Tips For Optimum Insect Control
By Janet Knodel*
Sunflower producers can minimize insect pest damage by adopting Integrated Pest Management (IPM) strategies — including monitoring for pests, using economic thresholds and combining various pest management strategies when available.
1. General Knowledge on Insect Identification — General knowledge about how to identify insect pests and also beneficial insects is an important first step for effective IPM. Pests need to be identified accurately because economic thresholds and control measures vary for different species. Many insects are beneficial, which may help reduce numbers of injurious insects. Recognizing which species are pests and which are beneficial is important.
Extension specialists and crop consultants should be able to help producers identify pests and beneficial insects and provide information about insect pest management. There are online guides to help, such as Sunflower Production A-1331 and Integrated Pest Management of Sunflower Insect Pests in the Northern Great Plains E-1457, both from the NDSU Extension Service.
2. Monitoring Pest Population Levels — Sunflower fields should be evaluated regularly to determine pest population levels. A weekly field check is usually sufficient, but field checks should be increased to two or three times a week if the number of pests is increasing rapidly or if the number is approaching an economic threshold.
Sunflower pests are not distributed evenly throughout a field, and fields should be checked in several locations. Some insect pests, such as banded sunflower moth, are concentrated in areas of a field or are more abundant near the edges of a field than in the middle.
Determining the extent of a pest population on the basis of what is found in only one or two small areas of a field is not recommended. At least five sites per 40-acre field should be monitored to collect accurate information on the population density and extent of the pest infestation. Sampling sites should be at least 75 feet in from the field margin to determine whether an entire field or only a portion of the field requires treatment. When infestations occur primarily along field margins, treating only the margins of the field can reduce unnecessary expensive inputs and still provide economic control. In most cases, 20 plants per sampling site should be examined, sampling in a Z or X pattern through the field.
Pheromone traps are commercially available for monitoring banded sunflower moth and sunflower moth. A sex pheromone (chemical) attracts the male moth into the trap. There are various types of traps for monitoring adult moths. Pheromone trapping of moths should primarily be used to determine whether moths are emerging or present in the area, and to determine their local populations. For banded sunflower moth, research shows that using trap catches is not a reliable way to determine treatment thresholds. However, for sunflower moth, insecticide applications should be considered when pheromone traps catch an average four moths per trap per day from the R3 through R5 growth stages.
The calendar on page 16Y is intended simply as a guide to when fields should be checked for possible presence of various sunflower insect pests.
3. Use of Economic Injury Levels and Economic Thresholds — One major component of an IPM program is determining when tactics should be implemented to prevent economic loss. Economic loss results when pest numbers increase to a point where they cause crop losses that are equal to or greater than the cost of controlling the pest. An economic injury level (EIL) is defined as the pest density that will cause economic damage. An EIL recognizes that treatment is justified for some pest species while others are not of economic importance.
An economic threshold (ET) is the level of pest density at which tactics must be applied to prevent an increasing pest population from causing economic loss. Usually the ET is lower than the EIL. The ET has been defined most extensively for economic insect pests. Fewer ETs have been established for non-economic pests, such as sunflower root weevil or sunflower bud moth.
The ET varies significantly among different pest species. Economic thresholds also vary with pest development stages. Crop price, yield potential, crop density, cost and effectiveness of control, and environmental conditions influence the ET and EIL. Generally, ET increases as cost of control increases, and decreases as crop value increases.
Established ETs for major sunflower insect pests are summarized in the “Quick Reference Guide” at the end of this article.
4. Cultural Control — Cultural control strategies, such as staggered or delayed planting dates, can modify the cropping environment and often mitigate pest densities. Planting date is a sustainable method for effectively reducing yield loss and/or oil reduction caused by several insect pests.
5. Chemical Control — Insecticides are a primary pest management strategy used for the control of sunflower insect pests in the United States, and there are many effective insecticides available. There currently are five different modes of actions, 15 different active ingredients, and more than 45 insecticides registered for insect control in sunflower.
