Leafhoppers & ohia trees


Nick, thanks for another article on ohia dying. This seems to be a recurring subject of great interest to residents. In Leilani Estates, the symptoms are that small branches can die anywhere on the tree and that the entire tree is brown and dead within two to three weeks. Can you please comment on the role of the two-spotted leafhopper? This was mentioned as a possible cause at a recent workshop in the Volcanoes National Park. — Jim

In order to research the answer to your question, I consulted three experts in the field: two from University of Hawaii and one from Department of Agriculture.

According to Brian Bushe with UH College of Tropical Agriculture and Human Resources, when the leafhopper Sophonia rufofascia was first reported in Hawaii, the population reached extremely high levels. When found in great numbers on uluhe fern and on ohia, significant damage and dieback occurred. Yet like most pests new to the atate, the population of leafhoppers eventually decreased due to natural biological control. This “good guy” activity was probably from a native wasp egg parasitoid attacking the leafhopper.

Pat Conant with the Hawaii Department of Agriculture reports that some Morella faya (also known as fire trees, an invasive species) and perhaps a few ohias may have been killed due to the leafhopper before natural control took effect. He also states that although the ohia decline could be strictly a natural phenomenon, in all probability, there are other factors involved — alien pathogens to name one. Unfortunately, there is a shortage of funds to accomplish the research needed to address the ohia dieback problem.

According to JB Friday, Forester with UH CTAHR Forestry Extension, there have been many cases of ohia dieback over the years, but he thinks there is something new or a new phase of dieback. Friday states, “I am sure it’s not just one problem. The leafhopper did indeed cause problems before the natural biocontrol was established, but I don’t see it starting to cause ohia dieback now.”

In all likelihood the leafhopper is not the cause of the ohia decline that has been observed as far back as 1906, with another major decline in the late 1960s. The leafhopper was first recorded in Hawaii in 1987.

As with a few other disorders, it would seem there is more than one causal agent. A complex of factors is involved, including not only the insect and fungal pests but environmental considerations as well.

Perhaps the best news is that recently Dr. Friday has been involved with surveying ohia dieback stands across lower Puna with the hope of finding a correlation between the decline of ohia and some environmental factor. Sites were mapped in relation to lava types, soils, and forests. The results are pending: stay tuned for updates.

I keep planting carrots over and over. Of all the seeds I plant, only a few grow. What is going on? Thanks, R.M.

What you are experiencing is quite typical. Carrots seeds are small and slow to germinate and the seedlings are fragile. Because of this, all sorts of problems can arise. When heavy rains occur, the seeds can easily wash away. Placing some type of cover over the seed bed, at least until the seeds have emerged, will help.

Soil preparation is important; few seedlings will be able to emerge through a crusty soil. Here some simple directions for planting carrots: 1. plant carrot seeds 1/4-inch deep in heavy soils, and 1/2-inch deep in light soils. 2. Thin out dense seedlings carefully in order to give roots enough room to expand normally. 3. Space plants 2 to 4 inches apart. But first of all, check the date on the seed packet to be sure the seeds are current.

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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 askthegardenguy@earthlink.net.

 

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