Stock Health and Condition
A complete review of stock quality is beyond the scope of this manual. However, certain aspects of stock health must be considered when selecting a stock type and when accepting stock for planting.
Succulence, hardening-off, and reflushing
Orders of summer and late-summer planted stock should be inspected for succulence (Plates 6 and 7). Succulent stock is more sensitive to handling stress and planting shock than properly hardened stock and, therefore, should not be shipped. If stock is too succulent, the needles may be damaged, the stem may break during handling, the stem may be subject to sun scald and frost damage, and the entire plant may desiccate. There is almost always a small percentage of succulent stock in a crop -- it becomes a concern when greater than 2% of the crop is affected. Table 9 proposes a classification of stock succulence for Pli, Sx/Ss, and Fdc/Fdi.
Plate 6. Spruce seedling on left has hardened off while the seedling on right is still succulent. The light green stem and bud colour indicates that this stock would be too succulent to plant. See Table 9 for more information on succulence. Photo credit: Clare Kooistra.
Table 9. Proposed stock succulence classification. Stock succulence for Pli, Ss/Sx, and Fdc/Fdi is decided based on the condition of the foliage, stems, and buds. If any of the morphology is considered soft, do not use the seedlings -- wait until they have hardened. If stock has reflushed, wait until it has hardened again. If stock is marginal, either wait or only plant sites with low soil moisture stress. For all other species, refer to the reforestation co-ordinator for guidance and assistance.
|Soft||Top 510 cm light green, soft, and flexible.||Top 25 cm lime green, soft, and breaking easily.||Terminal buds not noticeable.||No|
|Marginal||Top 25 cm light green, soft, and flexible.||Top 2 cm green and soft.||Terminal buds barely visible and green.||Maybe|
|Hardened||Top 2 cm dark green and stiff.||Top 2 cm mottled green-brown and firm.||Terminal buds straw-coloured and firm.||Yes|
|Reflush||Stem stretching under bud (candling).||Maybe|
|Soft||Top 510 cm light green, soft, and flexible.||Top 25 cm green and soft.||Terminal buds not visible.||No|
|Marginal||Top 25 cm light green, soft, and flexible.||Top 2 cm green and soft.||Terminal buds barely visible and green. Lateral buds small and straw-coloured.||Maybe|
|Hardened||Top 2 cm blue-green and stiff.||Top 2 cm straw-coloured and firm.||Terminal buds straw-coloured and firm.||Yes|
|Reflush||Terminal bud scales separating.||No|
|Soft||Top 510 cm light green, soft, and flexible.||Top 25 cm light green, soft, and flexible.||Terminal buds not noticeable.||No|
|Marginal||Top 25 cm light green, soft, and flexible.||Top 2 cm reddish green and soft.||Terminal buds barely visible and reddish green. Lateral buds small and straw-coloured.||Maybe|
|Hardened||Less than 2 cm dark green and stiff.||Top 2 cm brown and firm.||Terminal buds obvious, red-brown, and firm.||Yes|
|Reflush||Terminal bud scales straw-coloured, papery, and separating.||No|
Plate 7. Ba container-grown seedling that has reflushed in the nursery. Note that new foliage is lighter green than older foliage. Stock that has reflushed in the nursery may be too succulent to be shipped.
If in doubt about succulence, take a
If succulent stock is received in the field, suspend further shipments of the same seedlot. If the nursery or nursery service specialist does not want to release the stock because they consider it to be too succulent, believe them -- it is their job and reputation!
Double-sorting succulent stock (i.e., lifting only the hardy seedlings) is not recommended. Double-sorting a crop with a high incidence of succulence can damage the seedlings that are not lifted and is also a very expensive nursery operation. It is better to wait until the stock has hardened than to double-sort.
Root dieback can occur in any container size, but there is an increased likelihood of its occurrence in small container sizes and 2+0 Sp container stock types.
Root dieback, due to Cylindrocarpon, Pythium, Fusarium, and Phytophthora, has been found in all nursery-grown crops (Plate 8). Root disease occurrence can be stock type dependent and, therefore, it must be considered when selecting among stock types. For any one stock type, the likelihood of a root disease can differ among species and nurseries. Root diseases are most prevalent in vigorously growing container species (e.g., Fdc, Fdi, Ss, Pli, Hw) due to their larger root systems impeding plug drainage. They are found more commonly in 2+0 container stock types and small containers compared to larger 1+0 stock types because of the large relative size of the root systems in relation to the container size and the length of time grown in the nursery. Root dieback should not be confused with mycorrhizae (see mycorrhizal fungi on nursery stock).
Root dieback can be carried into the field. It can persist on stock and cause delayed mortality and poor growth. Due to the potential for mortality and the difficulty in detecting the condition, a conservative strategy should be to reject stock that has been found to display root dieback symptoms -- the seedlings with the symptoms will be the most severely affected, but seedlings apparently without symptoms can also display reduced vigour.
