Garden Guy: Alternate bearing of citrus

It has been an abundant year for citrus. But because the trees have been so heavily laden with fruit, I need to warn you about next year: Do not expect the same type of yields.

This is because many citrus fruits including sweet oranges, especially mandarins (tangerines), have a strong tendency to alternate bear.

Year after year, medium to heavy yields will alternate with a light yield. The reason for this is that it takes considerable energy to bring fruit to harvest. This is especially true for those varieties whose crops overlap, that is, the “old” crop is still hanging on when the tree blooms once again. In essence, a tree must rest the year following high production. Again, there is just so much energy to go around.

Alternate bearing isn’t always exact, but over many years you will see years of heavy production followed by years of low production.

To explain more specifically, because a tree carries such a heavy load of young developing fruit in the on-year, the number of summer and fall vegetative shoots that the tree produces will be reduced. These shoots carry flower buds for the following year’s production. Since the number of shoots is reduced, flower bud and thus fruit production will also be down, resulting in an off-year.

Alternate bearing can be offset by reducing the fruit load on a heavy fruit set year. This is accomplished by thinning some of the fruit before the summer flush. This will also cause the remaining fruit to grow larger. Pruning the tree will give similar results. It is also recommended to pick the fruit as early as possible.

A warning about

carpenter bees

Although carpenter bees feed primarily on pollen and serve a valuable role as pollinators, they unfortunately can cause serious damage around the home.

These bees do not eat wood, but the female bees burrow into wood and create galleries to lay eggs. Bare, unpainted or weathered softwoods such as cedar, pine, redwood and cypress are preferred. Common nesting sites include eaves, window trim, fascia boards, siding, wooden shake shingles, decks, ohia post supports, outdoor furniture, exposed roof rafters, wooden fences, and picnic tables. All these items can incur serious damage when left to repeated attacks by the carpenter bees.

Coarse sawdust the color of fresh cut wood will often be present beneath the entry hole; burrowing sounds can sometimes be heard from within the wood.

Female carpenter bees may be excavating new tunnels or enlarge and reuse old ones for egg laying. If the wood has been utilized for nesting year after year, the damage may be considerable.

Control measures

When building, use hardwoods, they are less attractive to carpenter bees as is pressure treating, painting and varnishing the wood. Fill existing and unoccupied holes with steel wool and caulk to prevent their reuse. In addition, entrance holes may be dusted with an approved insecticide.

Although these insects look similar to bumble bees, they are actually Sonoran carpenter bees. The female is black, and rather large, approximately one inch in length. They can sting when angry but are considered shy and rarely bother humans. The male bees are golden brown in color and lack a stinger. They inhabit the Hawaiian Islands, the Marianas, China, Japan, New Guinea and the Philippines.

Egg laying occurs year-round but may decline during the winter months. A ball of pollen is placed in the tunnel as food, one egg is laid on the pollen and the chamber is sealed with wood shavings.

Class

Announcement:

Vegetable Gardening

On Saturday, Feb. 8, I will be offering a gardening class, “Vegetables in the Home Garden, from 10 a.m.-12:30 p.m. at the University of Hawaii at Hilo UCB 118. Call 974-7664 or go online to register at http://hilo.hawaii.edu/academics/ccecs/registration/ There is a fee.

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.