We just received confirmation that kudzu bug adults have been found in two counties, one on a trap at the VT Tidewater Ag Research and Extension Center in Suffolk, and several on the side of a building in Mecklenburg County (see the attached map). These adults are the overwintering population getting active as the weather warms. They are about a month later than our first reports in 2014–the first in that summer emerged the first week in March in Chesapeake. This winter has been pretty cold and wet compared to some and could have caused this delay. Most likely more reports will start coming in soon. Updates will be posted. Kudzu_bug_traps_7_Apr_2015
Category Archives: Soybean
New Survey Shows High Level and Widespread Resistance of Thrips to Neonicotinoid Insecticides
Please see the attached report by Dr. Herbert (Virginia Tech) and Dr. Kennedy (North Carolina State University) regarding thrips resistance to neonicotinoid insecticides. NeonicThripsResistance
2014 Virginia Soybean Yield Contest
The Virginia Soybean Association in cooperation with Virginia Cooperative Extension would like to announce the 2014 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 my website: (http://www.arec.vaes.vt.edu/tidewater/soybean/). I look forward to seeing your entries.
Sudden Death Syndrome and Brown Stem Rot Showing Up in Virginia Soybeans (David Holshouser & Hillary Mehl)
Many fields are exhibiting symptoms of interveinal chlorosis and necrosis. In the some areas (hot spots), leaves are burning up and dying. In the worse fields, entire plants are dying. Sometimes the leaves are falling off the petiole; in other cases, the leaves remain attached. The symptoms look similar to, but usually worse than, various nutrient deficiencies. Actually, what is occurring is very similar to a nutrient deficiency in that something is restricting the roots and/or vascular system from moving water and nutrients through the plants. If you start seeing such symptoms, dig some roots and examine them. Then, split the stem and tap root. If you see any discoloring, then you likely have a stem/root disease.
Is this sudden death syndrome (SDS)? Maybe. We tend to hear a lot about this disease in the media, in a seed catalog ratings, and throughout many extension bulletins in the Midwest. Although the name makes the disease sound like the entire field is getting ready to die, this is not usually the case. Up until this year, SDS was neither devastating nor widespread in Virginia. However, we are seeing more than the usual cases this year.
SDS in Virginia Soybean
It appears that the disease spreads suddenly; you don’t see it one week, but the parts of the field begin dying the next. In reality, it has been building up slowly as the season progresses. The infection actually took place much earlier in the year. Regardless, SDS will rarely result in widespread death of the soybean crop. Instead, you will usually see it in spots and patches in the field. Worth noting is that SDS is commonly associated with soybean cyst nematode infestations. So, if your field has been diagnosed with SDS, then you may want to sample for nematodes. Below is a photo of one of our on-farm soybean variety tests. It is one of the worst cases of SDS that I have ever seen. Although a few varieties are more tolerant to the disease than others, it appeared to affect all of the varieties to some extent.
SDS in On-Farm Variety Test in Virginia
Although SDS is turning up in several fields this year, the same above-ground symptoms are also association with brown stem rot (BSR), which has been the most common root/stem disease in Virginia. Some of the plant samples that have come through our plant pathology lab have been diagnosed as BSR. It usually doesn’t cause widespread death and it usually limited to small spots or patches in the field. In general, it will not continue to spread over the rest of the field; however, the patches will enlarge over time. Yield loss is usually minimum and restricted to the infected areas.
SDS Symptoms in Soybean Stem
As mentioned earlier, if plants begin suddenly showing above-ground symptoms, dig the roots and split some stems. If the pith (center) of the stem and taproot right at the soil level is brown, then the cause is likely (but not always) BSR. If you see a white pith and the rest of the root is brown, then the disease could be SDS. Another diagnostic tool is to look at the leaves. If the leaflets fall off but leave the petiole attached to the stem, it is likely SDS. if the leaves don’t fall, it’s likely BSR. Finally, you’ll seed more rotted roots with SDS. But, to find the rotted roots, you’ll need to dig them up and wash the soil from the roots. Jerking the plant out of the ground will likely strip off most of the roots.
The last disease that could be a problem and exhibit the same symptoms is red crown rot (in peanut, this is called cylindrocladium black rot or CBR). This disease can however be recognized by red fruiting bodies found at the base of the stem. Red crown rot was more common when Virginia’s peanut acreage was greater and soybean and peanut were being rotated with each other.
Red Crown Rot in Soybean
Regardless of the disease, what can you do about it? Unfortunately, there is nothing that can be done this year. Foliar fungicides will not control a disease that is inside the stem and roots. But, in the future, rotate out of soybean for one or more years. Also, you may want to select a variety with resistance to that disease when you plant soybean in the field. Finally, as mentioned earlier, take a nematode sample. Just because you’re seeing SDS or BSR in your field this year doesn’t mean that you have nematodes. But anything that is restricting root growth could aggravate SDS or BSR; therefore the symptoms would be more evident in fields infested with nematodes.
SOYBEAN LOOPER ALERT
Soybeans in parts of North Carolina, especially in their eastern ‘Blacklands’, have been plagued by soybean looper infestations for a few weeks. I got the first report of infestations on our Eastern Shore earlier this week, and today, I got a report of a field hit in Southampton County.
Soybean loopers follow a pattern that we have seen in the past. They do not overwinter in Virginia so moths must migrate in from the south. Adult moths are transported short or long distances by weather fronts. It is not uncommon to find a few soybean loopers in any given field, any time during the season. But it is fairly uncommon to have large flights. The pattern that I have seen, and the one that is playing out this year is that when large populations build up to our south, moths are transported to our area in large numbers—and—most commonly in mid-September.
