Knowing how much, if any, nitrogen you lost during large rain events is a difficult question. You need to consider when you applied nitrogen, your soil texture, your source, the rain event intensity, among other factors. Take a look at this publication for a few things to consider after an intense rain event following nitrogen fertilization: Nitrogen_Corn_5June2018.
The decision of whether or not to replant arises every year; however, the wet soil conditions seem to have worsened the problem this year. There of course will be areas that the decision is easy – flooded areas resulting in almost no stand. But, what about fields that just are not living up to your expectations? I’ve seen and heard many reports of stands being reduced 25 to 50% of what was expected (keep in mind that our expectations are sometimes too high).
First, I must mention that final average stands of 60,000 to 80,000 plants/acre rarely profit from replanting. Only when you get below 50,000 can it be economically justified. I refer you to the seeding rate data shown. Note that yield does not fall off until seeding rates fall below 90 to 120 thousand seed/acre (76 to 107 seed/acre on productive soils). Stands generally averaged 75%; so, this is equal to 65 to 90 thousand plants/acre. Once you add in the cost and of and time required to replant, it’s not usually worth it – unless the stand less than this.
Determining whether or not to replant is hard. To ease the pain, I’ve summarized some relatively simple steps to help in your decision. One should incorporate 2- to 3-foot gaps into your decision to improve the estimation of yield loss.
Then, just multiply your counts by 1,000 to get plants per acre.
Or, use the Tables 1 or 2 to determine remaining plant population. The “hula hoop” method (Table 2) is valuable with drilled soybean or when rows cannot be distinguished. This involves placing a circular measuring device such as a hula-hoop on the ground and counting the plants contained within.
| Table 1. Plant populations of different row spacing with different plant counts per foot. | ||||||
| Plants/ foot | Row Spacing | |||||
| 36 | 30 | 24 | 20 | 15 | 7.5 | |
| Plant Population (1,000’s/acre) | ||||||
| 1 | 15 | 17 | 22 | 26 | 35 | 70 |
| 2 | 29 | 35 | 44 | 52 | 70 | 140 |
| 3 | 44 | 52 | 65 | 78 | 105 | 210 |
| 4 | 58 | 70 | 87 | 105 | 139 | 278 |
| 5 | 73 | 87 | 109 | 131 | 174 | — |
| 6 | 87 | 105 | 131 | 157 | 209 | — |
| 7 | 102 | 122 | 152 | 183 | 244 | — |
| Table 2. Hula-hoop method for determining drilled soybean populations. | |||||
| No. ofPlants | Inside Diameter of Hula Hoop | ||||
| 30” | 32” | 34” | 36” | 38” | |
| Plant Population (1,000’s/acre)a | |||||
| 6 | 53 | 47 | 41 | 37 | 33 |
| 10 | 89 | 78 | 69 | 62 | 55 |
| 14 | 124 | 109 | 97 | 86 | 77 |
| 18 | 160 | 140 | 124 | 111 | 100 |
| 22 | 196 | 172 | 152 | 136 | 122 |
| 26 | 231 | 203 | 179 | 160 | 144 |
| aPlants/acre = no. plants ¸ (3.14 x r2 ¸ 43,560 ft2) where r = radius of hula hoop in feet. | |||||
| Table 3. Yield response (% of maximum) of full-season soybeans to deficit standsa. | |||
| % Stand lost to gapsb | Remaining Plant Pop (1,000’s/A) | ||
| 70 | 105 | 140 | |
| 0 | 95 | 97 | 100 |
| 10 | 93 | 96 | 98 |
| 20 | 91 | 93 | 96 |
| 30 | 88 | 90 | 93 |
| 40 | 83 | 86 | 89 |
| 50 | 78 | 81 | 84 |
| 60 | 73 | 75 | 78 |
| aSource: Pepper and Wilmot. Managing Deficit Stands. 1991. Illinois Cooperative Extension Cir. 1317.bGaps of 12 inches or more; 30-inch rows | |||
Note that these data are from Virginia.
| Table 13.4. Yield response (% of maximum) of double-crop soybeans to deficit standsa. | ||||
| % Standlost to gapsb | Remaining Plant Pop (1,000’s/A) | |||
| 100 | 140 | 180 | 220 | |
| 0 | 80 | 88 | 95 | 100 |
| 20 | 71 | 79 | 86 | 91 |
| 40 | 61 | 69 | 76 | 81 |
| 60 | 48 | 57 | 64 | 69 |
| aSource: 2001-2004 experiments, Suffolk, VA.bGaps of 3 feet; 15-inch rows; MG 4 variety | ||||
Rainfall across the state resulted in in saturated soils and sometimes flooded soybeans or fields to be planted in soybean. Although fields are drying out, more rain is expected this weekend.
It’s difficult to know the long-term effect of flooding on soybean fields. Research is limited, but we do know that the fate of flooded fields will largely depend on 1) the development stage during which the flood took place; 2) the duration of the flood; 3) the temperature during and right after the flood; and 4) the drying rate after the flood.
Basically a flooded field depletes the roots of oxygen (O2), causing photosynthesis to slow. After several days without O2, the plant may turn yellow, grown very slowly, and possibly die. Other indirect effects of flooding can include reduced nitrogen-fixing bacteria (but they will recover), nutrient imbalances, and increased disease pressure.
For more detailed information, see a blog post that I wrote in 2013 at the Virginia Soybean Update site.
