Here are some recommendations for shade tree, woodlot and plantation
owners who want to keep their trees healthy during May and June by controlling
pests and other unfavorable conditions/ events.
|Pest or Condition||Trees||Recommendations
|Winter desiccation||All||Prune only those branches whose buds are dead. Previous
years' needles may be brown, but their buds may survive and grow. Always
cut outside the branch collar when pruning main branches.
|Branch breakage||All||Prune broken branches back to a main fork or the trunk.
If breakage is near the trunk, prune outside the branch collar.
|Pine bark beetles||Pines||Prune and destroy infested branches, or remove and destroy
the entire tree before the new generation of beetles emerges.
|Birch and elm leaf miners||Birches and elms||Spray foliage when mines first appear as yellow or white
leaf discolorations. Use acephate or other labeled insecticides.
|Sawflies||All||Hand pick and destroy larvae or spray these leaf and
needle-feeding pests when larvae are observed.
|Bronze birch borer||Birches||Prune dead branches. Remove and destroy seriously declining
trees before the next growing season.
|Cankerworms||Many hard-woods||Spray these leaf feeders when observed with labeled insecticides.
Bt is preferred.
|Spruce gall adelgids||Spruces||As buds swell spray with acephate, dimethoate or diazinon.
|Leaf-feeding caterpillars, lacebugs, leaf beetles, aphids,
and externally-feeding weevils||All||Spray with a labeled insecticide when damage is unacceptable.
Bt is preferred for caterpillar control.
|Scales||All||Spray with acephate or other labeled insecticides when
crawler stage is observed. Repeat as directed.
|Mite galls||Maple, elm, ash and more.||Spray dicofol (Kelthane) or other labeled insecticides
at budbreak and 7-l0 days later.
|Shoot boring weevils||Pines||Prune and destroy infested shoots and leaders before
|Root collar weevils||Pines||Remove duff around base of tree out about 1 foot and
prune lowest branches at least l foot up from ground. As a last resort,
drench root collars with acephate, diazinon or other labeled insecticides.
|White pine blister rust||White pine||Prune branches with dead needles or blistered bark.
Prune all branches up to 9 feet on stem in southern MN
and up to 17 feet in northern MN.
|Fireblight||Apples, crab-apples, pears, mountain ash||Remove infected branches 4-6 inches below visible infection.
Apply copper compounds when buds are showing 1/4 inch green tissue. During
bloom spray streptomycin at 3 to 4 day intervals to inhibit bacterial growth
and reduce blossom infection. Disinfect pruning tools with diluted bleach
after each cut.
|Anthracnose and other leafspot fungi||Hard-woods||Rake and dispose of/or burn fallen leaves and twigs.
Prune to increase air flow and leaf drying. At budbreak apply chlorothalonil,
mancozeb, Bordeaux mixture, benomyl, dimethyl phenylenebis or other labeled
|Dutch elm disease||Elms||Confirm disease by sending 6-8 inch sections from freshly-wilted
branches to Lab Services Div., Dept. of Ag., 90 West Plate Blvd., St. Paul,
MN 55107-2094. Remove and destroy infected branches or entire tree.
|Oak wilt disease||Oaks||Confirm as directed for Dutch elm disease. Install root
graft barrier first and then the remove entire tree.
|Needlecast diseases||Conifers||Apply chlorothalonil or other labeled fungicide for the
particular disease and host in order to protect young needles.
|Pine needle rust||Red pine||Eradicate goldenrod and aster in area as they are alternate
hosts for this disease.