Monday, November 25, 2013

When Is a Yam a Sweet Potato?


While enjoying the traditional Thanksgiving dinner, some people may ask, "What is the difference between yams and sweet potatoes?"  Are they the same 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. Yams and sweet potatoes however, 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. Yams, on the other hand, are a monocot, closely related to grasses. 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. 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. 

Garnet, Jewel, and Beauregard are orange fleshed sweet potatoes that  masquerade as yams in the local supermarkets.


Monday, November 18, 2013

Moths Attack Palms

A significant pest of Pritchardia palms is the banana moth, Opogona sacchari. The triangle palm is also attacked by this moth. It seems that the female moth targets wounded or stressed palm tissue to lay her eggs. Stresses can include drought, flooding, mechanical wounding, poor nutrition, and herbicide injury. The larvae generally feed on decaying and dead plant tissue but will feed on living tissue, too, causing extensive damage. In affected palms, larval tunneling, along with the characteristic frass (insect droppings), can often be seen. Fully developed caterpillars measure just over an inch. The adults have greyish brown wings are 3/8 to 5/8 inches long.

The main treatment is prevention: keep palms growing well; give them adequate fertilizer, and supplemental water during a drought. Gardeners also need to be careful with the weedwacker! Female moths are looking for wounds to lay their eggs. Bt (bacillus thuringiensis), an organic insecticide, can be applied to these wounds, as well as those caused during pruning.

For more information about this pest see the CTAHR Cooperative Extension Service publication, “Banana Moth – A Potentially Fatal Pest of Pritchardia and Other Palms”, by Scot Nelson and Mark Wright. For new readers CTAHR is College of Tropical Agriculture and Human Resources - University of Hawaii - Manoa. 

Monday, November 11, 2013

Controlling Insects with Neem


 The neem tree (Azadirachta indica) is a fast growing shade tree native to Southeast Asia and India. Compounds (Azadirachtin) extracted from the seed have been found to possess pesticidal qualities; the greatest concentrations of these substances are found in the seed.

Also extracted from the seed kernel is the oil. Neem oil, like other horticultural oils, works by suffocating the insect, coating its body and blocking the breathing openings. Products are available which contain neem oil alone or with azadirachtin.  In tests involving the control of aphids, products containing both had a greater efficacy than either ingredient alone.  Neem oil can also prevent the germination of some fungal spores such as powdery mildew. 

Azadirachin, the active ingredient in many neem products, actually consists of more than 25 closely related compounds.  They work in several ways. 1.  as a feeding deterrent against a number of insect pests. 2. to disrupt the molting process so the immature larvae do not develop into adults.  3. some insect larvae are killed by direct contact with the spray,  4.  adult insects are normally not killed but mating may be disrupted and 5. Azadirachtin also has a repellent effect on certain insects and mites.         

Insect pests affected by azadirachtin include aphids, beetles, caterpillars, lace bugs, leafhoppers, leafminers, mealybugs, psyllids, thrips and whiteflies.  Generally, neem will have less of a detrimental effect on beneficial insects (parasites/predators) compared to the broad spectrum pesticides.

Multiple applications of neem are generally recommended. Frequent spraying is more effective because neem does not persist on plant surfaces. Like other botanical insecticides, it is quickly broken down by sunlight and washed away by rain. For smaller plants, neem seems to work well as a soil drench; the product is absorbed by the roots and translocated systemically throughout the plant.

Another product sold as a fertilizer is neem cakes. They are the residual seed meal remaining after extraction of oil from seeds. 

Monday, November 4, 2013

Bolting in Vegetables


Bolting is the process of premature flower formation in response to high temperatures, as well as drought and starvation.  This unwelcome occurrence in leafy plants such as broccoli, cabbage, lettuce, and spinach,  takes the plant out of its leaf producing mode and switches over to flower and seed production.

Many vegetables are divided into two groups: cool season and warm season vegetables. Although in Hawaii seasons may vary little in temperature and many vegetables can be grown year around, some will do better when planted within the given time frame. 


Broccoli and lettuce are cool season vegetables. As long as the temperatures remain cool, the lettuce will continue to produce tender leaves, and the broccoli flower buds will remain closed. Generally lettuce and broccoli are planted from September through March/April.  During the hot summer months plants can bolt.  At higher elevations, cool season vegetables such as lettuce, beets, broccoli, cauliflower, chard, kale, peas, turnips and mustard, may be successful planted in late spring and summer.   

Warm season vegetables include tomatoes, cucumbers, melons, squash, peppers, corn and eggplant.