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.)

Armyworms are sneaky so watch your fields!

 Fig 1. Corn stand with all leaves
below the ear removed

Doug Johnson, UK Extension Entomlolgist and Will Stallard, UK ANR Agent.

Will Stallard, UK ANR agent in Casey Co., KY, came across an odd set of damage on a corn field. It seems that in about a 7-acre area all of the leaves on the corn plants below the ear level were gone, while leaves at and above the ear level suffered only minor damage. There were no pests present at the time of observation so what would eat all the leaves up to the ear, but not cause much damage above the ear? After several iterations of photos and some consultation about what might have caused this unusual damage pattern, and why, we have finally come to a conclusion.

Expect a Later, Wetter Grain Harvest, Get the Driers Ready

Chad Lee, Extension Agronomist, University of Kentucky

Corn was planted late and the cool and cloudy days are slowing development. Most corn hybrids in Kentucky need about 2,700 to about 3,300 GDD’s or heat units to reach black layer (physiological maturity). Looking at the GDD calculator on the UK Ag Weather Center, corn planted April 15, 2013 in Mayfield, Kentucky won’t get to 3,000 GDD’s until Sept. 1.  Corn planted April 15 in Henderson will get to 3,000 on Sept. 3. Corn planted May 15 in Lexington will get to 3,000 GDD’s about Sept. 27.

Kudzu Bug Moves Into Central and West Tennessee

Doug Johnson, UK Extension Entomologist

Kudzu bug continues to be found ever closer to Kentucky (KY). Until just recently, Kudzu bug in Tennessee (TN) was found only in the eastern portion of the state where few soybeans are grown. These infested counties are the closest to KY, but in an area of KY where few soybeans occur. Unfortunately, within the last week, this pest has been found in two additional TN counties. Both of these TN counties are soybean producing areas of central and west TN (See the Map).

Frogeye Leaf Spot of Soybean Active

I continue to get calls  indicating that the occurrence of frogeye leaf spot is pretty severe in some fields east of I-65, and especially in northeast KY.  Most of the fields affected began to show severe symptoms this week, but were relatively clean a week ago.  The main question being asked  is, “should I spray a fungicide?”.  The answer depends on the extent of the disease and the average stage of the plants.