What’s Wrong With My Fruit Tree? Holistic Pest & Disease Management Tips
Spring is here and so are the first signs of fruit tree pests & diseases. In this blog post, we hope to share an alternative 'paradigm' with which to view pest and disease issues in your fruit trees. While diseases (apple scab, fireblight, etc..) and pests (winter moth, codling moth, etc..) require different strategies, the core principles in dealing with them have some similarities.
For us, it comes down to four main concepts. Let's dive in.
1. The Disease Triangle and a Focus on Plant/Soil Health
The 'Disease Triangle' is a concept in horticulture & public health that posits there are three essential factors (susceptible host, favourable environment for disease, and pathogen) that are needed before there is a serious problem. This means that just because you see a pathogen does not mean it will become a problem. With regards to horticulture, the ways to mitigate each factor include:
Presence of the disease: sanitize pruning equipment
Favourable environment: get lucky with the weather, use rain shelters for some crops, prune for good airflow, and not when raining
Susceptibility of the host: plant in the right place and right soil type, ensure good airflow & drainage, practice 'competitive colonization' by using probiotics like effective micro-organisms & compost teas, work on mineral balancing, feed the plant with organic & mineral fertilizers to boost health As we can see, there is much more you can do as a horticulturalist to keep your plants healthy & happy and that is where you should start!
So when you see the onset of disease, start by giving your tree some love (liquid fertilizer, water, compost teas, effective micro-organisms) then continue to monitor while you develop the next steps.
Here is an excerpt from our Online "Grow Fruit Trees in the Pacific Northwest" Course:
* Mispeak in the example above - should say fireblight is bacterial in nature, not fungal.
2. Start with Proper Identification
Ok, you've given your tree some love, now its time to hone in on what's wrong. What is it you see? Leaf-eating caterpillars (winter moth, tent caterpillars, leaf rollers)? Wilting flowers with black stems (possibly fireblight)? Black stain and cracking on the stem (anthracnose or fireblight canker)?
You can't manage what you haven't properly ID'ed.
Here are some resources to help you ID your pest or disease:
3. Understanding Pest/Disease Thresholds and 'Breaking Their Cycles'
With Integrated Pest Management, a few pests can be tolerated. It is only necessary to take action when pest numbers reach a certain level. This level is called a 'threshold'. Only year after year observation will allow you properly assess whether a pest or disease may reach that threshold for your context, but it's worth monitoring.
In the example below, our good friend Chris discusses his 'do-nothing' approach to leaf rollers when he anticipates that they will not reach extreme levels of damage. 'Do-nothing' may not be the best description of Chris' approach. In fact, he's spent 10 years creating a multi-storied ecosystem of plants that attracts tachinid flies and parasitic wasps to help him control things like leaf rollers and keep their populations in check. In this case, the leaf-rollers simply thinned a little bit of fruit so that he didn't have to.
So it is not a 'leaf-roller' problem you have on your hands, but an 'ecosystem-service deficiency, specifically a 'deficiency in tachinid flies and parasitic wasps. Time to plant more dill, yarrow, anise hyssop and angelica!
It is also a good idea to understand the life cycle of the pest or disease. A quick Google search of "Fireblight lifecycle" will give you the following:
Or "codling moth lifecycle":
These are valuable tools for understanding how and when you might break the lifecycle of these organisms. For instance, the strategic use of chickens to clean up fallen fruit can help break pest cycles at their larval stage. Sanitary pruning can help break the cycle of fireblight before it releases spores for the next generation.
4. Last Resorts
You've decided to do something about your pest & disease. Acceptable thresholds have been exceeded and/or your tree's health is at risk.
For many fungal & bacterial diseases (fireblight, anthracnose canker for example), early detection and physical removal will go a long way.
For other pests, some sprays may be considered.
Here is a quick summary of some of the organic options that might work for you. See the PDF below for more information and timing and application processes. Avoid causing collateral damage to beneficial insects by properly identifying your pest and by using controls judiciously.
This PDF is extremely helpful for dealing with each individual pests & disease that are commonly found in the Pacific Northwest: