Thursday, June 2, 2011

Cucumber Beetles and Bacterial Wilt

These pictures show bacterial wilt.  It can start rather innocuously.  The first picture shows normal leaves and then, at the bottom, a few that are wilted but which don't look awful.  As soon as a day later the leaves and then the whole plant will wilt, then turn dry and crisp. This may start on just a part of a leaf, as in the second picture.

With the wet weather the gardens are getting in later than usual, but the pests have hatched on time.  So this year they're voraciously waiting for our seeds to hatch.  I think that seedlings are even more susceptible than seeds, and so I always grow my squash family plants from seed in the garden, rather than transplanting.

Striped Cucumber Beetles are about 1/4 inch long, with a rectangular back striped yellow and black.
They will feed on all cucurbits except watermelon, plus tomatillos and a few other plants.  (I've found them on tomatoes and milkweed).  They like the undersides of leaves, especially lower down on the plant, and the interior of blossoms.  (There is another species called Spotted cucumber beetle, which we don't have).

At least in the community gardens the beetles aren't here in large enough numbers to damage the cucumbers themselves, but they carry a devastating disease called Bacterial Wilt.

About 30 days after the infected beetles start to feed on a plant, the water-carrying pores in the plant stems become clogged with bacteria and the plant wilts dramatically and dies.  It's very important to get rid of the cucumber beetles, their eggs and larvae.  We may get as many as four generations during the summer, and if the last generation in the fall has fed from plants carrying disease, the disease will carry over the winter in the bodies of the cucumber beetles.  So pulling and destroying any plants with the wilt will also reduce the amount of disease next year.

The plants can be protected by floating row cover, or by spraying with a kaolin clay.  The floating row cover (the best known is Reemay, but you can get a lighter-weight insect control fabric, which is a spun polyester) keeps the beetles from getting to the plants, and is a useful solution for root maggots, potato beetles, and bean beetles as well.  The cover has to be removed at blossom time for pollination.  Otherwise you can get varieties that are parthenocarpic, meaning they don't require pollination.  They'll also be seedless if protected from pollination.  Johnny's seeds shows varieties that are parthenocarpic in their descriptions.

Surround is one brand of kaolin clay, available from Gardens Alive and perhaps other places, which will keep the cucumber beetles from eating.  These are the two best solutions to prevent feeding. I've found that the Surround even lasts through a rain or two.  The most difficult thing about it is application.  It tends to clog sprayers, but the fine mist of a sprayer covers better than applying by hand.  (You might experiment with Kaopectate, but I've really no idea if it would work, or if there's anything in it that would harm the cukes.  It's obviously edible, so that's not a problem.  Try it on just a few plants at first.)

The beetles can be killed with rotenone and/or pyrethins (sometimes called pyrethrum), acceptable on organic programs.   But even killing the beetles that have landed on the plants will potentially let them feed initially and transmit the disease, so prevention is the best strategy. (The disease is transmitted through their feces which contaminate the open wounds in the plant from their feeding).

The beetles are even more attracted to tomatillos than to cucumbers, so tomatillos can be grown as a "trap crop" to collect the beetles away from the plants you want to grow.  Then it's important to collect and destroy the beetles on the tomatillos, so they don't build up a big population that way. The tomatillos don't particularly suffer from the beetles, and you can use them in salsa.  I wonder whether having a large number of beetles that feed exclusively on tomatillos will reduce the number of infected beetles (since the tomatillos don't have bacterial wilt), but don't know if that's so. 

During cucumber beetle season turn over the lower leaves of plants in the early morning when the beetles are sluggish, and either catch the beetles and throw them into soapy water, or crush them.  They fly readily, so catching them in mid-day is difficult.  Also rub off the yellow eggs they've laid on the undersides of the leaves.

Some varieties of cucumbers and summer squash are more attractive to the beetles, and some are more susceptible to the disease.  If you pay attention to the varieties you grow you might be able to determine this.  County Fair is a variety of cucumber (available by catalog) reputed to be somewhat resistant to the bacterial wilt.

Another strategy is to plant successive crops of cucumbers.  Often we'll get some cucumbers before the wilt destroys the plant, so if you've planted every 2 weeks you may get an adequate harvest in spite of the disease.

This is the most challenging pest we face in our Community Gardens, since the damage from the disease is irrevocable.

Tuesday, March 8, 2011

A Very Different March

Just reading the entries from the daily log for last year, and finding we had a relatively warm March and I had started more seeds than I have to date this year.  But we had our largest March snowstorm ever yesterday, and the yard looks exactly like it did in the picture from the last post.  Very long winter.  122 inches of snow so far, and not enough of it has melted along the way.

I usually get stuck with no more space for the seedlings, and that sets them back.  Keeping them transplanted into new spaces each month is as important as starting them early; seeds started in March can still be a couple of inches tall in May if they haven't been transplanted and fed in a timely manner.

