New Kudzu Bug Find in Tennessee County Directly Bordering Kentucky.

The first capture of Kudzu bug in a Tennessee (TN) county directly boarding Kentucky (KY) has been reported. A TN Dept. AG plant inspector collected Kudzu bug from Claiborne Co. TN. This county borders Lee Co. VA. and Bell, and a small section of Whitley Co KY. The major roadway leading into KY is US 25E through Cumberland Gap and Middlesboro, KY. Fortunately, this was a very small collection of only three specimens, nearer to the upper reaches of Norris Lake than the KY-TN Line. Nonetheless, it illustrates the continual movement of this pest toward KY.

At present this find changes little concerning how this pest will impact KY grain crops. Whitley and Bell counties contain few acres of soybeans such that US Ag. Statistics does not provide an estimate of the acreage in these counties. However, Kudzu is present and the Kudzu bug feeds on a wide variety of legumes (plants producing pods) that might be produced in home and commercial vegetable gardens. Lack of a host is unlikely to be a controlling factor.

To obtain invasive stink bug updates for KY grain crops follow: @DrDougStinkBugs on Twitter.

SDS Revised Update

Since writing my last update on SDS, I have come to realize that the disease is causing more damage than I had intially thought (this is unusal). Thus, I decided the prudent thing to do was to provide an updated report on SDS.

Soybean sudden death syndrome (SDS) caused by the soil-borne, root-rotting fungus, Fusarium virguliforme, is evident in soybean fields across the state. The disease is quite severe in certain fields in west Kentucky where large areas of fields planted to susceptible and moderately susceptible varieties are affected. SDS has been seen in Kentucky each year since 1985, but incidence varies greatly, depending on the growing conditions. Generally cool temperatures and abundant soil moisture, both of which favor SDS, appear to have set us up for increased incidence and severity of SDS this season. The last time SDS was extensive in KY was in 2009.

Fusarium virguliforme infects roots early in the season and foliar symptoms normally appear during the soybean reproductive stages, as is the case in fields this year. In a more typical year (i.e., hot and dry during July/Aug), a greater extent of SDS is often associated with very early planting; doublecrop beans are rarely affected.  However, in a year like this one, planting date associations are blurred and we may find that the disease even ends up developing in doublecrop soybeans as well as full-season beans.

SDS is first evident in foliage as yellow blotches between the veins of leaves in the mid and upper canopy. In most cases, blotches coalesce and result in a yellow and brown discoloration between the veins, but the veins remain green (Fig 1).

Fig 1. Range of SDS foliar symptoms.

 

In severe cases, symptomatic leaflets will crinkle and eventually fall off, but the petioles will remain attached to the plant (Fig 2).  If severe symptoms develop during early to mid pod fill, pods may abort and/or fail to fill properly. Up to 85% yield loss is possible in severely diseased areas of fields. If symptoms come in when pods are filled or nearly filled, limited yield loss will occur even when severe foliar symptoms are evident. With SDS, the timing of symptom expression relative to crop stage is the main consideration when assessing probable yield damage caused by the disease.

 












Fig 2. Defoliation caused by SDS.

SDS can be evident in individual plants, groups of plants or in large areas of various shapes. Many times, symptoms will be most evident in compacted and/or low areas of fields due to the tendency towards increased moisture retention in those areas. Increased incidence and severity of SDS is often associated with stress/damage caused by the soybean cyst nematode.

Foliar symptoms are the result of a toxin produced by the fungus in diseased root tissue.
The foliar symptoms described above can look similar to stem canker, Dectes stem bore injury, and even pytotoxicity symptoms caused by certain triazole fungicides. Thus, foliar symptoms in and of themselves are not diagnostic for SDS. Additional SDS symptoms include severely rotted roots and a light brown discoloration of the stem when sliced open with a knife (healthy stems will appear a cream color). When all three symptoms are evident, you can be quite confident that you have made an accurate field diagnosis of SDS.

This disease is poorly named in that SDS does not usually suddenly appear, nor is the end result always death. In fact, SDS foliar symptoms first appear much like other diseases, a little at a time. It is only "sudden" if you have not been looking. I have seen plants with SDS recover (put out leaves without characteristic foliar symptoms) and in many cases the disease comes in too late to significantly reduce yields. That said, I am quite sure that SDS will significantly impact yields in many fields this year.

The best way to limit the development of SDS is to plant a resistant variety and to avoid very early planting dates.  However, there is nothing that can be done to slow or stop SDS once it is evident in a field.  Applying a fungicide WILL NOT HELP. 

