For:
By: Daniel E. Mullins
Extension Horticulture Agent
An Old Insect Control Practice Is Back Again
Some things come full circle, and a few of the older insect control practices are back again. The best example is the use of horticultural oils for controlling overwintering mites, scales and other insects on shrubs.
The use of these special oils dates fifty to one hundred years. One gardening reference dated 1904, recommended an emulsion of kerosene for controlling scales. This particular product is not currently recommended but there are milder oil based products that can be used.
Modern horticultural oils are highly refined and then have an emulsifier added so that the oil will mix with water. This emulsion can be sprayed on infested plants and it kills certain insects and mites by plugging up their breathing pores. Control is therefore achieved physically, rather than by poisoning the offending pests. Because of its mode of action, it is doubtful that insects controlled with oil sprays would ever develop resistance.
Sprays containing horticultural oil are routinely recommended for scale control on peach trees, camellias, hollies and many other woody plants. Properly used they are safe, yet effective. They are however, not without limitations. Following is some additional information about these special oils.
■
They are readily
available at local garden supply outlets and are sold under various trade names
and descriptions including dormant oils, summer oils, horticultural oil
emulsions and ultra-fine oils.
■ They do not control all kind of insect
pests. Though they are one of the few
products that will control adult, overwintering
scales, don’t expect to control caterpillars, beetles or grasshoppers with
oils.
■ Most oil sprays cannot be used at any
time of the year. Many labels suggest
using oil only when temperatures are mild – in the 40 to 80 degree F.
range. This means that the traditional
oil emulsions are applied during the fall and late winter to early spring
season.
■ Ultra-Fine oils have been developed that can be used during
hotter weather. They are more highly
refined and have been tested on plants at high temperatures with little or no
damage. When selecting a horticultural oil, read the label carefully and choose one
that is safe for the season that it is to be used.
■ Since horticultural oils control
insects by coating their bodies, uniform spray coverage of plants is essential
for good control.
Question of the Week: I would like to make my Amaryllis flower again. I have heard that the bulbs should be placed
in the dark until they start to sprout again and then replant them.
Answer: This depends upon whether they are growing in the ground or in
pots. If growing in landscape beds, just
let the tops die back naturally as winter approaches. They will remain dormant until spring and
resume growth naturally next spring.
Any that are being
grown in pots can be forced into growing and flowering faster if desired. To do this, remove the bulbs and cure them
for about 2 weeks, while exposing them to temperatures in the mid-seventy degree
F. range in a well ventilated area. They
can then be repotted and grown at the same temperature and under bright light
conditions. Your biggest challenge will
be providing enough bright sunlight while keeping them warm. Remember, they are tropicals,
so a single exposure to extremely low temperatures can ruin them.