Biological and Physical Controls for Bugs and Diseases

Bugs

If you suspect bug damage (or see it with your own eyes) first figure out which insect is eating your plant. (Diagnosing with Google, Master Gardeners or a nursery horticulturist.) Don’t panic if you just notice a few insects in or near your plants. Most are beneficial (because they eat harmful insects), harmless, or they’re harmful only in large numbers. And since larvae are usually more destructive than the adult insects, if you’re seeing adults the damage may already be done.

Is it really that bad? Have you considered tolerating a bit of imperfection in the garden? If the damage is minor and clearly not life-threatening, maybe “Live and let live” is a real option.

First Plan of Attack — Physical Controls

Hand-picking. Bad guys like Japanese beetles can be hand-picked and dropped in soapy water. Affected plant parts can be snipped of and destroyed (not composted).

Repellents — lots of choices here.

• A hard water spray will remove many insects, like aphids. Be sure to spray the under sides of the leaves, or your money will be wasted. Some gardeners add a drop of liquid dish soap to the water (preferably nonfragrant, colorless soap).
• An abrasive material like diatomaceous earth or eggshells around plants will keep soft-bellied insects like slugs away
• Some claim that coffee grounds repel or even kill the mighty slug, but there’s not enough caffeine in used grounds, so use the unbrewed type. Coffee itself is definitely too weak.
• Flowers like marigolds and herbs like garlic and chives keep many insects away.
• Traps are often effective but remember that beneficial insects (like ladybugs) could also be trapped, so monitor to make sure the trap is trapping what you want trapped. There’s debate about the use of traps for Japanese beetles over whether they should be placed 100 feet or more away from the garden (possibly in your neighbor’s garden) or around the edge of your garden. Don’t ask me. Just remember that if they’re not put in the right spot they’ll act as attractants, not repellents, so study and experiment. Traps using fermented foods or even beer (for slugs), are often effective and sufficiently selective.
• Copper strips can also be very effective barrier against slugs.

Disease

The great majority of microorganisms found living in gardens are the gardener’s friend. They help break down organic matter in the soil, convert nitrogen from the air into a form the plants can use, stimulate plant growth, and even kill garden pests. Only a few cause disease but once disease is present, there aren’t many cures available and the best alternative is often getting rid of the diseased plant altogether. That’s why prevention is so-so important. But because preventive sprays must be used early in season — before the problem appears — by the time you notice problems, it’s usually too late to do anything about it. What’s more, diseases are difficult to identify by name, making it even harder to treat them.

And ask yourself: Is treatment really needed? Mildews, a very common type of fungal disease, are unsightly but rarely fatal. If you hate the look, it may be easier to switch to mildew-resistant varieties of plants.

Biological Controls for Insects and Disease

They’re methods of disease control are those that use diseases and insects to stop other diseases and insects.

First, do what you can to attract beneficial animals to your garden. This will happen naturally if you 1) grow a diversity of plants, including some that are native, to provider food and shelter and 2), keep your garden free of chemicals. Providing water also helps attract beneficial animals but mosquitoes breed in standing water, so make sure it’s either moving or changed twice a week. Certain plants are especially effective in attracting good insects — like aster and mint. Just don’t try to get rid of all the “bad” insects because if you succeeded in doing so, the “good” insects would then leave to find better feeding grounds.

Some beneficial insects, like ladybugs, can be bought via mail order (their shelf life is too short to allow for in-store purchase). The results are mixed, however, with some gardeners seeing 90 percent of them leave their property within 24 hours.

Beneficial nematodes are microscopic worms that enter and kill a wide range of insects in the soil — like lawn grubs and Japanese beetle grubs. They already exist in our soil and have been declared totally safe (and therefore not in need of regulation) by the EPA.

The Bacterium thuringiensis (Bt) acts as a parasite to kill certain insects but it can kill too well. It not only kills gypsy moth and tent caterpillars but all caterpillars, including all sorts of butterfly caterpillars, even the beloved Monarchs.

Bacillus popilliae (brand name Doom) is a bacteria that kills only Japanese beetle larvae — not the adults, and no other insect. While safe for humans and other vertebrates, they’re slow-acting, work best on a regional basis, and may be losing its virulence.

Bacillus subtilis (brand name Serenade) is effective in preventing fungal disease.

Bats are a beneficial animal that are often overlooked. Sure, they’re kind of creepy but did you know they can consume as many as 1,000 mosquitoes an hour? So they say; I’ve never done the count myself. Go to the Bats page on this site for more information about them, especially how to attract them to your garden.