Maintaining the Integrity of IPM in Pennsylvania While Battling the Brown Marmorated Stink Bug

Posted: April 25, 2011

Pennsylvania tree fruit growers have embraced the principles of Integrated Pest Management (IPM) since the late 1960s and early 1970s. By one definition, IPM is the “utilization of all suitable techniques and methods in as compatible manner as possible and maintains the pest populations at levels below those causing economic injury.” The goal of IPM is to minimize the number and severity of perturbations in the agro-ecosystem while reducing the economic, environmental, and human health costs associated with the particular management option(s). Pennsylvania was one of the first states in the country to adopt the principles and practices of IPM in orchards by integrating the use of the black lady beetle Stethorus punctum – commonly referred to by most growers as the “black beetle” for the biological control of spider mites (e.g., European red mite and two-spotted spider mite). This program over the last 40 years was responsible for significantly reducing the number and amount of miticides used by fruit growers and reducing the severity of miticide resistance. More recently (2004 to present), the predatory mite, Typhlodromus pyri, has replaced Stethorus in many grower orchards as the principle biological control agent for spider mites in Pennsylvania.
Dr. Larry Hull, Emeritus Professor of Entomology, and
Dr. Greg Krawczyk, Extension Entomologist
Penn State Fruit Research and Extension Center

When the IPM program in Pennsylvania was developed and used by growers during the late 1960s through the mid-1990s, the majority of insecticides registered were primarily organophosphate (e.g., azinphosmethyl, phosmet, etc.) and carbamate (e.g., carbaryl, methomyl, etc.) chemistries—all of which were considered broad-spectrum insecticides, in that they killed many different species of pests as well as the natural enemies (i.e., beneficial predators and parasites) of the pests. Faced with these broad-spectrum insecticides, researchers at Penn State had to learn how to develop an IPM program for tree fruit crops using these types of materials. The selectivity of insecticide chemistries is divided into two categories, viz. physiological and ecological selectivity. Physiological selectivity is the property of a compound that discriminates in terms of mortality between two taxa (i.e., pest groups for example codling moth versus aphids) when applied at comparable rates of active ingredient. Over the past 15 years, growers have started to use many products (e.g., Confirm®, Intrepid®, Altacor®, Delegate®, Cyd-X®, etc.) for insect control in tree fruit that are defined as physiological selective insecticides. The majority of these products are relatively safe to many natural enemies inhabiting orchards. Ecological selectivity is the judicious use of pesticides, based on critical selection, timing, dosage, placement, and formulation of broad-spectrum pesticides (i.e., organophosphates, carbamates, pyrethroids, etc). Its goal is to maximize pest mortality while minimizing beneficial mortality and to alter the predator to prey ratio in favor of the former.

The IPM program in Pennsylvania has had to change and survive the challenges from many pest perturbations down through the years. For example, the tufted apple bud moth, once considered the number one direct feeding pest of apples from the 1970s through the late 1990s, quickly developed resistance to most of the organophosphate insecticides in the 1970s and 1980s and later developed resistance to methomyl in the 1990s. Brood X of the periodical cicada, which occurs every 17 years, had outbreaks in 1970, 1987, and 2004. Many of the insecticides used to control this pest were very harmful to the many natural enemies that inhabit orchards. The codling moth and oriental fruit moth developed resistance to a number of organophosphate, carbamate, and pyrethroid insecticides in the 1990s, which eventually led to the rejection and loss of thousands of loads of apples and peaches throughout Pennsylvania. Despite all of these perturbations over the past 40 years, the IPM program has withstood fairly well the majority of these challenges.

Fruit growers in Pennsylvania are now faced with the next major perturbation and challenge to their crops and their IPM program—the invasion of the brown marmorated stink bug (BMSB), Halyomorpha halys. As all of you are so keenly aware, BMSB was found in the Allentown area in the late 1990s and was occasionally found in other areas of the state over the past 10 years, but rarely causing any economic damage. However, in 2010 BMSB populations exploded on many fruit farms and other crops, especially in counties across the southern part of the state, causing damage to many peaches and apples with some growers losing over 50 to 60% of their peach crop to the ravages of BMSB, while some apple growers experienced damage to over 20% of their crop.

