What Harms Pine Trees?

Insects

• Numerous insects can harm pine trees, but scales and sawflies cause some of the worst damage. Tiny pine needle scales hatch in the spring and quickly settle into feeding spots where they remain for the rest of their lives. Scale feeding activity interrupts the flow of water and nutrients, which results in wilted, curled, yellowed or prematurely fallen needles. Predators such as parasitic wasps, lacewings and mites often control scale populations, but consider treating severe infestations with an application of horticultural oil. Pine sawfly larvae feed in clusters on old pine tree needles, causing tip dieback, wilting, defoliation and stunted plant growth. Insecticidal soaps typically work well on severe sawfly infestations. Prune out damaged needles and branches to help restore vigor and make your pine look more attractive.

Diseases

• Plant diseases occasionally affect pine trees, particularly fungal infections such as blights and root rots. Various root rot pathogens thrive in overly moist soil conditions, attacking the tree's roots and causing yellowing needles and stunted growth. Prevent root rots by planting your pine in a site with good drainage. Tip blight pathogens infect the tips of branches, causing the needles on the affected branch to stop growing, turn brown and eventually die. Severe infections gradually kill affected trees. Prune out blight-infected branches as soon as you notice them. Applying preventative fungicides in the spring can reduce the risk of fungal diseases. Stressed pines are more susceptible to fungal pathogens, so irrigate and feed your tree as needed to keep it vigorous and healthy.

Nematodes

• Pinewood nematodes can harm trees by causing a serious plant disease called pine wilt. These microscopic creatures enter trees through the feeding wounds left by bark beetles. Once the nematodes enter the wood tissue, they multiply rapidly and clog the transfer of water throughout the tree. Early signs of a nematode problem include green needles turning brown or yellow. Unfortunately, an affected pine tree typically dies very quickly once the needles become discolored. Remove and promptly destroy an infected pine to stop the nematodes from spreading to other trees in your landscape.

Environmental Conditions

• Both droughts and floods can harm pine trees growing in your landscape. Drought conditions strip moisture out of plant tissue, which causes older needles to turn yellow and prematurely drop from the pine. The stressed tree then becomes more susceptible to pine bark beetles. Mulching over the root zone can help retain consistent soil moisture during dry spells. Flood waters limit a tree's ability to access oxygen, which often results in yellowing needles, reduced needle size, defoliation and premature leaf drop.