SOYBEAN APHID UPDATE

We continue to get several calls daily about the soybean aphid (also known as the Chinese aphid or AsianAphid).  It is fair to say that probably every county east of Highway 81 and quite a few, if not all, of the counties west of Highway 81 have soybean aphids in at least some fields. In fact, in fields east of Highway 81, if you looked long enough you could likely find at least a few soybean aphids in nearly every field.  Here are our observations (and others’) and considerations if aphids are detected in your fields:

Numbers here at the Haskell Ag Lab appear, in general, to be higher in dryland than in irrigated soybeans.  The aphids tend to be in the newer leaves on the top of the plant, favoring the leaflets that have just expanded or are not even fully expanded yet.  Once populations reach over 200 or so per plant, some aphids will be seen on the stems as well.  As is common with most insect pests, some varieties seem to be “favored” by the aphid.

The aphids did not appear until about 2-3 weeks ago and with the soybeans currently in the R3 stage or later, there will probably not be a significant yield reduction in the vast majority of fields.  That being said, with our limited experience we advise growers to be extremely watchful over the next couple of weeks to observe what is happening with the aphid.  We are sure we will get questions on when it will be economical to treat.  Looking at data from other state’s trials, we have come up with a “rule of thumb” estimate as to the number of aphids needed before considering treating with an insecticide.

If 200 or more aphids per plant are present in 75% or more of the soybeans, it may be advisable to treat.  We regard this as a very conservative estimate.  Anything lower than this will likely not respond to an insecticide treatment.  Remember this is a field average.  There will be “hot spots” where numbers could be considerably higher.  Try to be objective and consider the field as a whole rather than to concentrate on the worst part of the field to make your decision.  One field in South Dakota experienced yield advantages from 2 to 11 bushels when treated on August 9, 2002 in the R5 stage.  However, the plants averaged nearly 1000 aphids per plant in this field.

Insecticide control was very good with all treatments in the South Dakota trial, experiencing over 90% control.  Rates used were Lorsban and Furadan at 8 oz per acre, Warrior at 1.92 and 3.20 oz per acre,

Asana at 5.8 and 9.6 oz per acre, and Mustang at 3.2 and 4.0 oz per acre.  The lower rates worked as well as the higher rates in this trial.  At this time of year, resurgence of the aphid population or possible spider mite flare-up will probably not be a problem.

SOYBEAN CYST NEMATODE FIELD DAY

The University of Nebraska Cooperative Extension and Pioneer are holding a Soybean Cyst Nematode Field Day on Monday, August 25, at 10:00 AM in Pierce County.  A luncheon meal and refreshments will follow the meeting.  The field is located 1 mile west of  Weetown on Highway 98,  1 mile south and ½ mile west.  From Pierce, go 3 miles east, 1 mile south, and ½  mile east.  Follow the signs to the meeting location.

Speaking at the meeting will by John Wilson, Burt Co. Extension Educator, who has been a leader in raising awareness of  the nematode, and Leon Streit, a Pioneer Agronomist.  Identification of the problem and solutions will be discussed

SOYBEAN CYST NEMATODE

In our meetings with growers and consultants over the last few years, we have often heard the comment that some area soybean fields are not yielding as well as they have in the past, or that they have not reached yield expectations relative to the type of soil and varieties planted.  While many different causes can reduce soybean yields, recent discoveries suggest that you should consider looking into the soybean cyst nematode as a potential yield- robbing problem.

The soybean cyst nematode (SCN) is the most serious pest of soybeans in the United States, causing farmers millions of dollars in losses each year.  It is a “stealth” pest in that often SCN will reveal no specific symptoms and its effects are often not dramatic.  Many farmers do not know their fields are infested with SCN until a severe problem develops.  Up to 30% yield losses can occur without obvious symptoms.

Previously, SCN had been known to occur in eastern Nebraska along the Missouri River; however, new information indicates a larger range across the state, particularly in northeast Nebraska. Recently, UNL plant pathologists reviewed the occurrence based on UNL and private lab records.  Positive SCN samples were found across more counties than previously reported. New counties with SCN were Boyd, Pierce, Antelope, Nance, Boone, Cedar, and Thurston.  It is likely that most counties in northeast Nebraska now have SCN in a least a few fields. Based on this information it would be good to check your fields for soybean cyst nematodes, particularly if you have a field that has been dragging in yield recently.

There are two ways to check for soybean cyst nematode. 1) Examining the roots or 2) submitting a soil sample to a laboratory. On the roots, cysts will appear as cream to brown-colored bodies, which are pinhead in size. They should be present on the roots anytime after the Fourth of July. If you decide to take a soil sample for soybean cyst nematode, this can be done at any time of the year, but populations will be highest at harvest. Often people take soil samples after harvest when things slow down.

 Once in a field, soybean cyst nematode will never go away. The key to keeping soybean fields at high production levels is to keep the population of soybean cyst nematode low. Populations are given as the number of SCN eggs per 100 cubic centimeters (cc) of soil (roughly half a coffee cup). Very high populations of soybean cyst nematode will develop in fields that are not managed properly. This is especially true in fields with sandy soils. If the nematodes are not detected soon enough and numbers become high, fields will need to be rotated to a non-host crop for several years. If there is a history of soybean cyst nematode in a field, choose a variety resistant to it. Unfortunately, most varieties in Nebraska have the same sources of resistance. This makes it difficult to rotate sources of resistance, which is recommended as part of an overall management strategy.   However, more seed companies are making more SCN resistant soybeans available in Nebraska.  If you cannot find a different source of resistance, at least rotate varieties. The most common source of resistance - PI88788 - is not the same in all varieties. The recommended rotation for fields infected with soybean cyst nematode is a six-year corn/soybean rotation (SCN resistant soybean - corn - SCN resistant soybean - corn - susceptible soybean - corn). The susceptible soybean is placed in the rotation so that SCN populations don’t develop their own resistance to the resistant soybean plant.

In fields found positive for soybean cyst nematode; plan to monitor the population every few years. Populations can and do change.