How are we going to control this pest in 2011? Many of you have heard us speak at the winter educational meetings about the prospects of controlling this pest, what products to use, and certainly what future research needs to be done. As you have heard, the near term solutions for BMSB will involve many different types of insecticides. Unfortunately, based on the excellent and recent laboratory data generated by Dr. Tracy Leskey and her research team at the USDA lab in Kearneysville, WV using a dry-film residual assay and the laboratory data that we generated at FREC this past winter and spring using a direct contact topical assay, the most effective insecticides for BMSB control belong primarily to the chemistries of the synthetic pyrethroids, the carbamate group – methomyl, the chlorinated hydrocarbon – endosulfan (i.e., Thionex®), and a couple of the neo-nicotinoids. As previously stated, the pyrethroids and methomyl are considered broad-spectrum insecticides that are highly toxic to many, if not all, of the natural enemies found in tree fruit. Because of this toxicity to natural enemies, Penn State entomologists have only recommended the pyrethroids before bloom on apple to minimize their toxicity. Growers who have used these products post-bloom on apples in the past have seen many flare-ups from European red mites, woolly apple aphids, San Jose Scale, etc.

Given the seriousness of the BMSB situation, the very high overwintering populations, its potential to possibly cause even higher levels of fruit damage in 2011, and given the fact that the most effective products for BMSB control are methomyl, pyrethroids, some of the neo-nicotinoid products (i.e., Actara®), how can growers successfully control BMSB and not completely destroy all natural enemies and the integrity of the IPM program in Pennsylvania? Growers need to only look back to what they did in the late 1900 era, when the only products available to them were primarily broad-spectrum insecticides. They will need to understand and employ all of the tactics used in applying the principles of ecological selectivity to this group of broad-spectrum insecticides. Listed below are some tactics growers can use to minimize the toxicity of these products to natural enemies while still controlling BMSB.

Selection of an insecticide – all insecticides are not equal in their toxicity to natural enemies. When selecting an effective product for BMSB control, always refer to Table 4-4 in the Penn State Tree Fruit Production Guide and determine its toxicity for the various natural enemies that may also be present. Choose the product that is the least harmful to the natural enemies.

Timing of an insecticide – proper timing is often the most effective and economical method of achieving differential insecticide selectivity for the pest/natural enemy complex. Only apply a highly effective insecticide for BMSB when they are in your orchards; therefore, growers must be very, very vigilant to monitor their blocks and surroundings and only apply these highly toxic insecticides when BMSB is present and a threat to their crops. 

Dosage – the toxicity of any chemical compound is directly related to its dose. When using one of these broad-spectrum insecticides for BMSB control, always apply the lowest effective dose possible. Not only will the lowest dose likely conserve some of the natural enemies, but it will also save you some money. 

Application techniques and methods – the only purpose in applying an insecticide is to kill the intended pest(s). Many growers in Pennsylvania have used the alternate row middle (ARM) technique of spraying to apply pesticides to their crops for over 40 years. We know from many years of research that this technique will provide effective pest control if done properly, but at the same time will allow for the survival of many natural enemies. Given the likelihood that the most effective control of BMSB will occur through the direct contact of the insecticide to this pest, the ARM method of spraying may be the best method to apply these broad-spectrum insecticides. By integrating low rates and frequent applications of insecticides (i.e., the original idea behind using the ARM method), better control of BMSB will likely be achieved while causing less harm to natural enemies. 

Selective placement – restricting an insecticide to a specific part of the tree or location within an orchard is another method to minimize the impact of toxic insecticides to natural enemies. Since BMSB is highly likely to move into orchards from the outside (e.g., woods, neighboring crops [soybeans, corn, vegetables], buildings, etc.), restricting the application of these broad-spectrum insecticides to border rows, etc., will likely conserve many natural enemies.

Overcoming the challenges of effective and sustainable BMSB control will not be an easy task in the near term. Much research needs to be done in order for us to develop the most effective management program for the long-term control of this pest. In the meantime, however, I also encourage growers to not lose sight of our current IPM program in Pennsylvania. We have achieved so much over the years and we have learned how to deal with those pest perturbations that seem to always occur. If we are not careful in how we manage BMSB, we may be causing many future pest problems for our industry by destroying the natural enemies that help us keep many of the other pests of tree fruits in balance.