Tiny white grubs/maggots eaten through sweetcorn stem

[lukens]

I have some sweetcorn plants, which are still rather small (due to lateish planting and lack of sunshine). Today I found one lying down and looking a little sorry for itself. I went to stand it up, but the stem seemed to have rotted through where it joined the roots.

I pulled up the roots, and whilst carrying the lot over to the compost I noticed a bunch of tiny white grubs or maggots crawling out of the stem.

Any idea what they are, or what I could do to protect my other corn plants?

I checked the others, and saw grubs around the stem of one other, which I picked off and squished with my fingers. They also seemed to be accompanied by a gang of ants.


Three of my cabbage seedlings in the same bed have also died. They seemed to have had all the side roots eaten off, and one of my kohlrabi (over the other side of the garden) is wilting in a similar manner. No sign of grubs on these, but there had been a lot of ants crawling in and out around the side of the stems, as with the second sweet corn plant that had the grubs.


Don't these pests know it's Fathers' Day?!

[Two_Sheds]

On your cabbage, it's most likely cabbage root fly.

On your sweetcorn, I would guess at fungus gnats: have you noticed black flitty flies hanging around the plants?

[lukens]

I've checked my books, and they say fruit fly maggots can do what I've seen on the sweetcorn. Looking on google images they look a bit more like what I saw (the fungus gnat maggots have more of a black head and black insides, it seems).

I think my sweetcorn has so little chance of reaching maturity anyway now, I may just give up and dig it up.

I had also sown some dwarf peas round the base of the corn, and they've done nothing, and digging around I can't find the seeds. There was no disturbance to the soil, as I'd expect if a mouse had taken them.

I'm not having a lot of luck. My broad bean have chocolate spot too, and my dwarf French beans seem to have given up the ghost; two beans are growing on one, but that's about it, they've not got any taller since planting out (the crazy warm week followed by the crazy cold and wet coincided badly with my hardening off and planting out).

Still, I have had one nice crop of radishes and one of pak choi.

[Two_Sheds]

Your problems are mainly down to the weather, not to you or your choice of plants. Sweetcorn & French beans need warm sunny dry weather. If we could've predicted the extended long cold spell, we'd have delayed the planting out.

I'm starting some more French beans off today, I just have enough time for a harvest (they generally take 3 months from seed to plate).

It's been a bad year (wet & cool) for Broad bean Chocolate Spot: "The fungus produces masses of air-borne dispersal spores under wet conditions which spread the disease." RHS

[lukens]

I also had some peas turn all yellow when I put them out in my plastic mini-greehouse thing to harden off just as the sudden heatwave hit, and I'm guessing it was the heat did them in. They're still struggling on, but have been well overtaken by some I'd sown about a month later.


I also took a picture of the maggots last night:



(bigger but just as out of focus version)

[vicky]

I'd re sow like TS suggests too. This week I sowed lettuce, basil, spring onion, french beans (dwarf), beetroot, spinach and carrots and I'm planting out squashes still so you could get some plants from the shops of those. It's not too late to sow things but I wouldn't bother with sweetcorn this late. The weather has really stuffed up lots of plants and so many are delayed in their growth - last year I had a courgette glut in june, this year not even one yet...

[lukens]

I've already resown some dwarf French bean, and have various other plants that are so far doing quite well, and others ready to plant out (including some gherkins which already have little babies growing).

Am wondering whether to give up on the sweetcorn altogether this season, and just plant something more hopeful in its spot. It takes up a lot of space, so if it's due to fail anyway, I may use the space for something more useful (and likely to succeed). I may give it a week or so to show willing, and if there's still little progress (or more are lost to maggots) I'll dig it out and replace with some oriental brassicas I've got seeds for (and which are said to like being sown after the longest day).

[Two_Sheds]

I also took a picture of the maggots last night:

yuk, that's nasty. They look quite big ... what size would you say they are? 1cm long?

I can't find any pests specific to sweetcorn, so I think they're opportunists who got in the soil. Have you over-watered would you say?

[lukens]

Ah yes, I guess there's nothing in that picture to give an idea of scale. You're possibly over optimistic about how big my sweetcorn had got. They are pretty tiny grubs, I'd say they were about 2mm long, 5mm at most.

I've not really watered at all, but obviously nature has been playing its part. They're also planted in my sub-irrigated raised bed (as illustrated here), so, in theory, they "self-water" via capillary action from the reservoir below.

I had also earthed up around the stems a little, as they were flopping over a bit in the wind, so this would have caused extra moisture around the base. I was worried this was a contributory factor, so have un-earthered up the remaining ones now they're a bit sturdier anyway.

They seemed mostly interested in the juicy your insides of the stem though, to the extent that I'd not really noticed them until they started crawling out, and I broke it open a bit more.

Two books I have mentioned fruit fly maggots tracking young sweet corn seedlings, a Joy Larkcom one, and a Which? one. They say they're usually immune after the 5/6 leaf stage, but mine may not quite have made it there yet.