Troublesome Spider Mites
- • Keep flowers and vegetables in peak condition by giving them a midsummer feeding with a fertilizer that is higher in phosphorus than in nitrogen.
- • Check for squash, or “stink”, bugs on squash and pumpkins. Hand-pick grey-brown adults and destroy red egg clusters on the leaves. Use pyrethrins to control heavy infestations.
- • Take care of your roses: feed, water, weed, mulch and remove faded blooms regularly. Spray if necessary at first sign of insect or disease problems.
- • Sow seeds of perennials like columbine, coreopsis, delphiniums and cone-flowers now for planting in the fall and beautiful blooms next year.
- • Impatiens will give you instant color in shady areas and continue blooming right through the fall.
The Trouble with Spider Mites
Spider mites are common pests in the urban landscape and can inflict serious damage to trees, shrubs and flowers. Hot and dry summer weather often encourages the outbreak of spider mites on garden or house plants. Cousins of spiders, spider mites are very small, rarely growing larger than a grain of fine sand. Although small, they can do plenty of damage by sucking nutrients out of plant leaves, and by injecting toxins which curl plant leaves.
The telltale signs of a spider mite infestation are stippled yellow, white or bronze leaves. Sometimes there is a silken webbing on the stems or leaves, and the leaves will appear very dusty and dirty looking. New growth may be distorted, and the plant may be unhealthy in appearance.
To determine if a plant is infested with mites, hold a sheet of white paper underneath an affected leaf and tap it sharply. Minute green, red or yellow specks the size of pepper grains will drop to the paper and begin to move around.
The two-spotted spider mite is one of the ‘warm season’ mites. This pest attacks over 180 host plants including field crops, ornamental plants, house plants and weeds. The females overwinter in the soil or on host plants. They become active in April and May when they seek out the undersides of leaves on suitable hosts. Each female may lay over 100 eggs.
European red mites attacks deciduous trees and shrubs. They are especially common on fruit trees and flowering trees such as crabapples, flowering cherries, pears, plums and hawthorn trees.
Spider mites can be controlled in different ways. They are attracted to dusty leaves, so spraying the undersides of the leaves with a strong blast of water twice a week will help control them. Add some insecticidal soap to the water for even more effective control. Horticultural oil and Neem oil are safe to spray on most plants and they will control spider mites very well.
Oils and insecticidal soap are contact insecticides that kill certain insects and mites by intervening physically, rather than chemically, with their respiratory processes. They affect pests that are present when the spraying takes place, but have little or no residual effect. Under optimum conditions, spider mites can complete their development from egg to adult in less than one week. Populations increase rapidly in warm weather and cause extensive plant damage in a very short time. So several applications 7 to 10 days apart will be necessary. Be sure to saturate the undersides of the leaves.
As with all insect problems, plants which are under
stress of some kind are more susceptible to insect attack. Make sure affected plants are receiving proper sun or shade exposure and the right amount of water. Keep your plants healthy and you will have fewer insect problems.
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