Management Options for the Control of the Brown Marmorated Stink Bug – A Pennsylvania Perspective
Posted: May 31, 2011
A summary of management options is presented in this article. Please scroll to the bottom and click on the attachments to view useful tables and figures.
Damage on fruit caused by BMSB feeding can occur throughout the entire growing season. Although the mechanism by which BMSB feeds on fruit is similar throughout the season, the time of the season the feeding occurs can have a profound influence on the type and appearance of the injury. For example, early season feeding usually causes misshapen fruit, whereas late season feeding usually causes depressions on the fruit surface and the appearance of necrotic tissue (corking) just below the fruit surface. Late season feeding injury is often confused with the physiological disorder called “corking,” which is caused by a calcium deficiency. Although the amount of damage varied significantly among various locations throughout the state in 2010, some stone or pome fruit orchards suffered more than 60 percent injured fruit by harvest.
The management options for BMSB populations are quite complicated and as observed last season by some growers dealing with this challenging pest, also quite frustrating. Despite using the best available practices to conserve our IPM program, utilizing the best recommended products and tactics that we knew last year to control BMSB, fruit injury levels in affected orchards ranged from low to extremely high and most well above acceptance levels for growers and costumers.
Before we suggest our current management recommendations, let’s try to evaluate some of the possible reasons responsible for the observed problems in the management of BMSB:
Unique elements of BMSB biology: Although more and more observations suggest that this insect can survive the winter without the protection of man-made structures, at this time we still believe most BMSB adults overwinter inside some kind of dwelling, and most of the time outside of orchards or other agricultural settings. In the spring, adult BMSB move from their overwintering shelters, but not necessarily directly to the orchard. It appears that any green plant can support their feeding habits. The spring emergence of adult bugs from overwintering sites appears to be very extended, lasting from late April until early June. These differences in the starting point for overwintering adults likely create a situation that allows all possible BMSB nymphal and adult stages to be present in the orchard at the same time. Throughout the season, for reasons not yet well understood, BMSB at any point can start moving into orchards or between orchards. Feeding on stone fruits seems to be the preferred early season behavior, but these hosts are not exclusive and any green, growing plants (including pome fruit) are also possible hosts. Reports in the scientific literature estimate that BMSB can feed on 250 to 300 different host plants. Later in the season (i.e., late June, July, August and September) various instars of BMSB are frequently observed feeding on apple, pear, and small fruits including various berries and strawberries.
BMSB behavior: Host choice is still not well understood. We still do not know exactly when, and more importantly why, BMSB moves from one host to another. Due to the very wide host range of this pest in our region, it is important to understand that BMSB can move to orchards at any time from May until October, including multiple, consecutive influxes from surrounding vegetation. Effective control of one wave of stink bugs in the orchard does not prevent another wave of BMSB from entering the orchard a short time later. And since BMSB is not a resident pest in the orchard, even the best management activities against BMSB in the spring will not prevent new stink bugs from invading again later in the season, even in October. Therefore, it is quite obvious that in addition to using effective insecticides, the most crucial, practical element for successful BMSB management is the development of a reliable pest detection and monitoring strategy.
Efficacy of insecticides: Our laboratory bioassays conducted during the fall, winter and spring of this past year evaluating the effectiveness of various insecticides against adult stink bugs demonstrated the availability of multiple active ingredients that are effective. These bioassays also identified a large group of currently registered products, which provided very minimal direct mortality of BMSB adults. Bioassays conducted by the USDA-ARS group in Kearneysville, WV and directed by Dr. Tracy Leskey concentrated on the assessment of activity of dried insecticide residues while our Penn State bioassays evaluated the mortality of adult BMSB caused by the direct contact of insecticides. Bioassays conducted at Virginia Tech concentrated on the mortality caused by the direct feeding of BMSB on various active ingredients. Although all of these studies used different methods, the results when evaluated together provide a good complementary picture of what to expect from various products. The “Lethality index” developed by USDA researchers provides information on efficacy of products against adult BMSB after exposing them for 6 hours to a dry residue of insecticides, while the Penn State “Percent mortality” readings provide information on the toxicity of adult stink bugs after direct contact with a 2 µl of an insecticide solution applied directly to the dorsal part of the insect abdomen. Both methods utilized long-term observations (up to 120 hours after treatment) to develop the final results.
