Article by Jack Bacheler
With many cotton fields just beginning to reach the second and third week of bloom, this is the prime time to be regularly checking 25 quarter-sized (a size range of 0.9 to 1.1 inches is recommended) bolls per field for internal damage from stink bugs. Weeks 3 through 5 of the bloom period is the time interval when the levels of stink bug-susceptible bolls are at their highest. This is also the time when a 10% damage threshold should be used (see Table 1). Remember that our goal is to reduce or eliminate an economically-damaging population of stink bugs, not to ineffectively try to reverse boll damage that’s already taken place. A number of consultants have realized that biologically, a true threshold would not, for example, automatically drop from 30% internal boll damage at midnight at the end of week two of blooming to 10% one minute later at 12:01 am at the beginning the third weed of bloom. Interpolating thresholds at or near blooming-based abrupt changes in suggested thresholds as one week transitions into another makes sense.
Using the dynamic threshold and selecting quarter-sized bolls gives us our best odds of keeping stink bugs below economically damaging levels based on recent boll damage. Because much of this boll damage is recent, the inner boll wall warts and stained lint that constitute a damaged boll may be subtle. Therefore, be sure to score a boll with slight inner carpal wall warting or stained lint as damaged, as this damage may have occurred in the past 24 hours, or less, and indicate a resident stink bug population.
|Week of bloom||Threshold
(% internal boll damage)
Based on calls and our own observations, we appear to have moderate to high levels of stink bugs in many areas of the state, with a few fields in the mid 20% boll damage level. Fortunately, up to this point many cotton fields are in the single digits for damage, though this could change during the next week as more stink bugs invade cotton fields and additional fields enter the third week of bloom when the 10% threshold is in effect.
We would advise that producers check with dealers and distributors as early as possible about product availability as shortages exist for many products this year.