Pest Problems Begin Early

Our early warm weather has brought with it an abundance of pesky insects. Fortunately, most cause little damage to garden and landscape plants. A few, however, do require some control measures.

Probably the most common insects out and about the garden these days are aphids. They are small, soft bodied bugs that can be found on the new growth of most plants. They come in a range of colors including; brown, purple, yellow, black, but most often green. Although small, they can be seen without magnification. Their favorites are roses, hibiscus, and most herbaceous garden plants. Because aphids are sucking insects they secrete a sticky substance called 'honeydew'. This substance coats nearby leaves and stems making them appear shiny as if lacquered. If you see the honeydew, look closely for aphids.

One aphid of note is the dusky-winged oak aphid. It has been coating the leaves of all the live oak trees in Tucson with a honeydew so thick it appears varnish-like. This aphid is not a finicky and seems to be quite happy dining on old, rather tough leaves.

Aphids seldom cause harm to plants. They are more of an unsightly nuisance. However, on young garden plants they can be very harmful. And in the case of the dusky-winged oak aphid, honeydew can be so thick as to cause a mess on cars, walks, and patios located under infested trees.

Aphids can usually be controlled by spraying with a strong jet of water from the garden hose to knock them off leaves and stems. Make sure to spray all around, both over and under the leaves. Aphids knocked off plants will not crawl back. Soap sprays can also be used for hard to control aphid populations, such as those on oak. Make your own soap spray by mixing 2 tablespoons of liquid dish washing detergent in one gallon of water. The soap brand "Dawn" has been shown to have the best insecticidal properties. Avoid using lemon scented types. Soap sprays are not harmful to beneficial insects.

Scale insects have been showing up on a number of woody plants including; loquat, rose, Indian hawthorn and pittosporum. They are small, usually the size of a pin-head up to one quarter inch in diameter, with a hard shell covering. They appear as a scabby covering, usually on stems but sometimes also on leaves.

Scale insects can be controlled by applying summer oil sprays in March. Summer oil sprays, such as Sunspray, can be purchased at garden centers. They are highly refined petroleum oils that can be applied during warm weather without injury to plants. The oil kills by coating the scale insects causing them to suffocate from a lack of oxygen.

With warm, dry weather comes another common landscape pest; the spider mite. Spider mites are small, almost microscopic, insect-like pests. They are not true insects but rather aracnids related to true spiders and scorpions. Like aphids, they suck out plant fluids. Unlike aphids, spider mites are found more commonly on older growth and nearer the ground. As they continue to feed, they work their way up farther into the plant. Evergreens, such as juniper and Italian cypress are favorite spider mite meals as are roses, pyracantha, oleander, and flowers both annual and perennial.

Plants infested with spider mites will display a characteristic brown cast to needles or leaves. Close examination will reveal tiny stippled spots of yellow or brown. To find the mites themselves, simply shake the foliage in question over a white sheet of paper. If you find small dust-like specks crawling about, your plant has mites. Like aphids, they can be sprayed off with a strong jet of water or a mixture of soap and water to wash them off. Repeat the water spray every 10 days until mites have been brought under control.

With the warm-weather arrival of bad bugs, also come the good guys that help keep them in check. Lady bugs, parasitic wasps, assassin bugs, lacewings and others are out and about, so protect them. Only spray with garden insecticides when pests are causing significant damage to plants and other non-chemical controls have failed. Water sprays, soap solutions, and oils will not harm beneficial insects. They will control most common garden and landscape pests. Remember, even organic insecticides derived from plant extracts, such as neem and rotenone, can kill our beneficial garden insects.