Program Summary
NEEDED RESEARCH AND DEVELOPMENT TO IMPROVE DWARF MISTLETOE CONTROLS' J. R. Parmeter, Jr., F. G. Hawksworth, and R. F. scharpfL Abstract: The speakers at this symposium have sum- marized the latest information on and experience with dwarf mistletoe control through forest management. This information, developed over many years by researchers and managers, provides a firm foundation for the control strategies we have discussed these past three days. The questions raised by speakers and participants indicate that the latest word should not be the last, however. Additional information is needed to refine present ap- proaches to control and to explore new control possibil- ities. The following is a brief outline of re- search and development needs as they were highlighted by speakers and participants. The list is not exhaustive, nor does it provide specific details. We hope that it does indi- cate the scope and magnitude of the job ahead. In the general area of dwarf mistletoe biology, some important information is lacking or incomplete. Broad aspects of host special- ization have been established for most species, but needed details, especially for A. tsugense
and A. occidentale/A. campylopodum, are yet
unclear. The range and significance of "cross- over" possibilities and their relationship to stand conditions need clarification and eval- uation. The basis for the "exclusion princi- ple" (if the principal parasite of a certain host is present in an area, other dwarf mis- tletoes rarely parasitize that tree) needs investigation, since it may have important implications in the management of mixed stands. Information on interactions among dwarf mistletoes and other forest pests is sketchy. Preliminary evidence indicates that mistletoes -'presented
at the Symposium on Dwarf Mistle- toe Control Through Forest Management, Berkeley, California, April 11-13, 1978. Ñ'~espectively Professor of Plant Pathology, Univ. of Calif., Berkeley; Forest Pathologist, Rocky Mountain Forest and Range Experiment Sta- tion, Fort Collins, Colo.; and Forest Patholo- gist, Pacific Southwest Forest and Range Exper- iment Station, Berkeley, Calif. predispose trees to bark beetles and perhaps to root diseases, but the influence of dwarf mistletoes on bark beetle dynamics, root dis- eases, or other pests needs confirmation and evaluation. Animals or birds may provide for non-ballistic spread of mistletoe seeds into uninfested areas. The frequency, range, and implications of such spread need evaluation. The incidence, behavior, and impact of dwarf mistletoes vary with differences in ge- ography, topography, habitat type, and envi- ronment in ways that are poorly understood. Determination of the bases for these varia- tions may permit recognition of presently un- recognized factors or stand features that limit dwarf mistletoes or their impact. Most general relationships between forest stand dynamics and dwarf mistletoe damage are well established. Quantitative differences in these relationships among the many host/mistle- toe combinations, stand types, and geographic areas are needed to establish accurate rate functions for predictive models and to provide data for sound management decisions. Among these functions, the quantification of : (1)
vertical spread rates in relation to host growth and crown closure rates, (2) "ladder-
ing" or "cross-walking" rates in relation to stand density, and (3) spread, increase, and damage rates in relation to stand manipula- tions deserve special emphasis. Questions regarding effects of dwarf mis- tletoes on wood quality needs answers in order to develop accurate impact assessments, espe- cially where stem infections are involved. The 6 (or 7) class rating system provides a good standard to quantify dwarf mistletoe in- tensity, but further data on the relationship of intensity to damage with different host/ mistletoe combinations under different stand conditions and management strategies are need- ed. Additionally, the standard intensity rating system may need modification for small trees. A pressing need frequently mentioned is that for models to provide accurate stand growth prediction, impact assessment, and cost/benefit analysis. The development of such models for different forest types, re- gions, and mistletoes species should receive high priority. Along with research directed to specific problems and needed refinements, effort should also be directed to exploratory or basic re- search that might lead to the development of new approaches to control. Resistance to dwarf mistletoes has been demonstrated, and possibilities for the development of resistant selections or the elaboration of resistance mechanisms should be explored. While native insects and diseases have not shown promise as biological controls, the search for effec- tive exotic parasites of mistletoes should be continued. Satisfactory chemical controls have not been discovered, but some level of testing should continue. Either chemical or biological controls could provide valuable ad- juncts to silvicultural controls. At present, fire has proved useful mainly in clearing areas of infected residual trees following logging. Fire may also be useful in eliminating brooms or infected branches from the lower crowns of small trees, but re- search is needed to evaluate such uses. As the maintenance of trees in parks, high-use recreational areas, and forest home sites becomes increasingly important, the de- velopment of special control methods (broom pruning, shoot removal, etc.) for different host/mistletoe combinations becomes increas- ingly important and deserving of special re- search effort. We have come a long way down some impor- tant roads to dwarf mistletoe control. One job ahead is to straighten and widen these roads so that they take us most directly and efficiently to our goals. Other roads have scarcely been explored or have proved too difficult to use at present. These should be investigated, and where they show promise, de- velopmental work should begin. Both refine- ment and exploration require our attention and support.