Question: I have two hazelnut trees and fight with the birds for the harvest each year. When I get hazelnuts, some are empty (have no meat). Is this a pollination problem?
What you describe sounds like “blank nuts.” Blank nuts contain no edible nut meat (called the kernel) or have a kernel that fills less than one-fourth of the shell. Blanks generally fall from the tree earlier than nuts with full kernels. Their shells also are easier to crack.
The cause of blank nuts is not fully understood. Blank nuts are not caused by a pollination failure; if pollination had failed, the shell would not have developed at all.
Research suggests that blank nuts often result from environmental or cultural problems such as insufficient soil moisture in midsummer, low light levels, or inadequate tree nutrition. Some varieties of hazelnuts (such as the cultivar ‘Barcelona’) are more likely to produce blank nuts than others.
Two insect pests can cause blank nuts: the brown marmorated stink bug (Halyomorpha halys) and the filbertworm (Cydia latiferreana). The brown marmorated stink bug inserts its mouth parts through the shell, injects digestive enzymes and feeds on the kernel. The amount and type of damage depends on when the stink bug feeds.
Feeding early in nut formation results in blanks; feeding at later stages of nut development causes malformed kernels or corky areas on the nut surface.
Damage resulting from the filbertworm occurs when the larva bores through the hazelnut shell and feeds on the kernel. The entry hole into the shell is difficult to see but the exit hole (after the larva has devoured the kernel) is usually larger and more obvious (see photo).
If you do not see evidence that the brown marmorated stink bug or filbertworm are causing the blank nuts, the best advice I can offer is to make sure that your trees are getting the care they need. Hazelnut trees like full sun and deep, well-drained soil. Irrigate your trees during the summer.
Fertilize them if growth is poor or leaves are pale green. If fertilizer is required, apply one-half to one pound of nitrogen per year, per tree, in early spring.
Hazelnut trees cannot pollinate themselves and require a different hazelnut variety that blooms at the same time for cross-pollination and nut formation.
For more information on growing hazelnuts, see extension.oregonstate.edu/collection/growing-hazelnuts-pacific-northwest.
Question: Our native soil drains poorly. I would like to build raised beds for growing vegetables. Is treated lumber a human health concern?
A variety of materials are used to build raised beds including bricks, concrete blocks and various types of wood. Lumber treated with preservatives, primarily heavy metals, lasts longer than most other types of wood when exposed to the elements, but leaching of the heavy metals into the soil and uptake by plants has been a health concern.
Research on this topic is limited but suggests the following:
• Leaching of heavy metals from treated wood does occur but residues in soil are 10-100 times lower than levels considered toxic to humans.
• Heavy metals are more likely to leach from treated lumber in contact with acidic soils than those in contact with the more neutral soils that are preferred by most vegetable crops.
• Metals that do leach into the soil tend to bind tightly with clay and organic matter particles, becoming less available for plant uptake.
• The amount of uptake by plants depends on many factors, including plant type, soil type and distance between the plant and the treated wood.
In 2004, the Environmental Protection Agency (EPA) withdrew wood preserved with chromated copper arsenate (CCA) from residential use (such as for raised beds) due to potential contamination of soil and groundwater with arsenic. Products that do not contain chromium or arsenic, such as alkaline copper quaternary (ACQ) and copper azole (CA), have largely replaced CCA and are considered safer.
Although the risk of uptake of heavy metals by most plants seems low, the following steps will minimize human exposure to heavy metals from treated wood used in raised beds:
1) Use lumber treated with ACQ, CA or other preservatives approved by EPA for use in raised beds. Do not use those treated with compounds like CCA, creosote, or pentachlorophenol, which are not registered to treat wood for consumers and should not be used in garden beds.
2) Consider putting a sheet of plastic between the treated wood and the soil.
3) Plant edible crops at least 12 inches away from the treated wood.
4) Peel root vegetables and wash soil from all crops grown in these beds.
If you remain concerned about exposure to heavy metals, use a rot-resistant natural wood such as red cedar or redwood or a non-wood product to build your raised beds.
Jeanette Stehr-Green is a WSU-certified Clallam County Master Gardener.
Plant clinic assistance
For more free gardening help visit a local Master Gardener plant clinic. Clinics are held from 9:30 a.m.-12:30 p.m. on Mondays through October at the Clallam County Courthouse, 223 E. Fourth St., Port Angeles. They are also held from 9:30 a.m.-12:30 on selected Saturdays — May 20, July 15, Aug. 19 and Sept. 16 — at the Master Gardener Woodcock Demonstration Garden, 2711 Woodcock Road, Sequim. For more information, visit extension.wsu.edu/clallam/mg/plant-clinics.
