Cotton Pest Management Newsletter #7
July 12, 2001

Cotton Situation:  The Georgia Weekly Weather and Crops Report for the week ending July8^th listed the crop as 76 percent squaring and 32 percent setting bolls.  Showers were more scattered during the past week and some areas could use a rain.

Insect Situation:  Some early planted fields are being treated for bugs based on the 20% internal boll damage threshold.  Scouts should begin monitoring quarter sized bolls once present and be observant for stink bugs and tarnished plant bug which can cause similar type damage to bolls.  Tobacco budworm and corn earworm populations continue to be low but sporadic as some non-Bt fields are being treated.  We would generally anticipate corn earworm numbers to increase in upcoming days.

“Bug” Damaged Bolls:  During recent days we have received several calls concerning internal bug damage on medium sized bolls.  As a reminder, bolls approximately the diameter of a quarter should be monitored for internal damage when scouting for bugs.  Bolls of this size can be easily squashed in the palm of your hand.   Internal damage is defined as a callous or warty growth on the inner surface of the boll wall and/or stained lint.  

Early planted fields are in the third to fourth week of bloom and some have reached the 20% internal boll damage threshold.   Although we have typically attributed the majority of boll damage to stink bug feeding, other bugs such as plant bugs and leaf-footed bugs may also feed on and damage developing bolls.   Stink bugs are being observed in some fields, but we suspect some of the boll damage which is being observed to be caused by tarnished plant bug.  Tarnished plant bug will feed on small bolls, less than 10 days of age, and causes internal symptoms of injury which are indistinguishable from stink bug damage.  Ultimately, the end result of damage should be the same.  Both adult and immature tarnished plant bugs are present in some fields.   Plant bugs have five nymphal instars or developmental stages.  Larger nymphs are greenish in color and can be easily recognized by the characteristic five black dots on the back.  Nymphs will often be observed inside bracts on large squares and small bolls or in blooms in infested fields.  Larger nymphs as well as adults can damage small bolls.  When in fields, especially if internal boll damage has been noted, scouts should be observant for both stink bugs and plant bugs which should give us an idea of which species is likely causing the damage.  Potentially this could aid in insecticide selection.   Although pyrethroids are not specifically recommended for plant bug control, good control should be achieved when used to control other pest such as corn earworm.  

Tobacco Budworm and Corn Earworm:   Mixed populations of tobacco budworm (TBW) and corn earworm (CEW) continue to be observed in southwest Georgia.   To date, TBW populations have been light; hopefully that will continue.  Will Duffie reported increased CEW captures in pheromone traps this week.   CEW populations generally peak during mid-July.  When mixed populations occur and TBW is the dominant species, the infestation should be treated as TBW especially if high numbers are present or in areas where pyrethroid resistant TBW is suspected.

Corn Earworm in Bt Cotton: Once Bt cotton begins to bloom, it is more susceptible to damage by corn earworm.  This is because toxin expression in blooms is lower compared with terminal growth and squares.   If larvae infest blooms, potentially they can survive to a size which can damage bolls.  When scouting Bt cotton be sure to check a minimum of one bloom, one bloom tagged boll (look under tags for larvae), and a boll lower in the plant canopy.  Scouts should also be observant for the presence of fall armyworm larvae.  Fall armyworm numbers in cotton have been low in recent years, but potentially they could be an economic pests.  Small fall armyworm larvae are often found in blooms or feeding on the inner surface of boll bracts.

Aphids:  Some aphids linger in fields, but if populations increase we would anticipate the naturally occurring fungus to cause numbers to crash.

CSRA Field Day:  The CSRA Conservation Tillage Demonstration Farm Field Day will be held on July 19, 2001 in Burke County.  Registration is from 8:00 to 8:45 and tours begin at 9:00.   For more information contact the Burke County Extension office at 706/554-2119.

Insect Updates:  Check the Cotton Insect Hotline (1/800-851-2847) for updates on current insect conditions.  The Cotton Pest Management Newsletter is also posted on the Internet at www.gaipm.org” and then click on “cotton.”

Sincerely,

Phillip Roberts
Extension Entomologist