Healthy Soils

Healthy soils are full of life. This life is comprised of literally millions of different species and billions of individual organisms both large and microscopic. Forty million bacteria can fit on the end of one pin. Other microbes include algae, protozoa, yeasts, fungi and nematodes. Some of these organisms feed on dead organic matter, while others feed on other microorganisms. As a group, they help to recycle nutrients, build the soil structure and most important, help to convert organic matter into rich, stable humus. It is the humus which is the life support system of the soil.

The following soil problems can be corrected by adding humus:

1. compacted soils,
2. fluctuating pH levels,
3. infertile soils,
4. sandy soils 
5. clay soils and
6. in addition, a soil rich in humus will help reduce pest insects and disease pathogens in the soil.

How do soil organisms build better soil? 
Bacteria – feed on organic matter, store and cycle nitrogen and decompose pesticides.

Fungi – some feed on dead organic matter like crop residues; others are parasites that attack other microbes. Some live in association with plant roots delivering nutrients to the plant.

Protozoa – eat bacteria, fungi and algae. The consumption of bacteria slowly releases nitrogen into the soil. Protozoa also convert organic nitrogen, not available to plants, to nitrogen forms which are available.

Mites – decompose organic matter.

Nematodes – these microscopic worms eat other worms in the soil and are an important part of the nitrogen cycle. Some nematodes attack plant roots but most are non-pathogenic.

Earthworms – expel partially decomposed organic matter which produces  nutrient rich casts. In addition, the worms create some small tunnels which aid in the development of good soil structure and water movement in the soil.

Horticultural Oil Sprays

Horticultural oil sprays have often been recommended as treatment for scale and other insect pests.Homeowners, however, don't always find them reliable. Are they not effective or are other factors involved?   The following information should be helpful.

Many pesticide labels, including horticultural oil, will give a time range in which to reapply the material, for example, in 5 -7 days. The reason for repeat applications is that certain stages of growth, like the egg and pupae stage, are not susceptible to insecticides as are the other stages of development. Consequently, eradication of a scale population, whitefly as well, may require as many as four applications. The 5 -7 day interval is to give time for the non-susceptible stage of the insect to develop to a susceptible stage.

Another factor is that horticultural oil is most effective when sprayed soon after the young scales, called crawlers, have emerged. This stage is susceptible to oil and other insecticidal sprays whereas older, usually darker colored adults are much less vulnerable. In fact, if the plant is sprayed when the majority of the insects are full grown adults, the results will be poor. Many of these adults may actually be dead, with eggs underneath the shell.

Be sure to apply a thorough coverage of the oil solution to both the top and underside of the leaves. In addition, it is prudent to make an application as soon as the insect pest is detected and populations are low. Do not apply oil when it is over 90°F.  Drought stressed plants can be injured when sprayed with oil. 

Concerning horticultural oils themselves, they are specially refined petroleum products, often called narrow-range or supreme oils. Some plant-derived oils are also available. One study has shown that the harsher organophosphate insecticides, like malathion, were no more effective than a thorough spray of oil or insecticidal soap alone, when properly timed. Another study found spraying oil on foliage once during the late spring was as effective as using a systemic organophosphate (acephate).