Plan your attack on greenhouse pests with these helpful tips.
Newberg, Oregon—With the weather outside still inclement, working in the greenhouse is a great escape. But even in this refuge, spring cleaning is unavoidable. A mountain of used, dirty plastic pots have amassed over the winter, and I am running out of room. I must drag out my large plastic garbage can and wash the pots. After years of experience, I am so accustomed to this drill, I could do it in my sleep: I make a 10 percent solution of bleach and water, which will kill any existing bugs and disease. Immersing entire stacks of old plastic pots together, I weigh them down with a brick to make sure they remain fully submerged. I soak them for at least 10 minutes (overnight if needed) to make sure they are sanitized. It is then a simple matter of lifting them out and letting them drain. Most of the dirt has been loosened with the soaking and is easily rinsed away with water. This is a convenient way to wash the pots, and I can pot up rooted cuttings while they’re soaking.
Now is also the time to institute a plan of attack on greenhouse pests. I take an integrated approach to pest control by using a combination of dormant oils, contact sprays, beneficial insects and yellow sticky notes to regulate and monitor pest populations. My initial strategy is to knock down any populations of overwintering pests and then to moderate their population with a follow-up use of predatory insects. My initial attack is to begin by spraying a fine-grade horticultural dormant oil (SunSpray). Direct contact is needed, so a thorough spray of both sides of the foliage is critical to success. The spray actually coats and smothers all those overwintering pests, such as scale and mites, that might have survived my fall applications. I particularly target all my evergreen herbs — good hosts for scale — such as bay laurel, citrus and myrtles. To control spider mites, I pay particular attention to various salvia species (S. rutilans, S. oppositiflora, etc.) and lemon verbena (Aloysia triphylla), which are especially susceptible to the mites. Checking the underside of old leaves of stock plants for white flies or the plants’ new, soft growth for aphids usually will give me a clue to my efforts’ effectiveness. If I do find pests, I grab an aerosol can of pyrethrum and do a spot spray. I have to watch for possible toxicity to the plants, so I avoid spraying in sunny conditions or applying the spray to very young plants with soft growth. I may spray a swarm of fungus gnats if they are present, but using predatory nematodes on a regular basis generally keeps them in control.
New insect pests sometimes do surprise me. Lately, I’ve noticed a tiny green larva that binds together the new tip foliage of rosemary, bay laurel and, occasionally, lavender. Since the foliage protects these pests, contact sprays are ineffective. I usually just prune off the tips of new growth or individually unfurl the leaves to expose the larvae. (My daughter’s pet fish love to eat these delicacies.)
New this year was a similar attack on my sweet violets, but this time, the leaves were thickened and contorted to protect a little white larva within. Since spraying was ineffective because the pest was protected, I carefully hand picked and disposed of the larvae. Although the exercise was time consuming, it was an effective treatment and so satisfying.
Not so satisfying is watching a plant suddenly wilt and die. Although I’ve only experienced occasional attacks of verticillium wilt in my garden, I have read about its devastation. This malady once was discovered on the national collection of monarda at Leeds Castle in England. The symptoms were contorted leaves and black centers in leaves eventually “wilting” the plant and killing it. The castle’s gardeners’ control was the use of an amended organic soil with added predatory fungi. They also found the same curative properties in composting grape skins, a practice that intrigues me. I live in wine country and will have to find out what the vintners do with all their compost after they make the wine. It might be a terrific preventive measure for our occasional encounters of the verticillium kind.
Even though spring is arriving, we still are facing pesky colds and flu. If I do get sick, it’s thanks to my children bringing the germs from their school. I am intrigued by an article I just received on the effectiveness of oregano oil in combating cold and flu viruses. In Canada, oil of oregano is becoming more popular than echinacea in fighting these types of infections. Recent research has shown oregano oil to have high antibacterial properties. With last year’s outbreak of Severe Acute Respiratory Syndrome (SARS) in Canada, oil of oregano was more popular than echinacea for herbal relief and building immunity. Additional research is investigating its high antioxidant properties. Although I occasionally take bitter echinacea tincture, the more palatable oregano would be less offensive. I guess I’ll eat a leaf of ‘Greek’ or ‘Kalitera’ oregano, or add an extra handful of oregano to the spaghetti sauce to keep my immunity and mental state shipshape until spring unmistakably has arrived and I can head outdoors.
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