Heavy Ears and Shallow Roots at Corn Harvest

Chad Lee, Extension Agronomist, University of Kentucky

The frequent and plentiful rains throughout this season have helped to produce some very large ears and rather small roots in many healthy corn fields. The frequent rains resulted in either surface compaction or sidewall compaction at planting in some fields, which greatly restricted root growth. However, the rains masked that compaction and allowed those corn plants to produce large ears. Whether healthy corn or corn with root restrictions from compaction, the combination of large ears, shallow roots and a prolonged drydown period increases the risk for corn plants to fall over. Stalk strength is good in many fields, but we have observed some late outbreaks of diseases, such as Gray Leaf Spot. Diseases like this could compromise stalk strength.

Soybean Sudden Death Syndrome Showing Up

Don Hershman, Extension Plant Pathologist, University of Kentucky

Soybean sudden death syndrome (SDS) caused by the root-rotting, soil-borne fungus Fusarium virguliforme, is beginning to show up in soybean fields across the state. To my knowledge, all of the sightings are in patches of plants or individual plants, and are not field-wide. SDS has been seen in Kentucky each year, to one degree or another, since 1985.

SDS (Fig. 1) is evident first in foliage where plants show yellow blotches between the veins.

Fig 1. Range of SDS foliar symptoms.

Sometimes this this early symptom can look almost virus like. In most cases, blotches eventually coalesce and result in a yellow and brown discoloration between the veins, but the veins remain green. In severe cases, the leaflets will fall off, but the petioles will remain attached to the plant. Foliar symptoms are the result of a toxin produced by the fungus in diseased root tissue.

Watch for Soybean Aphids.

Doug Johnson, Extension Entomologist

Figure 1. Soybean aphid on soybean.

Soybean aphid has been found in Kentucky since its introduction into the US. Nevertheless, it has not developed into a pest species for Kentucky grown soybeans. This is attributed largely to two factors: 1.) We do not have the plant host for the overwintering stage, meaning the aphid must migrate annually into Kentucky from more northern states and 2.) Soybean aphid populations do not do well in the hot temperatures of a Kentucky July and August. So, in a typical year this pest does not pose much of a risk.

KY Soybean Rust Update

Don Hershman, Extension Plant Pathologist, University of Kentucky

Soybean rust (SBR) has really picked up in Alabama, Florida and Georgia and has recently been detected in South Carolina and southeast Arkansas. There is no question that SBR is on the move, but more so in the southeast US compared to the mid-South.

Let me put all of this into the proper perspective. Based on the limited SBR activity in the mid-South to date, and the fact that we are monitoring five sentinel plots on a regular basis, it is very unlikley that SBR is here and that we are missing it. SBR in KY is dependent on spores of the SBR fungus blowing in from the south. Since most of our spores come from places like Texas, Louisiana, Arkansas and Mississippi, it is clear to me that the volume of spores available to infect soybean in KY is very limited at this time. I am sure this will change over the next month as SBR ramps up in the mid-South. But for now I feel like we are free and clear of SBR. Once spores do make it here, even if it is today, it will take 3 weeks for us to find the disease. Then it will take another 3 weeks for the disease to increase. This means that even if SBR spores arrive in here TODAY it would be the end of September before yield loss is possible. By then, the vast majority of fields will be at the R6 stage or later and will be safe. There may be some later planted fields that will still be at risk, but frost is probably the greater risk for those fields. This is all based on SBR spores blowing into KY and infecting crops today, which is highly unlikely. More realistically, we will not begin to be showered with SBR spores until early/mid-September because the disease still has to build up in the mid-South.  So, under this more realistic timeframe, SBR would not ramp up here until sometime in mid-October, which is just too late to do much damage.

Bottom line:  I am fairly sure that KY will again escape damage caused by SBR this season. Know that we are closely monitoring  the developing situation and will make it know immediately if the SBR risk status here changes. But for now, the SBR risk in for KY remains very low.

Watch for worms in grain sorghum heads

Doug Johnson, Extension Entomologist

Fig. 1. Corn earworm on Corn

Fig. 2. Sorghum webworm
 on sorghum

It is about the time of year for problems with corn earworm (Fig.1.) to begin in grain sorghum. Though I have not seen or heard of any local problems my colleague in VA, Dr. Ames Herbert, is beginning to see some problems. In Kentucky we generally see these problems in the area west of the Pennyrile Parkway and more importantly in LATE planted fields. You are also likely to see a mixture of worm species including the sorghum webworm (Fig. 2.)