Cotton Insect Newsletter Vol. 19, No. 12, August 1, 2001 Call 1-877-629-1474 for Cotton Insect Hotline

Cotton Situation:  After a week of showers and cloudy weather, you would think that most cotton fields would be in good shape for soil moisture, but lots of farms still need rain.  When you consider that fruiting plants need about 0.25 inches of water per day for optimum growth and development, it's easy to see why the little dab of rain received in most areas wasn't enough.  About the best we can say is there were some subsistence levels of rain during this period.  Most farms could use a good 2-3 inch soaking rain.  The soil moisture report from The South Carolina Weekly Weather and Crop Bulletin indicated the following soil moisture ratings for crop lands:  1% very short, 13% short, 73% adequate, and 13% surplus.  With a week of hot, sunny weather in the forecast, moisture ratings will likely be going down. More and more cotton fields are now showing plants with blooms in the tops.  Scouts will continue to see moderate-to-high levels of fruiting forms falling on the ground.  It's estimated that 85% of the fruit set on cotton plants come from squares set during the first 4-5 weeks of squaring.  The first 5 weeks of blooming are also the most productive in terms of setting bolls.  Later in the season, a high percentage of squares and bolls will fail to set for various and sundry reasons: like too much moisture, too little moisture, low fertility, etc.  Insect Situation:  The numbers of bollworm moths increased in pheromone traps over the last weekend in the Savannah Valley, and then egg counts in cotton fields increased as well with more 100+ fields.  Moth numbers remained about the same as the previous week in the Pee Dee; however, egg counts in some areas have increased to levels of 40-100+.  There are still lots of fields where pressure has remained very low.  In fact, I have seen fields of conventional cotton planted the last week in April here at the PDREC, where you find very few eggs and very little damage.  The plants have reached the cutout stage, so there are no small squares or juicy terminals to attract the moths to lay eggs.  There are also some plots that emerged 2-3 weeks later than the April-planted cotton in the same field.  Bollworm moths have preferentially deposited eggs on these plants and have damaged a large number of small bolls.  We saw something similar to this last year here on the station, where cotton was nearing cutout by the time the bollworms moved in.  Then, the combination of unattractive plants and high numbers of beneficials provided a protective curtain for that particular planting of conventional cotton. The next large insect problem in cotton will come from stink bugs.  Fran Arnette reported that stink bug numbers had increased greatly this week in the Pee Dee.  These are mostly green stink bugs with a few southern greens here and there.  There have been fairly high numbers of brown stink bugs reported so far this year, but pound for pound, the green and southern green stink bugs have the greatest potential to produce economic injury.  Mike Sullivan said that most growers in the Savannah Valley are spraying Bt-cotton for stink bugs this week. I keep getting questions from farmers like “Why do we have so many stink bugs?  Where do all the stink bugs come from?” and “How do you find stink bugs in a cotton field?”  First of all, we have a lot of stink bugs because they have a lot of host plants - - they will eat everything from tomatoes to pine trees.  So, basically they come from almost everywhere (answer to the second question).  Also, they don't appear to be affected much by environmental calamities or natural enemies.  Lastly, you find the stink bugs on cotton plants when they happen to be there.  But the problem is this: They may not be there when you are.  Early in the morning and late in the evening, they will often expose themselves and you can see them on the plants.  At mid day, they can be very elusive.   My personal belief (although I have no research to back it up) is that stink bugs tend to move in and out of fields.  Perhaps they get tired of eating cotton bolls and they need to feed on something else.  It's kind of like me when I have been at a 3 to 4-day conference in a hotel where I have been forced to feed upon fine, nutritious meals every day, the first thing I want to eat when I get away from there is a hamburger in a fast-food restaurant.  So, imagine a green stink bug leaving a field in search of a “big Mac” such as horseweed, dogwood, blackberry, coffee senna, pecan or another potential host plant; and then returning for a while to puncture a few more cotton bolls.  This would account somewhat for the elusive nature of the beast.  That's why we now recommend scouting for damaged bolls by opening 25 or more quarter-sized bolls per field.  Look for warty growth on the inner wall of the boll and discolored seed as evidence of injury.  Sometimes there will be exterior damage marks; Sometimes there will be none.  That's why you have to look inside before you call a boll damaged.  It's time-consuming and aggravating, but it's the only way to make sure there is an economic problem.  We consider 15% boll damage sufficient to warrant insecticidal treatment.    Aphid populations are rebounding in some areas of the state.  The fungus is here, so it should infect the aphids before they are able to inflict any economically important damage.    I received the first report of a fall armyworm observation in cotton yesterday.  It's time for both fall armyworms and beet armyworms to start showing up in cotton.  If you are a scout, stay alert for the worms and the damage they do to cotton plants.        Mitchell Roof  Extension Entomologist

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