Plate 8. Root dieback in Fdc PSB 313B 1+0. Notice the difference between the infested (on right) and healthy stock. The root tips of the root dieback stock are short, stubby, dark brown/black, and dead, while the unaffected stock has slender white root tips. Also note the poor cohesion of the tip of the infested plug. Photo credit: Rob Scagel.
Larch needle cast or Meria can severely affect the viability and outplant performance of Lw seedlings. Stock types with higher densities (e.g., PSB 313B) are generally more susceptible as the disease is enhanced by high humidity and reduced air movement. Field survival and performance has been shown to be significantly reduced with as little as one-third Meria-induced defoliation (Plate 9).
Plate 9. Meria needle cast on container Lw PSB 415A. Note the considerable number of needles that have been shed as a result of the disease. Photo credit: Dave Trotter.
Keithia foliage blight is frequent and most debilitating on Cw PSB 2+0 Sp (Plate 10). If large Cw stock types are required to deal with site factors such as brush or browse, consideration should be given to using large 1+0 stock types rather than 2+0 stock types. Like the storage moulds, the disease may reduce the vigour or kill seedlings if it infects the stem.
Plate 10. Cw foliage infested with Keithia. This is an example of severe Keithia foliage infestation. There are some lesions on the stem. This seedling would not be expected to survive. Photo credit: Gwen Shrimpton.
Storage moulds (Botrytis, Septonema, etc.) can be found on all species. They are particularly common in stock types with high densities (PSB 211A, PSB 313A), in 2+0 container crops, and on species with large, succulent, foliage biomass (Hw, Pli, Sx, Fdc). Damage from these diseases is frequently restricted to the foliage but when the disease infects the stem it may reduce the vigour or kill the seedling (Plate 11). If your stock is known to have a mould infection the following considerations will help to minimize the impact on outplant potential:
Plate 11. Severe storage mould (Botrytis) infestation on a bundle of Pli PSB 313B 1+0. The infestation has spread from the foliage to the stem. In such cases, the seedling would not be expected to survive. Storage mould does not occur on the roots (see Plate 17 for mycorrhizae). Photo credit: Dave Trotter.
Most insects problems are dealt with in the nursery but occasionally these can carry over into the field. Cutworms, marsh crane fly, and weevil larvae can build-up to significant numbers in a nursery due to high seedling densities, accelerated growth, and a favourable environment (Plates 12, 13, and 14). They may go undetected in the seedling plugs, surviving freezer storage and then appearing after the stock has thawed. Every effort should be made to contain the spread of these insects to the field and the source nursery advised of the situation.
Plate 12. Cutworm infestation found in a box of thawed 2+0 spruce seedlings. Photo credit: Dave Trotter.
Plate 13. Larvae of the European marsh crane fly on damaged 2+0 Douglas-fir. Photo credit: Jack Sutherland.
Plate 14. Larva of the black vine weevil feeding on the roots of a 1+0 container Douglas-fir seedling. Photo credit: Dave Trotter.
One insect that may present difficulties to reforestation specialists concerned with the regeneration of Abies species is the balsam woolly adelgid or BWA (Adelges piceae) (Plate 15). In particular, Abies lasiocarpa is extremely vulnerable to attack resulting in severe canopy injury and mortality. The other Abies spp show comparatively less susceptibility to damage by BWA. Currently, a provincial quarantine zone is maintained to prevent the spread of the insect by human means. The regulations demand that all B.C. nurseries apply for a permit to grow any Abies spp. and any nursery in the zone is not permitted to ship seedlings outside the zone. The regulations are under review and the status of Abies production in B.C. may change in the near future.
Plate 15. Amabilis fir showing balsam wooly adelgid damage. Note stunted needles and galled buds. Photo credit: Dave Trotter.
Mycorrhizal fungi on nursery stock
All conifers have evolved a dependence on certain beneficial fungi that form symbiotic "fungus roots" or mycorrhizae (Plate 16). The most commonly observed mycorrhizal association are ectomycorrhizae. They are easily recognized by the envelopment of the seedling roots by a characteristic fungal sheath and the mycelium or thread-like mould growth over the plug. The result is the proliferation of the distinct swollen, forked appearance of the smallest feeder roots. These mycorrhizae can be brown, white, yellow, or black, depending on the colour of the fungus colonizing the root. These fungi are highly beneficial to their hosts by enhancing water and nutrient uptake. In contrast to pathogenic fungi, the development of mycorrhizal fungi is distinguished by their occurrence on seedling roots without the accompanying symptoms of decay. In general, nursery managers strive to develop mycorrhizae but their development can vary greatly depending on seedling species, nursery location, spore inoculum, fertilizer, irrigation, and media regimes (Plate 17).
Plate 16. Close-up of ectomycorrhizae on a 1+0 spruce seedling.
Plate 17. Two Sx 412A PSB 1+0 seedling root systems from the same container showing differences in the degree of mycorrhizal association.
Multiple tops, or aborted terminal buds, are commonly encountered on the true firs as illustrated for subalpine fir in Plate 18. Similar morphology may occur periodically in Sx and Fdc/Fdi, particularly when the stock has partially reflushed following blackout. Abnormal morphology can also be caused by frost or Lygus bug damage. Unless these abnormalities are severe or due to nutritional deficiencies, the conditions do not persistin the plantation and should not be a cause for concern.
