Whitefly damage and control

[Purrfluff]

Greetings from the Pacific Northwest.

I noticed something for the first time the other day on one of my brussels sprouts plants. There was this buildup of something like looked fireplace ashes. But they weren't ashes and were much stickier. Then I noticed the substance on other leaves. And I found it on other plants.

I noticed two commonalities. First, the gunk was present mostly on leaves that had curled up and turned yellow. The curled up leaves hid the crud from me.

Secondly, the gunk and curled up leaves seemed to be mostly concentrated on budding points on the plants. I found it on brussels sprouts, broccoli, and cauliflower. By budding points I mean places where I think broccoli florets, brussels sprouts fruiting stalks, and cauliflower heads would have formed/grown.

I wondered why I hadn't gotten any sprouts or broccoli out of the starts that I bought (as opposed to the same kind of plants I started from seed). I haven't gotten anything from my plants started from seed because I started them too late. But the nursery starts were my insurance against that. I think the reason said starts didn't produce anything was because of this damage.

I did some research and I think what attacked my plants are some kind of white fly. Possibly the ash white fly or cabbage white fly.

While I did spray BT to keep down the imported cabbage worms (and it worked) I haven't used much of anything else. I didn't think it was needed. I foolishly thought the cabbage worms were my only insect enemy. And so I was only on the lookout for holes in leaves which would be indicative of cabbage worms. I put down sluggo to control slugs.

Instead this damage has created leaves that are curled up, yellowed, and stunted. And nothing grew from the area that was attacked.

I'm pretty pissed off at myself for not noticing this earlier. I should have. The yellowed, stunted leaves were right there in front of me. And I've seen teeny white insects flitting around some of my plants. I assumed they were newly hatched cabbage moths but I'm now 99% sure I was wrong.

So my question is... am I right? Is this some kind of white fly? Is the crud I am seeing their doing? And if it is white flies (or some other sucking insect) how do I control them? And why did they only go after a few kinds of plants? The leafy greens appear to have been completely unaffected in this fashion. Why?

On hand, right now, I have neem oil and insecticidal soap. I think both of those work reasonably well on white flies but I don't know how long they will last and how fast they kill the insect. Also, it's been raining almost every day here so anything I can put on the plants get washed off in about an hour.

I may have a window of dry tomorrow. So I'd like to hit them with something that kills them in a matter of hours. Because a day later the rain will wash everything off. I'm leaning towards neem oil because I am hoping it will be more effective more quickly than the soap. Plus I have a concentrate I can stick in the pressure sprayer.

What I've already done is is washed off the crud with water. I cut some of the leaves that seemed especially damaged. I actually misidentified the pest the first time and put down another coat of BT onto everything. Which will do nothing against the white flies, of course. But it might waste the last of the cabbage worms.

 

[Purrfluff]

Update and corrections:

It appears I spoke too soon. I found whitefly damage and that nasty sooty fungus on more plants. They appear to have infested each of the red cabbage plants. Primarily on the leaves where heads are forming. But I also found the crud on some kale.

The red cabbage plants I found the damage/crud on consisted of plants I started from seed as well as nursery starts. So I can't blame the nursery for these critters. And all of the kale was started from seed.

I can't really figure out a pattern to which plants they have infested. Perhaps there isn't one. The only firm commonality is that they did the most damage to the plants I didn't notice them on. Which is the real problem here: I didn't notice. I am rather ashamed of that.

The loose commonality I found is that they did the most damage on leaves that were curled up. Whether the leaves were curled up naturally (i.e. heading cabbage) or the result of their attacks (i.e. the kale). They seem to to especially like the soft points of new leaf and bud growth.

I truly don't know how to control these damn flies. It sounds like neem oil and insecticidal soap will kill them on contact in a few hours. But I think once those substances dry the whiteflies will just come back and start over.

I could try dusting with some kind of hardcore insecticide but I'm reluctant to do that. I don't want to kill every insect in my garden. Especially the honeybees. And since I don't think these flies discriminate in what they want to attack I figure I would have to dust everything in the garden. And that would kill they honeybees.

I suppose my best bet for now is to spray insecticidal soap on new growth periodically. And to check for their presence all the time.

What I really need is some kind of hyper effective repellent. I suppose interplanting flowers with the veggies next spring might help.