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Experiencing the World Through Plant Diseases

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The more we know about the world, the better off we are to coexist in it.

Four years ago, I visited Hanamiyama Park — located a few minutes’ drive across the river from downtown Fukushima City in the northern region of the main island of Japan — a privately owned property that has become a popular local tourist spot for cherry blossom viewing. Opened to the public in 1959, the owner/caretaker gave the chance for everyone to come and behold the carefully planted sloping hills flooded with cherry and plum trees of pink, rose, white, cream, and yellow.

It was also my first learning experience that sparked my interest in plant diseases, starting with an ominous but intriguing black tar-like substance stealing the color away from the scenic slopes.

Plant diseases and pests affect everyone, not just in Japan but, say, Africa, where climate change has caused major problems in maize production. With rising temperatures causing drier conditions and thus inviting new pests, Kenya expects a major loss in field production of maize, going from 2.1 million hectares of productive land to 1.2 million. These exacerbating conditions follow East Africa’s prevailing losses due to Maize Lethal Necrosis Disease.

Nearly 14,000 kilometres to the southeast, New Zealand is facing the decimation of its more ornamental myrtle trees, notably the pohutukawa tree (Metrosideros excelsa). The government, it seems, has tried to put a stop to the spread of the rust, but it’s clear the disease has already taken its toll on the country’s beautiful native.

Come back to Pennsylvania, and we’re now dealing with a disease once thought contained in the South. Sclerotinia rot, or white mold, affects over 400 species of crops and weeds and can survive up to 10 years in the soil. Even when tilled under once, it can resurface and generate once another till brings it to the surface again. The pathogen enters through senescing (dying) flowers.

While the disease can cause significant crop loss, efforts are underway to manage it (notice “eradication” isn’t the term here): cover crops such as alfalfa are viable alternative hosts for the disease, but monocots (grasses and cereals) are not and can be used in rotation. Otherwise, if the field cannot be planted with non-susceptible plant species, it must be left fallow for several years. Fungicide treatment is an option, albeit costly and requiring years of repeated treatment. Promoting airflow and laying plastic are other cited methods of reducing infection and transmission (Philip Gruber, Lancaster Farming).

Tar-like mold on Hanamiyama tree

Back at Hanamiyama Park, caretakers were at a loss for what to do about the black pitch — sometimes in globby clumps and most often in smooth, evenly spread patches — that appeared on the bark of so many cherry trees. Standing atop a ladder and shears in hand, one worker motioned towards the cherry trees lining the slope and commented “There’s nothing we can do”.

Other caretakers said although they didn’t know what was causing the problem, it did start from within, decaying the branches fully from the phloem to the bark. At the time, possible culprits included pathogens such as Septobasidium (velvet blight) or, less convincingly, Leptographium.

In our Commercial Vegetable Production class’s vegetable plot at Delaware Valley University, the inability to identify a disease and find a solution is just as frustrating as it must be for the employees of Hanamiyama Park.

A silvery pattern that began in the veins of zucchini squash leaves but quickly progressed to whole-leaf coverage vexed students and university professors alike. I reached out to the masses on Facebook in the “What’s Wrong With My Plant” group, an administrator of which cited — most likely — silverleaf whitefly as the culprit of our chrome-painted veggie leaves. The following photos show zucchini squash leaves progressing from very pretty silver venation to entire

Speckles of tan spots, on the other hand, turned out to be an easier mystery to solve and which is even occurring in my own South Philly residence: thrips are a common greenhouse pest, though its still vexing to know just where on earth how they just appear suddenly during early-stage vegetables’ growth. As well as for marijuana plants. Not that I have first-hand experience or anything.

Aphids on Artemisia annua

Equally arcane in origin were the aphids that happily took my (never-sent) invitation to dine on my fragrant Artemisia annua, or Sweet Annie, plant. Whether in the kitchen of my South Philadelphian rowhouse, a cornfield in Africa, or inside the branches of beautiful-but-doomed Japanese cherry trees, plant diseases are ubiquitously difficult to identify and, due to resistance development, difficult to manage.

