Wednesday, June 12, 2013

Blame it on the rain (Part II): Reprise of the slime molds

An aerial view of a grove of strange trees? Read on.
With all this wet weather we can expect to see a lot of plant diseases in the upcoming weeks. Oddly enough, damage due to root rots won't be evident on trees and shrubs until the weather turns hot and dry. That's when the damaged root systems won't be able to keep up with the demand for water in the foliage. All this is a story for another day, however. Today I want to revisit a group that was a blog topic two years ago: the slime molds. (See our archived post.) These are sometimes called myxomycetes, but don't let the Greek suffix fool you; they are not related to true fungi.

Stemonitis sp. (Photo: Matt Bertone)
We had several inquiries about slime molds during the last week of May. Fortunately they do no harm to plants, animals, or people, though some folks have been shown to be allergic to the spores. One inquiry was accompanied by a spectacular photo - not reproduced here - of Diachea leucopodia on grass blades. Another was the specimen of Stemonitis - probably Stemonitis fusca - pictured at right. It had been picked up off of a living room baseboard. This particular slime mold is usually associated with wood, sometimes indoors. The photo at the top of this blog was taken on a stump in Schenck Forest in Raleigh several years ago. In both pictures you can clearly see the thin "stipe" or stalk that supports each cylindrical spore-bearing "sporangium".

Remnants of slime mold fruiting on Japanese holly
A third specimen from that same week was submitted by one of our campus landscapers. She was concerned about white material on the foliage of a Japanese holly. This turned out to be another slime mold. Most of the sporangia had broken off, but a the base (called the hypothallus) was still stuck to the leaves. This particular case is covered in the "Geeks Corner" below.

Then yesterday while out looking for leaf spots on maples, I noticed some whitish gray tufts in a mulched bed in the shade of several trees. It turned out to be yet another slime mold, Acyria cinerea. The tiny sporangia are only about a millimeter-and-a-half tall, not counting the stipe. If you look closely, you can see that they are often in clusters.Within these sporangia, the white spores are held by a network of spiny threads called a capillitium. The characteristics of the capillitium are important in slime mold identification.
Capillitium and spores of Acyria cinerea at 400x.
Fruiting of Acyria cinerea on mulch
What we are seeing in all these cases is the end-game of the slime mold's life cycle. If the wind-dispersed spores land and find the right conditions they'll germinate into ameoba-like cells that will eventually become a multicellular, macroscopic, living film called a plasmodium. This plasmodium will slowly "crawl" or ooze around on wood or bark, in leaf litter, on dung, or on other materials. They almost always escape notice at this stage, during which they "feed" by engulfing bacteria, fungal spores, and probably  bits organic matter. Eventually the plasmodium switches gears and changes over to spore production, treating us to one of nature's great works of art. The Georgia Museum of Natural History has posted a gallery of myxomycete images by photographer Ray Simons.

Fruiting of Fuligo septica
Not every member of this group is quite as lovely. Fuligo septica, the "dog-vomit" slime mold, is gross in both the German sense of "large" and the English sense of "repulsive". It is very common on hardwood mulch and was highlighted in our June 14, 2011 blog. When the plasmodium first comes to the top of the mulch and before becoming a crust-covered mass of spores, it's basically a bright yellow froth. A picture of a more mature fruiting is shown at left. Up close, they don't look so bad, actually.

Sporangia of what is probably Physarum leucopus.
The width of this photograph covers only a quarter inch.
Geeks Corner. The slime mold pictured at right baffled me for a while. As a non-expert in this group, I was having trouble deciding whether there was lime in the capillitium or not. There are clearly lime deposits on the peridium (outer covering), giving it a frostly look. Using Martin & Alexopoulos's 1969 tome The Myxomycetes, I eventually keyed it out to Physarum leucopus. The reference states, "Before the peridium breaks, this species is remarkably similar in appearance to Didymium squamulosum." The key distinctions: white nodes in the capillitium, the lack of a columella, and the fact that the lime on the peridium exists as granules rather than crystals.

For anyone interested in learning more, I highly recommend starting with Stephenson & Stempen's book Myxomycetes: A Handbook of Slime Molds (1994. Timber Press).

Blame it on the rain (Part I): A multitude of millipedes

In the last couple weeks we have gotten a lot of rain. This can have both positive and negative impacts on pests and pathogens. One critter I have been getting a lot of calls and emails about is the greenhouse millipede, Oxidus gracilis (Polydesmida: Paradoxosomatidae).