This year I started 3 seedlings each of Tomatoes (Beaverlodge Plum, from Territorial), Peppers (Ace), and Eggplant (Nadia) about 3 weeks ago, so that I can start most of my seedlings later than usual.  This way I'll still have some very early produce without being burdened with too many big plants.  Usually by this time I'm setting plants outside on warm days.  No warm days this year!

I've also started all my onion seedlings (Ailsa Craig, Red Bull, Copra, King Richard Leeks, Purly Chives, and Nabechan scallions.)  I'll replant the scallions several times.  Started about 30 lavender, a dozen Magic Fountain Delphiniums which should blossom this year, oregano, sage, and rosemary.

Tuesday, February 8, 2011

The New Garden Year

My, my.  Once the garden started last spring I seemed to be too busy to write.  Maybe this should be an off-season blog, and I'll let you know about pests, diseases, and give some recipes, and then garden while the sun shines.

A friend told me in the fall, "Next year's garden never looks as good as it does now," and I'd have to agree.  My garden for the coming year is meticulously planned, I've ordered and gotten most of my seeds, and now I'm just waiting for a couple of weeks to start the onions, scallions, herbs, and long season flowers.

More about varieties soon.  I've changed my tomato varieties slightly, and added some lettuces.  Am planning lots of lettuce.  Will be growing kohlrabi for the first time.  Have never even eaten it, but one of my fellow gardeners swears it's wonderful, so I'm jumping right in with 3 varieties.  More kale, peppers, cucumbers.  Fewer tomatoes, no melons, fewer onions (they got a fungus disease last year).  Am growing some multicolored corn for the first time in a long time.

We're snowed under with a dangerous amount of snow, and it seems like a good time to dream garden dreams.  Will write more soon!

Tuesday, May 25, 2010

Root Maggots

Members of the cabbage family (and onions: see below) are sometimes damaged by the larvae (maggots) of a fly that looks a lot like a small house fly.  The flies lay eggs at the base of the plant.  The eggs hatch and then the maggots feed on the roots. Plants like broccoli and cauliflower will then wilt easily during the day, because they can't transport enough water up to the tissues with their reduced supply of roots.  The plants may simply fail to thrive, and the leaves can have a shriveled appearance.  If you clear the soil from the roots you may find there are not a lot of side roots, and you may see some of the maggots, which are 1/8 to 1/4 inch long, and white.  The plant might be saved by drenching the roots with a rotenone or pyrethrum solution, and pulling soil up over more of the stem, which can root along the stem.  Often though, it's more practical to pull the plants so you destroy the larvae, and replant.

The damage is most noticeable and distressing when the maggots get into radishes (which, after all, are enlarged roots).  You can sometimes see the actual maggots when you pull the radish, or at least see the brown tunnels along the top and sides of the radish.  If the soil clings in clumps to the taproot below the radish that's often a clue there are maggots, since in our sandy soil that wouldn't otherwise happen.  If you're not squeamish, part of the radish can often still be eaten.  But those radishes will be hotter.  The radish at the top of the post has not been damaged by a root maggot - notice that the soil did not cling to the root, as well as the absence of tunnels.

The key to prevention is to keep the fly from laying eggs at the base of the plants.  Pieces of cardboard, tar paper, or old carpet can have a slit cut to the center, a small circle cut for the stem, and then slipped around the stem to lie flat against the ground.  I haven't ever tried that method. What I've usually done is put wood ashes around the stem, or along the row of radishes, which in theory makes an inhospitable place for the fly to lay eggs.  I've had only moderate success with radishes doing this, but haven't had any problem with the maggots draining energy from my larger plants since I've done this.  Haven't yet done it this year even though the plants have been in the ground for a week.  This is a mistake, and I need to get to it soon.  I reapply the wood ashes after every rain that washes them away.  Right now it's hot and dry and so I'm watering a lot, making it impractical to keep reapplying. (I don't have root maggots yet this year.  These are pictures from last year.)

Some folks in the community gardens haven't had any trouble at all with their radishes, and others of us have had.  Considering these are flies you wouldn't think they'd stay in a plot, so I'm not sure what the reason is.  It might be a timing issue.

Onion maggots are a different species.  The fly lays one egg generally at the soil line, and when it hatches and starts to eat, the greens will start to yellow and maybe wilt.  When this happens there's no point in trying to let the onion continue to grow. You will usually find the maggot at the base of the onion itself.  Throw the onions or at least the maggots in the trash, not on the ground. Read more about them here. We also have onion maggots in the community gardens, but they haven't been a significant problem.  Or at least, they haven't been a significant problem for anyone except JP, who typically gets his shallots in very early.  One of the lessons is that the timing of planting can make a huge difference in protecting us from the emergence of some pests, or in trapping the pests in plants we can later discard, leaving our crop to grow on .