In any case, the laddered man at Hanamiyama probably carried the most effective method of stopping spread of disease: his pruning shears. While the destruction of diseased plant parts is often cited as an effective way to inhibit diseases in my DelVal classes, the Integrated Pest Management course offers a way to use several methods to combat diseases: safe fungicides, smart cultural farming practices (e.g., appropriate crop species rotations), diversity in plantings, and more. The more we know about how the world works, from Africa to Pennsylvania, the better equipped we are to adapt to it for our purposes rather than force it to adapt to our presence in it.


Getting Environmentally Involved in Philadelphia

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Japanese knotweed. Oriental bittersweet. Garlic mustard. Phragmites. Wineberry. Multiflora rose. Mile-a-minute weed. Lesser celandine, Japanese honeysuckle.

If one severely edited the plant ID walking tour to include only mention of PA invasives, this would be the list of botanical baddies detailed by volunteer plant expert Mr. Cloud at John Heinz National Wildlife Refuge. And yet, there was so much more than that at the refuge today.

Wild bergamot at the entrance to John Heinz Wildlife Refuge Visitor Center
Photo: John Heinz Wildlife Refuge Facebook page

This morning, a group of about 15 volunteer “Weed Warriors” donned their orange vests, grabbed some hedge shears, and headed out along the trails in search of two of the refuge’s worst invasives, Japanese knotweed (Fallopia japonica) and Phragmites, a waterside reed that can extend up to well over 15 feet at the wildlife preserve. A quick rundown on IDing these offenders, and the hacking began, feathery plumes and hollow red stems timbering over, revealing a hidden river and uncovering overshadowed and dormant red osier dogwood twigs.

According to the Great Lakes Phragmites Collaborative, who seems to be having an issue with the Phragmites reed based on the fact that they have a website dedicated to the plant: “Studies have shown that the lateral spread of rhizomes [horizontal underground stem that can put out more shoots] averages approximately 15.7 in (39.8 cm) per year, and stolons can grow up to 4.25 in (10.7 cm) in a day.” A British website dedicated to educating the public on the other invasive states that knotweed has a “growth rate of (approximately) 60cm a week or 8+cm a day.”

Needless to say, the refuge is always looking for volunteers to combat this never-ending battle. Two years ago was my first experience as a Weed Warrior — the trunks of the girdled invasive white poplar trees are since dead and decaying, but new growth (suckers) have thwarted all efforts, rising from the old growth like the heads of Hydra.

Beautiful, dainty Claytonia virginica

Still, the volunteers persist, and, if all the rest is edited back into Mr. Cloud’s tour following the three-hour Weed Warriors program — which occurs every second Saturday of the month — you’ll find there’s so much the refuge and its stewards have done to reintroduce native species while they hack away at the invasives. Mr. Kerr, who leads tree ID walks*, mentioned he himself planted some pawpaws, clearly happy and proud the tropical plant can handle the region’s climate, given its the northernmost point this tasty fruit-bearing plant can endure.

During his plant ID hike today, Mr. Cloud led his group to a small clearing along a trail to see how his Virginia springbeauties (Claytonia virginica) were faring. Single leaves — narrow and slightly thick — protruded from last year’s litter of dead leaves and plants, a welcome sight for the volunteer guide, who planted this small yet spreading colony some 10 years ago. His enthusiasm for all plants (being winter, the ID walk highlighted a lot of ground-hugging species, cresses and other edible winter/early spring sprouters) led to my introduction to the cup plant. The petioles (stalk that joins a leaf to a stem) of the cup plant, aka Silphium perfoliatum, are fused around the stem and form a cup, perfect for catching water.

Liquidambar styraciflua “Corky” bark
Image: Tom Potterfield

Near the visitor center, Kerr noted a strange-looking tree with very familiar fruits. Numerous sweetgum trees (Liquidambar) line the streets of Philadelphia, particularly Pine Street near St. Peter’s Church, where on more than one occasion their spiky fruits nearly sent me over my bike handlebars. However, this particular species, Kerr pointed out, produces a raised bark on its branches, an attractive trait in the horticultural business but unusual — he cited studies that suggest these serve as an addition to lenticels, the pore- or slit-like markings you see on many tree trunks and which allow for gaseous exchange.

