Monthly Archives: July 2012

Zucchini – Dead, but a Different Cause!

I’m a gardener who remember when zucchini was a new vegetable. On the farm we planted a pretty long row of this new squash and learned very quickly that it’s easy to be overrun with zucchini. They wouldn’t stop producing in upstate NY.

But in southern PA it’s a different story. My experience is that the zucchini plants only produce fruit for about 2-3 weeks and then they die. The problem has always been bacterial wilt. This disease is carried by cucumber beetles. When these beetles chew the leaves of zucchini, they leave behind droppings that have the bacteria Erwinia tracheiphila in them. This bacteria get into the plant, multiplies, clog up the xylem (the plant tissue that carries water from the roots to the stems and leaves) and the next thing you know, the zucchini plants are wilted and then dead. If you break the stem of a zucchini with bacterial wilt, you’ll see a sticky mucus-like substance in it – that’s the bacteria.

I’ve been dealing with this for years… until this year. For the first time the zucchini plants didn’t die from bacterial wilt. I’m not sure why, though I have two possible reasons. This year I planted a different variety – Zucchini Elite – which I purchased from Harris Seeds. It might be that this variety is somewhat resistant to bacterial wilt. The other possible reason is that last year I had hung a cucumber beetle trap in the garden. I know a lot of beetles were caught on the trap and, while I saw beetles this year, I didn’t see as many. Like I said, I’m not sure what made the difference this year.

While the zucchini didn’t die of bacterial wilt, they still died but they produced for about twice as long as other years. The killer this year wasn’t bacteria wilt but the squash vine borer (Melitta  curcurbitae.)

Squash Vine Borer Larva

The adult squash vine borer is a moth that looks like a wasp. It has two clear wings and two that are bright metallic green. The body is orange and black. The pupae of this insect overwinter in the soil and, here in PA, the adults emerge in mid to late June. The females lay eggs at the base of squash and in about 10 days, the eggs hatch and the larvae  tunnel into the stem of the plant. The larvae then feed on the inside of the stem and disrupt the nutrient and water transfer within the plant. After feeding from 4-6 weeks, the larvae leave the stems and pupate in the soil, waiting to emerge ten months later.

The borer damage causes the squash to wilt and then die. When I pulled the dead zucchini out of the ground this year I noticed that there wasn’t any mucus-like bacteria so I knew they didn’t have bacterial wilt. But what I did see was a white grub-like caterpillar inside of each stem – the squash vine borer larva.

Squash Vine Borer Damage

Pesticides don’t work very well on squash vine borers because, unless you’re able to kill the adults, once the larvae are in the stem, insecticides won’t touch them. Row covering is suggested to exclude the adults but I’ve never had very good luck with row covers. I also read that you can try planting a second crop later in the season. In northern areas this moth only produces one generation of offspring.  Zucchini planted in July will mature after the borers have finished laying their eggs.

I destroyed the plants that had squash vine borers to make sure the larvae didn’t get a chance to pupate. I also recently planted some more zucchini to see if a late planting will make a difference.

While the borers killed the zucchini, I harvested more squash than I ever have in the current garden. If I had to make a choice, I’ll take squash vine borers over bacterial wilt any day!

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Curcumas in Bloom

It took some time but the curcuma rhizomes I planted in May have begun to bloom. It’s been an interesting journey to get to this point in time.

Curcuma

I planted the five curcuma rhizomes in a large pot in early May. The instructions that came with the rhizomes had stated that it would take a while for them to start to grow. As a result I also planted a wave petunia in the pot so that there would be some color until the curcuma grew. I’m glad I did this or I would have had a pot of bare soil for weeks!

It took a little over a month before the curcuma sprouted and, while the weather was hot and humid, they grew slowly. One by one leaves emerged until the plants had 4-5 leaves and were about a foot tall. Recently two of the plant have sent up a flower stalk and they’re beginning to bloom.

One thing I’ve noticed is that the flower stalks are very sturdy. We had some strong winds but they didn’t affect the curcuma at all. Also this plant has had no insect damage. I’m looking forward to seeing the blossoms as they open more fully and finding out how long they last.

While the plants are smaller than I had expected, I have a feeling that the rhizomes will be a lot larger next year and that the size and number of blossoms should increase. But even if that isn’t the case, this is certainly an interesting plant and one that you’re not likely to see in many backyards.

Strawberries in July and Picnic Beetles

July Strawberries

Here it is, the end of July, and every few days I’m going out to the garden to pick strawberries. It’s so strange! The day-neutral strawberries that I planted in April are bearing a lot of fruit. Information that I’d read said that the strawberries in the summer would be small but I’ve been very pleased with the size of the berries. Also the inflorescences of the plants are sturdy and often hold the fruit above the ground, something you almost never see in a June bearing strawberry.

Close Up of a Picnic Beetle – note the knobbed antennae

The only insect problem I’ve had is the picnic beetle (Glischrochilus quadrisignatus). This beetle is one of a number of sap beetles that are drawn to overripe or fermented fruit. While I just learned the name of this beetle, I often saw it burrowing into the stem ends of overripe muskmelons when I was growing up.

One of the identifying characteristics of all sap beetles is their “knobbed” antennae. Picnic beetles are about 1/4″ long and black with four orange spots on the wing covers. When these beetles are disturbed they pull in their antennae and legs under their bodies and “play possum.” Once the perceived danger is gone, the antenna and legs re-emerge and the beetles go back to feeding.

Picnic Beetle Damage

Picnic beetles overwinter as adults in decaying organic matter. In the spring they lay eggs and the larva feed on plant materials and later pupate in the soil. New adults emerge in June and July. While this insect causes some damage to fruit, it’s more of a nuisance than anything else. Sanitation in the garden – removing any decaying or rotted fruit – will help to control them. I read that you can bait picnic beetles by sprinkling Sevin insecticide on a melon rind. The rind will attract the beetles and the Sevin will kill them.

