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Kaffir Lime Care – Bug/Fungus Problems

by Kasma Loha-unchit

19. What To Do When Bugs and Fungal Diseases Attack

A healthy plant is less susceptible to pest and disease attacks, so keeping your kaffir lime tree well cared for is the best defense strategy. Besides feeding and watering, providing good air circulation by proper siting and pruning is an important preventive measure. Cleaning up debris around the plant, such as fallen leaves and fruits, reduces hiding and breeding places for pests and decreases the likelihood of fungal spores growing on decaying matter. But even with the best of care, there are environmental conditions we don't have control over which may encourage pests and diseases to visit your tree, such as stuffy heat waves when the air is dry and still. Bug attacks generally take place when the weather is warm and are usually, though not always, less common during the cooler months of the year.

Ants are attracted by sweet citrus blossoms and pretty soon they might decide to hang around and farm aphids and soft scales for the honeydew-like substance these bugs secrete. So one way of preventing insect infestation would be to keep ants off your kaffir lime tree. Another good reason to keep these rascals off your tree is that they oftentimes pick up fungal spores on their feet as they soldier from plant to plant, thereby spreading diseases to otherwise healthy plants. You can use ant stakes, sprinkle borax or cinnamon around the perimeter of your plant, or use some other ant deterrent you find at your local Long's, Ace, or garden center. There are a multitude of products to choose from, some more natural than others.

Bugs, however, do not need ants to invite them to your tree. The most common insects attracted to kaffir lime trees are aphids, soft and armored scales and, although not as common, mealy bugs. Aphids like the sweetness of the blossoms and the delicious tender young leaves on the tips of the branches. Scales attach themselves to the undersides of leaves and along the branches and trunk of the tree and can be anywhere on the plant, though they love munching on the newly emerging leaves just as much as aphids. Often soft scales (they have soft bodies while armored scales are brittle) are accompanied by a greyish fungus that gives the leaves a black mildewy look. That's because the sweet honeydew they secrete are a perfect culture for molds. Mealy bugs are a big nuisance and hard to get rid of once they take up residence on a plant, but they usually aren't commonly attracted to citrus trees unless conditions are perfect for them. Some of the kaffir limes we picked most recently from Four Winds following a long, stuffy heat wave had mealy bugs attached to them, especially in the deep creases on the warty peel.

Whenever you notice the first signs of bugs on your plant, immediately take action and nip the problem in the bud before a full-scale infestation takes over. If there are just a few bugs, you can simply remove them with your fingers and squish them to death. If you can't stomach such violence, then you can spray them to death.

There are many products available in garden centers for getting rid of these bugs, some safer than others for the sprayer as well as the people who are going to eat the leaves in Thai dishes. The safest is definitely pure neem oil. It comes from an edible, medicinal plant that is highly prized in age-old Ayurvedic Indian and Southeast Asian traditional herbal medicine. Thais love to eat the very bitter (the whole plant is bitter) tender flower buds with a sweet tamarind sauce which cuts the bitter, grilled catfish and sticky rice. It's really very good and very good for you and comes much closer to being a Thai national dish than pad thai! So when you spray with a dilute solution of pure neem oil (available under the Dyna Gro label), usually 2 oz. to a gallon of water, you need not worry at all if some of the spray gets on your hands or face, or if you breathe in any of the fine spray should a breeze blow the mist onto you. You might taste a little bitterness at the back of your tongue 'cause you've just gotten yourself a small dose of medicine. No protective clothing is necessary when using this spray.

I heard a rumor sometime back that pure neem oil had been difficult to find in garden centers because Southeast Asians were buying it to take as medicine, which prompted some state agency to regulate its availability in California. I haven't checked recently whether it's back on the shelves since the bottle I bought years ago has a long way to go before it empties out. I haven't been sipping it for health.

