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Field and Forage Crops |
We now have everything across our own North Carolina Cotton Belt from 48-inch cotton with excessive water to 18-inch cotton fields that have begun to prematurely cut out. Expect our major insect pests (bollworms, stink bugs, and perhaps plant bugs) to likewise to be extremely variable in their severity for the remainder of the season.
Although the bollworm moth flight began abruptly near Rowland with July 25 and July 27 counts of 172 and 164, respectively, elsewhere the flight has been less impressive for this time of the season. This tardiness of this flight is certainly welcome given the generally later cotton crop across much of the state. Consider keeping up with the current status of the moth flight on-line at the Cotton Insect Corner web site. As of July 29, the moth flight is underway up through Craven, Onslow, Lenoir, Sampson, and probably Jones and Pender counties. This weekend should bring bollworm moths into Wayne, Greene, and probably Pitt and Beaufort counties. Although initial moth numbers are not high by previous standards, we tend to get a more accurate picture of the intensity of the moth flight in the second week. For at least the southern half of the state, twice per week scouting, where possible, is advisable at this time on conventional cotton. In this non-Bt cotton, two initial pyrethroid insecticide applications, preferable at a medium to high rate 5 to 7 days apart, is still the conventional wisdom. In Bollgard, Widestrike and Bollgard II cotton, bollworm thresholds are not typically met until somewhat later, and sometimes not all with this technology. Expect Widestrike to be intermediate between Bollgard and Bollgard II in its bollworm activity.
Stink bugs and their damage, though so far at much lower levels than in 2004, are present at high enough levels to cause decision-related "headaches" across much of the state. While many cotton fields are still relatively clean, many others are just under, right at, or just over the 10 percent threshold for internal boll damage to quarter-sized bolls (we have also received a few reports of cotton fields in the 15 to 20+ damage range).
In fields where we have stink bug tests in place in Edgecombe, Wayne and Scotland counties and in Union County in the western Piedmont, boll damage so far is relatively low (ranging from 2 to 7 percent). However, even where stink bug and/or plant bug damage is presently low, this damage is often very localized (differing significantly within and between fields) and will likely increase over the next few weeks. So be prepared to open a lot of quarter-sized bolls over the next 4 to 6 weeks, especially in fields that have been blooming for three weeks or more.
In Bollgard cotton, the decision of whether or not to add a pyrethroid insecticide to a stink bug insecticide such as Bidrin is a tough one prior to or during an ongoing moth flight, as these stand alone stink bug materials (Orthene and Vydate are two others) can make bollworm establishment much more likely, or more severe. In replicated tests here, in the absence of bugs, bollworm damage to bolls is often 2 to 3-fold higher and yields up to 100 pounds (lint) less in Bollgard plots oversprayed with Orthene (just prior to the moth flight) than in untreated plots. In cases of threshold levels of both bollworms and stink bugs (with a portion of the stink bug population brown stink bugs) or if partial thresholds of each add up to one or more, a pyrethroid plus Bidrin tank mix can be justified. If Bidrin (or other non-bollworm active stink bug material) is used alone for stink bugs or plant bugs and the major bollworm moth flight is either imminent or ongoing (without threshold levels of bollworms), be sure to scout that field within 3 to 5 days with an expectation of greater bollworm establishment. Under these latter conditions, one may likewise elect to add a pyrethroid to the stink bug material.
In some areas, plant bugs are also part of the stink bug scene, damaging bolls in a manner identical to stink bugs. Fortunately, assessing quarter-sized bolls for internal damage suffices for both species. Additionally, plant bug feeding on large squares often expresses itself as dirty blooms; that is, white flowers with darkened pollen anthers and sometimes dimpled petals. This type of damage is easily monitored. If the percentage of white blooms exceeds approximately 15 percent, this may indicate a treatable plant bug population. I have begun to receive reports of immature plant bugs in cotton fields with good moisture. Plant bug nymphs are sometimes an indication of upcoming, more damaging populations. In North Carolina, most insecticides that are active against stink bugs also control plant bugs, but not always vice versa.
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Last modified on August 1, 2005 by Stephen J. Toth, Jr.
