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Garden Guy: Pickleworm is wreaking havoc across the Hawaiian Islands


With my bittermelon plants, the fruit will set but will dry up and turn yellow. Is there an over-the-counter remedy for this?

Collect some of the yellow, drying bittermelon fruit and cut them open. It’s likely you will find larvae of the notorious pickleworm.

Visit my website, www.gardenguyhawaii.com, and search “‘pickleworm” for detailed information on this pest.

They are difficult to control! To date, exclusion seems to be the best method. Some insecticides are registered on cucurbits and have been successful in commercial crops. One of the lesser toxic insecticides that may be effective on the pickleworm is known as Bt, Bacillus thuringiensis, a bacteria which is deadly to the moth larvae, but not to humans. Good coverage, however, is essential but also difficult.

The pickleworm was discovered in Oahu in 2003, and by 2005, it had spread to Kauai, Maui and the Big Island. It attacks many cucurbits such as cucumber, squash, pumpkin, zucchini and cantaloupe.

I recently purchased a couple of beautiful Japanese maple trees on Oahu. I bought them in hopes of eventually making bonsai out of them, but they are too small at the moment and I am just focusing on keeping these young trees healthy. I realize that these trees are really hard, if not impossible, to raise here with the climate and the fact that our winter is not adequate for these plants to go dormant. Can my trees survive here? I also have a few problems with possible insects and/or disease. The leaves have little holes on them. Could you recommend some insecticide that won’t do more harm to these fragile leaves? I really would appreciate any insight and information concerning my issues.

Being a deciduous tree, the Japanese maple is indeed adapted for cold climates. Hawaii, as well as other tropical locations, does not provide the best growing environment, however, they will grow here.

I have one Japanese maple that is now 9 years old. Admittedly, it is not the most vigorous tree, and I think it is continually looking for winter. Sometimes it goes dormant in spring or even in the middle of summer, but it still grows.

One question might be, how many years can it survive without experiencing a dormant period?

There are more than 1,000 cultivars of Japanese maple. Obviously some will adapt to Hawaii better than others. Usually, nurseries select those varieties best suited for their area, in this case, the tropics.

The main problem is not climate, but an insect called Chinese rose beetle. It is this beetle that is making the holes in the leaves. In the evening, after sunset, which is the time they will be feeding, cover the plants with netting to exclude the beetle.

Another choice for control is to use a systemic insecticide with the active ingredient imidacloprid. Granules can be applied to the pots and watered in.

On my website I have a detailed report on this pest. Search “Chinese rose beetle” in the space on the left of the screen.

I am attaching the picture of some crusty stuff on the bark of the camellia sasangua. Can you tell me what this is?

Lichens are considered harmless as I have discussed previously. This organism consists of a fungus and an alga growing together in a mutually beneficial relationship.

Although they attach themselves to the tree, they are not pulling vital nutrients from the tree. It is often thought that lichens are injuring trees because they often look distressed while the lichens appear to be thriving.

The true scenario, however, is the tree begins to decline first by losing leaves, this allows more light to penetrate into the trunk. It is the increase of light which enhances the lichens growth. Bottom line: check for other causes of tree decline — lack of fertilizer, insect infestations (scale, aphids) and disease.

It has been found that most lichens will not grow in a smoky or polluted atmosphere. Therefore, when lichens are present, the air is relatively clean.

Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years. Email your questions to Sakovich at askthegarden guy@earthlink.net. You also can visit his website at www.gardenguyhawaii.com.

 

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