The greenhouse millipede (Oxidus gracilis) is one of the most common arthropods around. It can be distinguished from other millipedes by the size (~1"), brown color, and especially by the groove going across the top of each body segment
Photo by Matt Bertone
Millipedes are in a group of organisms, closely related to insects and spiders, called myriapods (which translates literally to "many-legs"). At first they may appear to be worms, but they have legs which worms lack. The most familiar are centipedes and millipedes, some of which grow to large sizes (some tropical centipedes are a foot long and can eat bats, lizards and rodents!!). While centipedes are carnivorous and have venom, millipedes are vegetarians that feed on decaying plant matter. Though they cannot bite, many millipedes defend themselves with toxic poisons that either taste bad or can cause sickness - but only when eaten. This is the reason why some millipedes you see are brightly colored and smell like almonds (related to the cyanide compounds they produce):

A larger relative of the greenhouse millipede (Polydesmida: Xystodesmidae) [~1.5" long]
Photo by Matt Bertone
The greenhouse millipede is a non-native species from Asia that has traveled throughout the world with humans. They are abundant under rocks and logs, in basements and in the soil - anywhere where there is some moisture. People tend to notice them sporadically until some event drives them out of hiding. In the case recently, our heavy rains from multiple storms have saturated the soil and make it difficult to survive for the millipedes. Their response is usually to move to higher ground like the foundations and walls of homes and other structures. They may even move inside, though if they get stuck it's bad news for them as they will inevitably die, and bad news for homeowners who have to clean up the carcasses and deal with a distinct odor they produce. In addition, their movement can sometimes be caused by them avoiding chemicals/pesticides that have been sprayed around their habitat, especially the mulch and gardens next to homes.

Greenhouse millipedes invading people's space.
Photo from Stokes Co., NC
Control, especially in the chemical sense, is usually not warranted. Simply vacuuming up the critters is often enough to get rid of them. They pose no harm to people and little to no harm to plants (sometimes becoming important in greenhouse situations - hence the name). So if you are seeing a lot of these worm-like organisms after rains or chemical treatments, be aware that the situation is (A) temporary and (B) the millipedes are harmless (some large ones even make great pets!).

Quick guide to centipedes and millipedes (and other look-alikes):
Does it have legs
> If not then it is likely a worm (though some maggots and other critters are similar):

Typical earthworm.
Photo by Matt Bertone
> If yes, but only up to six true, jointed legs (all on thorax) then it is an insect, likely a larva (caterpillar, grub, etc.):

A click beetle larva (Elateridae) - note only the thorax region has true legs.
Photo by Matt Bertone
> If yes and many legs then you have a myriapod*!
(*unless you have an isopod - pillbugs and sowbugs)

BUT is it a centipede or millipede?
> If it has one pair of legs per segment and is generally fast-moving then it is a centipede (also see house centipedes):

A typical stone centipede (Lithobiomorpha).
Photo by Matt Bertone

If it has two pairs of legs per segment and is generally slow moving then it is a millipede:

A granulate millipede (Polydesmida: Polydesmidae: Scytonotus granulatus)
Photo by Matt Bertone

Tuesday, June 4, 2013

Landscape Professional Field Day 2013

Post co-written by Matt Bertone & Mike Munster
Attendees enjoying the nice weather!
On May 15th, the NCSU PDIC set up shop temporarily at the 2013 Landscape Professional Field Day, held at the beautiful JC Raulston Arboretum. This small gathering focused on a half-day program of informative talks for those working mainly with landscape woody ornamental plants. While industry reps were showing their wares and the speakers were informing attendees of the newest issues in landscaping, we brought our microscopes and tools to get down and dirty with samples brought to us by meeting members.

Mike at the booth, full of samples from us and clients.
We prepared for it the day before by scouting local plants for disease and insect damage to use as "show-and-tell" examples. From the clinic we brought an arborvitae riddled with weevil damage (see this post for details), imported willow leaf beetles (one of the individuals seen here), Armillaria infected wood and a few other things. Matt brought in a number of samples from his yard including maple eye-spot midge galls, some dogwood with powdery mildew, camellia leaf gall (Exobasidium camelliae) and oak leaf blister (Taphrina caerulescens). We also had a Nandina showing "shoestring" foliage typical of infection by Cucumber mosaic virus.

Mike identifying diseases for a client.
Throughout the day we met new people and caught up with colleagues and clients. A few brought us some problems to diagnose, including an unhappy trio of containerized Liriope, one of which had classic symptoms of Fusarium crown rot. There was a sample of Eastern red cedar (pictured at right) that had to be brought back to the lab for diagnosis. Symptoms of Phomopsis tip blight and Kabatina tip blight are very similar. This one turned out to have Kabatina.A yucca leaf from there at the arboretum was found to have anthracnose, caused by the fungus Colletotrichum.

Matt at the scope with some sort of critter.
On the critter side, a client brought some lovely tree hoppers (see below) that were congregating on an oak in Wake Co. Matt assured him they were merely flashy and would not harm a mature oak. Later a graduate student working on witch-hazel (Hamamelis) at the arboretum was curious about strange growths on the leaves of the trees. Matt would tell you what they are, but that would ruin an upcoming blog post about them!
An oak treehopper (Platycotis vittata). Males and females may be horned or hornless.

All in all it was a beautiful day and it felt good to get outside - warm weather, interesting people/samples and a grill full of hot dogs makes for a great time! Until next year...