Pests often force gardeners to fight back

Unwanted guests in the garden pose problems that horticulturists everywhere must confront, at least occasionally. These visitors can be insects, weeds, disease organisms, even cute little furry creatures. Any of them makes horticulture in the Mojave more challenging than it is already.

Pests cause worry on many levels, but in general they are matters of concern for our own physical well-being or that of our pets, the cleanliness of our homes, or the survival of our gardens.

Some insect pests are simply annoying, such as houseflies. Other insects can wipe out a beautiful garden in no time.

Anyone who has seen a lush green tomato plant reduced to a skeleton virtually overnight will have strong feelings about the tobacco hornworm, the very large, very hungry caterpillar of a sphinx moth.

A potentially delicious crop of melons comes to ruin when squash bugs, voracious villains, appear in their thousands over a short period.

When weeds become too plentiful, they interfere with garden plants, even outcompeting them by pulling sparse nutrients and water from the soil, shading the desirable plants, or serving as a refuge for other pests.

A good feature of living in the desert is the lack of many plant diseases. Only three are major problems: powdery mildew, a particular problem for roses, although virtually every domesticated plant can suffer from this disease; crown gall, where woody plants develop tumors on the trunk, often near the base; and fire blight, which can blast many fruit trees, roses and ornamentals.

A healthy plant is generally better able to resist attack by insect pests or disease, but there are times when an infestation or an infection occurs despite our best efforts.

When troubles afflict our gardens, it might be tempting to grab any nearby container of poison and spray like mad. But it’s crucial to identify the problem correctly before spraying anything.

Conventional pesticides can be highly effective, but we might think of them more like the nuclear weapons of pest control. Seductive as they are, they can create further problems, damaging plants, pets, even people.

Organic gardeners resist that temptation, but still need to protect their plants from invaders. Fortunately, several effective controls are labeled for use in organic horticulture.

Insect pests have quite a few natural enemies, such as parasitic nematodes, lacewings, ladybugs and trichogamma wasps. These good agents may be susceptible to insecticides, so they should not be employed soon after using one of the poisons.

Organic insecticides can be derived from bacteria (Bacillus thuringensis is the best known) or fungi (Beauveria bassiana and Spinosad are effective and have become widely used over the past few years). Horticultural oils, neem oil, boric acid and diatomaceous earth will kill insects, both pests and beneficials. Some people who prefer folk remedies such as essential oils (peppermint, lemongrass, lavender) claim these are toxic to insect pests. These have pleasant scents, but independent research has not fully tested their effectiveness.

Horticultural and neem oils can be valuable in overcoming a fungal disease such as powdery mildew attacking a plant. Conventional fungicides are usually applied before an infection.

Weed control methods include herbicidal soaps, citrus or clove oil, horticultural vinegar, and corn gluten meal. All, except corn gluten meal, are “burn down herbicides.” These are compounds that kill only the above-ground plant parts, not the roots.

The gluten meal is applied to the ground before weed seeds emerge, hence it is a “pre-emergent” or “weed preventer.” None of these is effective on weeds that have a well-established root system.

Just because a compound is organic, natural or plant-derived, doesn’t mean it is harmless. The plant-derived products pyrethrum and rotenone are organic, but can be highly toxic to fish if applied too close to a body of water. Nicotine, a particularly dangerous compound, is present in all tobacco products. It is so dangerous that despite being plant-derived it is not considered “organic.”

Organic products have the advantage of being short lived in the environment. Some conventional pesticides are no more toxic than organic ones; however, they often persist in the environment for unacceptably long periods.

Always read the label to use the product safely. In the context of the label, the word “natural” does not mean anything. If a product is organic, it must state that. Most organic products will have the OMRI (Organic Materials Review Institute) logo on the label.

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