Photograph by Shari Kaplan

Going out of one's gourd is common during autumn, when the strange-looking, genetically unstable, inedible fruits are used as decorations.

There is hope in the battle to save oaks from beetles

By Tony Tomeo

Last week's column was certainly grim. Now it is time for some good news about the sudden death (syndrome) of oak trees. Although research continues, some procedures have already been successfully used to decrease the risk of infection. At least one insecticide has been successful at preventing new infestation and combating existing infestation. If identified early enough, some infected trees may be salvaged.

It is first important to know how to identify infestation of either the oak bark beetle or the oak ambrosia beetle. The bark beetle bores into the bark and cambium, expelling coarse, dark-colored frass. As the vascular system is damaged, the bored holes bleed dark, thick sap. Infestations usually originate near ground level.

Ambrosia beetles usually attack just above bark beetle galleries, but may infest large areas of the trunk extending far above ground level. They may also attack independently of bark beetles. Because they bore directly into the heartwood, their frass is finely textured and lightly colored, resembling dust. Ambrosia beetle galleries do not normally bleed.

If an infestation is identified, beetles should be eradicated as soon as possible before they emerge to attack other trees. The insecticide, known as Astro, may be applied to infested tree trunks so that both species of beetle come into contact with it at the openings to their galleries. The resulting dead ambrosia beetles clog the gallery entrances, suffocating the mycelia of the ambrosia fungus.

It is not yet known if the fungus continues to attack the trees after the beetles are gone. However, many trees, including several behind my office, have survived initial attacks and eradication of ambrosia beetles. It is also not known if the root rot fungus (an unidentified species of phytophthera), believed to be the primary pathogen that starts the whole process, continues to proliferate in the roots of infected trees. Soil fungicides are currently being tested.

Astro has also been used to prevent infestation. After application, beetles are killed as they try to bore into trees. Because beetles usually attack close to the ground, only trunks of the trees are sprayed. (Higher infestations usually only result from lack of unoccupied trunk space lower down.)

Regular applications should be scheduled so trees are not left unprotected between applications. Trees should continue to be monitored after Astro is applied. Those that have survived previous infestation are more attractive to the beetles than healthy trees.

Although the beetles seem to attack even healthy trees, their normal behavior is to attack stressed trees. It is still advisable to keep trees as healthy and unattractive to beetles as possible. Soil disturbances and supplemental irrigation within the root zone should be avoided.

Severely infected trees too damaged to be salvaged or trees that have been killed but still exhibit active infestations should be removed before beetles emerge to infest other trees. If treated properly, they do not require application of insecticide.

Any firewood should be covered with clear plastic so that beetles die as they emerge. As they try to fly away, they get stuck and drown in the condensation on the plastic. If black plastic is used, beetles will fly toward tears or under the plastic where light comes in, and escape. Some people bury the edges of the plastic so the beetles cannot go under. The beetles die within a few weeks, so the wood can be uncovered before it rots. Firewood should be used nearby and not sent elsewhere.

Squash of the Week II: Gourds

Like pumpkins, gourds are commonly seen this time of year but are grown through the summer. The most commonly grown are the yellow-flowered gourds, Cucurbita pepo ovifera. The fruit is small, hard and variable in shape and color. It may be round, oblong or bottle-shaped, often with a curved neck. Colors range from yellow, orange, brown and green. Fruit may be one color, but is more often two or more. Most are lumpy or "warty."

Gourds prefer full sun, warm temperatures and regular irrigation. Fruits are best kept off the ground by providing something for the vines to climb. Be aware that they can climb over 10 feet. It is best to leave the vines until they dry before taking the fruit, so it has the most time to develop. Another species of gourd produces the loofah sponge. A third species, the white-flowered gourd, produces fruit up to three feet long.

Those grown for ornamental purposes are not edible and genetically unstable. This instability explains why seed will not necessarily produce fruit similar to that from which it was taken.

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Horticulturist Tony Tomeo can be contacted at 408.358.2574.

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