Pest and disease control for your Roses

by the Garden Goddess

ello fellow Earthlings, and welcome to the rose garden. Last month we touched on beneficial insects. This issue we will be chatting about pest and disease control methods that don't require you to go out and buy any harmful pesticides or fungicides. So let's take a meander and get a gander at those rose bushes

It is widely known that roses can be a real pain in the *#!@ if they want to be, or are in any way not attended to. This is not so of a rose that is allowed to grow under natural condition without nitrogen-fortified chemical fertilizers and harmful insecticides and fungicides. The truth of the matter is that roses can be very easy to tend to if they are cared for with a light hand during the growing season. The fewer things that a gardener does to shock a natural balance of things, the fewer problems will arise as a result of that shock.

Chemical insecticides are only effective until the target pest develops a resistance to that chemical. Then it becomes necessary to alternate harmful substances to control an insect population that continually gets worse because of lack of competition and natural predators, due to high concentrations of chemicals. The major rose pests that we encounter here in Southern California can be controlled by establishing populations of two beneficial insects, plus periodic treatments with a bacterial and a tree sap extract.

The two beneficial insects are the green lacewing and trichogramma wasps. These two insects will guard your roses against everything from aphids to some scales and spider mites. Lacewings are very active and voracious feeders. Their target prey are aphids, mealybugs, some species of whitefly, juvenile scale insects, and some spider mites. The tiny trichogramma wasp is a parasite of caterpillars some species of bud worm. They will also antagonize a number of other butterfly and moth species. These parasites do not have a stinger (no need to fear them). They have an ovipositor that lays eggs inside the host; as the wasp larvae develop, they use the host as a food supply.

The bacteria that I spoke of is bacillus thuringiensis Kurstaki or Berliner, often referred to as BT. BT is a paralyzing bacteria that affects many species of worm and caterpillar including the leaf skeletonizer worm. By paralyzing the stomach of its host, this bacteria is very useful against its target pests.

The tree sap that I was referring to is oil of the neem tree of India. The active substance in this sap has been named Azidirachtin, after the botanical name of the tree. The extracted oils from the tissue and sap of this tree are very effective at repelling and keeping your rose bushes free of any sign of insects. Although it smells like hazelnut to us, it has the most repellent effect on pest insects. Neem oil is sold under the name Bio-Neem under the Safer label and Rose Defense under the Green Light label. These two products can be found at any garden supply store.

Controlling diseases in your rose garden is really not very difficult at all. There is no need for harmful fungicides that can cause severe physical problems, can have a negative affect on outdoor pets and bees, as well as wipe out entire earthworm populations from a single spraying. Balanced nutrition and a couple of minerals can keep your garden disease free without weekly exposure to chemicals.

Most plant diseases will leave a healthy plant alone. It is the same with us: if we're healthy, we don't get sick. Plants also have immune systems. This is where a balanced diet, containing the proper amount of copper, sulfur, potassium, magnesium and calcium, will ensure that certain very commonplace and damaging fungi don't get a foothold in your garden.

Potassium is very important for resistance against powdery mildew and rust on roses. You want to provide potassium from long-lasting natural sources, such as mineral deposits. When potassium is broken down in the soil, it will actually help to prevent the onset and spreading of powdery mildew and rust, which are tough problems for most chemical gardeners to control. High calcium levels, along with an abundance of naturally available magnesium, will cause your roses to produce thick, healthy canes without problems of slow root development in our heavy soils. Copper and sulfur are the two elements which I use as a spray fungicide if absolutely necessary. Other than dormant spraying, minimal spraying should be necessary to prevent fungus and disease if the roses are fed naturally.

It is pretty easy to control all or most of the marauders that attack your precious rose garden without the need to poison your environment. So, try these techniques before resorting to the application of napalm on the roses. Next month we will be discussing soil conditions and how to improve them. Come up and see me sometime!

  Got questions? Call the Goddess at her toll-free helpline at (888) 514-4004 or send email to The Garden Goddess is a trademark of the Organic Gardener's Resource and Design Centre of Encinitas.