Monday, October 24, 2016

Black Witch Moth

"May I borrow your house?" is the Mayan translations for Mah-Ha-Na. This is the name for the moth which often rests at night under the eaves of the house. The common name is Black Witch Moth, Ascalapha  odorata.

Its wingspan can reach 7 inches.  The wings are dark brown, and both pairs are crossed by a series of alternating light and dark wavy lines. There is often an iridescent blue cast over the wings. Females have pinkish-white bands across the middle of both wings, whereas the males lack these pale bands.  In addition to the Hawaiian Islands, they are common in the Caribbean, South and Central America and migrating into the continental USA and southern Canada in the summer.  

This moth lives in the tropical and subtropical forests where trees of the pea family grow. This includes acacias, albizia, cassia and samanea (monkeypod). The caterpillars feed on the foliage of these trees. The moth often flies great distances in only a few nights, hiding by day wherever it can find dense shade, frequently under the eaves of houses.

While they mostly fly during the summer season, in the southern areas of the United States and in Hawaii, they are also known to fly during late October, hence the name Black Witch Moth. 

Sunday, October 2, 2016

Why Leaves Turn Yellow


When the leaves of a plant begin to turn yellow, determining the cause will take some investigation. There are several possibilities:

         The first consideration is a lack of nitrogen, especially if a number of plants are affected and there has been no recent application of fertilizer.  Apply a high nitrogen fertilizer, and if after a week or so the plants begin to turn green, the problem is solved.

          If the plants don’t turn green, the problem could be a disease.  Plants can become infected with a fungus, especially when over watered, causing a root or crown rot.  Inspect the roots and the crown of the trunk.  Scratch into the bark of the trunk at the soil line and also into a piece of root.  If the tissue inside is brown or black, rather than light colored, a root or crown rot is evident.     

         Another common reason for a general yellowing is a lack of oxygen in the root zone.  This is due to too much water – over irrigation or too much rain.  As long as the soil drains well the problem is minimized.  But in clay soils, water does not drain well, resulting in a waterlogged condition.  Without adequate oxygen in the soil, roots cannot function properly, and the plant turns yellow.  If the condition continues, root rot will develop and the plant will die.  That is why so many planting instructions suggest to plant in a well-drained soil. 

         If plants are yellow and lack vigor, a soil analysis can identify nutrient deficiencies and/or a pH imbalance.  The pH reveals the acidity or alkalinity of the soil. Most plants have a definite acid/alkaline range in which they will properly grow.

         Although not common, there is always the possibility of persistent chemicals in the soil.  A soil sterilant or preemergent herbicide may have been applied to the soil.  These compounds can persist for many years.  Preemergent herbicides are those that are sprayed on the bare ground and become incorporated into the top few inches of soil.  At label dosages they affect only the target weeds and last from several months to a year.  But if an overdose is applied, the chemical will be there for many years and adversely affect many plants. 
         An infestation of microscopic round worms called nematodes (example, root knot nematode) can also cause plants to yellow and be stunted.

Monday, September 19, 2016

Poinsettia Scab Disease

Poinsettia scab is a disease caused by the fungus  Sphaceloma poinsettiae. It is a problem for greenhouse poinsettia growers in Florida and Central America and is quickly spreading to other regions. Some Euphorbia weed species are also hosts of the disease. It has been in Hawaii for many years.

The disease affects both the leaves and stems; small, round lesions form on the leaves. These spots develop whitish to brown centers, have a dark red to purple rim, and often show a yellow halo. Occasionally, an infected stem will grow six inches or more above the rest of the plants. This is due to the production of growth regulating chemicals called gibberellins, produced by the fungus.

The disease thrives in high humidity and wet growing conditions.  Splashing water will easily spread the spores from leaf to leaf and plant to plant. The key in controlling this disease is to stop the spread of the spores. When frequent rains occur, a cover over the plant or plants is one solution. Another approach would be to apply a protective copper fungicide that would prevent the splashed spores from starting new infections.  

Infected plants will usually continue to live. However, the severity of the disease is dependent upon the amount of rainfall. Remove infected leaves, and if appropriate, prune out infected stems.  Then apply either a copper fungicide or one with the active ingredient chlorothalonil (Bravo, Daconil). As new leaves emerge, reapply the fungicide. In the future, if the disease is not severe, removing infected leaves may keep the disease under control.