Over the last week we began to see a dramatic increase in aphid populations in our greenhouse, especially in the lettuce.
On the sticky traps, the number of winged aphids caught increased several times and the number of aphids that we see on the lettuce that we’re packing is definitely on the rise.
I think that aphids on lettuce is particularly difficult to deal with. Lettuce is a short lived crop, rarely in the beds longer than 6 weeks. Usually we treat aphids with parasitic wasps, but by the time they lay their eggs on the lettuce leaves, we are too short a time to harvest for the new wasp to emerge and continue laying eggs in new aphids. It also seems that the spaces in the foliage are difficult for the wasps to get into as they do not seem to parasitize the aphids that are down in the heart of the plants as well as they do the ones on the outside area of the leaves.
We did use the wasps (and a few are still around) which got ok control over many weeks, but the aphids seem to be 95% clear of parasitism right now so we brought in an experimental insect: lacewings.
Lacewings themselves aren’t experimental, but using them for aphid control on letttuce is a little unconventional. Like the parasitic wasps they tend to establish themselves in a place and reproduce there, so we are not sure how well it will work with this short-lived crop.
A challenge with the lacewings is that I’m worried about customers finding these jouviniles in their lettuce. I’m imagining that they would find it more disgusting and less interesting than I would.
Our biggest challenge using these insects is that I cannot put it out on the harvest side of the lettuce beds (because those trays are removed every 3-4 days. So I put it along the sides of the beds and also on the seedling side of the beds. I’m hoping that they are mobile enough to move the 15 feet towards the worst of the aphids and not stay on top of each other where they’re pictured here–otherwise they’ll eat each other and have no real impact on the aphid outbreak.
We’ll see how well this works. I put out 10,000 of the critters on an area that is 130’x21′ and I’ll let you know what I observe.