University of Maryland Extension

October Tree and Shrub Tips

dogwood foliage with powdery mildew<

Powdery mildew on dogwood turns leaves purple. Photo: D. Clement, UME

(More tips from HGIC)

  • The dryness and heat of the summer had an effect on many trees in our area in landscapes and in the wild. Prolonged heat and drought will cause premature fall leaf drop with many tree species, and their leaves may turn brown with no fall coloration.
  • It is generally not necessary to fertilize established trees and shrubs. If you do, wait to fertilize until late October or early November. Early fertilization may produce a flush of late, weak growth that will not harden off properly, predisposing it to winter injury. (PDF HG 23)
  • Mulches should be applied only 2-3 inches deep and kept away from tree trunks. Mature trees do not benefit from being mulched. They should only be mulched to keep lawn mowers and string trimmers away from trunks.
  • Now is a good time to plant trees. However, dogwood, tulip poplar, pin oak, and evergreens should not be dug up and moved (transplanted) in the fall; these species will usually fail to establish a root system in the fall. Be sure to keep all newly planted or transplanted trees and shrubs watered during dry periods this fall. If you plan to plant new trees this fall select slow growing species and avoid fast-growing trees such as Bradford pear, silver maple and Lombardy poplar, which tend to produce weak branches that break or split in storms. If you buy container grown trees be sure to spread the roots out in the planting hole. With balled and burlap stock cut the twine around the ball and cut away the nylon or burlap wrapping. Do not spread the roots of balled and burlapped trees and shrubs. (PDF HG 24)
  • Never carry a tree by its trunk, this can damage the roots. Instead always carry them by their root ball or by the container.
  • Tree and shrub branches should be pruned at this time only if they are dead or damaged. Wait until after all the leaves have dropped for all other corrective and cosmetic pruning. (Watch our Pruning videos)
  • Flower buds are forming or are already formed on spring flowering shrubs. To prevent reducing next year’s bloom, don’t prune spring-flowering shrubs until after they bloom next spring.
  • You may notice older leaves dropping from rhododendrons and other evergreen shrubs. This is normal for this time of year.
  • Poison ivy leaves turn red in the fall. Cut poison ivy plants down to the ground or spray with glyphosate or an herbicide tht contains triclopyr. Another possibility is to cut the vines to the ground and paint the cut surfaces with an herbicide labeled for brush and vine control as soon as the cut is made. Follow the label instructions. Remember, do not handle the hairy poison ivy vines wrapped around trees. Always wear protective clothing and gloves, and note that even once the vines are dead, the irritant oil in roots and vines can still produce a rash. It actually is not necessary to remove the vines from the tree trunk. (PDF HG 34)

Insects

  • By now, bagworm larvae have pupated inside the bags. Remove and dispose of bags hanging from trees and shrubs. There is no spray that is effective now. Early-June through early-July is the ideal time to control larvae with the organic insecticide Bacillus thuringensis or Bt (PDF HG 32) The timing will be determined by the weather.  If we have a warm spring, look for small bagworms feeding on evergreens in May and then treat with Bt.
  • Spruce spider mites are active on evergreen trees in the fall. Monitor for this pest by tapping branches while holding a piece of white paper underneath. Look for moving specks. They can be controlled with ultra-fine horticultural oil. Do not spray on blue spruce. Oil removes the wax that makes blue spruce blue. Also do not spray oil if the temperature will drop below freezing in the next 24 hours.
  • The hemlock woolly adelgid is active on hemlocks. A similar pest is present on larch trees. Adelgids are aphid-like sucking pests that appear as small, white, waxy, cottony-looking masses. Heavy infestations can debilitate trees, particularly when they are stressed. Ultra-fine horticultural oil is a safe and effective insecticide to use but should not be applied when temperatures are below 40º F. Do not apply if humidity is high. Thorough coverage of the foliage is essential to achieving good control. A dormant oil spray in February or March will also help to kill over-wintering adults. A drench of imidacloprid around the base of the tree is very effective. Follow label directions for rates and timing – this will give several years of control.

Disease

  • Even though it is fall, black spot on roses continues to be a problem. Continue to apply a labeled fungicide through the fall until all the leaves have dropped. Clean up all fallen leaves.
  • Powdery mildew is a common late summer and early fall leaf disease of dogwood, lilac and other landscape plants. Affected leaves turn white and droop. No fungicide sprays will be effective now. However, next year you can apply a labeled fungicide, or use a horticultural oil labeled for powdery mildew control and follow the label for application intervals. Try to select resistant cultivars when planting new landscape plants.
  • In the cooler sometimes wetter weather of October harmless toadstools and other mushrooms may be plentiful in turf around tree root systems. However, destructive wood rotting organisms produce conks, which resemble fleshy, shelf-like structures, on tree trunks and roots. Affected trees may be suffering from extensive wood decay and should be inspected for trunk soundness by a licensed arborist.
Maintained by the IET Department of the College of Agriculture and Natural Resources. © 2017. Web Accessibility