Friday, April 26, 2013

Proud Papa - Twice in One Month!

As I revel (quite sleepily) in the fact that I have a new little daughter, I am also very happy that my other babies from a clinic sample have been "born". Since I started this position I have been watching a trunk section of arborvitae (Thuja sp.; 'Green Giant' variety) that was submitted from Holly Springs (Wake Co.) following the decline and death of some trees.

Affected arborvitae (Thuja sp.) along the road.

When I first saw the section I observed a few large holes - about 1/4 inch in diameter - in the top with sawdust being pushed from them. This was clearly a boring insect, but was it a metallic wood borer (Buprestidae), longhorn beetle (Cerambycidae), or something else? Turns out, after prying some of the bark back, there were several large (up to 3/4 inch), legless larvae boring just under the surface. The larvae were very clearly weevils (Curculionidae), but what species?

Weevil larvae preserved for future study.

Because larval weevils are nearly impossible to identify, it was my goal to rear the larvae until they emerged as adults so I could then identify them. I waited...and waited...and waited. Some beetles (under the right conditions) can exist as larvae in wood for decades and even up to 50 (!) years - I wasn't going to wait that long. Fortunately, after removing a little more bark some weeks later I found pupae. Finally, adults in progress! A week or so later and I had adults which I identified as the cypress weevil (Eudociminus mannerheimii (Boheman)).

Cypress weevil (Eudociminus mannerheimii) showing life stages and damage.

This fairly large weevil (10-17 mm) is known from a few hosts, especially baldcypress (Taxodium distichum), but also Japanese cedar (Cryptomeria japonica), Leyland cypress (Cupressocyparis leylandii), and arborvitae (Thuja sp.). It's biology appears to be similar to the related pine regeneration weevils, Hylobius pales (Herbst) and Pachylobius picivorus (Germar). The beetles lay eggs on weakened or dying trees and the larvae burrow beneath the bark before creating a deeper hole to pupate in. Adults appear to emerge in the Spring and will feed on the bark of small, green branches. Because they generally attack already-declining trees they are not always the main issue. However, this sample had so many weevils in one small section that I believe they were a major factor causing health issues for the trees. Follow the links below to read more about this weevil and learn about management practices. In the mean time I am going to smoke my proverbial cigar and curate these specimens to go into the NCSU Insect Museum which only had four total specimens!

NCSU Entomology Insect Note on Eudociminus mannerheimii
UF Featured Creatures on Eudociminus mannerheimii

Monday, April 15, 2013

Be on the Lookout for Cedar Apple Rust

Most of us who live in the triangle are hoping for rains to wash away the yellow film of pollen coating our cars, houses, and sidewalks. Spring rains also jump start the most bizarre life-stage of cedar apple rust, a common disease that affects apple trees (and crab apples) and eastern red cedar trees.
Galls on cedar (Photo: H.D. Shew)
The cedar apple rust pathogen (Gymnosporangium juniperi-virginianae) requires two hosts and four spore stages to complete its complex life cycle. On cedar trees, the most obvious signs of infection are firm brown galls, which are about the size of a golf ball and are usually found scattered on the tree’s branches and twigs. After a heavy rain, the galls produce striking bright orange gelatinous horns, which are composed of millions of spores called teliospores. In dry periods, the horns can be seen as short spikes covering the galls. If you find a gall with dried horns, cut it out of the tree, place it in a glass of water and watch over the next few hours as the horns expand.
Gall with dry telial horns (Photo: H.D. Shew)
The cycle of wetting and drying can continue several times during the spring, and in each cycle the teliospores germinate and give rise to another spore type, called basidiospores. These basidiospores are forcibly discharged into the air and are wind-blown to nearby apple trees.

 Apple leaves and fruit are most likely to be infected when they are wet and temperatures range from 46 to 75 F. Yellow to orange spots are produced on the upper surface of the apple leaves one to two weeks after infection. The spots on leaves may be raised or swollen and infected fruit may be slightly distorted. Small black dots within the lesions signal the production of the next spore type, the pycniospores (also called spermatia). One to two months later, fringed cup-shaped structures (aecia) appear on the underside of the apple leaves and these contain aeciospores, yet another spore type.

The aeciospores are windblown to cedar trees in late summer to early fall, where they germinate and infect to produce galls. The galls produce teliospores in the second year after infection, completing the life cycle. G. juniperi-virginianae survives in the gall tissue for only two years. After its second year, the spore producing year, the pathogen dies in the gall tissue. On apples, the pathogen survives only a few months, just long enough to produce the aeciospores that infect cedar trees.
Symptoms on apple (Photo: E.C. Lookabaugh)
Cedar apple rust causes only minor damage to cedar trees from twig dieback. Damage to apple is more significant and can result severe defoliation and fruit blemishes. Since this pathogen requires both hosts to complete its life cycle, control can be achieved by eliminating one host from the surrounding area, although oftentimes eradication is not feasible or desirable. Additional control measures include the use of disease-resistant apple cultivars, properly timed fungicide applications on apple, and removal of cedar galls before spring rains.

Check out this cool video of telial horns expanding (Video: Arlene Mendoza-Moran)

Monday, April 8, 2013

More information about the 2013 strawberry virus outbreak

Many of you probably have seen an article in today's Raleigh News and Observer about virus problems in this year's strawberry crop. The Plant Disease and Insect Clinic has received several strawberry samples with virus problems in the past few months.

Here are some comments from Dr. Frank Louws, Extension Specialist for Strawberry Diseases in NCSU's Department of Plant Pathology about the strawberry virus situation:

This link will take you to an excellent article from Dr. Chuck Johnson at Virginia Tech about this year's strawberry virus outbreak. All the information for Virginia is true for NC and other states with this problem. The main question growers ask is: “What can we expect in yields?”. We have only limited experience with these viruses in our annual systems. However, we had a case of Strawberry Mild Yellow Edge Virus (SMYEV) in 2004, as shown below in Sweet Charlie plants photographed at full harvest. About 25 to 30% of the plants were affected by the virus and the virus dramatically affected plant growth and yield, as seen in the picture. This year, two viruses, SMYEV and Strawberry Mottle Virus (SMoV), have been diagnosed from problem fields. We do not know how these viruses will affect crop yields in 2013, but some reductions are expected. Specific recommendations for dealing with this problem can be found in Dr. Johnson’s article. With good management, this problem should not recur in future years.