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Managing Plantations:
Plantation management needs to address several concerns:
1) weed control
2) need for fertilizer
3) thinning and pruning where appropriate; and
4) protection against animals, insects and diseases.
The following discussion is intended to introduce you to the different aspects of managing a hybrid poplar plantation. For further details please refer to "High Yield Poplar Plantations in the Pacific Northwest."
Weed Control -
If the grower does not control weeds and grass adequately, hybrids will grow slowly and may not survive. Furthermore, weeds and grasses provide cover to voles, which can girdle and kill trees as old as 4 years. Growers usually control weeds in plantations by combining cultivation and herbicides, starting with a chemical spray before or soon after planting.
A number of effective weed control treatments that employ herbicides are used. The Pacific Northwest Weed Control Handbook lists the most commonly used materials and is updated annually. Refer herbicide questions to your Cooperative Extension agent.
Fertilization -
A vigorous plantation takes up as much as 200 lb of nitrogen (N) per acre per year. However, from 50 to 150 lb of N per acre per year is generally the rate applied. On fertile soils, including some old pastures, the nitrogen released from soil organic matter can be sufficient to carry the plantation for several years without need for added fertilizer. Usually fertilizer is not broadcast before planting or applied during the first year of growth.
Appearance of plants can indicate need for nitrogen. Leaves of nitrogen deficient plants are generally smaller, light green and sometimes even yellowish. When nitrogen deficient, the entire leaf becomes a uniform light green or yellow. Need for other nutrients has not been demonstrated in western Washington. However, zinc fertilization can be very beneficial on calcareous soils east of the Cascades.
Thinning and Pruning -
For all but biomass harvests, practice early thinning to one stem per stump before the second growing season; extra stems can be used for cuttings. Thinning or partial harvest of trees later in the life of the plantation may be desirable to make space for larger, better-formed trees for lumber or plywood. Clear, knot free wood adds value to such trees. For that reason, pruning of branches starting as early as year 1 or 2 in plantations for lumber or plywood may be advisable.
Insects -
Many insects feed on trees of the genus Populus. However, in the early years of plantations, insect damage was minimal. Now with the greater acreage of hybrid poplar, damaging outbreaks of certain insects have occurred. The following table lists the major insects feeding on Populus in the Pacific Northwest.
| Name | Damage (consult extension agents for control measures |
| Sawfly larvae | The active caterpillarlike larvae have defoliated plantations severly. Damage capability is particularly high with one species because it can produce several generations |
| Dark brown poplar aphid | Feeds early July-September. Damages leaves, causes early loss of affected leaves |
| Poplar leaf skeletonizer | Feeds in midsummer, damage is usually insignificant to moderate |
| Leaf-folding sawfly | Appears June-July, reduces leaf area; probably insignificant effects on growth. |
| Populus bud midge Big sticky bud midge |
Infects and causes enlargement of buds that set early (late spring and summer). Kills buds. Damage is mostly to lateral buds or to terminal buds of stressed trees, including newly planted trees. Can keep stressed trees "in check" indefinitely. |
| Poplar gall borer, a longhorn beetle | Bores into stems causing gall-like swelling and "cankers," weakens stems. May lead to secondary fungal infection. |
| Poplar leaf beetle | Vigorous leaf feeder occurring on "eastside" planting. May need to be controlled with pesticides. |
| Clear wing borer | Bores into trunks, often through branch pruning scars. Causes secondary fungal infection and stain of heartwood. |
| Poplar and willow borer | Bores into shoots and branches; can cause breakage, secondary fungal infections and stain of heartwood. |
| Thrips | Extremely small insects that feed on young expanding terminals and leaves and cause distortion and stunting of terminal growth. |
| Tarnsihed plant bug | Small (1/4 inch), brown with green underbody, active fliers. Stunts height growth of young plants. Causes malformed leaves and sometimes cankerlike lesions on young stems. |
Diseases -
Disease is probably the greatest threat to poplar culture. The following table describes the most common diseases affecting hybrid poplar in the Pacific Northwest.
| Name | Damage | Prevention or Control |
| Cladosporium herbarum | Random spotting of leaves and early leaf fall. Sometimes causes stem cankers | Resistant clone. Sanitation of fallen leaves |
| Black Stem | Dieback and bark death of branches and stems often of stressed trees. | Prevent wounding and stress in nurseries. Remove diseased plants from nurseries. Store cuttings at -3 C, and protect them from drying and heating. |
| Marssonina | Leaf spots and petiole lesions building slowly to sometimes epidemic proportions in late summer. | Resistant clones. |
| Septoria leaf spot | Bordered (targetlike) leaf spots develop early spring and late summer in susceptible material. | Resistant clones. Sanitation of fallen leaves. Spraying foliage and stems with appropriate fungicide. |
| Taphrina populi-salicis | Raised blisterlike bumps on upper leaf surfaces appearing in early spring. | Resistant clones. Sanitation of fallen leaves. |
| Shepherd's crook | Blackening and death of young branches, shoots and leaves. | Resistant clones. Sanitations of fallen leaves. |
| Poplar rust | Bright orange spotting of upper and especially lower leaves appearing as early as July | Resistant clones. Spray with fungicide. Consult your extension agent. |
Animal Damage -
Wild animals causing damage to cottonwood plantations include deer, elk, beaver, porcupines, rabbits, voles, and pocket gophers. Domestic livestock also can damage trees. Fencing may be necessary to protect the trees from large animals including beaver, which can decimate plantings near waterways.
Protecting the trees at planting from girdling with use of Vexar tubes or wrapping with foil or plastic appears effective. These methods are most appropriate for longer cuttings and whips.