Chipping in about using eucalyptus as mulch

Iplan to take down a large eucalyptus tree and I heard the wood chips from eucalyptus can’t be used for mulch because they are toxic.

Is that really true? It seems reasonable since I never see much growing underneath these trees. — A.J.W.

Here is some good news for you: several studies have shown eucalyptus chips do not contain any toxins.

The simple reason other plants have difficulty surviving underneath eucalyptus is competition.

Eucalyptus trees grow vigorously and consume a great deal of water and nutrients, thus creating a lack of these elements beneath the canopy for newly emerging seedlings. Eucalyptus trees also produce large amounts of litter that tends to smother young plants growing beneath.

To show the voracity of the appetite of these trees, here is an observation made in commercial citrus groves in California: the rows of citrus trees planted near the eucalyptus windbreaks were visibly smaller.

The effects of the far reaching eucalyptus roots can be seen seven rows away from the windbreak (about 125-150 feet).

In research conducted in California, eucalyptus wood chips were used to mulch avocado trees, both newly planted and older, existing trees.

Not only were there no ill effects from the eucalyptus mulch, but the avocado trees themselves used less water, developed a better root system and had fewer diseased roots than trees with no mulch.

Most other wood chips, including oak, conifer, sycamore, cypress, etc., are also good for mulch. Even chips from oleander plants can be used, but it must be composted for a time in order to allow toxic chemicals within the plant to break down before it is used.

See www.gardenguyhawaii.com for more general information on mulches and how they can help to conserve water, control weeds and improve soil fertility.

I planted some tomato seeds last month. The seedlings have been growing well.

Now, I can see they have white wiggling lines on the leaves. The lines don’t wash off.

Are they a problem?

I get this question often. These lines are actually tunneling within the leaf by the larval stage of a group of insects called leaf miners.

They are actually tiny flies (Order Diptera). The tunnels are made as the larvae feed between the upper and lower surfaces, meandering their way throughout the leaf.

Sometimes, black thread-like strips of frass (insect droppings) can be seen in the tunnels.

In most cases, the damage that occurs on the leaves can be tolerated because of several species of parasites which attack the larvae feeding within the leaf tissue.

As for seedlings, once they are set out, the plants tend to outgrow the pest while the parasites take over and minimize the tunneling.

Chemical sprays are generally not recommended because they would kill the parasites along with the leaf miner. Furthermore, spraying could hardly control the larvae that are well protected inside the leaf tissue.

Some gardeners pick off the infested leaves and discard them. This might not be a good idea because inside those leaves many parasites are waiting to emerge to attack more leaf miner larvae.

Class announcement

I will be teaching a class from 9:30 a.m.-noon Saturday, June 14. The class, “Tropical Fruit Trees,” will give participants the opportunity to learn the basics of how to successfully grow tropical fruit trees in the home garden.

This workshop will cover basic care: plant nutrition, soil preparation, propagation, flowering and production problems along with the common disease and insect pests.

Some of the trees to be discussed are avocado, papaya, mango, banana and lychee.

Call 974-7664 to register; or go online at http://hilo.hawaii.edu/academics/ccecs/fitness/

There is a fee.

The class will take place at the University of Hawaii at Hilo.

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. Also, visit his website at www.gardenguyhawaii.com.