there could be some lower test weight and seed could contain more foreign material (from the dried up sprouts).  However, the light seed will likely be blown out the back of the combine.  If you do observe the problem and it is severe, I suggest that the air on the combine be adjusted to remove those light, sprouted seed at harvest.  Too many sprouted seed in the bin could lead to rejection by the buyer.