Monday, September 15, 2014

Soybean Sudden Death Syndrome Update

There have been numerous reports across the state of soybean sudden death syndrome (SDS) showing up in certain fields since August. SDS, which can be a devastating disease, is caused by the soil fungus Fusarium virguliforme (Fv).  Fv is actually a soilborne fungus that attacks roots early in the season and later causes a root rot. Infection is favored by cool soils with good moisture; thus, this spring was perfect for infection in most full-season fields. As plants go into the reproductive stages, the causal fungus produces a plant toxin that causes above ground foliar symptoms of yellowing and tissue death between the veins (see below picture), and later defoliation. If the disease comes into the field during the early pod development stages, and enough of the field is impacted, SDS can result in almost total yield loss. This is, however, an extremely rare event in KY. More typically, the disease causes significant yield losses in spots in a field - usually the lowest portions where soil moisture is greatest - but the majority of the field has little to know yield impact.  That is, most plants either escape disease altogether or symptoms come in after mid to late -pod fill. Plants showing late symptoms will generally yield very well. Thus, the appearance of symptoms is not necessarily a good indicator of yield loss potential. Timing of symptoms is everything when it comes to SDS.

SDS is variety dependent. Many cultivars are available with respectable resistance to SDS. Some are fully susceptible. That is why fields with a history of SDS should always be planted to a resistant cultivar. SDS is also favored by early planting. This is because infection by the Fv is greatest when soil is cool and wet. Generally, very early planting dates meet these requirements for infection in most years. That is just one reason why growers take a great risk when planting soybean in late April.  For exactly the opposite reason, double crop soybeans rarely show significant levels of SDS. This is because doublecrop beans are planted in late June to early July. Soil temperatures and moisture levels are rarely highly conducive to infection by the SDS pathogen during late-planted situations.

If you have a field that you think has SDS, the most desirable way forward is to send a sample to one of our two Plant Disease Diagnostic Laboratories for confirmation. Foliar symptoms can be mimicked by other diseases and even certain insects, so confirmation based on foliar symptoms alone may not yield an accurate diagnosis. But the foliar symptoms coupled with rotten roots and a milky brown stem discoloration (when a longitudinal cut is made into the stem) are the "trifecta" of symptoms for SDS. No other soybean disease will show those three symptoms at the same time.

Note: Foliar fungicides do not have a direct effect on SDS.  However, in rare instances a very limited (favorable) indirect effect may be evidenced by a slight reduction in SDS foliar symptom severity. This indirect effect is unpredictable, but when it occurs is related to stress reduction following the application of certain fungicides, especially strobilurin fungicides. Currently available seed treatment fungicides are ineffective at reducing infection by the SDS pathogen, Fv.  Beginning next year, a seed treatment product may be available that is capable of reducing infection by Fv (there by reducing SDS). More on this potential breakthrough later.

Wednesday, September 10, 2014

Tuesday, September 9, 2014

Got Fall Armyworm? Want Some More!!!

Doug Johnson, Extension Entomologist, University of Kentucky
Patty Lucas, Extension IPM Specialist, University of Kentucky

Fig.1 FAW moth capture in UK-IPM trap in Princeton, KY
For the past week or so we have been dealing with large populations of fall armyworm (FAW) caterpillars. These hungry little pests have devoured alfalfa, forage and lawn grasses while munching around the edges of soybean fields. I am sorry to inform you that while this problem is decreasing it may also reoccur.

The caterpillars that have thus far caused our damage are probably the result of an increase in FAW moths during the last week of July. You must remember that FAW has been trickling into KY for several months and is a normal part of the pest pressure in August and September, particularly in the western 1/3 of the state. You can see this “pulse” in Figure 1. Also note that this graph is updated every week and can be viewed on the IPM web pages at:

http://www.uky.edu/Ag/IPMPrinceton/counts/fall/fawgraph.htm

Thursday, September 4, 2014

2014 Wheat Contest Winners are Available

The 2014 Wheat Contest Winners are available online. The highest yield submitted was 120.26 bushels per acre by Jeff Coke in Daviess County. Jeff's field was disced twice. The highest no-tillage yield reported in 2014 was 115.98 bushels per acre by Duncan Gillum in Todd County. Both Jeff and Duncan are repeat winners from 2013. Area winners for 2014 included Merle Coblentz, SBJ Fischer, Gary Summers and Homestead Family Farms.

Tuesday, September 2, 2014

Something is Definitely Up with Fall Armyworm!!

Doug Johnson, Extension Entomologist, University of Kentucky

Something is most definitely up with armyworm (Mythimna unipuncta), fall armyworm (Spodoptera frugiperda) or both. I have received information from six counties in less than a week indicating the

Tuesday, August 26, 2014

Poor or No Soybean Nodules in Many Fields

Chad Lee, Extension Agronomist, University of Kentucky

A field with soybeans with nodules
and soybeans without nodules. 
Several soybeans have turned yellow in the past few weeks and further examination revealed little to no nodules. The problem has occurred with seed inoculated in the bag and seed inoculated at the farm. It has even occurred in cases where a 2x rate was applied at the farm. Several brands of inoculant have been indicated. It has occurred in fields all across the state. The problem has occurred in full season soybeans and in double-crop soybeans.

May Not Be A Problem, But Trapping Large Numbers of Stink bugs!


Doug Johnson, Extension Entomologist, University of Kentucky

Certainly this is the time to be checking your soybeans for the presence of stink bugs. I have not noticed economically important problems in the beans I have sampled, but stink bugs are certainly common and our light traps have been capturing very large numbers compared to previous years.