Early Spray Gets the Moth
Wednesday, April 2, 2008
filed under: Insects
Sunflower insects are generally a sneaky bunch. You never know who is going to show up for dinner. Last year (2007) there was a high infestation of the sunflower head moth from Texas all the way to Manitoba. This insect is quite foreign to the northern production region, but conditions were obviously right to move the moth that far north.
Dr. Larry Charlet of USDA-ARS Sunflower Research Unit at Fargo, N.D., emphasizes that with prices at record levels, no one wants to lose valuable production to an insect. He and other entomologists recommend staying of top of the insect populations this year — and make sure, if an insecticide application is warranted, it is done sooner than later.
Charlet emphasizes that the other insect to monitor closely is the banded sunflower moth. This one can also slip through the radar screen, with populations being inconsistent from year to year. “It is not as easy to scout for as are the red or gray seed weevil, and timing is critical to prevent applications in the field too late to provide adequate control of the banded sunflower moth”, Charlet advises.
Sunflower (Head) Moth
This insect overwinters in Texas and migrates north with wind currents. It generally doesn’t get as far as the Dakotas, but it should be scouted for just in case. According to the NDSU Sunflower Production handbook (September 2007 edition), the moths are highly attracted to sunflower that is beginning to bloom. Individual female moths will deposit up to 30 eggs per day on the surface of open sunflower heads.
The eggs hatch within 48 to 72 hours, with the newly emerged larvae feeding on pollen and florets prior to tunneling into developing seeds when they reach the third instar growth stage. The tunneling continues throughout the remainder of the larval stage. A single larva can feed on up to 12 seeds; so losses can be significant, depending on the number of larvae in the head. A disease known as Rhizopus head rot can occur as a secondary problem due to the tunneling damage from the moth larvae. That often results in complete damage of the head.
Scouting is mandatory! The NDSU publication states that sampling sites should be 75 to 100 feet from the field margins. The traditional X pattern should be used, counting moths on 20 heads per sampling site for a total of 100 heads. Entomologists stress that early morning or late evening is the best time to scout, as the moths are most active during those periods.
Charlet and Dr. Jan Knodel of NDSU are in the process of establishing a national sunflower moth monitoring network using pheromone traps. More than 30 volunteers from seven states and one province will be setting up pheromone traps and providing weekly readings of moth populations. “We hopefully will get a handle on the movement of this insect starting in south Texas. A webpage on the NSA website (www.sunflowernsa.com) will track the weekly updates,” according to Charlet.
The NSA will also alert extension people, seed company representatives and certified crop advisors via email if moth populations are showing up in their areas. Crop advisors wanting to ensure that their email address is included should contact the NSA office at 701-328-5138.
The economic threshold for control of the sunflower head moth has been one to two adults per five heads at the onset of bloom or within seven days of the adult moth’s first appearance. Charlet indicates that with prices high, careful monitoring of fields is critical. He warns that in his experience, poor control is usually due to fields not receiving timely treatments.
“Spraying should begin at the onset on bloom if the moth numbers meet the threshold level,” Charlet says. “Too often, farmers wait until 30% bloom to make the final decision to spray. The applicator is most often not going to be able get out to your field the next day. Or, the weather may not permit an application. By then it may be too late and the damage done.”
Also, reinfestation can occur. So fields need to be continually monitored until they have matured beyond the point that the heads are still attracting moths. If populations are high and moths are still being detected in the field, a second application may be required to protect the crop.
Charlet also warns that insecticides can volatize during the heat of the day and never fully reach the canopy to provide adequate coverage on the sunflower head. So spraying early in the morning or in the early evening is the most efficient spraying time to ensure pesticide penetration. This timing will also prevent destruction of bees and other pollinators that are active in the field during the day.
If spraying needs to occur in the heat of the day (90°F or higher), or if there is concern about control due to high numbers, the applicator should definitely increase the amount of water — possibly up to as much as five gallons per acre — to ensure adequate coverage on the plant.
Banded Sunflower Moth
The banded sunflower moth has traditionally been the “northern cousin” of the sunflower (head) moth. It is most often found in treatable numbers in North Dakota, South Dakota, Manitoba and Saskatchewan. The banded moth does overwinter in the northern region, as opposed to the head moth that migrates from the south.
According to the NDSU Sunflower Production handbook, the moth is recognizable by the dark band across its forewings. The moths begin emerging from the soil about mid-July and are present in fields until the middle of August. The adults tend to congregate in the field margins, on weeds or in adjacent crops during the day and then move into the sunflower fields in the evening.
Egg laying begins on the outside of the bracts of the sunflower head, with eggs hatching in five to eight days. Larvae feed on the florets. As they grow, they burrow into the developing seed and consume most or all of the kernel. Each larva consumes five to seven seeds. Damage can be considerable if the population is high.
Scouting for adult banded moths is similar to the sunflower moth. However, checking field margins is important because banded sunflower moths rest in those margins.
A new scouting procedure has been developed for egg sampling. Dr. Jan Knodel, NDSU extension entomologist, says the procedure makes egg sampling simpler and quicker and may provide producers with more time to react if a treatment is needed. Although the eggs are small (1/50th inch), they don’t move like adult moths, thus making them easier to find on the back of the outer floral bracts.
Scouting needs to begin in the R-3 bud stage for either adult moths or eggs, according to Knodel. She also recommends the importance of timely spraying. “The prescribed treatment time is at R5.1, when the first outer rings are flowering.”
She also cautions against spraying too late — especially if earlier-than-normal egg laying is being observed. “The banded sunflower moth is a bit more forgiving with a delayed spray because the larvae are more active on the surface of the heads,” Knodel says. “If you are going to the expense of spraying, it is important to get your insecticide sprayed on during early flowering rather than late flowering.”
Spraying the ditches and headlands can be effective when populations of banded sunflower moth are low. However, with today’s high market prices, the economics of treating increases as treatment thresholds decrease.
(For a detailed analysis of an economic injury level, go to pages 50-51 of the Sunflower Production handbook. This can also be found on the NSA website under the ‘grower’ and production handbook section. At these prices the current threshold level is very low.)
Knodel notes that “there are many effective insecticides registered for control of banded sunflower moth and sunflower moth in sunflower.” However, proper spray timing, rates and adequate coverage (3-5 gal/ac by air) is more important than the selection of insecticide for control. Knodel also recommends using the higher rate when temperatures are hot( >90°F) or to obtain a longer residual. Remember to apply insecticides early in the morning or late in the day to minimize adverse effect of chemicals on bees and other pollinators.
Knodel is also establishing a monitoring system for the banded sunflower moth. “We have cooperators throughout North Dakota, Minnesota and Manitoba,” she reports, “and will be developing a weekly map to predict moth pressures for the NSA website. Cooperators will use pheromone traps, and populations will be monitored and reported on a weekly basis.” The information will also be emailed to all interested parties.
Both Knodel and Larry Charlet recommend that monitoring for the various sunflower insects is especially important this year in order to maximize yields and take advantage of the high market prices. Information on the major sunflower insect pests is available on the NSA website and various state university websites.
The National Sunflower Association has provided funding for a post-doctoral scientist to begin work on genetic resistance to the sunflower moth and two stem insects. For more information, go to the January 2008 issue of The Sunflower magazine. The article can also be found on the NSA website under the archive section, insect category or www.sunflowernsa.com/ magazine/details.
— Larry Kleingartner