To reduce any potential risk of insects developing genetic resistance to insecticides, producers should treat only when populations exceed the ET. If applying more than one application during the growing season, using the full rate of insecticide and rotating modes of action (e.g., pyrethroids, organophosphates, neonicotinoid) will help prolong the effectiveness of available products and reduce the risk of insecticide resistance. Insecticide selection should take into account efficacy (kill), residual activity, resistance management, worker safety, price, availability and preharvest interval.
Once the decision to treat has been made, correctly applying and timing the spray application to achieve maximum control is critical. To optimize foliar coverage, growers should increase pressure (40 psi), increase carrier (10 gallons per acre (gpa) of water by land, 3-5 gpa by air) and use small droplet-size nozzles. Proper timing depends on the targeted insect pest. For most of the head-infesting insect pests (such as banded sunflower moth and red sunflower seed weevil), the “best” sunflower plant stage at which to treat is the R5.1 growth stage, or when pollen shed is just beginning.
Confection sunflower generally needs two or three applications of insecticide to protect against insect pests due to the industry’s standards for low insect damage. In contrast, oilseed sunflower usually requires at least one well-timed insecticide application. Application at an earlier growth stage may be warranted if monitoring reveals higher-than-normal pest activity.
For flowering sunflower fields, foliar insecticides should be applied early in the morning or late in the day to minimize adverse effects on honey bees and other pollinators. It is also a good idea to select more bee-friendly insecticides, if possible. For example, one common sunflower insecticide, Asana® XL (esfenvalerate), actually has a bee repellent in the it that makes these fields unattractive for pollinators after treatment. Be sure to communicate with and notify local beekeepers at least 48 hours before the insecticide application.
The use of neonicotinoid insecticide seed treatments, such as Cruiser® 5FS (thiamethoxam), has increased dramatically in sunflower during the past several years. In the 2008 Pesticide Use and Pest Management Practices in North Dakota (W-1446 NDSU Extension Service), 92% of sunflower acreage in North Dakota was treated with an insecticide seed treatment or an insecticide/fungicide combination.
One of the results of increased usage of insecticide seed treatments has been the general decline of populations of sunflower beetles. This was a fairly common economic insect pest of sunflower in the northern Great Plains in the 1980s. We also have seen the loss of the older chemistries of insecticides, such as lindane (an organochlorine) in 2007, due to health and environmental risks. These older insecticides applied to the soil or seed were very effective against sunflower stem weevil and wireworms and had long residual activity. Unfortunately, some of the newer neonicotinoid insecticides are not as effective in killing sunflower stem weevils.
6. Host Plant Resistance — Host plant resistance uses the plant’s own genetic defense mechanisms to reduce the damage from insect pests. There are three major mechanisms of host plant resistance: 1) antixenosis — plants are not preferred by insects; 2) antibiosis — plants have an adverse effect on the biology of insects; and 3) tolerance — plants have inherent abilities to withstand the attack of insects.
Genetic resistance offers an alternative pest management strategy that can decrease economic losses from sunflower insect pests while also reducing input costs. It likewise can be integrated with pest management strategies, such as cultural and biological control. Resistance to certain sunflower insect pests (banded sunflower moth, sunflower moth, sunflower midge and sunflower stem weevil) has been identified in some developed sunflower germplasm and in some native sunflower species. The nature of the resistance mechanisms resulting in the reduced seed damage in the germplasm merits further investigation.
Knodel, J.J., G. Brewer, and L. Charlet. 2007. IV. Pest Management – Insects. In Sunflower Production, D.R. Berglund (ed.), NDSU Ext. Serv. A-1331 (EB-25 Revised). 26-53 pp.
Knodel J.J., L.D. Charlet, and J. Gavloski. 2010. Integrated pest management of sunflower insect pests in the Northern Plains. NDSU Ext. Serv. E-1457, Feb. 2010.
* Janet Knodel is extension entomologist with North Dakota State University, Fargo.
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