Sunday, August 1, 2010

The Potato Murders


I've always figured that potatoes are so plentiful and cheap year round, why grow them? Especially here in the Northwest, with spudsy Idaho just next-door. We've got enough potatoes to power a satellite radio.

And then I ate some super fresh just-out-of-the-ground local new potatoes from our farmer's market last year. Carlos roasted them with some olive oil, sea salt, and fresh rosemary. Holy potatoes! Rich delicious food of the gods. The potatoes were the side dish of that meal, but they are all I remember. I felt I had discovered a whole new vegetable (tuber, whatever).

So in early March, we were in the garden center browsing for veggie starts and seeds, when we came upon the wooden bins full of seed potatoes. It felt like a grocery store - you grabbed a handful of potatoes and put them into brown paper bags for weighing at the register. But the thought-bubbles above our heads were filled with visions of putting a single French fingerling into the ground and waiting for it to magically multiply, and buying some wooden bins of my own to keep in our cool dark garage to store the bumper crop of potatoes through the winter, and at Thanksgiving proudly informing the guests that the mashed potatoes on the table came from my garden . . . and so on.

Things went swimmingly for a while. I cut and planted the seed potatoes according to the guidelines in my trusty "Growing Vegetables West of the Cascades." Their green sprouts popped up quickly and grew fast. I hilled compost around their bases, and they kept growing. And then. Something attacked them, one by one, consuming the leaves, turning them yellow, and eventually, causing the entire plant to shrivel.

At first I thought, okay, I overplanted, so it's fine. I can sacrifice a couple of potato plants and still get plenty of potatoes for two people. But no, the vermin weren't satisfied with just a few, and ultimately took my entire crop (6 plants). I thought it was slugs for a while. And I do think that some of the early damage may have been slugs. But every morning I looked for slugs and didn't find any. Instead, one morning, I found this:

The gooey substance looks like it could be slug slime, but I'm not sure. And what is that little orange bug all about? Is it the dreaded Potato Bug??

Anyhow, I long ago gave up on any hope of potatoes. The plants died before they could even flower. But this morning, as I was pulling some weeds and digging around in the soil, I literally fumbled across - yes! - a yukon gold potato . . . and then another, and another. It's a VERY small crop, but a crop nonetheless.

I cradled them into the upturned tail of my t-shirt, careful not to drop any, and ran inside the house shouting happily to Carlos. We plan to roast them for dinner tonight.

So, insect detective, what/who do you think murdered my potatoes in their tender years? I would like to know so that the same thing doesn't happen next year. Obviously, potatoes are pretty resilient, if they can produce spuds like this even after a beheading. Just think what a healthy plant will be able to produce! Thanksgiving 2011 here we come.


Good news first: That is not the dreaded Potato Bug - or Colorado Potato Beetle, which oddly isn't found in a large part of Colorado. What you've got there is a Flea Beetle (I think). Specifically, I think it's a Tobacco Flee Beetle. They don't generally destroy potato plants, but they can vector diseases. Based on damage, you might have had flea beetles on your tomato as well. They prefer tobacco, potatoes and tomatoes. They jump when disturbed, hence the name "flea" beetle. They chew small roundish holes in leaves. They overwinter in debris on the ground, and they attack almost immediately after emergence. So make sure you clean all that stuff off the ground (around your tomatoes too) when you're finished with them. Maybe even turn the soil over this fall.

Insecticides are rarely necessary. You could cover the young seedlings next year. Once the plant is established, Flea Beetles rarely do much harm. Hilling the mulch around the stem helps to prevent populations. It can also cause some problems from molds and other diseases if applied too early. A tin foil mulch seems to work well. Some species really like yellow sticky traps. We normally use sticky traps to monitor populations, but they can help control Flea Beetles. You should buy some anyway, just to see what's flying around when you aren't home.

Fun Fact: plant leaves reflect light smack-dab in the middle of the yellow spectrum, at 550nm. The cones in human eyes interpret this as the color green, because our eyes are pretty green-centric. Leaves are technically yellow. Insects see them as yellow with a hint of green. So, when we want to attract insects, we make cards that are hyper yellow. It looks like the "healthiest" most awesome plant. So the poor little guy lands on it and gets stuck.

