Tuesday, December 20, 2016

Citrus Skirt Pruning

Occasionally citrus trees have been pruned up off the ground. Some have asked, "What is the reason for this?"

Skirt pruning of citrus has been around for a long time in those countries surrounding the Mediterranean Sea. The skirt of the tree includes those branches which hang down and touch the ground or are near to the ground.  In Italy, the skirts are pruned as high as the goats can reach.

In the United States, California in particular, skirt pruning done with clippers or a pruning saw, not goats, is a recent development and mainly came about as a means of controlling snails in the orchard.  By skirt pruning, usually 18 – 24 inches, snails as well as ants are denied easy access into the tree. Then the trunk is the only route.  Farmers can concentrate their pest control efforts on a small area, the trunk, rather than spraying the whole tree with pesticides. In the case of snails, copper foil is often banded around the trunk; snails will not cross the copper band. For ants a sticky material is sometimes applied.

Skirt pruning will also help control brown rot disease of citrus fruit. Since low hanging fruit is eliminated, the overall fruit quality will improve. 

Thursday, November 17, 2016

Yams or Sweet Potatoes?

What is the difference between yams and sweet potatoes?  Are they the same, yet by a different name?
Many years ago orange colored sweet potatoes were introduced to the Southern United States. In an effort to distinguish these from the traditional white-fleshed potato, producers called them yams, which is the Anglicize African word, nyami. Today, most of the starchy tubers consumed in the US and labeled as yams are in reality sweet potatoes. Yet yams and sweet potatoes are not the same; in fact, they are quite different from each other. 

As far as botanical order is concerned, they are at opposite ends. The sweet potato is a dicot, set in the morning glory family. The sweet potato, whose sweet and moist flesh varies in color from white to yellow and orange, is native to South America; the skin is typically smooth. Garnet, Jewel, and Beauregard are orange fleshed sweet potatoes that often masquerade as yams in the local supermarkets.

 Yams, on the other hand, are a monocot, closely related to grasses. In contrast, yams are dry and starchy and rather bland. While yellow or purple in color, the skin is rough and a bit shaggy. Yams are native to North Africa and Asia. They range in size from that of a small potato up to 150 lbs. Yams are a primary agricultural crop in West Africa, where 95 percent of the world's yam crop is grown.  Incidentally, both yams and sweet potatoes can be purple.

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. 

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.

Sunday, September 11, 2016

Bamboo Spider Mite

The bamboo spider mite is a common pest of bamboo and will occasionally attack rice and sugar cane.  Mite damage can potentially lower the bamboo's aesthetic and economic value. The mites have a flattened body, which is straw-colored to greenish yellow with small blackish green spots.

Mite feeding will result in chlorotic (pale yellow) areas on the upper leaf surface. On the underside of the leaf, mite colonies will be found under tightly woven webbing. Generally the mites remain under the web to feed and lay eggs.

A couple of miticides, Avid and Floramite, are registered in Hawaii and are quite effective. Silicon-based surfactants such as Silwet and Silgard are recommended for use with Floramite.
Before buying any of the above products, however, try spraying with a soap solution or a commercial product like Safer Soap. They usually do a good job.  Make sure to spray the undersides of the leaves, good coverage is important. Come back in seven to ten days for one or more repeat applications. 

Photos: Oregon State University

Tuesday, August 16, 2016

Mealybugs and Aphids on the Roots

Pineapple mealybug             

 There are species of aphids and mealybugs that attack the roots and the crown line of plants. Many times when plants are pulled out of the pot, whitish fuzzy bugs in the soil or on the roots can be seen; they are the root aphids or root mealybugs.

In Hawaii, the pineapple mealybug is common. The adult females are described as plump and convex in body shape and pinkish in body color. Primarily a pest of pineapple and other bromeliads, yet these mealybugs also attack banana, celery, citrus, cotton, coffee and hibiscus. Wherever pineapple is grown, the pest is present including all of the major Hawaiian Islands. Plants rarely die from a mealybug infestation.

Control of this pest depends on controlling the ants which provide the mealybugs shelter and protection from predators and parasites. Without ants, mealybug populations are small and are slow to invade new areas because of the presence of the many natural enemies (the good guys) that are in Hawaii.

In infested areas of the garden, after the crop is removed, the soil should be turned over and all crop residue removed including grassy weeds which may harbor the mealybugs.  Host plants of this pest (listed above) should not be grown in this bed for at least a year.