Sandalwood Trees in Hawaii

Sandalwood trees (Santalum sp.) are classified as hemi-parasites. The term describes a plant that is green and can produce its own food but also derives water and some nutrients by attaching to the roots of other plants. This process can effectively join together whole plant communities through their root systems. The plants that donate nutrients to sandalwood are called hosts; sandalwood trees do not grow well without a host. In fact, this ‘inter-cropping’ is not only possible but necessary. 

According to the publication, Species Profiles for Pacific Island Agroforestry, S. ellipticum, one of four species known as Hawaiian sandalwood, can “… successfully develop into relatively large individuals when growing with endemic species such as Wikstroemia sandwicensis (‘ākia) and a fan palm Pritchardia remota (loulu) in windward, lowland areas. In more xeric (dry) environments it has developed successfully in association with the endemic shrub Chenopodium oahuense (‘āheahea) and Chamaesyce hypericifolia. Apparently S. ellipticum, is flexible in the species it can parasitize for needed nutrients.”

Santalum ellipticum is endemic to the Hawaiian Islands. It is found as a sprawling to bushy shrub near the ocean shore. It is occasionally found as a larger shrub to small tree in dry gulches, on slopes, and frequently in rocky habitats. S. ellipticum is adapted to arid habitats with typical summer drought in leeward lowland locations.

Hawaiian sandalwood species generally resist most insect attack; sometimes infestations of whitefly or scale insects can be found. Insecticidal soap may be used to treat such infestations. Slugs and snails will also feed on newly sprouted plants. The trees generally tolerate a broad range of soil conditions but show a preference for well drained neutral to slightly alkaline soils.  Since many Hawaiian soils tend to be acidic, an application of lime would be appropriate to bring the soil closer to neutral. The wood of the sandalwood trees is often used for carving handicrafts, art, musical instruments and decorative furniture.  

Avocados and Clay Soils Don't Mix

Avocado trees, planted in a clay soil in an area of high rainfall, will frequently be unhealthy. Various species of trees can tolerate ‘wet feet’ such as the great magnolias of the South which grow in the swamps. Other trees, like avocado and citrus, do not like to sit in water. In order for most trees to thrive in places of high rainfall, they must either be able to tolerate lots of water or be grown in well-drained soils. Unfortunately, a clay soil does not facilitate good drainage.

A key element to remember is that roots need oxygen as much as they need water. When it rains, water fills the air pockets in the soil. For good plant health, a portion of that water needs to quickly drain away to allow the air to come back. In clay soils this does not happen; the clay holds onto the water.  

In arid climates, farmers who have clay soils simply apply water less often. In tropical climates, the clay soil has little or no chance to dry out; oxygen is excluded, and the roots die. In the case of avocados, it has been shown that after 72 hours in a water logged soil, their roots begin to decline.  Once this happens, leaves turn yellow and drop resulting in twig and small branch dieback.

Clay and rain are a bad combination for many plants. There is not much to be done for existing trees; the soil can’t be changed neither can the rain be stopped. A good recommendation is to plant on a slope where there is better drainage. Sometimes trees can be planted on mounds about 3 feet high. It won’t do any good to dig a hole, put the tree in and fill the hole with a different type of soil. That is like putting sand in a bathtub, plugging the drain and planting a tree in it.

Pests of Azaleas

Azalea foliage appears whitish, silvery or somewhat bleached, what's the problem?  There are three common pests that can cause this appearance: lace bugs, thrips and mites.

Lace bugs have piercing-sucking mouth parts which remove the sap as they feed from the underside of the leaf. This feeding damage detracts from the plants beauty, reduces vigor, and makes the plant susceptible to other problems.

The adults are about 1/8 to 1/4 inch long, with a brownish black coloration to them. But the highly sculptured, transparent wings have a lacy appearance, thus giving the insect its name. The immature stages of the lace bug are flat and oval with spines projecting from their bodies. Another way of identifying the lace bug is the presence of dark droplets of excrement on the undersides of the leaves. 

The following azalea cultivars have resistance to the azalea lace bug: ‘Dawn,’ ‘Pink Star,’ ‘Ereka,’ ‘Cavalier,’ ‘Pink Fancy,’ ‘Dram,’ ‘Seigei,’ ‘Macrantha,’ ‘Salmon Pink,’ ‘Elsie Lee,’ ‘Red Wing,’ ‘Sunglow’ and ‘Marilee.’

Thrips are small, dark colored insects less than  1/20 inch long. They are typically found on the undersides of leaves. Like lace bugs, tiny black specks of excrement on the undersides of the bleached leaves are clues to the presence of thrips.

Mites are tiny pests, related to spiders and have eight legs as opposed to the six on insects. They also have piercing mouth parts which suck the juices of the plant cells and cause a yellow to bronze stippling of the leaf. They are typically found on the underside of the leaf but with heavy infestations; yet mites will feed on the upper surface as well.

Control for all three is similar. Although there are general predators for these pests such as spiders, predatory mites and ladybird beetles, they are not efficient enough to keep these pests in check. Sometimes the pest can be knocked off the plant with a heavy spray of water. Applications of insecticides such as horticultural oils, neem oil and insecticidal soaps can be effective for temporary reduction of the pest population. It is best to apply them when the pest population is low. Thorough cover is essential, covering both the top and the bottom portions of the leaves. Repeated applications at 5-10 days apart, are usually required for good control.