The surest and safest way to protect plants from root maggots and many other pests is to cover them with a grow fabric made of spun polyester.  It does warm the plants somewhat (we don't need that) and reduces the light transmission marginally (which is fine for us).  It's a nuisance to deal with, but very effective.  I've never done this for root maggots, but last year I covered my cucumbers for 3 or 4 weeks to give them a head start over the striped cucumber beetle.  More on that later.


The cutworms are out in full force right now.  They are the caterpillars of a fairly nondescript moth, and I explained about protecting your transplants with a cutworm collar here: (scroll down to "adding a cutworm collar").

One of the things I do with seedlings which are impractical to protect with collars, is to leave a few weeds in the row so there's something to eat besides my seedlings.  About the third week of June the cutworms will have pupated, and/or the stems of large plants will have gotten large enough and tough enough so you can remove the collars and weed close to the plants.  As we've had a warm spring it may even be possible this change will take place by mid-June.

I find a few when digging transplant holes or weeding with a hoe, and dispatch them then. They usually curl up when you find them, but they may be out straight as well.  They eventually grow to about an inch, (which this one was) but you may find much smaller ones now, just beginning to feed and grow.

Thursday, May 20, 2010

Saving Milkweed

Milkweed is one of the most beautiful flowers we can grow in the garden, and the fragrance is intoxicating.  It's also food for monarch butterfly larvae (it's the only food the caterpillars eat).  This site even suggests planting it for that purpose.  Lots of other insects and bees love the nectar too (see the small bees at the upper left of the blossom in the picture). Monarchs are so challenged with loss of habitat in their winter grounds in Mexico that it's a privilege to do everything we can to help their numbers remain high. 

In the garden it seems to be a weed, but in fact except for its inconvenient size and shade (which in our hot garden can be an advantage) it really doesn't behave like a weed.  The root is one substantial tap root, which reaches down a considerable distance, and therefore brings up minerals from below the level that other roots typically reach.  Because it doesn't have much in the way of lateral roots it doesn't interfere with the growth of nearby plants. So it's a great way to grow organic matter for next year's garden.

So I leave as many milkweed as I possibly can.  This year I designated a spot for them, approximately where they were last year - but instead they have moved (or been dragged by the tiller?) elsewhere.  Once the plant matures the long roots stay in the garden and send out runners from which new plants will emerge.

Here are a couple of pictures of the plants just emerging- the shoot can also have a reddish cast:

Japanese Beetle Larva

This ugly grub is what the Japanese Beetle looks like at this stage.  Notice how large it is - much larger than the Japanese Beetle itself.  It's these larvae that eat the roots of grass in lawns and destroy large patches.  Reseeding is only moderately successful if there's an infestation of the Beetles, because these voracious grubs will hatch each year.

About 35 years ago my family had a significant Japanese Beetle problem, and we treated both our back and front lawns with Milky Spore disease, which kills most of the larvae.  Enough survive to carry on the disease, and it's only been in the last 3 or 4 years that I've seen any Japanese Beetles in my yard again. So it solved our problem for 30 years.  It's moderately expensive, but only needs to be applied once.  Just google the disease and you'll find tons of sources and information.  I'm pretty sure the local garden centers have it too.

Ideally, neighbors would treat their lawns too, but the nature of the disease is that over time it will infect enough larvae so the numbers in the neighborhood will be reduced.  We treated only our lawn, but it was still very effective. Milky Spore Disease is not a short-term solution for the garden, and is only to be applied to lawns, not gardens, anyway.

Japanese beetles have become more and more of a problem in the community gardens (from which I collected this specimen a couple of days ago), where there are large dead patches of lawn adjacent to the gardens.  They are notorious lovers of zinnias, and so zinnias can be used as a trap crop. In other words, you can grow some sacrificial zinnias to protect other nearby plants that they might like, and you can collect the beetles from the zinnias. Evening primrose (a weed) also serves as a trap crop.  The food crop they attacked most were the snap peas.  In the garden I knock the adults into soapy water (don't try plain water!)  The container of soapy water needs to be positioned under the beetles, since they tend to drop as soon as disturbed, so it's not easy to pick them up.

You may also see miniature versions of this larva, about 1/4 to 1/2 inch in width, and these are the larvae of the masked chafer beetle, related to the Japanese beetle.  The brown chafer eats roots of plants in the garden and is a more significant pest than we're usually aware of, because they're usually at ground level.  When digging in the spring you may find little nests of these larvae. 

These are both related to what I grew up calling June bugs or May beetles (saw one in April this year).  These are shaped like the other chafers, but are much larger, with a dark brown shell.  They are not a significant pest for us in the garden.