North Carolina cotton producers planted over 575,000 acres of Bollgard cotton in 2003. Because Bollgard cotton has averaged only about 0.8 applications of insecticide for late season insects compared with just over 2.7 for conventional cotton since its introduction in 1996 (Bacheler, 2003a), stink bug (and to a lesser degree, plant bug) levels and damage have increased dramatically. During this period, stink bug damage to bolls on Bollgard cotton was more than 3-fold higher than that caused by bollworms (Bacheler and Mott, 2003a). With the expansion of Bollgard II in 2003, the anticipated labeling of Widestrike cotton in 2005, and the expected labeling of VIP cotton in 2006, the caterpillar treatment for caterpillars is unlikely in most grower situations (Bacheler and Mott, 2003b), and late season plant and stink bug damage to bolls is expected to increase even more than with Bollgard cotton.
University entomologists recommend assessing stink bug-susceptible bolls (most often quarter-sized bolls) for treatment thresholds (Bacheler 1993; Greene, J. K. and G. A. Herzog 1999a; Greene, J. K. and G. A. Herzog 1999b; Greene, J. K. and G. A. Herzog. 2000b). Research to date suggests that 3 to 3.5 week old bolls are no longer susceptible to stink bug damage (Greene, J. K. and G. A. Herzog. 2000a). One significant problem with presently-recommended thresholds for stink bugs and plant bugs is that they are static (remain the same) throughout the boll production and maturation period. Unfortunately, a threshold level that may be appropriate 4 weeks after bloom initiation, when most bolls are susceptible, may not valid later in the season when most bolls are too mature (or large) to be damaged.
This proposed research, begun in 2002, will evaluate the concept of using a practical "boll-sizing" device in the field as the basis for quickly and reliably adjusting stink bug and plant bug damaged boll thresholds upward during the season to account for a maturing (and less susceptible) boll population.
a. To determine the growth curves of bolls of various varieties, 1st and 2nd positions, with and without irrigation, and both early and late in the bloom period .
b. To utilize the above growth curves to determine if a simple BollChecker template can be used by scouts in the field to separate stink bug-susceptible from resistant bolls.
c. To determine if this device will serve as a rapid means utilizing appropriate boll maturity-based thresholds.
2002: In 2002, we measured the diameters of 10 varieties representing different rates of boll growth (e.i., boll sizes), according to Daryl Bowman, NCSU's cotton breeder and Official Variety Test leader. These bolls were tagged, and the diameters measured weekly with digital calipers. This study was carried both early and later in the boll production period, and with both 1st and with 2nd position bolls. Degree days accompanying boll growth were also accumulated. 2002 probably represented minimal boll growth due to the extremely dry conditions and lack of irrigation. The raw results of the 2002 research are shown in the associated Excel and HTML files on our web page.
2003: The methods of tagging and measuring bolls was the same as in 2002. However, the variables were: 2 Varieties (a large bolled variety- FM 989 BG/RR, and a small bolled variety- DP 555 BG/RR); 2 moisture levels (irrigated and non-irrigated), 2 fruiting positions (1st and 2nd position bolls), and 2 boll tagging timings (1 week after bloom initiation and 2 weeks later). Also a larger sample size of bolls was tagged and measured. As in 2002, the data are presented in the associated Excel and in the HTML files without interpretation.
We plan to use the above information, and that gathered from our 2004 and 2005 tests, to develop and validate dynamic, maturity-based bug thresholds that accommodate the increasing resistance of the boll population to bug damage via boll maturation.
Bacheler, J.S., and D.W. Mott. 2003a Relative status of boll-damaging insects in Bollgard vs. conventional cotton in North Carolina, 1996-2002. In, P. Dugger and D.A. Richter (eds.), Proceedings, 2003 Beltwide Cotton Conferences. National Cotton Council, Memphis, TN (in press).
Bacheler, J.S. and D.W. Mott. 2003b. Efficacy of Bollgard II cotton in non-enhanced agronomic conditions in North Carolina. In, P. Dugger and D.A. Richter (eds.), Proceedings, 2003 Beltwide Cotton Conferences. National Cotton Council, Memphis, TN.(in press).
Greene, J. K. and G. A. Herzog. 1999a. Development of damage thresholds for stink bugs in cotton. 1998 Georgia Cotton Research and Extension Reports. UGA/CPES Research-Extension Pub. No. 4: 194-200.
Greene, J. K. and G. A. Herzog. 1999b. Management of stink bugs using symptoms of boll injury as a monitoring tool. In Proceedings, 1999 Beltwide Cotton Production Conferences, National Cotton Council of America, Memphis, TN, 2: 1041-1044.
Greene, J. K. and G. A. Herzog. 2000a. Effect of life stage of stink bug and boll age on feeding potential and cotton yield. 1999 Georgia Cotton Research and Extension Reports. UGA/CPES Research-Extension Publication No. 4: 247-250.
Greene, J. K. and G. A. Herzog. 2000b. Managing stink bugs in cotton using a damage threshold. 1999 Georgia Cotton Research and Extension Reports. UGA/CPES Research-Extension Publication No. 4: 236-242.