pests

Asparagus, Asparaguses, Asparagi?

/ Robinne Weiss / 2 Comments
asparagus spear infected with phytophthora
Asparagus spear infected with phytophthora

It’s asparagus season, and we are enjoying spears from our own plants, though not as many as we’d like.

We moved crowns from our old house to the new, and have had rather mixed luck. Some didn’t survive transplant. Others grew poorly last year, and did not show their faces this year. Still others sprouted this year, but have been succumbing to phytophthora infection—a new challenge for us.

Phytophthora asparagi is an oomycete. Its long-lived spores overwinter in the soil and infect asparagus roots and spears. Phytophthora infection interferes with water transport in the stem, causing shrivelling and a ‘shepherd’s crook’ curl to the spears.

Oomycetes were once thought to be fungi, because their growth forms can be similar. They are, however, genetically distinct and are now known to be more closely related to kelp than fungi. Many oomycetes are plant pathogens, and some, like late potato blight, sudden oak disease, and Phytophthora asparagi are of economic importance.

We never had trouble with phytophthora at the old place—our well-drained soil with excellent nutrient levels kept it at bay. But at the new property, the heavy clay soil devoid of nutrients provides perfect conditions for phytophthora growth. 

Two months ago, before we’d identified phytophthora, I planted a packet of asparagus seed. I wanted to fill in the gaps in the asparagus bed, where our transplanted plants had died. Now, with 38 beautiful asparagus seedlings in the greenhouse, I’ve got a different plan for them.

Michigan State Extension recommends fungicide and careful selection of planting site to control phytophthora. I’d like to avoid the fungicide, but I can manage the soil, at least a little.

asparagus seedlings

My little seedlings will need about 18 months in pots before I can plant them out. That’s plenty of time to prepare a special raised bed for them, filled with compost, sand, and soil for high-nutrient, well-drained growing conditions. In the meantime, we’ll enjoy the asparagus we are getting, and do our best to keep the old plant alive until the new ones can be harvested.

And, just so you know, the plural of asparagus is asparagus.

Nature Red in Tooth and Claw

/ Robinne Weiss / Leave a comment
Photo: Eric Weiss

It’s not often you witness outright thuggery in nature. Predators hunt prey—they have to, because otherwise they starve. Predation is never pretty, but it is what it is. 

Sitting at my desk, procrastinating … er … writing this morning, I saw brutality, pure and simple. 

A pair of magpies was chasing a starling. They caught it and brought it to the ground. Standing over it, they pecked at its eyes. At first, I thought they were trying to kill and eat it. But after a few minutes, they got bored. The starling managed to fly off. The magpies followed, caught it and brought it back, only to repeat the eye pecking routine. Three times while I watched, they allowed the starling to escape, then brought it back to peck at it. Always at the eyes.

Eventually, they bored of the sport. They wandered away from the hapless starling to forage in the lawn nearby. After a few minutes, starling and magpies flew off in opposite directions.

I suppose it shouldn’t come as a surprise. Australian magpies have a reputation as aggressive, intelligent birds that like to play. They brazenly steal food from the chickens, fighting right back when a chicken lunges at them. And I’ve watched as gangs of juvenile magpies have tormented my cat, swooping low over him as a team, trying to get a peck in while he swats at them. And I’ve been on the receiving end of magpie parents defending their nests with noisy dives at my head.

In general, magpies eat invertebrates—they were originally introduced to New Zealand to help control crop pests. Research on their effects on native birds indicates they only rarely kill other birds, and their aggressive pursuit of larger predators like harriers may even provide some protection to smaller birds.

Still, I can’t help thinking magpies are the bullies of the playground. They’re fine as long as you’re not their target. Fascinating for me as an armchair naturalist, but I’m thankful I’m not a small songbird.

Summer Stocktake

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Mid-April, and it’s time to take stock of the summer’s garden. 

Compared with gardens at the old house, this year’s was a disaster—stunted plants that died off early, solanaceous crops decimated by viral disease, and heat and drought that I struggled to combat with irrigation.