In short, here are a few pointers for flooded fields. If soybean have not yet been planted:
For flooded fields that have been planted:
Though it has been around for several years, the Crop Protection Network (CPN) has recently added several publications on disease management in corn, soybean, and small grains that are relevant to growers, crop consultants, and extension personnel in Virginia and the surrounding region. These can be accessed at the CPN website cropprotectionnetwork.org. As stated on the website:
“The Crop Protection Network (CPN) is a multi-state and international partnership of university and provincial Extension specialists, and public and private professionals that provides unbiased, research-based information. Our goal is to communicate relevant information to farmers and agricultural personnel to help with decisions related to protecting field crops.”
Extension specialists throughout the country (including myself) contribute to the publications and other resources posted on the website. An example of a recent publication on optimizing fungicide use for control of Fusarium head blight can be downloaded below. The CPN library includes over 30 publications on crop management, and additional publications are in development.
Fusarium head blight (FHB) risk for Virginia continues to be to high throughout the state due to recent wet, warm weather (http://www.wheatscab.psu.edu/). Most of the wheat is past the flowering stage and no longer at risk, but later flowering wheat may still need a fungicide application. Triazole fungicides including Prosaro, Caramba, and Proline are recommended. Do not apply fungicides containing a strobilurin since this can increase DON. For wheat that is past flowering, a fungicide application will not reduce FHB or DON contamination of the grain. Grain harvested from fields with signs and symptoms of FHB should be kept separate from non-infested grain.
For assistance with disease identification or management recommendations, contact Dr. Hillary L. Mehl, Extension Plant Pathologist (hlmehl@vt.edu).
Recent heavy rains have led to temporary flooding of numerous soybean fields throughout Virginia and put us behind with soybean planting . Only 26% of the crop was planted as of last week. And it looks as if we will have another bout of rain this weekend.
Although you will be tempted to get back into these fields as soon as possible, I caution you to hold off until the entire field dries to a point where you will not damage the soil, especially around the seed. Planting into wet soils can compact the soil around the seed, making rapid seedling growth difficult. For continuous no-till fields, you can also cause some long-term compaction that will not be easily removed without tillage. I usually advise to wait another half or full day before you think you can get back into the field. In the long run, it will likely pay off.
When should we get into a big hurry to plant? Planting date research indicates that we usually don’t see a rapid decline in yield until mid-June. Below is some Virginia research to verify this.
Although the below multi-state data is double-crop soybean, it also illustrates the point well.
So, you are likely to lower your yield much more by planting too wet than delaying the planting (or re-planting) until the last week of May or the first week of June. Still, only you know your operation. If you still have hundreds, or maybe even thousand acres to go, you may not want to wait too late.
I have received several reports from Virginia Beach and Chesapeake of armyworms infesting wheat and hay in large numbers. Neighboring regions of NC are experiencing similar outbreaks.
Overall, these infestations are rare in our state, but scouting is recommended. Fields treated previously with pyrethroids may be at higher risk because they contain fewer natural enemies to combat pest outbreaks. Armyworms feed at night and may be found under residue and at the base of plants during the day. Oftentimes, they can be seen curled into a c-shape (see photos below). Thresholds are one larvae (0.75 in or longer) per linear foot in barley and 2-3 per foot in wheat. Refer to Chapter 4 of Virginia Tech’s “Pest Management guide: Field Crops” for products and rates labeled for armyworm control in our state. Pay attention to PHI before making an application. Pyrethroids can be effective against armyworm. Good coverage is critical, especially in high residue fields.
Photos courtesy of JB Rigg, Helena Chemical.
Three-day forecast for Fusarium head blight (FHB) risk on susceptible wheat varieties.
FHB risk is increasing in Virginia and will continue to increase over the next several days. Risk is highest on the Eastern Shore, but susceptible varieties such as Shirley that are flowering over the next week will be at moderate to high risk in many portions of the state. Growers should monitor the FHB risk tool (www.wheatscab.psu.edu) as their wheat crop begins to flower. Consider applying a fungicide if risk is moderate to high, especially on susceptible or moderately susceptible varieties. Wheat that has completed flowering is no longer at risk. Fungicides should be applied at early flowering or up to one week later. Do not apply a strobilurin-containing fungicide since this can increase DON contamination. Recommended fungicides include Prosaro, Caramba, and Proline.
Steve Rideout, Extension Plant Pathologist at the Eastern Shore AREC, confirmed stripe rust on research plots of Shirley on Monday. FHB risk continues to be high on the Eastern Shore, so growers in this part of the state with varieties that are susceptible to stripe rust should consider an application of Prosaro, Caramba, or Proline since these will control both FHB and rust.
Stripe rust on wheat.
For assistance with disease identification or management recommendations, contact Dr. Hillary L. Mehl, Extension Plant Pathologist (hlmehl@vt.edu).
Research data, such as those here Seeding Rate-May 2018, showed that saving seed at planting does not return high yields or economic profit. To achieve high yields, we recommend planting 5 or 6 seeds per foot of row, assuming a germination of 80% and above. This is in particular necessary for large seeded cultivars like Emery and Wynne, and under irrigation. If germination is lower than 80%, which may be the case this spring for some seed lots of Wynne and Sullivan, 6 to 7 seeds are safe to plant but nothing above that. At least, we have not recently tested or heard of a benefit to increase the seeding rate above 7.
