The week started out on the wet side with a sustained rain event moving through the area Monday with rain amounts varying in the 1”-5” range with 2”-4” totals being quite common. Corn plant development ranges from V13 (collar on Thirteenth leaf) to V16 with some plants in protected areas starting to poke tassels out later in the week.
| Planting Date | GDU’S | Plant Stage | Growth Stage |
| 15-Apr | 1148.5 | Collar on Sixteenth Leaf | V16 |
| 23-Apr | 1100.5 | Collar on Fifteenth Leaf | V15 |
| 30-Apr | 1066.5 | Collar on Fourteenth Leaf | V14 |
| 08-May | 969 | Collar on Thirteenth Leaf | V13 |
We accumulated 125.5 Growing Degree Units (GDU’s) during the week which average out to 17.93 GDU’s per day. This is 21.5 GDU’s less per week and 3.07 GDU’s less per day than the 30 year average.
| Dates | 2015 GDU/Day | 30 Year GDU Average/Day | Difference/Day |
| July 5-11 | 17.93 | 21.00 | -3.07 |
| July 1-11 | 26.29 | 32.57 | -6.29 |
| Dates | 2015 GDU/Week | 30 Year GDU Average | Difference |
| July 5-11 | 125.5 | 147 | -21.5 |
| July 1-11 | 184 | 228 | -44 |
As we move closer to tassel/silking the amount of GDU’s a plant needs to add another collar or growth stage reduces. From emergence to V6 it takes 85-90 GDU’s to put on a leaf/collar and from V6 to V14 it takes 65-70 GDU’s to put on a leaf. Once the plant reaches V14 to V18 (pre tassel) it takes roughly 55-60 GDU’s to put on a collar or growth stage.
| Growth Stage | GDU’s |
| Emergence to V6 | 85-90 |
| V6 to V14 | 65-70 |
| V14 to V18 | 55-60 |
On an average year mid pollination for most hybrids in our area will be 1250 GDU’s with the latest mid pollination at 1340 GDU’s on a 111 day hybrid and the earliest would be 1202 GDU’s on a 92 day hybrid. The 30 year average in Southern Minnesota for tassels dates or mid pollination of 1250 GDU’s is July 19. Comparing Central Valley data for tassel dates from 2007 to 2014 our average tassel date is July 19 with the earliest mid pollination being July 7 in 2007, and the latest mid pollination being July 30 in 2013. (If you took out the years 2013 and 2014 the average tassel date would be closer to July 16). The way things are shaping up I wouldn’t be surprised if our average tassels dates would be July 19-20.
| Average Tassel Date | Year | ||
| 07-Jul | 2007 | ||
| 23-Jul | 2008 | ||
| 27-Jul | 2009 | ||
| 12-Jul | 2010 | ||
| 21-Jul | 2011 | ||
| 08-Jul | 2012 | ||
| 30-Jul | 2013 | ||
| 24-Jul | 2014 |
Receiving moisture just prior to and during pollination increases the probabilities of having a successful pollination period. If history (40-50 years) is an indicator, the likelihood of receiving rainfall from July 15-21 is approaching 80%. (We always seem to have rainfall during the Waseca County Fair, which along with Dodge County is taking place July 15-20th). We are starting to see higher levels of Eye Spot occurring as well as some early stages of Northern Corn Leaf Blight (NCLB) starting to show up. With the hot humid weather conditions that are predicted we may see NCLB as well as Eye Spot reach levels that would indicate a fungicide application. Soybean plant development ranges from unifoliate (VC) on some replanted soybeans to full bloom (R2). Soybean plant height is approaching 24” tall or morel on some early planted fields.
| Planting Date | Plant Stage | Growth Stage |
| 28-Apr | Twelfth Trifoliate to Full Bloom | V12-R2 |
| 03-May | Eleventh Trifoliate to Full Bloom | V11-R2 |
| 10-May | Tenth Trifoliate to Full Bloom | V10-R2 |
| 01-Jul | Unifoliate to First Trifoliate | VC-V1 |
The Soybean Aphid population has grown since we first spotted them in late June (Friday June 26th Agronomy Update), put not at the levels that I would normally anticipate. With that being said Soybean Aphid populations can grow rapidly and be a yield robber very quickly. 
In my experience I tend to find Soybean Aphids sooner in fields that:
- The first or last planted soybeans
- By wooded areas that have buckthorn in them
- Soybeans with Seed Treatments with absent or less active insecticidal properties
- Fields with lower Potash (K) levels (140 PPM or less)
Unlike the Soybean Aphids the Septoria Brown Spot we have found in fields is starting to get worse, due mainly to our more moderate temperatures and increased moisture levels, from rain, dews and higher humidity. The concern that comes about with Septoria is that it starts to defoliate the soybean plant from the bottom up. What this fungal disease does is infect a portion of the leaf and much like other diseases it moves and infects the rest of the leaf, which shuts down the photosynthetic capabilities of that leaf. This will move from the bottom of the plant upward from leaf to leaf and plant to plant. By reducing or shutting down the photosynthetic “factories” in the leaves you reduce that total area in the plant that can help fill beans in pods, which reduces yield not only by reducing the number of beans and pods but also reduces the actual size of the soybean seed. 
As you are out walking soybean fields’ plants that have Septoria Brown Spot will lose their leaves and will fall to the ground. The photo above shows affected leafs still attached to the petiole but if you look closely to the left of the affected leaves you can see leaves that have already fallen off of the plant. As soybeans start to flower and enter full bloom (R2) the rapid uptake of potassium (K) and nitrogen (N) is starting. At R2 soybean plants have taken up 15% of that years N and K needs for the year, and by early to mid-August when soybeans plants have reached the beginning seed stage (R5) they will have taken up 70-75% of the N and K needs for the growing season. The implications of not having enough nutrients available to the plant now will become more visible and taking a tissue sample at this stage will help plan for that field’s fertility program in the future. Soybean plants will flower and put on vegetative growth at the same time. Peak flowering occurs at beginning pod development (R3), with flowering continuing until beginning seed (R5) or shortly thereafter. Not every flower or blossom will produce a pod, in fact it is not unusual for soybean to abort 60-70% of its flowers. The issue with aborted flowers is that it provides and opening for a fungus Sclerotinia sclerotiorum (which causes White Mold) to enter the plant. White Mold favors cool wet weather conditions in fields with dense canopy’s and high fertility levels. Fields with heavy manure applications or high nitrogen levels are more prone to white mold. Historically fungicides and “burner” type of herbicides have had mixed success in helping to control white mold, with that being said new products have come into the market place that initial data indicates good, to very good control of white mold. If you have had a field with a history of white mold and were going to apply some method of control now would be the time to do so. Upcoming Events:
- Central Advantage Plot Meriden July 14-15th
- Waseca and Dodge County Fair July 15-19th
- Central Advantage Plot Kenyon July 16-17th
- Land Use Expo Monday July 20th 10-3PM Rodney Krell Farm 2 miles north of Blooming Prairie on HWY 218
- Rice County Fair July 21-26
- Central Advantage Plot Blooming Prairie July 22-23rd **Date Change***
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