Jul 28, 2011

IPM approach thriving, despite threats

Integrated Pest Management (IPM) is a philosophy that applies the principles of ecology, especially population biology, to the management of pests in agricultural or managed systems. IPM considers the impact of actions taken on farm economics, worker safety, the environment and the consumer.

The foundation of a good IPM program is built on a sound understanding of biology (pest and natural enemy), identification (taxonomy) and ecology. IPM bases actions to mitigate pest populations on need. Actions are only taken if the pest population exceeds a level requiring a response to protect the crop from damage. Therefore, sampling and action thresholds are critical foundational components of a good IPM program.

Predictive models are also valuable tools to make sampling activities more efficient and the implementation of tactics more effective. IPM does not rely on a single tactic but utilizes multiple tactics to mitigate the negative impacts of pests. These tactics are used in an integrated approach with a goal of limiting use of tools that disrupt natural controls.

IPM can also be viewed as a continuum between different approaches to crop protection. The extremes in this representation would be the conventional system, generally dominated by the use of one tactic, synthetic pesticides, and the organic system – considered a more holistic approach to crop protection but one that is highly legalistic (limited by specific and somewhat arbitrary rules).

IPM systems can be characterized as moving away from traditional conventional crop protection approaches. Bio-based IPM places more emphasis on conserving biological control, while semi-organic IPM stresses use of organic controls for arthropod pests and diseases but is not as restrictive as certified organic systems on weed control and nutrition management. The goal of IPM is a stable and sustainable crop protection approach that ensures grower profitability while minimizing negative impacts on the environment, farm workers and the consumer. Crop protection programs can be moved along the continuum between conventional and organic by several factors, including regulatory actions limiting pest control tools, the introduction of new pests, uncertainty over rules governing chemicals allowed in export markets, demands of buyers and a lack of unbiased information on how to use various pest control technologies.

For purposes of this article, I am limiting my focus to apple IPM in Washington and am dealing specifically with arthropod pests.

The key arthropod pest in the apple system is the codling moth (CM) Cydia pomonella. The key pest of an agricultural system is the one that, if not controlled, would cause severe crop loss; therefore, most pest control activities are directed at the key pest, and it is often these activities that disrupt natural controls for other pests.

The CM larvae bore into the apple fruit, thereby making them unmarketable. Even a small CM population, if it is not suppressed, can result in crop loss that is economically unacceptable to a grower. Because tolerance of CM is low, there is little opportunity to rely on biological control (predators, parasites or diseases) as a primary control tactic. In addition to the CM, there are several other pests that directly attack apple fruit. These include leafrollers, thrips, scales and true bugs like stink bugs and the mullein plant bug.

While these pests can cause severe crop loss, their presence in orchards varies from region to region, and their impact on different apple varieties varies. IPM seeks to take advantage of natural enemies to control some of these pests or to implement selective chemical control programs that do not disrupt biological control of other pests.

Secondary pests (aphids, leafhopper, leafminer, spider mites) do not directly attack apple fruit but feed on foliage, bark or roots and indirectly impact fruit quality if their populations get too high. Because these pests have the potential to be controlled biologically, the goal of IPM is to adopt practices that conserve their natural enemies in orchards.

Pest models that predict the development of a disease or arthropod pest have been valuable tools in IPM programs. These models associate environmental conditions with the development of diseases or predict the seasonal development of arthropods.

With the development of the WSU Agriculture Weather Network (AWN) in Washington state, automation of model delivery became a possibility. AWN maintains and provides access to environmental data from more than 130 stations throughout the state. A team led by Vince Jones from WSU developed the Decision Aid System (DAS), a web-based system that delivers information on 10 insect, three disease and two horticultural models. DAS integrates model output with management recommendations and links to a database of pesticides recommended by WSU for control of pests. This system allows users to create a personal profile where they specify the weather stations and models they wish to access. DAS represents state-of-the-art technology for delivering critical information in real time to assist growers and crop consultants in making pest-control decisions. It represents the kind of decision support systems that Washington tree fruit growers and consultants have said they want more of.

Threats

The arrival of new pests from overseas represents the greatest threat to apple IPM programs. While research solutions will be found to deal with these new pests, it is highly likely that IPM programs may need to temporarily revert to reliance on broad-spectrum chemical controls, once again limiting the impact of biological control in orchards.
Two recent examples of threatening pests are the Spotted Wing Drosophila (SWD) and the Brown Marmorated Stink Bug (BMSB). The original home of these pests is Asia. How they were introduced into the U.S. mainland is not known but is likely tied to increased worldwide trade.

SWD is a pest of many berries and soft fruits, including cherry. Unlike most drosophila, this species can deposit eggs into healthy fruits or berries. The full impact of SWD is yet to be determined, but one thing is clear: Its presence has dramatically changed IPM programs in cherry production.

BMSB is a pest that has gradually increased in importance over the last decade after being detected in the United States in 1994. It has spread over most of the country. Last year, it caused severe crop losses in tree fruit orchards in the eastern United States. BMSB also is present in Western states, albeit in low levels. The main concern about BMSB is that the OP-alternative insecticides that are now a key part of the apple IPM program do not provide effective control.

Despite such threats, the current research and education efforts on enhancement of biological control promises to provide increased stability in IPM programs over time.
Incorporating pest resistance into commercially viable apple varieties is a long-term goal for IPM programs, but with the recent publication of the apple genome and new tools available to breeders, such a reality may be closer than any of us anticipate.

A longer version of this article appears in the April 2011 issue of Compact Fruit Tree, a publication of the International Fruit Tree Association.

By Jay F. Brunner and Mike Doerr, Washington State University