Suggestions for BMSB Management in PA fruit orchards
The laboratory bioassays conducted this past winter demonstrated various efficacies of currently registered insecticides against BMSB adults (Table 1). With 10 various active ingredients (from four different Insecticide Resistance Action Committee [IRAC] Groups) causing above 50 percent mortality during the direct contact bioassays, it appears we have enough products to control BMSB populations that enter orchards throughout the entire growing season. The challenge with this seasonal approach is to manage the usage of these various products so they provide not only the best control for all injury causing stages of stink bug, but also all other pests present in orchard throughout the season. These available products are not equal in their efficacy against stink bugs and they are also not equal in their activity against other pests at the time when insecticide applications might be needed. A grower can choose to ignore these other pests and concentrate only on the management of BMSB, but based on our experience from the era “before the stink bug,” it might not be the best option especially with known pressures in our orchards from such pests as codling moth, oriental fruit moth, and leafrollers, etc.
When developing a seasonal strategy to manage BMSB at any particular location, the following factors need to be considered during the planning process:
Insecticides: The efficacy ratings either for direct contact or residual toxicity against BMSB are two of the most important factors in choosing the best product(s), but growers should also consider the time of the season and what other pests are likely active in the orchard. Also, factors such as an insecticide’s pre-harvest intervals, the number of available applications per season, and the amount of an insecticide active ingredient that can be used for the entire season (please be aware of multiple products with the same active ingredients) need to be critically assessed. While it may be wise on stone fruit to use the more effective products earlier in the season, the same products on apples may be much more valuable for BMSB control in August, September or October. Since all products have a limited number of applications and active ingredients that can be used during a season, utilizing the most effective insecticides before they are essentially needed, will likely leave us with only less effective alternatives later in the season.
Expected sources of BMSB influx: Population pressure from BMSB is not uniform from outside or within any particular orchard, but it also fluctuates during various times of the season. Some orchard blocks located next to woods may not have to deal with stink bugs until later in the summer, blocks next to various kind of dwellings most likely will be affected earlier in the season, while blocks located inside other large groups of orchards may experience only low pest pressure throughout the season. However, in every orchard, due to the ability of adult BMSB to move quickly among various hosts, a constant and vigilant monitoring program is the very basis for successful management.
Crop/block specific characteristics: Factors such as different harvest dates for fruit, the mixture of cultivars, surrounding vegetation as a possible source or barrier for BMSB populations during the season and the attractiveness of the crop to BMSB mandate individual treatment strategies for each separate orchard or block within the orchard. While some fruit blocks might require seasonal, intensive management options against BMSB, other blocks might require a less intensive program. Unfortunately, there is no “one size fits all” recipe for successful management in dealing with this pest.
Necessity of controlling other pests: In orchards that experience continuous, seasonal pressure from BMSB, seasonal control options must be carefully selected. In selecting these control options, growers should also consider what other fruit pests and beneficial natural enemies may be affected by their selection of products used against BMSB. Detailed monitoring of all pests will be crucial in order to prevent additional crop losses caused by the “normal pests.”
Planning for a seasonal insect control program: Since we currently cannot predict when BMSB will move into orchards and how intensive their populations and feeding will be this season, we should prepare ourselves for a season-long monitoring and management program. Also, the results of our early season management activities will likely not minimize the pest pressure that fruits experience in late summer and early fall. While BMSB can cause fruit damage at any point during the season, maturing fruit likely represent the most attractive and most likely available source of nutrients for this insect and therefore pest pressure may be the strongest as we move into the late summer and early fall period.
The brown marmorated stink bug is here and most likely will be an important and serious threat to our fruit system for a long time. Over time, we will learn how to manage this pest more effectively. New tools such as insect behavior modifying materials (e.g., a sex pheromone, an attractant, repellent or deterrent) will likely be required to successfully control and minimize the threat from this pest. In the meantime, with the knowledge we have and the tools that are available, we need to try to “outsmart” this pest in order to continue to produce the best quality fruits. This new, exotic pest will require new management approaches, but until we can field test some of our BMSB management hypotheses, these ideas will remain just “concepts” which may prove attractive in theory but difficult or even impractical to implement. As the growing season progresses, we will continue to “learn as we go” and continue to provide the newest information to growers as fast as possible.
Current and new updates and recommendations will be posted at the Penn State FREC web site (http://frec.cas.psu.edu/) as they become available.