April 12, 2018

Gypsy Moth Caterpillars -Scout for them now

We often don’t think of gypsy moths as damaging conifers but it can be a big problem!  Left unchecked young trees can be killed in a single season.


Spruce trees killed by gypsy moth defoliation in the 2017 growing season – Upstate NY.

Scouting for egg masses in nurseries and Christmas tree plantings is important from autumn to early spring before the eggs hatch into tiny caterpillars.     It’s not too late! Stick your head in the trees and look at the trunks to see if there any tan-white egg masses.

Gypsy moth egg mass on trunk.

Egg mass removed from tree.

Egg mass broken up to reveal individual eggs.


Recently hatched caterpillars on the egg mass.

Normally the caterpillars begin to hatch outdoors sometime in early May.

Young caterpillars on the move!  These hatched  from an egg mass that was left in the lab for several days at room temperature.

Close up of a  juvenile gypsy moth caterpillar.

The young caterpillars are the most susceptible and easiest to control compared to caterpillars that have grown larger.
For more information see the Cornell Insect Diagnostic Laboratory factsheet on gypsy moths.

July 8, 2014

Tree Diversity Minimizes Pest Problems

A diverse Christmas tree planting.

A diverse Christmas tree planting in Upstate New York.

A large planting of a single species is easier to manage and harvest but can be a windfall for pests. Monocultures allow insects and disease to expand rapidly as the pest can move unimpeded from one plant to another. After the devastation that occurred in community forests with streets lined exclusively with American Chestnuts (Chestnut Blight) and American Elms (Dutch Elm Disease), planting a diversified mixture of trees is now the standard practice among municipalities.

Dead Fraser fir with healthy Canaan Fir foreground and turkish fir behind. side.

Dead Fraser fir with healthy Canaan Fir foreground and Turkish fir behind.

Many nursery and Christmas tree growers also know the advantages of growing a variety of species.   They’ll choose tree species to fit their different environments on their farm.  Then just like the smart investor who has diverse portfolio to minimize risks in the future, diverse plantings can prevent pests from moving in and wiping out all the trees.  Even landscape designers when working with customers who envision a planting of a single species will often try to specify a mixture of similar species to increase resilience.

There's increased interest in Turkish firs such as this example of Abies bornmuelleriana because of it's root rot resistance.

There’s increased interest in Turkish firs such as this example of Abies bornmuelleriana because of it’s root rot resistance.

Having a diverse planting works because most insects and diseases have preferences for the host species they feed upon.  Many simply cannot live on a different genus, for example it is rare to find an insect or disease that lives on both fir and spruce trees.  In addition certain sites on a farm or landscape may be more conducive to one species over another.   For example if  a species is mis-matched on a site with soil conditions it cannot tolerate, then the whole planting may succumb to a root rot.

Growers taking notes on new tree species they may want to add to their plantings at Cornell Plantations.

Growers taking notes on new tree species they may want to add to their plantings while at Cornell Plantations.

Cornell Plantations is one place where you can experience and compare a wide variety of deciduous trees and conifers.   Although their plantings extend over several acres on campus, a concentration of conifers can be found at the Kienzle Overlook. http://www.cornellplantations.org/our-gardens/botanical/kienzle-overlook .  At this website you can find a list of the 80 + conifers species that are in that planting.

Phil Syphrit

Phil Syphrit

Phil Syphrit pms26@cornell.edu is the curator of this collection and can help answer questions on some of these unusual conifers if you are interested in adding them to your plantings.

June 12, 2014

Pine Sawflies

Notice needle damage on pine trees?  Look close.  It may be caused by conifer-feeding sawflies.

Sawflies feeding on Scotch pine

Sawflies feeding on Scotch pine

Sawflies? As larvae they look caterpillars which might develop into moths, their name implies they’ll be flies, but they actually become non-stinging wasps as adults. And the saw? As adult wasps the females cut slits in pine needles with saw-like structures on the tip of their abdomens and lay eggs into these openings.

Checkout the synchronized movement they make to deter predators!

Although there are several species of sawflies that can be seen on conifers the gray-green European Pine Sawfly (Neodiprion sertifer) is represented in this post. 

European pine sawfly group

European pine sawfly group

Sawfly Management

  • Monitor to detect infestations before they reach a size that can cause significant needle loss.
  • Know that sawfly larvae are attractive as food to parasites and predators and are usually kept in check by these natural enemies.
  • If a small outbreak occurs they can often be handpicked, or pruned out and destroyed.
  • For rare situations where the population of sawflies are high insecticides labeled for their control can be used.
individual pine sawfly

Pine sawfly larvae

July 8, 2013

White Pine Weevil

Dieback due to white pine weevil larva feeding.

Noticing a wilted leader on pines or spruces?  White pine weevil is likely the culprit. Although it’s almost officially summer when the symptoms are first noticed it all started back in the early spring when, on a warm day in March- April, the female weevil lays her tiny eggs a few inches below the terminal bud. Those eggs soon hatch and the young larvae start to consume the stem’s vascular tissue.    With the loss of this vascular pipework the tree’s terminal leader wilts and brown dieback soon becomes visible.

With the bark peeled back, a white pine weevil larva is visible inside spruce leader.

In late July and August adult weevils emerge through small holes they carved at the base of the dead terminal.  After the adult weevils emerge they enter leaf liter and are not seen until March of the following year.  If you prune out and destroy the affected leaders before the holes appear and the adults emerge (Late June to mid-July for most of New York) you can reduce numbers of adults that will lay next year’s eggs.

Exit holes of at base of area damaged by White Pine Weevils. Prune and destroy before these are visible.

A blue spruce disfigured due to a missing leader caused by White Pine Weevil damage.

White pine weevil is one of the earliest pests we treat for in the spring.  Knowing when to treat can be tricky.  Using growing degree days in the spring can be helpful to prevent damage.  

See the Insect Section of Pest Management Guide for Commercial Production and Maintenance of Trees and Shrubs for growing degree day target window for treatment  and other control information.