Plate 18. Morphology of Bl PSB 410 1+0. From left to right: "typical" conifer morphology, complete reflush, multiple top, and aborted apical bud with a subtending lateral assuming apical dominance.
As with most agricultural crops, the production of conifer seedlings for reforestation sometimes requires the responsible use of pesticides. In general, industry policy is to use pesticides only after other non-chemical methods of control have been ineffective. When pesticides are necessary, residues on the stock can be a concern to those handling the seedlings. Over the years, in consultation with reforestation specialists, tree planting companies and regulatory agencies, pesticide reporting guidelines have been developed to ensure forest worker safety. These include; the marking of seedling boxes with the last pesticide application date and chemical used; a list of all pesticides applied to the seedlings during the growing season; distribution of supporting documents (e.g., MSDS, pesticide labels) to district and industry staff; and worker safety procedures. If no pesticides have been applied to the seedlings over a 12-month period then the seedling boxes may be labeled "pesticide-free."
Without adequate interim storage, the quality and vigour of any stock type can be quickly compromised. Larger stock types require more space for interim storage than small stock types. Spring-shipped container stock types are the least sensitive to rapid deterioration of stock quality related to storage length and condition. The speed with which stock can be planted may be the deciding factor in stock type selection if reliable interim storage cannot be assured. Such a situation favours the smaller, more easily stored and transported, and more plantable stock types.
Prolonged storage depletes
Summer shipment of seedlings is nearly twice as expensive as spring shipment because it involves more handling concerns, and includes fewer seedlings per shipment. If a summer shipment is selected, arrangements should be made early to ensure that overnight refrigerated transportation will be available. The crop should be cooled before packaging (10 to 15° C) to minimize heat buildup in the cartons. Refrigerated transportation of seedlings to remote sites can also be difficult to ensure.
If refrigerated transportation cannot be assured, the planting program may have to be run as a hot-plant operation with only small amounts of seedlings being lifted and shipped at a time. The cost of small shipments can be high. Arrangements should be made to have crops lifted and shipped throughout the planting program -- even through the weekends. No prolonged storage under ambient conditions is recommended for summer-shipped stock. Storage up to one week is tolerable if the boxes are opened and well-ventilated, and if shaded storage such as under a heavy tree canopy can be provided. Seedlings must be misted and/or watered while in this interim storage.
Planter availability and experience
Some late summer and fall planting projects may not be possible because of a shortage of planters. Because of the labour supply situation at this time of the year, you may have to pay a premium price for planting. Summer-planting programs can also be jeopardized because the planting contractor may be on a tight schedule to move on and may not stay if the seedlings are not available on time or if site conditions are not appropriate.
Availability of planters with experience planting BBR/PBR can be a major limitation to the use of these stock types. BBR/PBR stock types require special planting and handling practices. To plant BBR/PBR, planters need to be familiar with the care and interim storage of these stock types. Most planter experience is with container stock types. Availability of experienced planters is a necessary precondition to ordering either BBR or PBR stock types. If experienced planters are not available, anticipate the need for training and closer supervision.
Physiological Test for Seedlings
To determine the physiological state of seedlings, use one of the following physiological tests.
Root growth capacity
The prime test is the root growth capacity test. A sample of the seedlings is placed in an ideal growing environment for seven days before the new root growth is evaluated. If the new root development is very low, stock is re-tested. If it remains low in the second test, advice is given to plant seedlings at a higher density, anticipating some mortality, or it may be recommended that the seedlings be discarded.
Note: For ministry seedlings, this test is performed on all spring-planted stock and results are available from nursery services.
This test is not available for the summer/fall programs as the seedlings are still in active root growth.
A second test of the vigour of seedlings is a flushing test. This is usually a 14-day test in a growth chamber for cold-stored, spring-plant stock only. It is used to determine the nature and vigour of the stock's new growth flush. This test is useful if there is concern whether buds are matured sufficiently or to determine the effects of handling stress prior to planting.
To determine the vigour of stock after storage or during summer planting programs, samples are taken and outplanted at a controlled nursery environment. This test is designed to provide information to the field staff on the health of their stock prior to planting (spring planting only) and to provide a check for field staff if plantation failures occur (spring and summer planting programs). Contact nursery services for more information.
Pre-storage storability test
This test can have a major positive impact on the success of long-term overwinter storage because it determines the state of dormancy and frost hardiness of a seedling in relation to fall lift and the placement of seedlings into storage. It is recommended that representatives of all seedlings by species, elevation, and latitude be passed through this test and that lifting and storage only occur once the seedlings pass the storability criteria of the test.
During the growth phase of seedlings, few tests have been developed to determine seedling health. One method that has recently become available is a variable fluorescence determination. If it is suspected that seedlings have been damaged or appear in poor condition, this test can provide data on the vigour of the photosynthetic system of the plant. Nursery services and others can provide this test as the need arises.