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Wednesday, July 31, 2013

Lygus Reach ET in a Few Fields

Lygus have been a common occurrence in our cotton fields so far this season, but we had not seen any fields at economic threshold (ET) until today.  This morning we double checked a couple of fields in Swisher County behind our field scouts and confirmed that Lygus were at ET at those sites.  We would now like to get the word out to consultants and producers alike.  It is very likely a few other area cotton fields are now at or nearing ET as well.  These two fields (two fields so far) are far from the majority.  Only through careful scouting were the problematic populations found.

A useable threshold for Lygus is 1 insect every 2.5 feet with a quick 10% increase in Lygus caused fruit drop, but we tend to start considering a spray when we find 1 insect every 3.5 feet with the associated fruit loss.  Normal plant fruit loss is currently picking up also as fields set more and more blooms to bolls so there is a need to make certain you are dealing with Lygus induced fruit shed.  A cotton plant will commonly shed some of its bolls is doesn’t think it will be able to support them later in the season for multiple reasons. This is quite common as it is impossible for a cotton plant to mature into harvestable bolls every square put on, especially this season with our fruit set riding so high.  Plant induced fruit loss tends to be limited to dime sized bolls, while Lygus can impact anything from squares to larger bolls.  Often a Lygus feeding “dot” or site can be found on the damaged squares and bolls just before they are shed.  If your fruit loss looks like it covers several different sized squares and bolls and a few are noted with the feeding “dots”, it is more likely insect induced than normal plant drop.  If that drop is more than 10-15% of the plants’ fruit and there is a Lygus every 3.5 feet or less, it is probably time to consider applying some insecticide.  Keep a sharp lookout for these insects to prevent them from causing your field yield loss!
Good Luck!                                                    Please call or come by the office if you have any questions.  Thanks!

        Kate                                                                                                                     Blayne

Thursday, July 11, 2013

Fleahoppers and Lygus Populations

Right now, we have seeing both Lygus and fleahoppers in our Hale & Swisher County program fields, but not at economic threshold (ET) yet.  Because several of our program cotton fields have been so close to economic levels, it is likely several other area fields are nearing or are at ET.  We have been finding some high beneficial populations and they have probably kept the fleahoppers from reaching ET so far in our fields.  We recommend keeping a very close eye on your cotton’s square drop percent and plant bug populations.

            Cotton fleahoppers are very flighty, small, pale green to whitish color.  The adults can fly, and the wings rest flat across the back.  The nymphs are pale green and very small, ranging from the size of a grain of dust to almost the size of the adults.  Feeding with their stylet-like sucking mouthparts fleahoppers can kill a square on a cotton plant.  The ET for these insects is 25% to 35% plants infested or roughly 1fh. / 1.5 - 2 ft., with square drop considerations.  In match head squaring stage cotton, this would be about 10% square drop, while in three fourths grown square cotton it would be 15 - 20% drop.  Once a cotton field’s stage can be measured by nodes above white flower (NAWF) fleahoppers are rarely an economic concern.

            Lygus are larger than a cotton fleahopper, and can range in color from pale green or almost yellow.  They always have a distinct triangle on the thorax, which is made by the crossing of their wings across their ‘backs’.  The larvae tend to be greenish and have dark, distinct black spots on their backs.  The ET for Lygus also requires similar fruit drop considerations, but their ET is usually considered in Lygus per row ft.  The official Lygus ET is 1 Lygus / 2 ft. but in most entomologists consider this per foot ET something of a sliding scale with crop stage as well as fruit retention considerations.  If you have 1 Lygus / 3.5 ft. in a field with match head squares and a significant amount of dropped squares, it may be time to consider spraying.  One Lygus / 2.5 ft. for blooming cotton with the same square drop considerations seems to be a practical ET.  Lygus do cause economic injury to developing bolls causing drop and/ or damage to the boll up to 350 heat units.  For fields nearing cut-out, an ET of one Lygus per 1.5 ft. seems to work well.  Adult Lygus can fly in and out of a cotton field, and often will when they are just passing by.  It is not uncommon to find a sharp increase in square drop, but not find any Lygus present.  This usually indicates that Lygus stopped briefly in route for a more preferred host.  In these situations keep an eye out for Lygus nymphs soon as it is possible that the passing Lygus adults laid eggs in the cotton.  Unfortunately, the eggs are too small to be found.  The nymphs lack wings and cannot easily leave the area. 

            We prefer to use drop cloths in conjunction with whole plant inspections to evaluate in field plant bug populations and influence upon fruit loss.  Drop cloths can be used to find both of these true bugs and, if the insects are sufficiently stunned from the ‘thrashing’ of the cotton plants, can provide a good platform to identify these pest’s rather distinctive appearance.  We are keeping a very close watch on these guy’s populations now and would be surprised if no area fields are at currently at ET.  We recommend or area producers and consultants stay vigulant.  Lygus bugs and fleahoppers are both hazards for developing squares and we have both of them here now.

Good Luck!                                                           Please call or come by the office if you have any questions.  Thanks!

        Kate                                                                                                  Blayne

Written by Kate Harrell, Intern with the Plains Pest Management Association and Texas A&M AgriLife Extension – IPM, Hale & Swisher County.