But compared with what I expected, the garden was a huge success. I managed to provide the plants enough nutrients and water that they all managed to give us something. We had enough peas, corn and carrots to freeze some. We gorged on strawberries and melons. I gave away heaps of zucchini. The laundry room is piled with pumpkins. We’ve got more garlic and onion than we’ll be able to eat before it starts to sprout. And we’ve had a steady supply of tomatoes, eggplants and peppers. 

The stars of them all have been the carrots. Last spring I blogged about how well my carrots germinated this year—better than they ever had before, which was quite a surprise in the new garden. At the time, I reserved judgement—it was too much to hope the carrots would grow well in heavy clay soil studded with rocks.

But all summer we’ve been eating beautiful carrots, and last week I harvested everything remaining in the bed, because the slugs and slaters were taking their toll. The fridge is packed with carrots now, and I blanched and froze several kilograms as well.

In spite of everything, it was one of the better years I’ve had for carrots. To be fair, the roots are small, compared to the old garden. Some are bent where they hit a rock, and many broke off when I tried to lift them—if they penetrated too far into the clay, they were nearly impossible to harvest.

But even the purple carrots grew, which is quite an accomplishment for me—in past years, the purple carrots have done well in early spring, but then have been decimated by aphids, so we only ever eat them as baby carrots. Last week I harvested quite a few nice big purple carrots.

Best of all were the Paris market carrots—little, super sweet round roots perfect for lunch boxes and snacks. Their shape made them easy to pick, so there weren’t any left when I harvested the lot last week, but they’ll definitely be in next year’s lineup as well.

Overall, I consider the summer’s garden to have been a success. It’s looking pretty bare out there now, and I’m hauling cow manure from the neighbour’s place and incorporating it into the soil, so by spring I hope to have a few more nutrients available for the plants. I’m already looking forward to next summer.

Problem or Inspiration?

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The other day I planned on making roast potatoes for dinner. I brought in a colander full of spuds from the garden—more than enough for dinner.

Unfortunately, when I started cutting them I found many of them infected with zebra chip (caused by the bacterium Candidatus Liberibacter solanacearum), which turns the flesh brown. My planned dish of potatoes was looking pretty empty.

I could have gone out for more potatoes, but instead I took advantage of the resources on hand in the kitchen. I added a shallot and a few chopped tomatoes, sprinkled it with salt, pepper and rosemary, and popped it into the oven (at 210ºC for about 40 minutes for anyone interested).

The result was utterly satisfying and arguably better than the plain roast potatoes I’d originally planned. Instead of a problem, the rampant zebra chip became delicious inspiration.

Now, if I can only remember that for all the other problems in life …

Beach Hangout

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We nipped out to the beach after dinner on Saturday. We had a nice walk on our lovely, lonely bit of coastline.

But the beach was busy with youth hanging out (up to no good, probably). Some were alone, and some were in groups, strutting their stuff.

But these youth weren’t your usual crowd of city kids, they were juvenile spotted shags, Strictocarbo punctatus punctatus, also known as spotted cormorants, parekareka, and kawau tikitiki.

Shags were once heavily persecuted as pests. Fisherman believed they destroyed the fisheries, snapping up all the commercial fish and decimating their numbers. Research has shown, however, that their impact on fisheries is minimal. On the other hand, there is some evidence that, in our area at least, shag populations are hurt by commercial fishing. Spotted shag populations on the Banks Peninsula rose from 9,787 pairs in 1960 to 22,123 pairs in 1996 following a reduction in commercial fishing around the peninsula. Illegal shooting can also cause local population declines.

The spotted shag is a marine species, never venturing far from the sea and feeding in deep water up to 16 km from shore. They’re gregarious, breeding and roosting in colonies with up to 2000 birds. The groups of juveniles on our beach were small—a few dozen birds at most. These birds were probably born on cliffs around the Banks Paninsula, and when mature, they’ll head back to those cliffs to lay eggs and rear their young.

