Recent mild temperatures and the mild winter are setting the stage for rapid development of marestail/horseweed (Conyza canadensis) this spring. Marestail was particularly troublesome last year in soybeans. Marestail can germinate in both the fall and the spring. It is more likely to overwinter in the rosette stage during mild winters. If you wait until your typical burndown the marestail may start bolting and therefore be more difficult to control. Adding to this difficulty, many marestail populations are resistant to Roundup (and other glyphosate containing products). You should scout your fields targeted for soybeans now to identify overwintering marestail. Marestail control can be achieved with 2,4-D or dicamba now and still offer plenty of time to avoid plant back restrictions (up to 15 days for 2,4-D or up to 28 days for dicamba). Glyphosate resistant weeds and the difficulty in controlling more mature weeds underscore the need to scout fields earlier and use some alternative herbicides in your program. Always consult the product label for specific instructions.
The Virginia Soybean Association in cooperation with Virginia Cooperative Extension would like to announce the 2016 Virginia Soybean Yield Contest. The purpose of the Virginia Soybean Yield Contest is to emphasize and demonstrate the practices necessary to produce maximum economic yields, to recognize those producers who grow high-yielding soybeans, and to gather data on the practices utilized by these outstanding producers. With the help of various seed companies, we reward and promote the achievements of Virginia’s most productive soybean farmers.
There are four Soybean Yield Contest categories: 1) Full-Season, Non-irrigated; 2) Double-Crop, Non-irrigated; and 3) Irrigated (Full-Season or Double-Crop; and 4) Most Efficient Yield (MEY). First, second, and third place winners of the full-season, double-crop, and irrigated contest will be recognized with appropriate trophies or plaques. In addition, cash awards of $200, $100, and $50 will be presented to the first, second, and third place winners in each of these categories. The winner of the MEY contest will receive a plaque declaring him or her the most efficient soybean producer in Virginia for that year.
Printable entry forms and contest details can be obtained from your County Agent or on the Soybean Extension and Research website.
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.For 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.
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.
It’s hard to believe, but June is here and we need to start thinking about increasing our soybean seeding rates. I’ve been recommending only 100 to 115 thousand seeds per acre for full-season production, enough to give you 70 to 80 thousand plants – yes, that’s all you need to maximize yield.
But as the season gets shorter, yields will start falling with delays in planting date. On average, we lose about 1/2 bushel/acre per every day we delay planting after the middle of June. The graph below shows the results of last year’s 4-state early wheat harvest/soybean planting double-crop study. Note that yield does not decline very much during the first week or two of June, but rapidly drops off afterwards.
The main reason for this yield decline is that the crop struggles to develop enough leaf area to capture 90-95% of the sunlight by early pod development, due to the shorter growing season. We can alleviate some of this by narrowing rows and increasing seeding rate.
I usually suggest that farmers plant enough seed to result in a final plant population of 180,000 plants/acre for double-crop soybean. That means planting 200,000 to 220,000 seed/acre. Yes that is a lot of seed, but my research shows that yields (and profit) continue to increase up to this seeding rate, especially when planting is delayed until late-June and early-July.
There are stipulations. More productive soils and irrigated soybean usually require less seed. Good years that allow lots of quick growth require less seed (but who can predict a good year?). Later maturity groups may require slightly less seed. Less seed are needed as you move south (growing season is longer and you can plant a later relative maturity). I think that a soil profile that is full of water at soybean planting (this year) might allow less seed to be planted – but I have not documented that – It just makes sense to me that plants will grow better when the small grain has not depleted most of the subsoil moisture.
What about now? How many seed/acre do we need to plant in the first week of June? Here are my suggestions. Keep in mind that these are general guidelines; you need a gradual increase in seed/acre. I’m assuming 80 to 85% emergence for June/July plantings. To easily determine how many seed you need per row foot, see VCE pub 3006-1447, Suggested Soybean Seeding Rates for Virginia
May: 100 to 115K
June 1-7: 120-140K
June 8-14: 140-180K
June 15-21: 180-200K
June 22-30: 200-220K
Do soybean inoculants work? Yes. Soybean cannot fix its own nitrogen without the symbiotic relationship formed between the roots and a soil bacteria called Bradyrhizobium japonicum. Soybean inoculant contains this bacteria.
Do you need to inoculate your soybean seed? Maybe. If you’ve never grown soybean in the field that you plan to plant them, definitely add the inoculant to your seed. Or better, inject some liquid into the furrow (you’ll get 3 to 4 times the amount of bacteria). Also, if you don’t have a long history of soybean in the field, inoculate; it will likely pay off.
