Are those bugs still alive?

The short answer

Touch one.

• A live aphid moves, or squashes wet and green.
• A shed skin is dry and chalky. It flicks off and leaves nothing behind.

It takes two seconds and it decides whether you have a problem or a memory of one.

This one is my own observation rather than something I am citing a paper for — but it is easy to check for yourself, which is most of what a test needs to be.

Why it matters more than it sounds

Aphids leave their old skins behind every time they moult, stuck to the leaf where they were sitting. A colony that has been dealt with — by a spray, by predators, by a change in conditions — leaves the leaf looking exactly as infested as it did at its peak. Pale specks, in the same places, in the same numbers.

So a grower checks, sees what looks like a live population, and treats. Then checks again a week later, sees the same specks still there, concludes the treatment failed, and escalates. It is possible to run that loop for a fortnight against an infestation that ended before it started.

Counting is only worth doing once you know what you are counting.

Identifying what you actually have

The reference text for the field describes foliar aphids on cannabis as soft-bodied insects forming dense, largely stationary colonies — typically on stems and the undersides of leaves. That combination is the useful part: something clustered and not moving much is a different problem from something scattered and fast.

It also makes a point that saves a lot of arguing: several aphid species turn up on cannabis and they are hard to tell apart by eye. If you cannot name the species from a phone photo, that is not a failure of your photo. Work from what the colony is doing and where it is sitting instead.

The one that is not on the leaves at all

This is the detail I would most want a grower to know, because it sends you to the wrong place otherwise.

There is an aphid that lives on the roots — the rice root aphid — and it will not show up in any amount of leaf inspection. The plant just underperforms. The tell described in the chapter is indirect and easy to miss: winged aphids appearing in a hydroponic system are a cue to go and look at the root zone, because that is the dispersing stage of something that has been living below the line the whole time.

If you have unexplained stunting and you have seen winged individuals, look at the roots before you spend another week on the canopy.

On what to do about it — deliberately not on this page

I am not going to tell you what to spray. What is permitted on a flowering cannabis plant depends on where you live and changes over time, and a stranger on the internet is the wrong source for that decision.

What I will say is that the chapter discusses control in a few broad families — physical removal such as rinsing, soap- and oil-based products, and biological control using parasitoid wasps that specialise in aphids — so that you know the shape of the options before you go and find out which of them apply to you. Check your own jurisdiction and your own stage, and treat that as the actual first step rather than a formality.

What would show that I have this wrong

If you touch several and they move, you have a live population and the rest of this page is beside the point — go and deal with it. And if what you are looking at is not on the leaf surface at all but in the tissue, sorting by leaf age or spreading into new growth, then it may not be a pest at all: start with the pattern.

Where my device fits, stated narrowly

Croplock does not identify pests for you, and I would be wary of anything that claimed to from a photo of a two-millimetre insect. Where it helps is the same place it helps on everything else: it photographs the same plants on a schedule, so “were these here last week” is a thing you can look up. The touch test is yours and it is better than any camera.

Sources

• Lemay, J. & Scott-Dupree, C. “Insect Pests.” Ch. 9 in Cannabis in Controlled Environment Production (CRC Press). DOI 10.1201/9781003150442 — foliar aphid colony behaviour, the difficulty of species-level identification by eye, the rice root aphid, and the winged-aphid cue to inspect the root zone.
• The live-versus-shed-skin touch test is my own observation and is given as that, not as a finding from the chapter.

More of these at Answers. The device is at croplock.com.