Thrips

Description

Thrips are tiny insects which measure about 1/50 inch. While the most common species known to feed on African Violets is yellow in color, they may also be brown or black. Thrips thrive on the flowers and leaves of African Violets, especially the underside of the leaves. Because of their very small size, you may not see them unless you are using a magnifying glass. For this reason, your first clue that Thrips are present will probably be the light yellow powder which Thrips leave on the flowers. This is actually pollen which has been spilled from the anthers as they feed on the flowers. If left untreated, Thrips can cause severe damage to African Violets.

Of those Thrips known to feed on African Violets, the most common species is Frankliniella occidentalis.

Distinguishing Symptoms

• Flowers have a light yellow powder on them. This is actually pollen which has spilled from the anthers as Thrips feed on the flowers. While this typically a tell-tale symptom of Thrips, keep in mind that Earwigs also leave pollen on flowers. However, whereas Earwigs tend to leave clumps of pollen, Thrips will leave a fine powder of pollen.
• Leaves have streaks on the underside of them. They appear silver or gray in color. These streaks are left by Thrips as they suck the juices from the Violet. They may also appear as silver speckles.

Note: While it is important to distinguish pollen left by Thrips from pollen left by Earwigs (see above), it is also important to distinguish pollen left by Thrips from pollen which has naturally spilled from mature blossoms. Therefore, check the underside of the leaves for silver or gray streaks. If your Violet has both of these symptoms, it probably has Thrips. To be sure, hold some of the Violet's flowers over a sheet of paper and give them a gentle thump. If Thrips are present, you will see some of them drop onto the paper. You may need a magnifying glass to correctly identify them.

Other Symptoms

• Leaves darken on the edge. Edges appear brown in color (necrosis).
• Leaves have brown spots on them. These will be most visible on the underside of the leaves.
• Leaves have white spots on them.
• Flowers are blotchy or streaked.
• Flowers turn brown or have brown spots on them.
• Flowers are damaged. They may have holes in them.
• Flowers are smaller than normal.
• Not flowering.
• Plant growth is slow.
• Visible insects. Thrips measure about 1/50 inch in length. The most common species is yellow, but they may also be brown or black. Because of their small size, you may need a magnifying glass to correctly identify them.

Treatment

Some advise using Malathion to treat Thrips. This may be effective on some species of Thrips, but the most common species is resistant to Malathion. Also, Malathion may discolor the flowers of Violets. A more reliable treatment employs Acephate, a common ingredient in household insect sprays. Acephate sprays of this type, however, may damage foliage due to a specific additive found in these sprays. As an effective alternative, use a soluble powder, and mix your own spray. Be sure to spray all of your Violets, not just those which currently exhibit symptoms. Thrips spread quickly, so if even one Violet has them, all are at risk. After this initial application, spray twice more at seven day intervals. This will rid your Violets of any unhatched Thrips which may not have been affected by your first application.

As an alternative to traditional chemical treatments, try spraying with Neem (Azadirachtin). Neem is a substance which has natural insecticidal properties, and according to currently available research, it is biodegradable and non-toxic. When sprayed on African Violets, it discourages Thrips by making the plant unpalatable. Though Neem does have some systemic effect in plants, spray it as you would other contact insecticides, being sure to spray in areas where Thrips are known to cluster.

Finally, remove all flowers and buds from your Violets. This procedure has been shown to significantly enhance the effectiveness of the treatment, whether spraying with Acephate or Neem.

Prevention

After working outdoors, always change clothes before handling indoor plants. Always wash hands before handling your Violets, and keep pets away. Finally, keep in mind that Thrips are very small. They also fly. A typical screen, such as one might put on a window or door, may not prevent Thrips from getting indoors.

Important Note on the Use of Pesticides

Please note that almost all pesticides are formulated for specific uses and conditions. When applied incorrectly, pesticides can cause ill health or damage to plants. Therefore, when using any kind of pesticide or chemical treatment, always apply as indicated on the product label.

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