Tuesday, October 30, 2012

Bt - An Effective, Organic Pesticide

Bt, which is the bacterium, Bacillus thuringiensis (sold as  Dipel, Gnatrol, and Thuricide) is an effective organic pesticide specific to caterpillars, fungus gnat and mosquito larvae.

The problem is that Bt does not kill immediately, and therefore, gardeners may think the product is ineffective. The bacterium produces a toxin that, when ingested, causes gut paralysis and eventual death. The affected caterpillar will stop feeding within hours of ingestion, but it may take a day or two to actually die.

In addition, Bt rapidly degrades in sunlight. For best results, applications should be made in the late afternoon. Most caterpillars feed after dusk anyway.  Bt is especially effective against the green garden looper which commonly attacks many vegetable crops and some ornamental crops, including ti and tropical foliage. 

Tuesday, October 23, 2012

Low Yield in Dragon Fruit

Dragon fruit are produced on a climbing cactus plant, with triangular fleshy stems, known as pitaya/pitahaya; the fruit is also called pitaya. 

Dragon fruit plants prefer a warm, moist climate with rich organic soil. It is not suitable for areas with extreme high temperatures and intense sunlight. It requires 25-50 inches of rainfall annually.  Excessive rain can cause flower drop and the fruit to rot.

Many species of pitaya are self-sterile and because they bloom only at night, successful pollination is difficult to achieve for adequate fruit bearing. Many of the insects that pollinate other flowering plants are not active at night.   Therefore, moths and bats are the likely pollinators for pitaya plants. If moth and bat populations are low, pollination will be limited and hand pollination may be required.
Dragon Fruit Varieties -   Pine Island Nursery

Commercial plantings of pitaya can be found in Vietnam, Taiwan, Malaysia and Israel. In Hawaii, where it is known as paniniokapunahou or papipi pua, a famous hedge of this cactus grows at Punahou School in Honolulu.  From July to October this hedge creates a spectacular sight of large, white blooms.

Friday, October 19, 2012

The Jaboticaba Fruit Tree

Jaboticaba is an unusual tree with the fruit produced directly upon the trunk and larger branches, singularly or in clusters. Most people consider it to be a native of Brazil, having been widely cultivated in domestic orchards of South Eastern Brazil since colonial times. The trees are slow growing; some are 4-5 foot shrubs while others can grow 15-25 feet tall, rarely more.

Jaboticaba trees are usually raised from seed. The seeds, being polyembryonic, can give rise to 3-4 seedlings.  Some varieties are propagated by air layering. 

Depending on the source, jaboticaba seedlings require anywhere from 6 to 15 years before they bear fruit. If the tree blooms during a period of drought, many flowers will desiccate causing a decrease in production. In their prime, they bear fruit profusely and repeatedly, often four to five times per year.

It has been reported that solitary jaboticaba trees bare poorly compared with those planted in groups, indicating that cross-pollination enhances productivity.

Tuesday, October 16, 2012

Preemergent Herbicides

 Preemergent herbicides, also known as soil-residual herbicides, are applied to the soil before the weeds appear in order to prevent their germination.  In some cases, they will also inhibit young weed seedlings from growing.  After application, the herbicide is activated when incorporated into the soil or when water is applied (irrigation or rain). The residual effect of the herbicide will last from several weeks to a number of years, depending on the particular herbicide used, the rate of application, and soil characteristics. The more common preemergent herbicides will persist in the soil from 1- 12 months. Some herbicides must be activated within 24 hours of application while others can wait up to 21 days. Best results are obtained when a half inch of water is applied to the area immediately after application. 

Preemergents can be applied either as liquid or granular with a fertilizer spreader.  They can also be applied over the top of existing ornamentals and groundcovers if the label permits.  In Hawaii, preemergent herbicides may not last as long as the label indicates since they generally degrade faster under wet, warm conditions.

In choosing the right herbicide, first determine the type of weeds that need to be controlled. Since many homeowners do not know the names of the various weeds, at least determine whether the weeds are broadleaf or grassy weeds. This is essential since herbicides are categorized as to whether they kill broadleaves or grasses. Some herbicides crossover and control both types of weeds.  It is important to read the label carefully since it will tell you what weeds the product will control.

Next, determine where the herbicide will be applied - turf, flower beds, edible plants, around trees or shrubs. Situations differ between herbicides. Some are allowed in vegetable gardens while others are not. Some are labeled for turf, and others are not. Again read the label carefully. 
The following are some preemergent herbicides that are registered in the State of Hawaii.
  • ·        Ronstar (oxadiazon) - provides preemergent and early postemergent control of a variety of annual broadleaf and annual grassy weeds (greater activity on broadleaf weeds). It may be used on established perennial turf such as bermudagrass, perennial ryegrass, St. Augustine grass, seashore paspalum, and zoysiagrass, and around woody ornaments, shrubs, vines and trees.
  • ·        Impede (oryzalin) – provides control of a variety of annual grasses and broadleaf weeds in flower beds, groundcovers and around trees and shrubs. As with many of the preemergent herbicides it will not work on weeds already growing.  It lasts up to 4 months and is not registered for use around edibles or lawns.
  • ·        Preen (Trifluralin) – for use in flower and vegetable gardens and around trees and shrubs. Not for use on lawns; for control of a variety of both grassy and broadleaf weeds.
  • ·        Gallery (isoxaben) – for the control of a variety of broadleaf weeds in turf, ornaments and groundcovers.

