Disease Insight

Young trees with fireblight strikes

A new growing season approaches, and behind the expanding buds lurk the pests and diseases that can threaten a grower’s bottom line. Fortunately, researchers continue to develop the management protocols necessary to keep bugs and blights at bay. We’re so comfortable with these controls that they can become just another part of our annual checklist, along with flushing irrigation systems and tuning engines.

While there may not be a major news flash in regards to your particular crop this year, chances are that there will be a pest, disease, or disorder that will become a significant problem for you in the near future. This isn’t intended to be a scare tactic, but a reality check—Mother Nature is geared towards overcoming your crop protection strategies. Predicting what she might have in store can help you plan for the future.

Some of the researchers who contribute to Good Fruit Grower focus on a particular fruit crop and become intimately familiar with that organism: they continually improve our understanding of the best conditions for production. Conversely, they can identify environmental stresses that tax the plant’s resources, making it more susceptible to opportunistic pests and diseases. Other researchers focus upon those opportunistic organisms, similarly learning the details of their life history and environmental requirements.

A mélange of environmental conditions—including temperature, moisture, light, and nutrients—influence important field dynamics such as fruit set, pest reproduction, and disease intensity. When environmental conditions are altered, so are plant, insect, and disease dynamics. It’s not necessarily easy to predict net effects. For instance, the frequency or severity of particular pests, diseases, and disorders may increase, decrease, or remain unchanged in response to an environmental shift. Perhaps the most significant shift we’re witnessing today is climate change. How will regional changes in temperature and water availability affect insect and disease management?

Every species has what’s known as a range of tolerance for a specific environmental factor: growth and survival is optimal within this range. As the factor increases or decreases outside this range, mortality increases. While this may spell doom for the species as a whole, many species are able to migrate with changing climate patterns and invade new territory. For example, the United States is experiencing an increase in mosquito-borne diseases as winter temperatures become less severe. From an agricultural perspective, we might expect to see pests and diseases associated with subtropical regions wending their way north. Temperate plant species would push their northern borders.

What happens when water availability is added to the equation? With increased water during the growing season, plant growth should flourish, as will many pests and diseases. Excessive rainfall in the winter, however, may injure plant and pest populations alike by waterlogging soil and creating anaerobic conditions; this might be exacerbated with warm winter temperatures that limit the amount of water tied up in snow and ice. Decreased water availability brings yet another set of possible outcomes to the plant-insect-disease associations.

These previous suppositions were based on crops, pests, and diseases currently coexisting in the same region. What happens when a new pest or disease is added to the mix? This is where the relatively new science of invasion biology can help predict impacts. Severe outbreaks almost always result when a new organism invades a region, as its natural controls may not be present. A new pest in an orchard will impose yet another strain on the crop—and the grower.

It’s readily apparent that predicting the results of any but the simplest alterations in environmental conditions is difficult. Pathologists agree that identification and management of new diseases and pests will be critical for our agricultural economy. So, now we return to those researchers who’ve contributed their knowledge of diseases and disorders to this issue of Good Fruit Grower. They are the ones who, with their intimate knowledge of the environmental requirements of apples, or cherries, or fungal leaf spot, are best positioned to understand these unknown climate, pest, and disease challenges to your fields and orchards.

See what they have to say this month!