Spider mites are nearly invisible, but the damage they do to plants certainly isn't. By piercing leaf cells and draining their contents, spider mites mark their feeding sites with distinctive speckling. During an untreated infestation, the speckling spreads. The leaves turn yellow or red and may begin dropping. The pests also drape their hosts in fine webs. Because they're not insects, spider mites are resistant to broad-spectrum chemical insecticides. A better solution is to spray them with organic, plant-based neem oil.
About Neem OIl
Neem oil, extracted from the seeds of the tropical neem tree (Azadirachta indica), has been used as a natural pesticide for centuries. It's available as granules, dust, wettable powder and liquid concentrate, but the most user-friendly products are ready-to-use sprays.
Neem oil contains several mite-toxic ingredients. Azadirachtin, the most powerful one, repels new mite infestations and discourages feeding in existing ones. More importantly, it disrupts the young mites' hormones so that they're less likely to mature and reproduce.
Timing the Spray
While neem oil is safe enough for use in organic gardening, it has drawbacks. First, the wet oil is lethal to bees. Spraying in the late evening or early morning gives it time to dry before bees begin pollinating. A late-evening application also reduces the chance of sunburn. Neem oil may burn leaves when the sun is on them or the temperature is at or above 85 degrees Fahrenheit.
Pretreatment Testing and Preparation
Check your product's label for a list of neem-sensitive plants. If your infested plants aren't listed but you're still hesitant, spray a few leaves and flowers and wait a day. If they wilt, the plants are sensitive.
Neem oil may harm water-stressed plants, so water well before using it. Choose a calm, dry day with no rain in the 24-hour forecast, so the oil won't wash off before it dries. Protect your skin, eyes and lungs from the drifting oil spray with a long-sleeved shirt, long pants, waterproof gloves, safety goggles and a respiratory mask.
Some people dislike the oil's garlic-sulfur smell. For an odor-free house, move mite-infested houseplants to a well-ventilated area or shady outdoor spot for treatment.
Spraying and Followup
Spray the plants until the neem oil runs from all their surfaces. Thorough coverage is essential, so make sure the spray coats the backs of the leaves.
To wipe out an existing spider-mite population, repeat the treatment after rain or in one week. After that, spraying every two to three weeks, or at the oil label's recommended intervals, prevents reinfestation.
Keep people and pets away from the sprayed plants until they dry. Wash the clothes you wore when spraying in soap and hot water before wearing them, and store the unused oil out of direct sun at an above-freezing temperature.