FIELDAND
FORAGE
CROPS
FIELD
The information and recommendations in this newsletter are applicable to
North Carolina and may not apply in other areas.
The recent rainy weather over much of the state following the warm, dry spell last week has created excellent growing conditions for cotton, but also extreme variability in the potential for thrips damage. Thankfully, some of our cotton is now at the 5 to 6 true leaf stage and beyond the point of thrips damage. On the other hand, populations of migrating and established thrips in many areas are potentially very high (50+ immature thrips per plant in the untreated check, 23 behind Gaucho seed treatment, and 1.2 immatures per plant following one Orthene foliar spray in a Rocky Mount test at 3.5 weeks after planting), so any points of susceptibility must be monitored carefully. Be careful of situations in which thrips levels and damage to cotton seedlings have been low up to this point, but the at-planting insecticide has begun to play out. Monitoring for immature thrips and damage to buds or young leaves should continue until cotton reaches 5 to 6 true leaves with adequate moisture.
In North Carolina, we still appear to be headed toward higher tobacco budworm levels on mid-June to early July cotton than in 1996 and 1997. However, fruit and terminal removal studies conducted over the past 6 years suggest that minimal spraying will likely be required if growers and consultants follow the new higher thresholds (15 percent live budworms in terminals or 8 percent budworms on squares). High mortality of budworms feeding in the terminals (primarily due to predators) is a common site in June to early July. Scouts should begin focusing on budworms this coming week in the southeastern counties of North Carolina. Tracer at the lowest labeled rate is the preferred material for this generation.
I continue to receive telephone calls about cutworms damaging cotton -- probably up 5 times more previous years. About 80 to 90 percent of the reports are in no-till or reduced tillage cotton. In the above situations, or where weeds have been burned down prior to planting, stands should be monitored for damage and live cutworms hiding in the soil near the base of the cotton plants. Cutworm monitoring and treatment decisions tend to be judgement calls as a number of factors must be taken into consideration. Additional information on cutworms can be found in the May 29 issue of the North Carolina Pest News.
Plant bug monitoring technically begins at the onset of squaring. Monitoring pinhead squares for high retention levels remains the most efficient indirect method of monitoring for plant bugs, that is, if the retention of pinhead terminal and pinhead lateral squares is 80 percent or greater no accessing live thrips populations is needed. Fortunately, square retention of most fields typically runs in the 90's. I will provide more information on plant bugs in the coming week as squaring begins.
At this time of year, other insect pests found in cotton should
cause no damage or minimal damage in most fields. Yellow striped
armyworms are a bit more common this year. These foliage feeders,
even when they are easy to find, are seldom plentiful enough to
cause economic damage. Cotton aphids are light so far this year
(unlike 1997); we will probably get a better idea of their levels
once cotton begins blooming. Spider mites require building their
populations on other hosts (corn, ditch banks, roadside vegetation,
etc.), along with prolonged hot, dry weather and sandy soils to
reach economically significant levels. We will begin to get a
handle on the potential size and timing of the major bollworm moth
flights when the prior generation becomes established on silking
field corn. Fall armyworms will not be found on cotton in any
numbers until later in the season -- usually late-July to early to
mid-August in our southeastern counties. Stink bugs may have
survived at higher levels following the mild winter, so Bollgard
cotton may warrant closer monitoring for brown and green stink bugs
this year.
Web page last updated on June 8, 1998 by Stephen J. Toth, Jr..
