More info for the terms: cover, fire management, natural, shrubs
Chemical control: Blueberries (Vaccinium spp.) exhibit variable
susceptibility to herbicides such as 2,4-D, 2,4,5-T, glyphosate,
karbutilate, and picloram [8]. Various herbicides, including
dichlorprop, picloram, 2,4-D, and glyphosate have been applied to
velvetleaf blueberry to facilitate conifer release [26,72]. Plants are
resistant to Asulam and Terbacil, although Dicamba and 2,4-D may reduce
shoot numbers during the year after treatment. However, rhizomes may be
undamaged by herbicides and often resume growth during the second year
after treatment [90]. The response of velvetleaf blueberry to various
herbicides has been documented [72,90].
Mechanical treatment: In northeastern Minnesota, mechanically clipped
velvetleaf blueberry plants produced flower bud numbers equal to those
on unpruned plants. Plants pruned mechanically, or by fire, exhibited
increases in stem numbers over unpruned controls. The effects of
fertilizer and mulch on pruned plants has been examined in detail.
Application of fertilizer may significantly increase flower bud numbers
on clipped individuals but typically reduces flower bud development on
unpruned plants. Unpruned plants generally exhibit increased stem
growth after fertilizer application, but fertilization has little effect
on mechanically pruned plants [76]. Mulch does not generally increase
flower bud numbers or vegetative growth of pruned plants. Its use
should be avoided on recently pruned velvetleaf blueberry [76].
Environmental considerations: In a number of recent studies, chemically
treated velvetleaf blueberry plants have been found to produce fruit
which exceeds permissible levels of herbicides [26,72]. In a
northeastern Ontario study, 50 percent of fruit tested was found to
exceed FDA safety standards. Much of the affected fruit grew in easily
accessible areas, such as along highway right-of-ways. Possible human
health risks are unknown, but approximately 0.3 percent of all wild
blueberries and red raspberries (Rubus idaeus) in Ontario are treated
annually with herbicides [26].
In many parts of the East, widespread use of insecticides has decimated
populations of wild bees which formerly pollinated blueberry fields. In
some locations, it is now necessary to supplement natural pollinators
with honey bees to ensure adequate fruit set in commercially managed
fields [58].
Velvetleaf blueberry is very sensitive to sulfur dioxide pollution and
may be a useful indicator for monitoring acid rain [90].
Commercial propagation: Numerous cultivation techniques have been
applied to commercially managed blueberry fields [76,98]. These include
applying mulch, fertilizer, or herbicides, and pruning with fire or
mechanical means [see FIRE MANAGEMENT CONSIDERATIONS]. Various
herbicides can be used to control plants such as kalmia (Kalmia
angustifolia) and little bluestem (Schizachyrium scoparium) which
commonly compete with velvetleaf blueberry in commercially managed berry
fields [30,95]. Disease and insects can greatly reduce fruit yields
under certain circumstances. Because clones differ genetically in their
resistance to disease, selective breeding has been used to develop
resistant strains [59]. In commercial blueberry fields containing both
velvetleaf and low sweet blueberry, yields are often lower than in
fields made up of only low sweet blueberry. Cross pollination
apparently results in reduced fruit set [1].
Berry production: Fruit production in velvetleaf blueberry fluctuates
annually according to the genetics of the individual clone, weather
conditions, and insect availability [5,94]. However, fruit production
is often good [16] and nearly all berries contain some viable seed [90].
Pollinators are required for good fruit set [94] and dry, warm weather
during flowering generally results in more active insect pollinators and
better fruit set. Late spring frosts can greatly reduce fruit
production [90]. In Newfoundland, reduced fruit production has been
correlated with heavy June precipitation and in Nova Scotia, warm
temperatures and ample sunlight enhanced fruit yields [31]. Fruit
production of velvetleaf blueberry typically declines as clones age
[75]. Production often peaks 10 to 20 years after fire, just prior to
canopy closure [90].
Damage: Plants may be damaged by cold winter temperatures. Shrubs are
often killed to ground level in the absence of a protective snow cover.
Spring frost damage reportedly occurs at 30 degrees F (-1 degree C) and
may be "complete" at 14 degrees F (-10 degrees C) [90].
Livestock: Ericaceous shrubs such as velvetleaf blueberry tend to
increase in response to heavy livestock grazing [28].
Wildlife considerations: Blueberries are an extremely important food
source for bears. In many areas, bear-human conflicts are most likely
to occur during years of Vaccinium berry crop failure [55,70]. Both
black and grizzly bears typically exploit areas with dense
concentrations of berries. The habitat value of blueberry shrubfields
to grizzly bears can be increased by permanent, or at least seasonal
road closures, by coordinating timber harvest dates to have minimal
impact on habitat use patterns, and by considering the cumulative
effects of habitat modification across a broad area. In general, site
preparation should include minimizing soil compaction, using cooler
broadcast burns rather than hot burns, or by eliminating site
preparation entirely wherever possible. Grizzly use is favored where
hiding cover is retained by treating small, irregular patches instead of
large contiguous areas, and by leaving stringers of timber within larger
cuts [96].
