Dealing with Crop Disease and Pests

The wet summer that we experienced created an ideal situation for crop diseases and pests this year.  While some of those may not have been observed when they first occurred, they are making their presence known now.

Thankfully, some of the pest and disease occurred late enough in the season that yields should not be effected, specifically southern corn rust and sugarcane aphids.  Southern corn rust is not new to McLean County, but it does not occur every year.  Sugarcane aphids, on the other hand are not only new to McLean County, but new to Kentucky.

The sugarcane aphid is a grain sorghum pest.  They are small, pale insects with a pair of dark tubes extending from the top rear of the abdomen. The feet and antennae of the insect also are dark.  Sap feeding by large numbers of sugarcane aphids can reduce plant vigor and grain yields.  The first sugarcane aphids were found in McLean County the first of this month.  Thankfully our grain sorghum is already past the boot stage and everyone’s crop is headed out, drastically reducing any chances of yield loss.  However, if fields are heavily infested it can cause problems at harvest.  Sugarcane aphids leave a sticky, honeydew-type substance on leaves that could potentially gum-up equipment during harvest.  If producers fell that their fields have large enough quantities to damage equipment during harvest, Sivanto 200 or Transform WG can be applied.  These are the only two products labeled for Sugarcane Aphid control in grain sorghum.  It is vitally important that we protect the products that we have by not over using them.  Do not apply unless the threshold is met and do not apply more material than the label allows.

Two other pest that are making their presence well known this year are palmer pigweed and waterhemp.  Both glyphosate resistant invasive weeds continues to expand across the Commonwealth.  Last year both species of weeds were found in McLean County and this year they are not an uncommon sight.  Unfortunately, it is easier to find Palmer amaranth and waterhemp populations in grain crops later into the season after the plants have begun to produce new seed. Unlike the more common pigweed found in Kentucky, Palmer amaranth and waterhemp have smooth stems and often a longer seedhead.

After Palmer amaranth and/or waterhemp become established they can be very difficult to control because many populations of this plant are already resistant to glyphosate and the cost for weed control in these crops can more than double. When only a few plants are spotted in a field it can be worthwhile to physically remove and destroy these individual plants. Fields or portions of fields with large infestations may justify destroying plants by mowing or tillage in order to limit the production or spread of seed. Growers who plan to harvest these heavily infested areas would be advised to combine these areas last to minimize the introduction of new seed into other fields. Furthermore, an attempt to clean the combine, grain carts, trucks, and other equipment used to destroy or harvest the crop would be advised, but will not be easy since the small round seed size are not much bigger than a period.

Please be aware of a new corn disease called Tar Spot that was identified in Indiana recently.  This was the first observation of tar spot in the United States.  Since this is a new disease, there is little information out there about it.  However, Purdue has put out a publication on it.  It can be found online at http://extension.entm.purdue.edu/pestcrop/2015/Issue24/#1.

For more information on crop diseases and pest, contact the McLean County Cooperative Extension Service at (270)273-3690.  Educational programs of the Kentucky Cooperative Extension Service serve all people regardless of race, color, age, sex, religion, disability or national origin.