Scouting time
Migratory moths can appear in large numbers virtually overnight, so scouting for moths should begin as soon as the first flowers open and continue every 24-48 h until pollen shed is complete in a majority of plants. Since moth migrations are spotty and each field has its own unique phenology, it is not advisable for growers to simply follow the management decisions of neighbors; there is no substitute for scouting individual fields. Fields that have been sprayed should be revisited to determine the efficacy of treatment as soon as the re-entry interval expires. The treatment threshold is considered to be 1-2 moths per five plants; projected crop value can be used to elect the low or high end of this range. Moths usually rest underneath leaves in the daytime and will fly up when disturbed. If moths are very abundant, their presence will be readily apparent in daylight hours, but if marginal numbers are present, scouting should be conducted an hour after sunset when moth activity on flowers reaches its peak. Use a flashlight to count the moths on a series of 20 flower faces in at least 5 locations in the field.
Sampling method
Historically, sunflower moth activity has also been monitored with commercially available pheromone traps that attract and capture male moths. Traps are best placed on T-posts above canopy level at least 10 rows into the field on north and south sides, at least 4 traps per field. Trapping should begin as plants enter the R-5.1 stage (ray petal emergence) and trap catches monitored daily through the R-5.8 stage (flowers 80% anthesis complete). Insecticide applications should be considered whenever pheromone traps average four moths per trap per day. If trap catches average less than four per day, field scouting is justified to determine whether the action threshold has been reached. Trap catches averaging less than one per day usually have resulted in non-economic infestations. However, it is questionable whether the information provided by trapping is sufficiently useful to justify the additional labor it requires, especially when certain outcomes dictate manual scouting before a decision can be made. Strong winds can lead to 'passive catch' of other moth species that can be difficult to distinguish from sunflower moths once they are stuck to glue in the trap. In addition, doubts have been raised about the persistence of the pheromone lure under Kansas field conditions that typically involve high temperatures and strong winds.
Thresholds
Successful management of sunflower moth hinges on rigorous monitoring of individual fields and prompt insecticide application once theshold numbers of moths are detected. The goal is to kill adults and early instar larvae before physical injury occurs to the flower heads that can permit fungal infection. Fortunately, early instar larvae remain vulnerable to contact insecticides for several days before causing such damage because of their pollen-feeding habits and their mobility on flower faces. Later instar larvae feed more aggressively and bore into the receptacle where they may avoid contact with insecticide, creating multiple infection sites for Rhizopus fungi that can quickly rot the head. Rhizopus infections can also invade vascular tissues and become systemic within upper parts of the plant, resulting in reduced seed fill.
Early planted fields typically suffer the most damage from migratory flights in Kansas. Fields planted in early July or those that bloom after August 10 are less likely to develop economic infestations, but may still be affected by second generation moths emerging locally from patches of wildflowers or adjacent early-planted fields where the pest has not been adequately controlled. Geographically, average moth pressure tends to decrease somewhat from eastern to western Kansas, probably reflecting the prevailing paths of summer winds.
Chemical control
If moths are above threshold, an insecticide treatment should be applied once the majority of blooms have opened and begun shedding pollen (stage R-5.1). Most failures to obtain control are thought to result from delayed treatments. The objective of an early application is to kill female moths before they lay eggs, and young larvae while they are still feeding on pollen and before they bore deep into the head. Scouting should continue after an early treatment as additional applications may be required when moth pressure is heavy. Whereas some growers opt to spray automatically at R-5.1, the advantage of scouting is the possibility that treatment can be avoided if moths remain below threshold, or delayed until later in the flowering cycle when blooms are fully expanded, increasing the chance that a single application will suffice. Once flower disks are fully expanded, or significant numbers of larvae have entered the flowers, treatment is far more efficacious when applied directly into the faces of the flowers. This is best accomplished in aerial applications by flying each application pass from an easterly direction, rather than making passes back and forth over the field. Use of a ground rig, although more time consuming, will permit more effective application of insecticide in a larger volume of water to provide better coverage. Organophosphate materials have somewhat better residual activity than pyrethroids, whereas the latter have repellent properties, but both can lose their efficacy quite quickly under Kansas summer field conditions. Several new formulations combine active ingredients with different modes of action (organophosphate + pyrethroid, or organophosphate + neonicotinoid) to increase efficacy.
Non-chemical controls
Pollinator Safety:
The need to control pests on a crop in bloom raises concerns about potential impacts on pollinators. Sunflower growers should also be aware that most insecticide applications against sunflower moth carry a hidden cost in terms of yield reduction. Although commercial varieties have been bred to be self-compatible and hence less pollinator-dependent, studies have shown that cross-pollination by insects improves seed weight and oil content. Insecticide applications should be made early morning or late evening when pollinators are not flying; evening is preferable because this permits overnight dissipation of material before pollinators return to the field. However, the requirement for low wind conditions is a priority that may trump this concern. Pyrethroids tend to be safer for bees than organophosphates because of their repellency, provided bees are not sprayed directly. Dusts and wettable powders tend to be more toxic formulations for bees than solutions and emulsions, and micro-encapsulated insecticides are especially hazardous. Of particular interest is a new class of insecticides called diamides that disrupt insect muscle contraction, as several studies now suggest they have a high degree of safety for pollinators. Diamides act as ryanodine receptor modulators to paralyze insect muscles and must be consumed by the insect to reach their active site. As of 2012, both Bayer and Dupont have registered diamide insecticides for use on commercial sunflowers in Kansas (Belt® and Prevathon®, respectively) and preliminary trials indicate good levels of control can be achieved with these materials without endangering bees. Growers and applicators should refer to the most recent edition of the KSRE publication 'Sunflower Insect Management Guide' for a table of registered materials and application rates.
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