Threecornered Alfalfa Hoppers Heavy in Some MS Cotton and Soybean Fields

Based on calls I have received over the last week and what I am seeing in my own research plots, this is shaping up to be a big year for threecornered alfalfa hoppers (yes this is the correct spelling, according to the Entomological Society of America).  Seems like every year I see a few cotton plants with injury symptoms from TCAH but this year in my Starkville plots it is considerably more.  In my soybean test plots in Starkville, I have never seen as many TCAH’s in 6-8” soybeans than I have present now. Since this time I have talked to several consultants that have actually had to make treatments for them in cotton.  Usually damage is confined to field borders but this year seems to be more widespread across whole fields in the areas where they are present.  To date most calls have been from the south delta and hill region around the south delta.  Typically cotton plants that have been injured from TCAH’s appear stunted, leaf veins begin to turn dark red, and leaves take on a red/orange appearance (kind of looks like a small cotton plant with bronze wilt).  There will also be a knot or multiple knots on the stem usually below the cotyledons.  When soybean plants are injured early from TCAH, they are more susceptible to lodging later in the year, but if the plants do not lodge they usually go on to produce normal yields.  This is not the same situation with cotton.  A large percentage of cotton plants will not recover or will bend over and break or even die outright.  They are difficult to scout for on small cotton and soybeans and most often we see the injury after the fact.  I have had some success in both crops by doing visual searches early in the morning before they become active.  In cotton, you can usually ease up and examine the plants and will see them sitting on the side of the stem or a leaf petiole.  Treatment would be justified if they are reducing plant stand below a desired level in both cotton.  In soybeans, take the handle of your sweep net an push the plants over to the side and examine look for plants that snap or with girdle lesions to get a count on injured plants.  Generally, main stem girdling occurs on soybean plants less than 10-12’ in height.  In cotton, main stem girdling usually ends around 8-10 nodes. There is no question that seed treatments have decent activity on TCAH in soybeans and I suspect that they do as well in cotton but there are a lot fewer plants per acre in cotton and they do have to feed to pick it up.  Control options would be similar in cotton as in soybeans.  Pyrethroids and Orthene will work well in both crops but don’t treat either crop unless absolutely necessary because you can flare mites in cotton and reduce beneficial insects in soybean which will open you up to corn earworm outbreaks potentially.  See pictures below for symptomology.

TCAH on Cotton Stem

TCAH Damaged Plant (right) Showing Stunting and Girdle

TCAH Damage With Girdle

TCAH Girdle Cotton Plants