A mealy bug saga

[Les.Needham]

The main nursery that I use imports all of its plants from some Dutch company. I have noticed a type of mealy bug on some of the plants, a type that I have not seen before: abundant wool, flat elongated bodies. Then I saw it on a lemon tree and was told that it is a common pest of lemon trees known as cotton fly. Cotton fly it certainly is not. Mealy bug it certainly is. However I was given the appropriate insecticide for this 'cotton fly', which came in an unmarked bottle, with instructions for 30ml to 10lt water. I suspect that this may be diazinon or a form of it. I came away with the idea that it was thoroughly dangerous stuff (diazinon is banned in the EU).
There are more genera of mealy bug than there are species of Mammillaria! Some are specific to certain plants. There is even one that confines itself to pink hibiscus. I think that the one I have seen is the citrus mealy bug. Do you think we are fighting a losing battle? Especially if it is being imported from Holland.

[iann]

You quite possibly have the right name. This and the Longtailed Mealy are the common above-ground species found on succulents. Long tails are usually the Longtailed Mealy (although there are other species with longtails) and no tails are usually the Citrus Mealy.

Certainly there is a reservoir of pests in large-scale horticulture that the growers are not especially keen on eliminating. You should probably consider that any cactus bought from this sort of large-scale supplier is infected. Of course there is always a chance that any cactus from anyone is infected so you should take precautions with any new plant, especially once you get your own collection clean. Buying bare-root cacti is a great idea, and if you buy them in soil take them out of it immediately, inspect, throw away the soil which is garbage anyway, and treat the plants in an attempt to kill anything you didn't spot.

Attacking an existing infestation is difficult. The spray you have been given, assuming it is Diazinon, will kill them but it is not systemic and it will be difficult to eradicate mealies with it. You will have to spray repeatedly, at least three times a few weeks apart. Does the bottle even come with instructions? I'm not against insecticides but plain brown bottles are just irresponsible.

A better way to attack mealies is with a systemic insecticide. There are at least four different ones still available in the UK and possibly more where you are. Get one, water the cactus with it in diluted form and fingers crossed you have killed them all. Water the whole collection since they've probably spread. Plan on doing it again later in the season or next spring in case anything survives. Ideally do it with an insecticide from a different group, although that isn't possible (legally) in the UK.

Incidentally they aren't native to the UK and they won't survive outside over winter. You can probably kill off a fairly severe infestation just in an unheated greenhouse assuming the plants can take it.

Next week's lesson: root mealies

[Liz M]

Interesting, I was repotting some severely neglected Haworthias and found one which had some different mealy bugs to what I am used to. It was larger and fatter than the 'normal ones' and most significantly, when I squashed it, it was creamy coloured rather than the usual red. Is this the shape of things to come? Help1

[iann]

Citrus mealies are described as having yellow body fluids, but I can't say I've ever crushed one.

[Werewolf]

Ian, you say there are four insecticides available in the UK that can be effective against mealy but also that we cannot legally use different groups of insecticides. Forgive the ignorance of a non-chemist but is what you are saying that there are four different brand names all with the same active ingredient and that presumably, therefore, there is no point rotating those brands?

[iann]

All systemic insecticides currently available to the public in the UK (and theoretically throughout the EU but not always enforced) are neonicotinoids and resistance to one of them is likely to mean resistance to all four, but there would be little correlation with resistance to insecticides of other groups. There is some point to rotating insecticides within the same group, but it is nowhere near as effective as rotating with different groups. One more reason why EU bureaucrats are dumb

[McFarland]

just to take neonicotinoides as an example, as I don't really know much about other classes of pesticides, having been gardening organically for 5 or 6 years (since I started gardening really)

http://en.wikipedia.org/wiki/Neonicotin ... tal_impact

apart from the bee problem there's also:

Studies conducted on rats suggest that the neonicotinoids may adversely affect human health

there's a reasom the dumb EU bureaucrats don't want us spraying chemicals all over everything

[DaveW]

Never squashed a mealy on my plants in 50 years that had red blood Liz, so I presume what is common in UK collections is not the cochineal mealy bug raised usually on Opuntia's for its red colour, which was frequently used as a food and cosmetics colour in the past, and often still is!

"Health fears over artificial food additives, however, have renewed the popularity of cochineal dyes, and the increased demand has made cultivation of the insect profitable again, with Peru being the largest exporter"

http://www.businessinsider.com/how-coch ... nks-2012-3

Evidently the cochineal insect is a scale insect too in later life, not the mobile mealies most of us get.

http://en.wikipedia.org/wiki/Cochineal

http://www.learn2grow.com/problemsolver ... ybugs.aspx

Looking on the Web there are several insects seeming to be dubbed "cotton fly" Les, so you really need to identify which it is.

http://www.cottoncrc.org.au/industry/Pu ... Solenopsis

I would suggest you collect a sample of the mealy concerned and post it to your local agricultural institute for identification, asking what insecticides are appropriate for it's control.

DaveW

[iann]

just to take neonicotinoides as an example, as I don't really know much about other classes of pesticides, having been gardening organically for 5 or 6 years (since I started gardening really)

http://en.wikipedia.org/wiki/Neonicotin ... tal_impact

apart from the bee problem there's also:

Studies conducted on rats suggest that the neonicotinoids may adversely affect human health

there's a reasom the dumb EU bureaucrats don't want us spraying chemicals all over everything

You completely miss the point in so many ways.

Poisons are dangerous. They kill things, and at the very least they aren't going to be good for you. The "bee thing" is 90% eco-mentalist propaganda. Insecticides obviously kill bees, but the trouble we are having with bees at the moment is for the most part not caused by any particular class of insecticides or even by insecticides in general. The timeline and the geographic distribution of the problem simply don't match the use of Neonicotinoid insecticides. For example, Australia is a heavy user of the insecticides but colony collapse disorder is unknown there. If people spent more of their energy actually trying to work out what the problems were instead of just blaming the thing they hate the most, the bees might have more chance.

More importantly, and this was the point I was making, banning everything except one class of insecticides (and not even because they are nominally the safest, but simply because they are the ones that big global agribusiness has chosen to sponsor) leads to cross-resistance and hence over-use, which leads to worse effects on both human health and killing beneficial insects. It is a stupid policy, as is banning the sale of Malathion for use as a garden insecticide but continuing to allow it in children's shampoo, and innumerable other cases that have nothing to do with safety and everything to do with idiots making up arbitrary rules because that's all they know how to do. If I were more cynical I might say that the rules are being made by those big agribusinesses to let the monopolise their own products.

[McFarland]

I do agree with you about the influence big business has on the EU, specifically the chemical companies, and also the GM companies which are often the same thing.

Still though I can't believe you discount the numerous studies which have shown links between bee decline and neonicotinoids, and not just CCD specifically. Anyway sorry to hijack the thread, I just think people are a bit gung-ho with chemicals sometimes!