Entomologists seem to be routinely bad at predicting insect outbreaks prior to the growing season, especially when it comes to cotton. We are far more comfortable (and less helpful) with explaining insect pest outbreaks during and at the end of the growing season.
Unfortunately, many interrelated factors impact the severity of the upcoming pest year. For example: pest survival during the winter, the abundance and quality of nearby crop and weed hosts during the spring and early summer months, the development of the cotton crop, and weather prior to and especially during the growing season.
In North Carolina, all of our major insect pests- thrips, bollworms, stink bugs, cotton aphids, and others — undergo several generations on other hosts before moving into cotton, making early predictions even less reliable. Despite the above qualifications, lets take a stab at what we might expect in 2005.
(1.) Thrips have been on and off in recent years — 2000 to 2002 witnessed high thrips levels, while 2003 was very light and 2004 moderate in most areas of the state. At least in part due to our cooler seedling grow-off conditions, and our high ratio of surrounding weed and small grain thrips host vegetation to our small 14.5 acre average cotton field size, thrips levels are often higher and more damaging in the Carolinas and Virginia than elsewhere in the Cotton Belt.
If needed (this was the case with approximately 55 to 75 percent of North Carolina’s cotton acreage in 2000 through 2004), a foliar treatment for thrips is often best timed when seedlings are difficult, though not impossible, to monitor — at the appearance of the first true leaf. In this region, with the seed treatments Cruiser and Gaucho Grande, plan on at least one foliar spray. With the high thrips levels that are all too common here, consider the upper labeled end of rate ranges for these foliar sprays. With an at-planting treatment of Temik 15G (still the standard for thrips control in North Carolina), possible foliar sprays should be based on a combination of scouting for both damage to newly unfurling buds and leaves and live thrips.
(2.) Plant bugs will likely again be kind to most producers in the pre-bloom period (we have averaged approximately 3 percent to 8 percent treated acreage over the past 6 years), but may be a another headache in post-bloom Bt cotton, particularly in our far-eastern counties.
Both 2003 and 2004 witnessed moderate to high plant bug levels during the early boll set period. Weekly square retention counts should define most potential problem fields up to about a week or two beyond bloom initiation. The crushing or cutting of quarter-sized bolls is probably best correlated with treatment need in the post bloom period for both plant bugs and stink bugs, though monitoring ‘dirty blooms’, visual observations for adult/nymph plant bug ratios, and sweepings are also helpful.
(3.) Stink bug damage in 2004, in both conventional and on Bollgard cotton, was far and away our earliest and highest on record (I go back 33 years at NCSU). Although our high adoption rate of Bt — 83 percent in 2004 — may account for some of this massive outbreak, much of this onslaught was probably weather related, as 2002 and 2003 were both light stink bug years.
To make matters worse, the harder to control brown stink bugs were also plentiful in 2004. No matter what 2005 has in store, we need to be paying more attention to the bug complex in our Bt cotton. Additionally, as Bollgard II and Widestrike varieties become more widely planted in 2005 and beyond, our expected lack of treatment for caterpillars in all but a few circumstances will likely result in greater potential buildups of bug pests.
Adequate sample sizes, lots of interior boll examinations, and green vs. brown adult ratios of stink bugs are a must in Bollgard fields. Fortunately, the three or so applications typically sprayed on conventional cotton usually keeps stink bug and plant damage to bolls low, although this was not the case in 2004.
Fortunately, despite heavy stink bug damage, record yields were harvested in many North Carolina counties. Unfortunately, the potential lesson of how costly bug damage can be was lost on most of our producers.
(4.) Bollworm moth levels had seesawed up and down for the past 7 years here until 2003, when both 2002 and 2003 were rough bollworm years; 2004 showed only moderate bollworm levels. However, in 2004 we had more than our share of tobacco budworms, which caused significant late season boll damage in many North Carolina cotton fields.
Averaged over the whole state, late season boll damage to conventional cotton from the bollworm/budworm complex was our third highest since 1985. To keep abreast of bollworm moth flight, counts from light traps throughout the cotton production area of North Carolina can be found on line at our project’s Web page (www.run.to/cotton) beginning in early July.
(5.) Other caterpillars, such as fall and beet armyworms, European corn borers, and loopers continue to cause only minimal damage, although fall armyworm damage to bolls was moderate in some eastern counties in 2004. Unlike its Bollgard predecessor, Bollgard II and Widestrike show high resistance to armyworms and loopers.
Weather patterns during the upcoming crop year will essentially determine the timing and intensity of our potential 2005 insect outbreaks. Meteorologists, let alone us, have difficulty in predicting weather patterns more than about a week in advance. On the plus side, sound insect and plant monitoring and well-timed sprays where needed play a major role in making the best of what nature has in store for us this season.