Additional choices are available for use in woody ornamental plantings.  They are Casoron, Rout, Ornamental Herbicide 2 and Snapshot TG.  These should not be used in herbaceous ornamental beds; they have the potential for injuring herbaceous plants.

For more detailed information, download the CTAHR (College of Tropical Agriculture and Human Resources - University of Hawaii-Manoa) publication Weed Control Options in Landscape Beds and Groundcovers. 

Tuesday, October 9, 2012

Beware: Fertilizers Can Burn Plants

 If you water plants with ocean water, the salts in that water would eventually accumulate to a level that is toxic to the plant -- assuming a good rain doesn’t come each night to leach out these salts. Whether its ocean water, manure, or fertilizer, each contains salts that can accumulate to a toxic level. Salts are not just sodium and chloride found in ordinary table salt. The nitrates, phosphates, sulfate, etc., found in fertilizer and manures are also referred to as salts.

As an example, one cup of calcium nitrate fertilizer may be recommended for a large tree and one tablespoon for a small shrub.  Do not think that if one cup or one tablespoon is good, that two are better.  No matter how good a fertilizer is, too much, can burn and even kill a plant.

When plants are over fertilized, in approximately one to two weeks the tips and edges of the leaves will begin to turn brown.  With a slight overdose, tip burn may be all that occurs. A larger overdose will cause many or all of the leaves to turn brown and drop off.   Eventually, as the excess fertilizer is leached out (diluted and carried below the root zone), the plant will put forth new roots and new leaves.
Handle fertilizers with care.  Used properly, they will nourish plants; overdosing can cause injury. 

Friday, October 5, 2012

Myths and Facts of Companion Planting

Companion planting is the establishment of two or more plant species in close proximity so that some benefit is derived - usually higher yields and the control of pests. The fundamentals of companion planting have evolved over the years from a combination of historical observations, some unconventional testing and some scientific research. 

Science has consistently shown that many companion plantings offer no pest control benefits when grown under controlled conditions.   Other companion plantings, however, do have chemical components that repel pests, although the effect is often localized and the benefits do not extend to neighboring plants of different species.While research has not verified all the combinations that have been passed down over the years, there is validity with some of the plant mechanisms that create these beneficial associations.

1. Trap cropping – a given pest may have a preference when it comes to hosts. So when collard greens are planted next to cabbage, the collards will draw the diamond back moth away from the cabbage. Thus the collard crop will be heavily infested while the cabbage is hardly touched.

2. Nitrogen fixers – legumes such as peas, beans and clover, with the help of a  bacteria that live in their roots, will capture nitrogen in the soil and convert it to a form that plants can use.   As an example, beans are sometimes interplanted with corn to reduce the need for nitrogen fertilizer applications.

3. Physical spatial interactions – tall sun loving plants may be planted with low growing shade tolerant plants.  Thus, garden space is better utilized, producing higher total yields per area of land. 

4. Biochemical pest suppression – some plants exude chemicals from roots that will suppress or repel pests and even protect some neighboring plants.  The African marigold releases a chemical called thiopene that repels nematodes.  Another example is when rye is mowed and placed in beds as mulch; a chemical is leached from the rye residue and will prevent weeds from germinating but will not harm established vegetables in the bed.

5. Beneficial habitats - Certain plants can be used as insectary plants to attract and support beneficial insects. It is often the immature stage of an insect that provides the vital service of biological control. But the adult stage must eat, too.  Planting a field of a variety of blooming plants will provide nectar and pollen for these adults. They will be drawn to the area, feed, reproduce and remain.

Here are a few specific examples that researchers have identified:
  • Boston fern leaves contain a feeding deterrent effective against the Southern armyworm. 
  • The leaves of a tomato plant contain a chemical that is toxic to some weevil species.
  • The cabbageworm is controlled by planting mint nearby.  Rosemary, sage, peppermint, thyme and catnip are other helpful plants to control cabbageworms and aphids. 
  • Sweet basil (Ocimum basilicum) tends to repel aphids, mosquitoes and mites.  Planting basil among tomato plants controls tomato hornworms.  
  • Thyme planted with cabbage controls cabbage maggots, white cabbage butterflies and imported cabbageworms. 
  • Nasturtiums are often used as a trap crop for aphids. 
In many plant species, science has discovered beneficial attributes in companion planting. Problems sometime arise, however, when garden enthusiasts attempt to apply this information to their garden.  The facts are true, but the application is often misguided.

Here is an example: It is true that certain species of marigold produce chemicals that repel nematodes.  But there are a few important factors to consider. 1) The correct species of marigold must be planted and at the proper high densities. 2) Correctly planted, marigolds will suppress the nematodes and allow for a susceptible crop to be planted, but only for one season.  It is necessary to continue alternating the marigolds with the desired crop.