Mealy infestation in large collection (institute sized)
 

I recently poped into my local botanical gardens to volunteer my horticultural and botanical skills. Turns out know one has touched their orchid house in two years, it is in a pretty sad state and they have said I am welcome to have at it. Aside from being a cultural jumble, there is a serious mealy infestation that has already taken a few plants. To make matters worse they will be moving to new facilities, and thus, taking this infection to a new site in three months.

To keep consise, how would exparienced growers here tackle an infestation of at least 30 of 150+ pots of all different familes?

My plan is to start weekly alternate neem/oil/soap/pyrethroid-garlic saturations in the evenings (we are coming out of winter now), then re-saturate in the mornings to remove residues. Then what? Start repoting by medium/wetness type?

Pretty much all the plants are labelled to species, and mostly all have cultural conditions documented on the labels, but I am in waaay over my head.

HELP!

If it's that bad of an infestation, I think you're going to need a really good commercial - systemic - insecticide. Something based upon acephate (Orthene) or imidicloprid (Merit) would be my recommendation.

AND... Add an insect growth regulator (IGR) like Enstar AQ, and it'll really help.

I knew that would be the first suggestion, cheers Ray. The problem I have is that the Head of the Gardens refuses to use "chemical" controls. While I am hesitant myself for environmental reasons, it does seem it could be either do it or loose the collection. How does one argue for that?

I thought that may be an issue.
Best thing to do is to isolate the affected plants and follow your regimen. Repot those first, after a couple of sprays - but obviously spray the entire collection. I have had good results with sucrashield as another alternative. Best to alternate types of spray - I have used neem and Dr Bronner's soap/alcohol too.

Thanks :) I am not sure if it is appropriate to post pictures of the facility but I may do as I start to work though the collection.

Should I be worried about the timings of re-potting? Many of the affected plants cultural notes say re-pot after flowering. Is this just to avoid 'sulking' or is it a life or death decision?

coming into Spring for you, I wouldn't worry too much. Probably getting a repot will override all other concerns.

I say let the collection die. I know that sounds drastic but the director is a troglodyte. Spraying with an approved insecticide/fungicide shouldn't be an issue. It's like saying, "if God had wanted man to go to the moon, He would have put him there." Spraying, in the low doses prescribed, has such negligible effects on us it's foolish to allow a collection like this to die due to his stupidity. We breathe in more crap in one day than what will be sprayed on the collection. So in my opinion, let the collection die and maybe the board will get rid of him. Then maybe someone with some common sense will replace him.

All institutions here are now fighting organic (MNHN, Serres d'Auteuil, Serres du Sénat…).

Now to stop on a large scale (pun intended) without chemical will be some job.

- Trash the eventual hybrids that can be find easily, especially on catts like and oncidium like. See with the director before doing so. The aim is to limit the number of plants to treat and not arm the collection.

- I'd start by a general cleaning by mechanical means (be it by hand of with water), and general water (1l)/alcohol (3 tsp)/safer soap (liquid, 1 tsp) spraying everywhere. repeat every 2-3 days, and if you see one mealies : spray on the spot. It's a contact killer.

- You can use Neem as long as it's fresh and duly emulsified with safer soap, not to clog stomates, or it'll kill the plants even more surely.

- If there's nettles near, or you can have good nettle manure, spray with a 2% solution, it's repulsive, they don't like it at all. Fresh nettles will be killing them (24h maceration 1 kg in 10 liters, dilute 5%)

- Clean the area. (you should find one or two volunteers to help, there's an orchid society around?)

- Repot everything that can be so without trouble (for example, don't on catts not issuing new roots). Those that can't be, maybe a bath with a little alcohol in it (I tried one teaspoon per liter on big hybrid phals, it's does marvels, be careful, soak before, and flush after. I have not tried on small roots or temperamental plants so be careful.

- Here the Museum in Paris, and the senate GH use a spray with essential oils when the auxiliaries are not enough. As you're in a hurry, the auxiliaries are not an option fast enough. The spray : for one liter of water, 3 tsp of safer soap, 10-15 drops of essential oil of cinnamon bark (not another kind of cinnamon EO!).

The combo alcohol/soap and nettle manure helped me to stop a mealies invasion in a month, with 2 applications of each when needed after a total cleaning, nettle bath, and repot. Chemicals (when working) could be of help, sure, it means less work, but it won't mean not to clean the bugs away, not to repot.

First things first: get some help of one or two persons into orchids, you'll need them, and clean the mealies away with a douche and a tooth brush to start the elimination.

I agree in principle with James, but another approach might spare some of the plants.

Discuss with the director & get approval to do some triage. Identify and segregate plants that show no infestation from plants that do show infestation. For the infested plants, determine if any of them are:

(a) Otherwise diseased (fungus, bacteria, probable virus, etc.) Get permission to discard any that appear to be virused. Decide if the others are worth treating.

(b) Rare or unique. A rare or unique species, or even some rare old hybrids, may be worth saving, if they are not virused.

(c) Any NOIDs in the collection? For a botanical garden, these should be discarded anyway (again, with permission).

If the orchids have mealybugs, the orchid house will have mealybugs. You may want to research whether there are any mealybug predators that are approved as biological control, such as Cryptolaemus montrouzieri (Mealybug ladybird), an Australian native. I think Cryptolaemus montrouzieri have been used in NZ as well. They have been introduced in some places here in the USA for mealybug control (they work on some scale insects, too). Check with any university in your area that has an entomology department. See if the director will approve this biological approach.

I really have to bite my tounge to this reply. I almost consider your comment racist, and I cannot stand people whom try to use "if God had wanted man to go to the moon, He would have put him there" to prove a point. "If God wanted Americans on the earth, he would have put them there", its a complete rubbish statement! On top of that, it is this attitude, from your generation, that has got this planet into the state it is in. The less toxic chemicals used in day-to-day situations the better. Negligible effects on us at the point of time while spraying, but what as every man and his orchid house is spraying and discharging into the environment where it is bioaccumilated? This is a botanical garden where a healthy ecosystem is encouraged. I don't mean to offend you but pull your head in buddy.

Just to clarify, I am a volunteer and am being relied on not out of laziness but out from need for lack of funding which is a systemic problem for ANY not-for-profit institution in New Zealand (and probably the world). They have taken up my offer to help as I am a locally-reputable undergraduate botanical ecology student with well-known enthusiam for orchids, that is able to work independantly and thus not require them to sink resources they don't have into training someone.

Ray, Orchid Whisperer, and lepetitmartien exactly the advice I needed.

I'll keep you all updated, I imagine this will be a long battle.