So they really were just hanging out on the beach, just like teenagers from Christchurch hang out on the beach on weekends, away from the adults, goofing off and getting takeaways.

A Weakness for Weevils

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I was excited to find a new weevil on our property the other day. At least until I identified it.

Meet Otiorhynchus sulcatus—the black vine beetle—pest on a wide range of garden plants, including grapes, black currants and strawberries (all common in my garden).

I admit, I have a weakness for weevils—no matter how much of a pest they are, I think they’re cute. And this one is no exception. She’s lovely, in spite of her diet. And I’m certain she’s a ‘she’, because no males of this species have ever been found. The black vine beetle reproduces parthenogenetically, producing viable eggs without the need for fertilisation by males. 

This ability is the result of a bacterial symbiont in the genus Wolbachia. When researchers in California eliminated Wolbachia in black vine beetles (by giving the beetles antibiotics), the beetles’ unfertilised eggs were no longer viable. It’s a clever little ploy by the bacterium to ensure its own reproduction—only infected insects can reproduce, and they can do so without the trouble of finding a mate (I wrote more about this fascinating relationship in Putting the Science in Fiction and on Dan Koboldt’s Science in Fiction blog).

Another cool feature of the black vine beetle is that it is flightless. It’s not uncommon to find flightless insects and birds here in New Zealand, but it’s a little unusual to see it in invasive pests like the black vine beetle. Native to Europe, the black vine beetle is now distributed all around the world. Pretty impressive travelling for a 6 mm-long flightless insect.

Apparently black vine beetles can cause significant damage to plants. The larvae eat roots in the soil and do the most damage, particularly in potted plants, where root growth is limited. I’ve decided not to worry about them at the moment. I’ve got more damaging pests to worry about, and to be honest, I wouldn’t mind seeing them again. They are awfully cute.

Sticky Feet! The Eucalyptus Tortoise Beetle

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Hanging up the laundry this morning, I found this lovely beetle making its way along the washing line. It’s a eucalyptus tortoise beetle (Paropsis charybdis). I see them occasionally, but with only one eucalyptus tree in the yard, they’re not common.

I’m quite fond of tortoise beetles. This one isn’t much to look at, but many species are sparkling gold, and my first glimpse of them, as a kid, was a truly magical experience that I’ve never forgotten. What tortoise beetles have in common is their domed tortoise-like shape.

Their shape, combined with some pretty awesome feet is what keeps them safe.

Tortoise beetles have wide pads on their feet (this one obligingly sat on a clear surface and showed its feet under the microscope). The pads are covered densely in short hairs, like the bristles of a toothbrush. Each hair is moistened by oil, which helps it stick to the waxy surfaces of leaves in the same way two wet drinking glasses stick together if they’re nested. The oil bonds to both surfaces and acts as glue. When disturbed, the tortoise beetle presses its feet against the surface, employing as many as 60,000 sticky bristles (about 10 times more than other beetles have) to keep it attached. These sticky feet, combined with the dome-like shape make it difficult for predators to dislodge the beetle.

Entomologist Tom Eisner performed a series of elegant experiments with the palmetto tortoise beetle, attaching weights to the beetles to see how much force they could withstand before being pulled off a leaf. He found they could hold up to 240 times their body mass. Those are some seriously sticky feet!

So if their feet are so sticky, how do they walk? Eisner showed, by looking at palmetto beetle footprints on glass, that when they walk, they don’t let all the bristles on their feet touch the surface. Their full adhesive power is only deployed for defence.

I don’t think anyone has tested eucalyptus tortoise beetle grip strength, but it’s definitely impressive. I popped this one into a narrow jar, and it never hit the bottom—it reached out with one leg, like some movie superhero, and grabbed the smooth wall of the jar, arresting its fall. Then, when I tried to get it out of the jar, it stuck like glue to the side. I had to slide a stiff piece of paper under its feet, prying them up one by one. It was obliging for the photo shoot, but when I tried to let it go, it stuck itself to the paper. It took a few determined nudges, but eventually I got it to the edge of the paper and it dropped off.

