For the small vegetable grower, there is little room for loss to pests. Still, the old paradigm of striving to achieve a sterile growing environment has passed. We all now understand that it is far wiser to work within the natural framework -the food webs- to achieve a balanced equilibrium with multiple feedback loops and as diverse a number of players as possible. The more diversity there is, the more stable the ecosystem will be and the less likely there will be population outbreaks of pests. This, of course, makes the task many magnitudes of degree more difficult, although perhaps more intriguing. There are many common rules of thumb, common sense practices and techniques, however, that will provide a degree of simplicity to a very complicated and multi-faceted problem.
Most of the concepts to consider fall under the heading of IPM: Integrated Pest Management. IPM can become complicated, but in it's essence, it is a system by which you know your crop, you understand the potential for pests for that crop, monitor for those pests, know the pests that arise, and use multiple approaches to to synergistically prohibit their populations from growing past a known threshold, using the least toxic methods first, and monitoring those populations to know when to act, and how aggressively. This is obviously more difficult than spraying non-selective powerful pesticides on a regular basis -but is vastly safer, healthier, more cost effective, and more sustainable. Even the most powerful pesticides we have in our arsenal have become useless to some pest populations due to their ability to evolve and develop resistance. Working with the natural systems instead of against them always wins in the end.
A healthy plant is more resistant to pests and disease. Just because a plant is growing quickly does not make it healthy. Quick succulent growth due to aggressive fertilizing with high nitrogen fertilizers is a prime target to many pests, insect and fungus alike. Using low strength organic fertilizers eliminates the possibility of abiotic damage due to salts and also allows the plant to develop at a lower pace with stronger cell walls and higher concentrations of tannins, alkaloids, and other natural pest deterrents. Using a balanced, complete fertilizer also helps plants develop their natural barriers to infection. Using a fertilizer comprised of meals, guanos, and minerals also means the nutrients will be released slower and more evenly because they must be made available by the biological activity in the soil.
A healthy soil will encourage healthy plants as well as encourage beneficial soil micro flora and fauna that can help protect plants from pests. A healthy population of mycorrhizae fungi can help protect the plants from stress by supplying the plants with micronutrients and water that they may not have been able to get on their own. Pests are naturally drawn to stressed plants. Some soil fungi can also kill harmful nematodes and other pathogens. As a rule, soil that has good structure is better drained and there is a higher percentage of soil pore space with more oxygen. This is only possible with humus and the regular addition of organic matter. More oxygen in the soil eliminates the populations of anaerobic organisms that can be detrimental to good plant health.
One basic pest management method is exclusion. An example could be using a fence. A basic fence can keep out many larger pests, deer and pets being major players. Another popular measure would be to employ regular use of "floating" row covers. These lightweight spun cloths can be placed on hoops to protect growing crops or even laid directly over sown seed beds to protect the seeds and seedlings from birds. Gophers can be mitigated by using gopher wire or even galvanized steel beds. Bird netting can be used to drape over crops nearing maturity to protect ripening fruits and berries. Copper barriers can stop mullusks.
Traps can be deployed. Gopher traps take time to master, but are very effective. Snail and slug traps are easy. Earwigs and sow bugs can also be trapped if they are a problem. "Trap Plants" -such as an agapanthus or other similarly strap shaped leafy plant can be used to trap snails for collection. Sticky traps can be used to both catch and to monitor populations of whitefly, thrips, and other small insects. Pheremone traps can be used for some moth pests as well as yellow jackets (which don't harm plants). "Tangle foot" and boron based traps can help mitigate ant activity and populations, thus disrupting them from "farming" homoptera insects such as aphids, mealy bugs, and scale.
"Know Thy Pest"
If you understand the lifecycle of the pest in question, you can use less input to have a greater control. Sometimes, a simple spray of water during a critical moment of the pest's life cycle is enough to dramatically reduce their population and eliminate the need for further action. Most pests have multiple natural predators. Knowing the life cycle of the predator can also help you promote their populations. Being able to identify their eggs, their adult forms, and avoid removing parasitized pests ("mummies") can help keep high populations of beneficial insects around. Sometimes adjusting the irrigation and moisture level can help reduce pest problems as well. Examples would be red spider mites, powdery mildew and downy mildew. Knowing the pest, of course, must follow good observation. Looking for damage -symptoms, as well as signs- actual pests, is key. Regular monitoring and being alert is a good habit to develop. It is also important to know how the pest overwinters -so that cultural measures such as mulching and leaf disposal can be used to reduce secondary infections and overwintering pests. Sometimes a simple crop rotation can obliterate a pest population.
It is good to have some tools on hand for when a pest problem reaches your threshold of tolerance. Soaps and oils can be effective methods to knock down pest populations safely and efficiently. Soaps work by dissolving the waxy cutin layer of the exoskeleton and allowing the pest to die by desiccation. Oils work by suffocating the pest. In general, soaps work really well when it's hot and dry. Oils can be enhanced by using Neem, a natural pesticide from the Neem tree. Another tool, Diatomaceous Earth, is a fine powder of ancient diatoms that can be used on pests with hard exoskeletons to scratch their cutin layer and allow them to desiccate.
Compost tea that has been "brewed"... oxygenated -contains populations of beneficial organisms that can help protect and to treat many plant pathogens and other ailments along with promoting healthy soil biology. Specific bacteria, such as Bacillus thuringiensis can be deployed to target lepidoptera larvae such as the corn ear worm. Another bacteria, B.subtilis shows great efficacy on a wide range of bacterial and fungal diseases. These bacteria are so specific in their action that they can be used right up to the day of harvest. Pyrethrins are also good natural pesticides derived from Chrysanthemums. Look for formulations that have OMRI listing (Organic Materials Review Institute) on any spray you use in the garden and follow the label directions. Remember to always strive to use the least toxic methods first.
Using a combination of healthy soil and plants, good cultural techniques, and regular observation can go a long way towards eliminating pest outbreaks. Strategically spot treating at the right time for a targeted pest is the only time spraying should be necessary. Knowledge is power. The more you learn about the pests and their natural predators, life cycles, and preferred habitat, the easier it is to manage them with little input. A great resource besides the web is the Master Gardener Help Desk. If you have a symptom or a sign and want more information, bring in a sample or call the Desk.
UCCE Master Gardener Desk
1682 Novato Boulevard, Suite 150-B
Novato, CA 94947
(415) 499-4204 Email: HelpDesk@MarinMG.org
Hours: Monday-Friday 9:00 AM-Noon and 1:00-4:00 PM