Pesky pests I

Funny how one thing leads to another …

I posted a comment on the Garden Dum website (based in Australia) to the effect that the yellow and black ladybirds (Illeis galbula) we find on cucurbit leaves and that are thought to control powdery mildew, actually spread it, don’t they?

The article author, Jennifer Stackhouse, politely queried where I might have got such an odd notion from, so I linked to this Royal New Zealand Institute of Horticulture article about powdery mildew by Jane Wrigglesworth that says: “But if you think these beetles will help control powdery mildew, think again. They actually carry spores of the disease under their wings from plant to plant.”

I also quoted from the 2005 book, Backyard Battlefield (Random House), by entomologist Ruud Kleinpaste who says, “Sadly, observing these elegant creatures in my veggie garden I think I have gathered enough evidence to accuse them of spreading the fungus from leaf to leaf and plant to plant.”

Illeis galbula on a courgette leaf. Photo: Sandra Simpson

So far, so good. Jennifer double-checked my information against that available in Australia and came back with information from Denis Crawford, an insect photographer and garden writer.

“I have heard this story before,” Denis says, “but it is not supported by any scientific literature I can find.” He quotes an excerpt from a paper (one of the few, he says) which examines the biology and behaviour of the fungus-eating ladybird Illeis galbula:

“Feeding behaviour is remarkably uniform, both larvae and adults graze fungal spores and hyphae from surfaces of leaves. When Oidium sp. is dense, they feed on a front and visibly clear large areas of the leaf’s white fungal covering; if infestation is light, both larvae and adults search leaf surfaces at random and if nothing is found, adults fly off.”

Denis suggests it may be possible that the beetles spread the fungus as would any other insect which walks over the spores and moves to another leaf, as would water drops, wind, etc. “The ladybirds almost certainly do more good than harm.”

So I contacted Murray Dawson, RNZIH webmaster, to share this information and wonder if he knew any more … and Murray was kind enough to let me know that Denis who, it turns out, is writing a book on garden insects had also been in touch seeking clarification.

I wonder if it’s one of those things that has been said often enough that people now accept that the ladybirds spread the fungus, and repeat it as a truth to other gardeners. If any readers have any ideas or knowledge, I’d be pleased to hear them. Just click on the “reply” tag underneath this post.

PS (May 5): In the latest edition of the weekly Get Growing email newsletter I find Lynda Hallinan also repeating the story that the ladybirds are pests.

Sunday Digest

Vicky Schulze of Rotorua wants to start gardening classes including for those who live in flats with small or no gardens. “You will be amazed what you can grow in pots … you don’t need a huge paddock to grow vegetables,” she says.

Classes will include how to save seeds, how to grow from seed, how to care for plants and how to save the harvest, including freezing, preserving and making jams and chutneys. To find out more call or text Vicky on 027 782 9145.

There are a couple of local garden events coming up – the BOP Bromeliad Group Open Day is on February 13 and on February 15 Gerard Martin at Kings Seeds is looking for some human guinea pigs to help him choose some new microgreen mixes for spring. Full details on the Events page.

Flaming Petal is the blog of Jane Wrigglesworth, “writer, editor and grower of cut flowers”. You may know her name from NZ Gardener magazine or NZ House & Garden. The blog features to-die for photos and short posts.

Federated Farmers, bless their corduroy trews, have decided there is nothing wrong with pesticides containing neonicotinoids, saying there is no evidence the artificial compound has anything to do with the alarming fall in our honeybee population.

Meanwhile, this week three major British companies have taken products containing neonicotinoids off their shelves – prompting a call for chemicals to be banned in agriculture – after studying scientific evidence.

This article quotes Lord Peter Melchett, Policy Director at the Soil Association, as saying: “A recent EFSA (European Food Safety Authority) report labels neonicotinoids as an ‘unacceptable’ danger to bees.” However, British farmers are also denying a link.

Another report on the subject.

And while we’re on the subject of sprays and their use – a Roundup-resistant grass has been found in a Marlborough vineyard.

So here are some home-made natural sprays for the garden from Justin Newcombe, until last week the garden writer for the Herald on Sunday. Click on the “sprays” photo for a printable list of recipes (Adobe reader required and watch out for typos).