If you cant find 100 percent pure neem oil, there are a number of products that contain a 70 percent "clarified hydrophobic extract" of neem oil as their active ingredient, mixed with 30 percent "other" or "inert ingredients" (I wish they would list these so I know how much I need to protect myself when I'm spraying). One such product is called "Rose Defense" made by Greenlight and another is sold under the Garden Safe label as a fungicide. There're probably others.

Another 100-percent-safe spray is a completely natural product called Organocide. Robert at Hortus Botanicus Nursery in Fort Bragg, one of my favorite places to visit when I'm up along that part of the coast, swears by it for all his tropicals, including his large collection of carnivorous plants which resent any kind of insecticidal sprays. It's not available in the Bay Area, but can be purchased from the hardware store in Willits. It's a mixture of sesame oil and edible fish oils, without any unlisted "other' ingredients. Although it's perfectly safe to get the spray on you, you might not want it to since it has a rather strong fish odor. Your plant will smell fishy too for a couple of days after spraying, but the leaves are perfectly safe to eat the same day you spray and probably does best in a seafood dish! Michael always can tell when I've sprayed any of my plants with this oil; he says it makes the garden smell like a dead fish! But it's just for a day or two. I believe Organocide originates from Florida where it is popular among organic growers who have to spray when temperatures are high, something usually not recommended for other oil sprays. It's also formulated to treat citrus diseases. It works very well but tends to leave a sticky residue on your plant.

With oil-based sprays like neem, Organocide or a horticultural oil, it helps when you are mixing the oil with water to add a few drops of biodegradable dishwashing soap. Shake well and the soap will help act as an emulsifier. You should still periodically shake the bottle during the spraying session to make sure the oil is well mixed with the water and does not come out heavy in spots on your plant. Instead of buying an oil spray, some people say it's just as effective to use any cooking oil mixed with water and a few drops of dishwashing soap.

Both pure neem oil and its derivatives and Organocide are effective against insects as well as fungal diseases, which insecticidal soaps aren't.

Although insecticidal soaps are effective against a wide range of insects, you need to take more care in protecting yourself from the spray. They are usually made of derivatives of different kinds of oils but there usually is a very high percentage of "inert ingredients" which aren't listed and I'm a bit leery about unknown substances that might get on me while I'm spraying. One common product is sold under the Safer label as an insect-killing soap. I don't particularly like its smell which reminds me of something that might be harmful to my health. I would give the leaves a waiting period following spraying before they are used in cooking. On the other hand, leaves sprayed with neem oil solutions are perfectly safe for eating on the same day. Same for organocide, but the leaves will taste a little fishy.

Unlike toxic, chemical insect sprays, which kill insects both on contact and leave a poisonous residue that continues to kill insects that eat the leaves, edible oil-based sprays and insecticidal soaps kill insects on contact only by smothering them. Therefore, you may need to spray more than once to control the problem. Insects are good at hiding and some may escape your spraying to re-establish the colony. The eggs they lay in the soil may hatch into the next generation of adults in the colony. Others in residence in nearby plants may decide to move and take over the vacuum. It's usually recommended that you spray two to three times in intervals of 7 to 10 days to eliminate successive generations of the insects.

Fungal diseases usually manifest as spotting on the leaves or a filmy substance covering the leaves, causing them to change color, shrivel and eventually drop off. To prevent fungal spores from spreading, avoid wetting the leaves when watering the plant, especially late in the day. Fungi multiply in damp, dark conditions and do much of their spreading during the darkness of night when humidity is higher. That's why it's better to water early in the day than in the evening; this allows the leaves and the surface of the soil to dry before nightfall. As mentioned, neem oil-based sprays and Organocide will take care of both insect and fungal problems.

It's best to do your spraying either early in the day before the sun hits the plant and when the temperature is well below 80 degrees, or late in the day after the sun has passed. Ideally, the leaves should have dried before the sun hits them, or else they might become sun-scorched.

If you would like a copy of this article in Adobe Acrobat (PDF) format for your own personal use, please contact Kasma.

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