The task of protecting our region against numerous invasive species, plants or otherwise, certainly seems insurmountable, but efforts like those going on at John Heinz National Wildlife Refuge — as well as Greensgrow Farms, Morris Aboretum, Academy of Natural Sciences lectures, and Chemical Heritage Foundation, to name an honorable few — are exactly the kind of passion- and concern-driven programs in which we should all be getting involved. What better to spend a much-deserved, post-knotweed-removal lunch break on a Saturday with friendly, like-minded individuals talking about all-things-plants? And it’s not all strictly plant science, ID, invasive vs native dialogue and the like — I got three bloody good recipe uses for that useless sage taking up window space in my kitchen.

Sign up to volunteer at the Refuge here
Greensgrow Farms volunteering here
Bartram’s Garden volunteering here

*The Refuge has a lot more than plant/tree ID walks. Check out their full current programming here.

To Sow a Delicious Invasive

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Today, I was excited to sow my stratified garlic mustard seeds. May the ignorant of botany-based bloggers be aghast and rank me among those who still opt to use kudzu for soil control.

Garlic mustard leaves and flowers

Garlic mustard leaves and flowers

I’m a massive fan of Alliaria petiolata, or garlic mustard, and have been since being introduced to the leafy green living in Ridley Park, Delaware County, with my sister. Her boyfriend had pointed it out as a nuisance that kept popping up in their yard, and I immediately recognized it from a book, strangely enough, given to me as a Christmas gift by my sister some years ago.

The Complete Guide to Edible Wild Plants, Mushrooms, Fruits, and Nuts by Katie Letcher Lyle is one of the few books I’ve taken to writing notes in the margins, and it’s from this handy guide I first heard of garlic mustard and its wonderful culinary and medical uses.

True to southeast Pennsylvania, the author sufficiently describes the plant as appearing “to have infiltrated fields, paths, and the edges of woods with its pretty, light green, scalloped round leaves that smell and taste faintly of garlic.”

And she goes on to mention mustard garlic’s invasive behavior, which may be thanks to its allelopathic tendencies, basically putting out chemicals in the soil to inhibit the growth of certain other surrounding plants.

Milkweed at John Heinz National Wildlife Refuge at Tinicum

Milkweed at John Heinz National Wildlife Refuge at Tinicum

I saw widespread evidence of this during my brief volunteering with the Visitor Center at John Heinz National Wildlife Refuge at Tinicum. The largest remaining freshwater tidal marsh in Pennsylvania, this refuge is home to protected nests of bald eagles and turtles and a fertile grounds for native milkweeds and toadflax.

Unfortunately, given the refuge’s disturbed and industrial past, it is plagued by invasive species like white poplar (Populus alba), false indigo-bush (Amorpha fruticosa), and, of course, garlic mustard.

And there exist numerous news articles on methods and proposals for the eradication of garlic mustard, all of which seem so very deplorable: the introduction of rogue and unpredictable weevil predators, fire control, chemical spraying, etc.

Mile-a-Minute Weed in Cobb's Creek in Delaware County

Mile-a-Minute Weed in Cobb’s Creek in Delaware County

Whilst volunteering for Weed Warriors, a program run by the refuge, I listened to veteran volunteers lament the spread of garlic mustard throughout the refuge, overcrowding and -shadowing other potential plants. The only other contender for worst invasive, according to them, is mile-a-minute weed, or Persicaria perfoliata. And during my time with the refuge’s visitor center, I was elated when the volunteers told me I could harvest garlic mustard to my heart’s content.

And while I’m skeptical of the green’s affect on asthma, I was happy to fill up to my heart and bodys’ content with Vitamin C and absolute tastiness. Both the leaves and stems are fantastic in any rice dish and even in a simple salad. Though, as Lyle wisley points out in her book, the leaves mustn’t be boiled/cooked so much that they become slimy; adding them in to a boil or steam in the last few minutes is best.

Though I’ve since moved from Delaware County, I hope to rejoin the refuge’s volunteer force, not just for the garlic mustard but because I really do trust and believe in their efforts to rehabilitate this fantastic preserve. You can join me this spring and summer in my eradication efforts/harvesting by reaching out to the Friends Group coordinator Suzanne Kelley at