January 12, 2013
Winter has traditionally been the time for garden cleaning. Early winter rains have germinated a multitude of weed seeds and a warm, wet fall has inspired the snails and slugs to increase their feeding. The best strategy is manage those pests and others is by fine-tuning the garden ecology.
Gone are the days of garden hygiene to the point of sterility. Gone are the organophosphates and systemic chemical controls. The modern gardener understands that working with the natural systems and tweaking them to promote a balanced equilibrium of healthy populations is the key to success.
This controlled homeostasis will minimize inputs of time and energy as well as toxics and collateral damage from the use of pesticides. By understanding historical pest activity in the garden, the good garden steward can strategize ways to avoid use of pesticides altogether.
The ideal garden ecology that inhibits pest population spikes is one in which the soils, hydrology and biodiversity have been addressed in a holistic way. When all three are in excellent shape, plants are not stressed and pests rarely get out of hand. Addressing drainage problems is easier when you can see where the water flows and pools. Inundated and compacted soils can go anaerobic and cause plant stress and create shallow root zones. When soil has good structure — thanks to organic matter and a diverse ecology of microorganisms — erosion is minimized, soil aeration is increased, water is better able to infiltrate, and disease resistance is maximized through biological action.
While it may be too wet to work some soils, it is never too wet to add compost, mulch or both to the surface of the soil. The micro-arthropods and earthworms will work their magic to chip, shred and move the organic matter down into the soil profile to feed a growing diversity of beneficial soil organisms. If the soil temperature is below 50 degrees, many of the organisms will hold off on making nutrients available to the plant roots, but they will be better poised and ready when the temperatures climb.
While it may not make sense to think about irrigation during the winter, it is actually the best time to look at the garden and consider changes that would better group plants by plant community, by irrigation zone/valve or "hydrozone" — grouping plants with similar water needs in one watering zone.
An overwatered plant is going to put on fast, succulent growth that has thinner cell walls and less-defensive compounds to deter pests and pathogens. A drought-stressed plant will appear as an easy target to boring insects. Moving thirstier plants out of a hydrozone of more drought-tolerant plants now can save water and reduce plant stress and pest issues next season. Adjusting emitters and sprays for plants that have outgrown the current system layout also will reduce crown rots and other plant stressors. Consider transitioning older sprays to a more-efficient drip system that also reduces the conditions that favor fungal diseases on leaves.
Increasing the biodiversity of the garden allows for improved niche management. While any living system is dynamic in nature, a healthy, diverse system is one in which the available food is quickly assimilated, the habitats are continually occupied and there is adequate competition to provide for natural selection. In such a system, a pest or pathogenic organism will have its population numbers held in check.
Let's say a fungal mildew spore lands on a leaf. If the leaf's surface is populated with a diverse array of organisms such as bacteria, beneficial fungi and other protozoa, the disease-causing spore will likely be quickly eaten or not find an available niche from which to infect the plant.
Most modern garden ecologies are not diverse panaceas, however, and pest populations can get out of balance. That's when Integrated Pest Management comes in handy. The tenets of IPM lead the steward through a holistic process whereby the nature of the pest and its relation to the host plant including the pest's life cycle, overwintering sites and natural enemies are better understood. Through the synergistic and strategic use of physical and cultural control strategies, the pest population is brought back into balance, not eliminated.
The use of less-toxic pesticides such as Organic Materials Review Institute listed products, is a last-resort strategy and understood to include collateral damage to beneficial populations within the ecology. Biological controls, including the introduction of beneficial organisms such as bacteria, nematodes and insect predators, are the preferred control strategies when physical and cultural controls miss the mark. Planting to encourage birds and predacious insects is one of the best pest management strategies.
Finally, winter pruning that promotes quick wound closure and opens up canopies to greater sun exposure and air circulation the coming season can dramatically reduce pests and diseases.