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I'm new to Salvia and to top it off this is the first time I have EVER had mealy bugs. I noticed them on my black and blue, 3.5 foot tall salvia, but did nothing at first because I was busy, forgot about it, didn't think much about it... Anyway, I went back to that part of my garden a couple weeks later and the salvia was dead looking on the branches (half of them at least) with the bugs AND they were spreading to sages and lavenders and across the ground from one plant to another.
I did lots of reaseach and came to the conclusion they were mealy bugs (although, I didn't see any of them crawling). I sprayed with insectisidal soap, nothing, ~ week later I used some pesticide I had in the garage that said it killed meally bugs. They stopped spreading , but there was no difference in the way they looked. Just white up and down stalks. I cut the dead parts of the plants off.
Now we are finally getting winter weather, and the remaining dead salvia stalks are still there with this white stuff all over them.
Question: Since the season is over, I was planning on cutting back the salvias and sages and other dormant plants now.
What can I do to encourage these plants to rebuild their strength and return next year?
Or are they most probably already dead?
Should I dig them out and sacrafice possibly live plants to erradicate the bugs?
The white stuff seems to just sits there and stare me, and I just stare back because I don't know what to do.
Ants are the primary vectors for mealy bugs, since they produce honeydew that the ants crave. They can make a mess of my stock plants if I do not control them.
They can be easily killed at the nymph stage, which is when they look like off-yellow near microscopic dots. The adult males look like small mosquitoes and fly (a telltale sign), and the fertilized females are the stationary ones that lay their eggs underneath themselves and then die, allowing the first instars to build up strength. If you wipe off the white fuzzy mass, you will find the babies underneath as a soft yellowish powder.
Since they need to be exposed for insecticide and predators to kill them, I spray the infected sites with a fine jet of water to dislodge them, the same way you remove sucking aphids from stems. In the case of the aphids, the jet tears off the aphid from the stem, leaving their stylets stuck in the stem and making the aphids unable to reestablish themselves on a fresh stem.
After the mealys are exposed, spray the plant with your insecticide (Safer soap or a harder chemical). Control the ants at the same time with a bait.
if safer's doesn't work well for you, if doesn't for me, try parrafenic oil, usualy sold as sunlight oil. it is a petroleum based oil, but it isn't a poison, it suffocates the blasted things and the bugs don't get resistant to it, like harsher chemicals. Salvias are not listed as safe, so try 1 and see what happens, damage usually shows in a day or 2, read instructions and here in the humid South, I stay at least 5 degrees under max safe temps. Never got them on my salvias but it sure wipes them off the camellias and hollies. it is not a systemic spray, so you need to reapply every week to 10 days till they are dead, not gone, they tend to adhere long after they are dead, they dry and stick, scales, similar pests do the same, peel one off and see if it is soft underneath, if soft, alive or recent dead. hard and dry, dead. Good luck, persistent and damaging but not immedieatly deadly
One other thing about mealy bugs. They can also attack roots. Lift a plant out of its pot and check for white fluffy, fibrous looking blotchs, usually an eight of an inch or less. The mealys might look more like a white fungus attack at first. This is probably how they overwinter as well, and ants are probably the way they get there. You can help a plant recover by hitting the root ball with a drench. I am not sure safer soap will work here, especially if the plant is frequently watered. Since the natural media for the roots is moist, the root tips might be damaged by the treatment. Here I tend to use the harsher chemicals, especially if it is a rare plant and there are few or no other clean stock plants.
It is a good idea to burn the cut back contaminated plant material, since it harbors pest eggs and pupae as well as tissue infected with both dormant and active pathogens. The material should be dry when burned. When you do this, make sure you are not violating outdoor burning bans. For the homeowner, the burn will likely be over in a few minutes. With my collection, I need to watch the burn for as much as 40 minutes..
I never had a problem with mealy bugs in my whole life, until 2 years ago. Now I'm suffering payback! Safer Soap is always my first line of defense. They laughed at it; in fact they seemed to thrive on it! So I started up the scale, first with pyrethrin, then rotenone, you know the drill. I could knock them down, but never get rid of them. They'd be back within 2 weeks. That white cottony stuff they put out protects the bug underneath pretty well. Unless you use a jet spray like Rich_d suggested, the insecticide won't get through to the bug. I've finally got them under control (but not eradicated!) by using a combination of bermudakiller and Rich_d's approach. I mix up a batch of sun oil, pump my sprayer up to the point where I think it's going to explode or I'm going to suffer a heart attack (whichever comes first), and blast everything in sight. Unfortunately, "blasting" them also spreads them if the oil doesn't actually get to the insect to kill it. I'll be doing it again this year I'm sure, but I'm "going to ground" this year with DY-Syston or Merit in addition to the oil blast. But oil gave me the longest respite from these nasty things.
Did you have a very hot August and drought, like we did in central North Carolina? They may have always been there, and discovered some stressed plants. Ants will certainly reinforce their sweet tooth for particular plants.
Systemics would get rid of both the foliar and root mealys. The effectiveness would be increased if the plants are made more vigorous by adding compost (worm castings work well). Tomato plants with phosphorus deficiencies attract whitefly, so there may also be a nutrition imbalance, like too much nitrogen and not enough potassium, phosphorus, or trace elements like boron or manganese. An incorrect pH might lead to the inability to absorb micronutrients like iron. Finally, some plants can get too much of particular nutrients. South African proteas like phosphorus poor soils and our normal fertile soils will kill them.
As new plants are introduced from the wild, collectors should record the soil type and exposure to help settle problems like these.
Sunlight oil is a petroleum based oil, known as paraffinic oil. Sold under several names, but sunlight is the only one available here., Ultrafine used to be offered as well Do a net search but also a price comparison as the prices vary widely but are fairly consistent at the big box home improvement stores. Buy several bottles if you find it as it sells out fast, keeps for years and is poorly restocked. One thing that is most important is contunued use till all eggs have hatched and have been killed before thay can lay again. Look up life cycle and see the time from hatch till the next generation, usually a week to 10 days is enough, but not always.
Rich, as i can't burn often, esp. in the current drought, I usually put insect ridden brush into plastic bags and seal till i can burn. I wanted to know if you had any better ideas?
bermudakiller, keep the material as far away from your plants as possible. Storing in a dark bag will probably cook the critters during hot summer storage, but the bags will get fragile and tatter readily from UV photodegradation.
For mulch, if you can't find worm castings, use hardwood bark mulch (not ground brush with lots of wood tissue or pine bark mulch), and dress the mulch with coffee grounds to provide nitrogen. There are three benefits to using grounds: worms love them, the nitrogen breaks down the mulch into ideal compost, and the leftover caffeine will probably deter ants and other pests.