But what if you are rotating the land to soybean on a regular basis? You are not likely to get a yield response. In a 2-year study on soils that were rotated regularly with soybean, I only found 1 of 18 sites that responded to an inoculant. And the site that responded was land that had only been in production for less than 5 years (formerly pine trees). In all fairness, one inoculant product at one other location (SUF DC, 2012) did yield more than the untreated check.
There are some caveats that I should mention. Sometimes, a yield response if more probable. If you haven’t grown soybean in the last 4 to 5 years, then it may be good insurance. If the field was flooded or if it experienced extreme drought conditions in the previous year, bacteria might have died off; therefore, there is a greater likelihood of a yield response to the inoculant.
In summary, inoculants do work and they are good insurance treatments. But, they will rarely result in a yield benefit if the field has been regularly rotated to soybean.
If you do decide to use an inoculant, follow the label closely. I prefer to apply the inoculant as close to planting as possible. Note that certain chemical seed treatments (including molybdenum or “Moly”) can injure or kill the bacteria. The less time that these chemicals are in contact with the bacteria, the better.
My usually answer to this question is “No…at least not on a big part of your acreage.” But, let’s rephrase the question to “Can you plant soybean in April?” The answer is clearly “Yes, you can…but don’t plant the entire farm in April.” Below, I’ll discuss the reasons for these answers.
What are the advantages to planting in April? One advantage is that the crop mature earlier. A general rule of thumb is that planting 30 days earlier will allow you to harvest about 10 days earlier? Only you can decide if harvesting 10 days earlier is an advantage though. So, ask yourself if this fits into your operation.
You can also gain another 10 or so days by selecting a variety that is at least a full maturity group earlier (e.g., MG 4.5 instead of a 5.5, or a 3.7 instead of a 5.0). You’ve then changed your systems substantially. Such a system is commonly referred to as the Early Soybean Production System (ESPS), which is now the most common soybean production system in the Mid-South/Delta growing region of the country.
But choosing an earlier variety and/or planting early is not just about harvesting earlier. You will also place the most critical time of soybean development (pod and seed fill) earlier in the season. For the Mid-South that regularly experiences drought in August, the ESPS puts those critical stages into July and early August; thereby avoiding the driest (and maybe hottest) time of the year. In addition, this system captures more sunlight per day during the pod and seed development stages (i.e., the days are longer in July than in August which are longer than in September), With more photosynthesis per day during these stages, we can gain yield potential. Early planting was also found to be beneficial in the Midwest; I suspect that the longer days were the primary benefit there. So theoretically, yield potential is greater with early planting of early-maturing varieties, even if drought in August is not the major concern.
Although similar benefits are possible in Virginia, planting early with an early-maturing variety can result in lower yields. Why? First, droughts in Virginia are intermittent. In some years, August is our driest month, in others it is July or June or September or…. Furthermore, most of our soils hold very little water. In some soils, we are 10 days from the last rainfall to a drought. Add to this that the hottest and usually driest time is late-July and early-August, and you have a recipe for disaster with early planting and/or early maturity groups.
But, what if you irrigate? These are the fields that I would use an early soybean production system. A high plant-available water-holding capacity soil also helps. At least you can avoid the drought stress. And because the season is naturally shorter, you will likely spend less on irrigation. But, there is still the heat risk. Only time will tell if the benefits outweigh the risks. Even in irrigated fields, you may only want to dedicate a small portion of your acreage to an early system.
A final risk from planting early is seedling diseases. It may take 2 to 3 weeks for soybean to emerge if planted in April. So, be sure to use a fungicide seed treatment.
In summary, there may be benefits to planting early and/or using earlier-maturing varieties. But, I think that the risks outweigh the benefits, especially in rainfed conditions.
Virginia Soybean Variety Test yield data are now available and can be found at my website – Virginia Soybean Extension & Research.
If you have comments or questions, please contact me.
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.
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.
As I’ve driving throughout Virginia these past few weeks, one thing that is evident is the large amount of vegetative growth on our full-season soybean. While adequate vegetative growth is necessary for maximum yield, it can work against the crop in seasons that experience August/September droughts. In much of Virginia, soil moisture was depleted rapidly due to this large amount of growth and the lack of rain in August and September resulted in pod and seed abortion. I’ve seen many fields that look relatively good from the windshield, especially after some rains perked up the plants. But, closer examination revealed few pods or few seed in the pods. In general, I think that farmers will be disappointed in their full-season yields.
On the other hand, timely rains during August and/or September in some parts of Virginia allowed these full-season soybean to match this seemingly excessive growth with lots of pods and seed. In such scenarios, 60 to 80 bushels per acre are possible. The only thing that may work against such a crop is, ironically, excessive vegetative growth that is causing or might lead to lodging. I always remind those that complain about lodging that 20 bushel soybean do not usually lodge.