The eucalyptus tortoise beetle is not native to New Zealand, and is considered a pest in the forest industry here. Still, I have to admire the beetles’ sheer tenacity, and am willing to share my eucalyptus tree with them for the opportunity to see those sticky feet in action.

Fabulous Flatworms

/ Robinne Weiss / 3 Comments

Australian flatworm

One of the common animals in my yard and garden is the flatworm. Strictly speaking, “the” flatworm here in New Zealand is actually multiple species—possibly up to a hundred—but they have been poorly studied, so it’s unclear just how many species there are.

Flatworms are some of the most impressive predators in the garden, able to consume prey up to 55 times their own size. That’s the equivalent of your house cat taking down a female elk. They eat snails, slugs, and earthworms, digesting them externally before sucking them up with one or more mouths located midway along their bodies.

I love to find flatworms around the yard. They come in striking colours, and some have lovely brown stripes—the orange Australian flatworm (Australoplana sanguinea) is most common in my garden, followed by the relatively nondescript brown New Zealand flatworm (Arthurdendyus triangulatus). Like the slugs they eat, they prefer damp places, and they protect themselves with a layer of mucous. Flatworm mucus is stickier than slug mucous, and they use it to attach themselves to their prey during feeding.

New Zealand is full of non-native invasive organisms, but New Zealand flatworms are one of the few organisms that have turned the tables and become pests overseas. They are easily transported in potted plants, and have successfully invaded Ireland and Scotland. Though there was widespread panic at first about their potential to threaten the local ecology, they appear to have caused little damage to earthworm populations in the UK. Like most cold-blooded animals, their appetites are small. Far from being a devouring hoard, each flatworm can manage, on average, just one earthworm per week. And if they don’t manage to find an earthworm every week, it’s not a problem—they can go a year without eating.

Backyard Biodiversity

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Craterium minutum

I know it’s been a good weekend when I arrive in my office Monday morning to find my microscope in the middle of the desk, and dirt and bits of plant material strewn about.

It means I’ve been outdoors, seeing cool stuff, identifying plants, insects, or other organisms.

Once you start looking at and identifying what lives around you, the variety is astounding. A glance at the citizen science website iNaturalist shows a pile-up of dozens of observations at our address—and those are only the species we’ve bothered to upload.  I’ve identified 58 species of weeds in the vegetable garden alone. We have half a dozen slime moulds, dozens of fungi and lichens, who knows how many insects and other invertebrates. Then, of course, there are the birds, rats, mice, stoats and other vertebrates. I’ve never bothered to make lists of anything beyond the weeds.

So here in the dark depths of winter, I’ve decided to start a comprehensive list of the biodiversity on our little acre and a half. It will take time. It will require my microscope and many Monday mornings brushing dirt off my desk. But wouldn’t it be cool to know exactly how many other species we share this patch with?

And though many of the species I’ll put on my list are ones I’ve noted many times before, I’m sure some will be new and surprising, like the beautiful slime mould, Craterium minutum my daughter found last week.

Because, the truth is, we needn’t travel far to find natural wonders. We merely need to look closely and have a sense of wonder.

Currant Clearwing

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Mating currant clearwings. Photo: Plantsurfer, public domain

They’re the most beautiful pests in the garden. Currant clearwings are moths, but they would like you to think they’re wasps, with their clear, narrow wings and yellow stripes. The deception deters predators who don’t want to tangle with a dinner that stings.

Adults emerge in early summer. They lay their eggs on the growing tips of currants and gooseberries. The caterpillars hatch out and burrow into the stems, killing them.

We’ve had the occasional currant clearwing in the past. Mostly, I let them go, because there were few of them, and I do like the way they look.

But this year there are many, many more than usual. I’m squishing all that I see. They leave gold dust on my hands when I do.

Hopefully, my efforts will be effective, and we’ll go back to just a few currant clearwings next year, so I don’t have to kill so many of these beauties.