Mealybugs and climate

[ElieEstephane]

So i've been thinking about this a lot. Do mealybugs prefer certain climates or weather conditions? I ask this because i've never had any mealbug infestations (knock on wood) and i wonder if i'm lucky or they just don't like my conditions
I've only had one condition with a plant i got from the nursery and had only 1 mealybug. I killed it and that was it.
I've had a large infestation of (harmless) collembolas but once i could not water my cacti for 3 consecutive weeks in the heat of the summer and they were completely wiped out.

[7george]

There are several forms (species) of those and at least some of them are not scared of cold winters. I've seen some at Cotoneaster branches in my garden and also over native Opuntia plants in local habitats.

But the heaviest infestation spotted was been on cacti sold in some garden centers and other type of stores selling cacti with other stuff, like IKEA. After that I rarely take cacti from these places or I used extra caution if liked something there.

I also new a guy, being also cacti seller that was bringing nothing but seeds into his collection trying to avoid any possible infestation.

[ElieEstephane]

When i buy any new cacti, i immediately quaratine them and ditch the old soul. As you say they are always havily infested. But as soon as they go in the new mix and full sun i never saw anything again.
You say they tolerate the cold. Perhaps they don't tolerate the heat?
I found a couple of mealybugs earlier this year on one of my backup jacarandas which was immediately next to my agaves and cacti but they never bothered to visit them. They were around 4mm.

[mmcavall]

Perhaps they don't tolerate the heat?

I can assure you that they tolerate, or even love, heat.

[ElieEstephane]

Then i guess i'm really lucky

[DaveW]

If you don't have any mealies on your cacti they cannot spread. However most of us have a few, often imported on plants we buy or obtain from other collectors, even if we do not always see where they are hiding. I have even picked up pots with plants in and though the plant looked clean there were mealies on the underside of the pot and on the staging.

Generally mealies like the warm and dry climate of our greenhouse. If you spray your plants with water or water overhead you usually find them on the dryer side of the plant around the back where you cannot see them where the water misses, unless you turn the plant to look.

The problem with mealies is one dose of insecticide may kill the bugs but not their eggs which hatch out later after the insecticide has lost it's potency, since by design these days few insecticides are very long lasting to save any toxic build up of them. Therefore you need several applications spaced out at intervals over the year to kill the new ones that emerge from the eggs before they can lay again. Few insecticides are in fact ovicides (meaning they kill the bugs eggs) which are usually insecticide resistant. Therefore read the insecticide instructions and use at the frequency recommended. Don't think you know better than the insecticide manufacturer.

http://ipm.uconn.edu/documents/raw2/htm ... play=print

Another problem can be the prophylactic overuse of insecticides (when no pests are obvious) as this can build up resistant strains of the bugs. The world is now getting the same problem with the over use of antibiotics for both humans and animals in the past, where antibiotics that once were useful are now ineffective against what they previously were used for, and we have fewer and fewer effective ones left. It is always good policy to not use the same insecticide continuously, but switch to another to hopefully kill the resistant bugs the previous one left behind, even if you revert to the previous one again later. Even alternating between systemic and contact ones occasionally may help.

https://en.wikipedia.org/wiki/Pesticide_resistance

[ElieEstephane]

I think i would opt for a soapy water soak rather than applying insecticide. The only plants i use insecticide for are roses. They attract all kinds of insects from the 4 corners of the world.
Do you grow roses Dave? I hear brits are famous for their rose bushes

[mmcavall]

I recently applied imidacloprid (systemic insecticide) for the first time. I used to have some mealybugs here and there, mainly in the Ascleps, but without serious problems. But now I noticed two new species of mealybugs in my plants (interestingly, not in the Asclepiads). One attacks the top of the plant, and the other (or maybe they are the same) attacks the roots. When I notice that a plant stops growing and is looking sick, I check the roots and I find the pests there. This was not a problem 6 months ago, but now they spread in the collection, sucking even the "precious" Mesembs seedlings…that’s why I chose a systemic. Soapy water would not reach the roots. I hope I dont need to use this product very often.

[7george]

One attacks the top of the plant, and the other (or maybe they are the same) attacks the roots.

I think these are different, but could be one that lives above and below soil surface.

Talking about the climate again I agree -- mealybugs like hot and dry climate but this doesn't mean they die easy in the cold.

This topic is able to stop me buying new plants cause right now I see no mealybugs (knock on wood) over my cacti.
But a day ago I saw some red mites crawling and sprayed those with oily emulsion. Spring is coming: bugs started waking up.

[DesertSun]

Oh yes, they do love heat, hot and dry is their best I think. I know from a cactophile greek friend who occassionally has them in her cacti and sucs. Of course, the same goes for spidermite infestation. I have too noticed that big stores that have plants, like Ikea, do have some plants infected. I once bought an infested with mites Crassula muscosa, I wasn't careful enough, got rid of it after trying for a week with soap/alcohol and water mix. Does anyone use this? I think the best is to treat them manually if the infestation is on a small scale. The mealy bugs you can see are more "innocent" than the root ones, as you can always take action to control their population when they are on the upper part of the plant, but when they are in the roots...aargh

[7george]

Mealybugs on Opuntia monacantha, San Diego. They like fruits too.

[Steve Johnson]

I think the following will help us shed some light on the subject...

Wikipedia article on citrus mealybugs, the primary culprit attacking stems and spines of cacti:

https://en.wikipedia.org/wiki/Planococcus_citri

From Cactus Nursery (http://www.cactusnursery.co.uk/mealy.htm):

"Root mealybugs (Rhizoecus falcifer) are among the worst pests of cacti and other succulents. They live almost exclusively on roots and the parts of the stem that are below the surface. They are similar to [above-ground] mealybugs in that they also secrete whitish, woolly, or powdery wax. Root mealybugs prefer dry substrates. They multiply particularly rapidly during the dry winter dormancy period. Affected plants look pale, become sickly, and gradually die. Plants damaged and weakened by root mealybugs are especially susceptible to fungal diseases."

After being pretty much mealy-free for about 6 years, my collection was hit by both kinds last winter (yes, winter -- in spite of all the rain SoCal got, there were enough warm days in my part of L.A. to bring it on). While the experience I have could be useful, unfortunately I don't have enough time to post a presentation to cover all the bases. Hopefully I can put a good one together for y'all later this year. In the meantime, here's an online seminar that may come in handy:

https://www.ctahr.hawaii.edu/haraa/CPSS ... inoids.pdf

[DesertSun]

Thank you Steve, for the interesting information!

[ElieEstephane]

Thanks steve!

[keith]

MERIT I was told it worked better against root mealy bug than above ground mealy bug. I have found it works against both as long as the roots are working on the plant. I get above ground mealy bug on Dudleyas and they are hard to control . I will spray with soapy water and it works OK, not great but OK. I also use MERIT it can work well if the plant roots takes it up , with Dudleyas that means in winter or Spring not Summer. Or if its bad I just cut the stem off and throw it out and let the plant grow new stems.

From the article

Merit (Marathon) is highly effective against aphids,
Chinese rose beetle, azalea lacebug, soft scales &
whiteflies, and moderately effective against mealybugs.