Now we have Hurricane Joaquin bearing down on us. This could greatly change our yield potential, especially in our large full-season soybean with a good pod and seed set that is not yet fully mature. With this in mind, I thought that I would review lodging’s effects on soybean yield.
How much will the lodging cost us in yield? This will depend on the degree of lodging and the stage that the soybeans were in. In general, I’d say that our full-season crop is rapidly approaching maturity. Fields planted to earlier maturity groups are physiologically mature (R7, 98-100% of the final yield has accumulated), some are ready for harvest. Many fields are still in the R6 (full seed) stage. Most double-crop soybeans are in the R5 (beginning seed, seed are not yet touching in the pod) and R6. Yield is most severely affected by lodging when the lodging occurs at the R5 stage. Although yield is still affected at R6, yield losses are only half as severe at this stage. Although at a more susceptible stage, double-crop soybeans are much shorter and will not likely have as severe lodging as more full-canopied full-season soybean.
So, what’s my estimate on the amount of yield loss? First, we have to distinguish harvest or traffic loss from physiological yield loss. Harvest losses can vary anywhere from 3-10% depending on many factors. In some cases, we may have to run the combine of the most severely lodged soybeans in one direction.
There is little data on physiological yield loss, but what’s out there seems to be pretty consistent. What do I mean by physiological yield loss? That’s the loss in yield from lodging if all of the soybeans that are now on the plant can be harvested. In controlled studies where researchers simulated lodging and compared it to a crop that was artificially supported, losses have ranged from 0% to over 30%. Why such a range in yield loss? It depends on the severity of lodging and the stage of development in which the lodging occurred.
Let’s first address the severity of lodging. Soybean researchers have traditionally rated lodging on a scale of 1 to 5 as follows:
1.0 = almost all plants erect
2.0 = either all plants leaning slightly, or a few plants down
3.0 = either all plants leaning moderately (45O angle), or 25-50% down
4.0 = either all plants leaning considerably, or 50-80% down
5.0 = all plants down
Yield loss will be minimal unless most plants are leaning at a 45O angle or more. Otherwise, yield losses can range from 10-35%, depending on the stage in which the lodging occurred.
Why does lodging cause yield loss? It’s not completely clear, but the generally accepted reason is a reduction in net photosynthesis. With less photosynthesis, there is less energy going to the developing pods and seeds. When plants are lodged, relatively less of the upper leaves and more of the lower leaves are exposed to sunlight. The upper leaves are more photosynthetically active and the lower leaves are less active. When lodging occurs, the entire energy-producing mechanism is disturbed. In other words, we are now exposing less of the most productive leaves and more of the least productive leaves to the sun. So, yield will decline.
Let’s assume that lodging rated above 3.0 will cause a 10-30% loss. Now the severity of the yield loss will depend on the development stage that the soybean plant was in. As I said earlier, there’s little hard data on this subject, but a few older experiments give us some information. In a study conducted in 1972-73, S.J. Woods and M.L. Swearingin of Purdue University indicated that the R5 stage was the most critical time for lodging to occur. At this stage, yield was reduced by 18-32%. At stages R3 and R6, yield was reduced by 12-18% and 13-15%, respectively. Details of that experiment are shown to the right.
In that study, the plots were manually lodged with a long aluminum bar at the indicated soybean stage. Although lodging ratings were not given, I would consider it to be in the 3.5 to 4.0 range from the description given. Two varieties were tested. ‘Corsoy’ was more susceptible to lodging, but was able to branch more; therefore, it yielded higher when lodged. ‘Wells’ is more resistant to lodging, but did not branch as much; therefore, was unable to compensate as much for the lodging. In the natural lodged plots, only slight (2.0 or less) lodging occurred.
From the above data and a few other studies, I’d estimate that where lodging is moderate to severe and the soybean are in the early R6 stage, we could lower our yield potential by 10-15%. If the plants are still in the R5 stage and lodging is severe, losses could be 15-25%. If soybeans are in even later stages (mid-R6), yield loss will be less. If physiologically mature (R7, one pod on the plant has reached is final mature color), 98 to 100% of the dry matter has accumulated and losses will be nearly zero (assuming no harvest losses). Most of our full-season soybeans are close to physiological maturity (R7). Plus, plants with fewer leaves lodge less.
In summary, there may be some yield loss due to Hurricane Joaquin. Yield losses will be greater with later maturity groups or in double-crop acres that have good growth. But, hopefully, the hurricane will move off the coast and the only soybean we need to worry about lodging are those with very high yield potential.