Okay, so I don't think Flea Beetles are the primary problem. The goopy stuff really really looks like slugs to me. Slug boards are a cheap and easy way to monitor. Slugs and snails like how damp and cool it is underneath, so they aggregate there (I almost wrote "congregate", and pictured my professors' shaking their heads while murmuring "teliological, Amy." As if I don't anthropomorphize every other sentence. I mean, I just said slugs "like" it.) You can just pick them off and kill them. Another thing that works is inverted melon rind. This is an expensive fix if you do it throughout the season, but works well with an acute problem. Or if you just ate a juicy melon :)

I'm concerned with the yellow leaves. Unfortunately, that's a pretty vague symptom. I did a little research on potato plants, because I don't know much about them. A LOT of attack potatoes that you don't routinely encounter elsewhere. Weeds, nematodes, wireworms, and a staggering amount of diseases. I can rule out most of the diseases, because they affect the tubers rather than the leaves.

I don't suppose you've saved and/or looked at the roots? Nematodes cause yellow leaves above ground, but they leave distinctive root galls. If you have nematodes, you might want to plant a nematode resistant tomato there next year, and put your potatoes elsewhere. Certain ground cover crops will actually reduce nematode populations in the Pacific Northwest: rapeseed, mustard, oilseed radish, or sudangrass. Alfalfa retards population growth. Whether you decide to rotate crops or not, make sure you get all potato plant matter removed from the area, as that can make them multiply. Also, make sure you only use composted manure, as that's a common way they are introduced. Then again, they could have come from your seed potatoes.

It may not even be nematodes. It looks - from the pictures - as though the lower leaves are healthier than the newer shoots. This rules out a number of diseases. Are there streaks, lesions, or powdery things on any of the stems? If not, that rules out a number more. This could have been psyllid yellows. It also could be cucumber mosaic virus (vectored by aphids), curly top virus (vectored by leaf hoppers), leaf roll (which is a seed virus that can be spread by aphids).

To prepare for next year:

Now: Remove all of the potato matter above and below ground. If you can't get everything below ground, then maybe rotate next year. Wherever you plant, you should start with the soil now. This is going to sound weird, but cultivate your weeds. Keep watering the soil to get your weeds to come up healthy. You want to know what weeds grow there. Not all weeds invade the tubers, but some can. If you have any of those, you can treat them. But, for a little while, I'm telling you to water your weeds. In the late winter/early spring, till the soil. Then cover it with a heavy piece of plastic or tarp. This will not only suffocate the weeds, it will also heat the soil for when you plant.

Handling of seed potatoes: Make sure you get certified stock. Sometimes viruses and nemotades come from the seed potatoes. Certified seeds aren't guaranteed to be disease free, but they come from stock that hasn't shown any diseases for a number of generations. Closely examine the seed tubers you choose. When you get closer to buying them, I can give you some pictures of problems to look for. Keep the tubers in your wine fridge, at about 50-55 degrees F, for at least 2 weeks before cutting them. They need about 90% humidity, though, so you might want to keep them on a damp cloth, rotating regularly. If you have them longer than two weeks, keep them in the refrigerator until 2 weeks before cutting. It's best if you cut them when they are just starting to sprout. Make sure you clean your hands and implements between each tuber, so you won't spread any diseases that might be present in one of them.

Planting: Don't expose the cut seeds to intense sunlight or wind. The soil should be moist, at least 45 degrees F, and ideally warmer than the temperature of the seed. This ensures quick healing. If you have to cut the seeds before you can plant, keep them at 50-55 degrees, make sure they are moist, but make sure there's plenty of airflow. Otherwise they'll start rotting. We might look into some possible fungicides to apply to the soil at planting. I'm unaware of any organic options, but they're out there. Too much compost in the soil can exacerbate problems. Too little affects crop yield.

Pre- to early emergence: Monitor for weeds. If weeds become an issue at this point, treatment may be necessary. You can't use vinegar here. This is one of those, might consider Round Up times, but that's another post. At emergence, put up sticky traps to monitor insect populations. We might consider some clear insect covers - although I'm not sure how much light the plant gets. They do a good job of letting light through, but Seattle's a lot darker than I'm used to! Water as much as you need to.

Full emergence: You'll want to keep an eye on weeds, and keep up the sticky traps. You don't want to water as much. Only water if the soil is cracking (does that even happen there?), to avoid certain types of rot to the potatoes and stems. This is a good time to start mulch hilling.

Harvesting: You should kill the vines before harvest, while leaving the tubers in the ground. This allows them to mature. When you're ready to harvest, water the soil to loosen it. This will reduce bruising. Make sure to examine the new potatoes for any damage. They might still be edible and tasty, but they can also help point to problems to anticipate for next year.

Whheeew, that was long winded! I'm sure you know a lot of this stuff. It's mostly new to me, so I figured I'd err on the side of bombastic. You mentioned (one time, I believe) the idea of growing potatoes in barrels. I wonder if that might make the problems easier to diagnose. Just a thought.

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