Another important factor to be aware of is that almost invariably, these large flights result in large worm outbreaks IN FIELDS THAT HAVE BEEN PREVIOUSLY TREATED WITH PYRETHROIDS. Our current research is showing that pyrethroids are hard on beneficial insects and spiders that feed on looper eggs and small worms. If destroyed, a much larger percentage of looper eggs hatch and a larger percentage of worms survive.
So, if a looper infestation is discovered in a field, what is the threshold and what products provide the best control. We do not have a threshold for loopers but lump them into a general leaf defoliators ‘guild’ which can include many leaf eaters (Japanese beetles, green cloverworms, grasshoppers, bean leaf beetles and others)—and base a treatment decision on the total leaf area destroyed by the guild. We recommend not treating fields with fully developed seed unless 35-40% of the leaf area is eaten and bugs are still present.
We also know that soybean looper is a unique pest in that large numbers can completely defoliate a field in a short period of time, in as few as 5-7 days if numbers are really high. So here is a looper rule-of-thumb. Treat if you get 12-15 or more in 15 sweeps and the field has not reached full pod maturity (pods yellowing and seed getting hard).
Do not use a pyrethroid for loopers. These critters are hard to kill and the best success will be with non-pyrethroids like Belt at 3 oz, Prevathon at 14 oz, or Besiege at 10 oz. Other products that contain sinosad may also be effective.
Now is a Good Time to Evaluate Your Varieties for Foliar Diseases
September is a great time to evaluate your crop and the performance of varieties that you chose. In addition to general growth and health of the crop, take some time to determine if you have any of the below diseases. If so, you could be losing some yield. If you sprayed with a fungicide and still have disease, reconsider the product and rate used and the time that the fungicide was applied. Keep in mind the weather conditions when the application was made and the conditions 2 to 3 weeks after or before the product was applied. Cool temperatures (70’s) and high relative humidity (>95% for 12 hours or more) will usually increase disease incidence.
Another caution is to never diagnose a specific disease on the plant without verifying it with a person trained to identify plant pathogens. Only when the reproductive structures are found on the leaf can a disease be confirmed. Many things will cause look-alike symptoms. Be sure before you cast the blame. There are more diseases than just the ones shown below, but these are the most common. Brown spot is normally found in the lower part of the crop canopy (the lower leaves), Cercospora blight and leaf spot will be found throughout the canopy, and the frogeye leaf spot and downy mildew tend to be found in the upper part of the canopy.
BMSB and Kudzu Bug Update, Sept. 4, 2014
Although numbers are still generally very low, our field scouts and others have found BMSB and kudzu bug in a few new counties this past week. The eight new counties added for BMSB are Gloucester, Charles City, Hanover, Spotsylvania, Rappahannock, Prince George, Suffolk and Chesapeake (thanks Stan Winslow for the Chesapeake report). The two new kudzu bug counties are James City and King William (thanks Paul Bodenstine for the King William report). See the maps below for the most recent distributions. Although there may have been a few fields treated for these pests, as far as I can determine most have not. We know of one grower in Campbell County who had some threshold numbers but only in a few patches along one field edge. He elected to spot treat only these patches and so far, our post treatment visits have shown that this strategy was successful, that is, no reinfestation and no spread.
Corn earworm update: few moths but with high tolerance to pyrethroids
Although we hear rumors of worms in soybean fields, our scouting does not confirm this. We are finding almost none in either full season or double crop fields—and others are reporting the same. The full season crop is quickly approaching the ‘safe’ zone, that is, the point where pods are too tough to be attractive to insect pests. But, the summer is not over yet. Because corn is slow to dry down this year, we may still see a corn earworm moth flight into soybean fields, and if this happens, double crop fields would be a primary target. This is also true for stink bugs. As we get into late summer and early fall, stink bugs will be attracted to double crop fields. We strongly recommend that you begin checking double crop fields.
Because of the very weak corn earworm moth flight, we have not been able to capture and test nearly as many moths for pyrethroid tolerance as we have in the past. But all indications are that levels are high (see the graph below). In the most recent sample more than 40% survived the vial challenge. If this high pyrethroid tolerance level coincided with a large flight the large numbers of worms in fields, we would no question be recommending non-pyrethroids. But with this weak flight and the low numbers of worms in fields, I think we can get decent enough control with high rates of pyrethroids, alone.
Brown marmorated stink bug (BMSB) and kudzu bug (KB) in more counties but numbers still very low
We are still finding BMSB and KB in new places—7 new counties for BMSB (Sussex, Albemarle, Cumberland, New Kent, King George, Isle of Wight, and Surry), and KB in 3 new counties (Mathews, Mecklenburg, and Virginia Beach)—but numbers in all locations are way down compared with last year (see the maps below). No fields are at threshold for either pest, but a couple of fields were identified in James City County that have some infested edges. The full season crop is going to be safe from injury soon, when plants grow through the R6 stage. As the season moves into late summer and early fall, double crop fields will provide one of the few good late season food sources for all stink bug species—so they will need to scouted until they are safe from injury.
Brown marmorated stink bug distribution in Virginia–August 21, 2014 report
BMSB was found in soybean in nine new Virginia counties this past week: James City, Caroline, Stafford, Culpeper, Fauquier, Nelson, Rockbridge, Henry, and Montgomery. The highest numbers of BMSB occurred in a Warren field (5 nymphs and 4 adults per 2-minute visual inspection), followed by Augusta (5 nymphs and 1 adult per 2-minute visual), Fauquier (5 nymphs), Buckingham (4 nymphs), James City (3 nymphs, 1 adult), and Appomattox (3 nymphs, 1 adult). Thanks to our soybean scouts and to Dr. Tom Kuhar for their updates this week.