If I was growing thousands of strawberries I might resort to the bait technique to control picnic beetles. But with 25 plants, the simplest thing to do is not let the strawberries get too ripe before picking them. Also, if the beetles have only eaten the tip of a berry, I’m more than happy to cut off the damaged part and use the rest of the fruit.

The day-neutral strawberries are exceeding my expectations. They bear much better than the old everbearing strawberries and they taste great. I can’t wait to report back on the September crop!

Weed du Jour – Yellow Nutsedge

Yesterday I saw a man sitting in his front lawn pulling weeds. The weeds he was pulling had grass-like leaves with a greenish-yellow color. They were growing in clumps and were about twice as tall as the surrounding grass. This man has yellow nutsedge in his lawn.

Yellow Nutsedge

Yellow nutsedge (Cyperus esculentus) is found throughout the US while its relative, purple nutsedge (Cyperus rotundus), is a weed of the southern US. Yellow nutsedge is an interesting weed. While it looks like a grass, it’s actually a sedge. Sedges are a large family of plants that include water chestnuts, papyrus, sawgrass and others. There are two specific things that are unique to a sedge: the stems are triangular and the leaves form in groups of three. Grasses have round or oval stems and their leaves usually form in alternate pairs.

Yellow Nutsedge Root System

Yellow nutsedge, sometimes called nutgrass, is a perennial weed that emerges from May to mid-July. This weed can spread by seeds, but this isn’t its primary way of propagating itself. Instead, nutsedge has a large root system with many rhizomes (underground stems) that can grow into new plants. This alone would make nutsedge a difficult weed to control but it has one more trick in its arsenal. Small tubers (1-2 cm long) form at the end of the rhizomes. They are first white, then brown and finally black in color. A single plant can produce hundreds or even several thousand (!) tubers in a single growing season. These tubers can’t sprout until they’ve experience a chilling period but they can stay dormant in the soil for more than 10 years. To make things worse, the rhizomes are fairly brittle so when you pull a nutsedge plant out of the ground, most of the tubers break off and remain in the soil.

Yellow Nutsedge Tuber

In some parts of the world nutsedge is grown as a crop and the tubers – called tigernuts – are harvested and eaten. This would certainly be an easy crop to grow since nutsedge will grow almost anywhere!

But if you’re like me and nutsedge is a weed and not a crop, there are a few things you can do to control it. If there are a few plants growing in your lawn or garden, pulling them and throwing out the plants is your best approach. You’ll never eradicate it from the ground but you can keep it under control if  you continue to pull the plants when they’re young.

If you have a lot of nutsedge in the lawn, there are various sedge herbicides that will control it. These herbicide works best for spot application and when the nutsedge plants are small. If you have large clumps of nutsedge in open areas, a glyphosate herbicide, i.e. Round Up, will kill the weed but be careful – it will also kill any other plant that comes in contact with it. The benefit of glyphosate is that it will kill the rhizomes and tubers as well.

Yellow nutsedge is a tough weed. If you see it in your yard, you can guarantee that there are plenty of little tubers in your soil just waiting for the right conditions to grow. This is one of those weeds that you can only control.

As far as the man I saw pulling the nutsedge out of his lawn, he’ll be able to control this weed for now. But if I go back next year at the end of July, I’m certain that I’ll see him sitting in his front lawn once again, pulling more nutsedge!

Rex Begonias: Parenchyma and Propagation

Rex Begonia

Rex begonias – the “king” of the begonias – are plants with their own unique look. These begonias aren’t grown for their blossoms; they’re grown for their foliage which comes in various shapes and colors. Rex begonias are great houseplants and they grow well in outside pots in semi-shaded areas.

What I find interesting about these begonias is the way that you can propagate them. Stem cuttings of these plants root easily but the most common way to multiply rex begonias is by using leaf cuttings.

To do this, you simply take a begonia leaf, turn it over and make a small cut across each of the main leaf veins. Then you place the leaf on potting medium right side up and use pebbles or floral pins to ensure that the back of the leaf is in contact with the medium. Within a month, small plants will begin to grow where the cuts were made on the leaf. These can then be removed and put into separate pots.

I’ve done a lot of propagating over the years but I’ve only recently started using leaf cuttings. I’m amazed how a rex begonia leaf with a few cuts on it can turn into a number of cloned plants.

Adventitious Shoots forming from Parenchyma

What’s even more amazing is how this happens. Within plants there are a number of different kinds of cells and one of them is called parenchyma. This kind of cell is found throughout the plant but is especially present in the leaves. Parenchyma is usually the center part of a leaf, sandwiched between the epidermis cells. In the leaf, parenchyma cells photosynthesize but they also serve for wound healing. In some cases, parenchyma is also the source of adventitious roots and shoots. (Adventitious roots and shoots are simply roots and shoots that grow from an “unexpected” location, like a leaf.)

Adventitious Shoots on a Rex Begonia Leaf

When you take a leaf of a rex begonia and make cuts across the main veins, you expose the parenchyma cells within the leaves and they begin wound healing. But if this leaf is place on a potting medium, the same parenchyma cells will develop adventitious roots and shoots. The roots develop first and then the leaves and shoots will emerge and a new plant will begin to grow.

I find this is fascinating! If we were like a rex begonia, we could cut off our hand, make a cut on each of our fingers, place the hand on a growing medium and clone ourselves. But of course this wouldn’t work – we’re not plants and we don’t have parenchyma! But rex begonias do and it’s amazing to watch a leaf produce a number of small plants, each a clone of the parent plant. All of this is thanks to the parenchyma cells within the begonia leaf.

Weed du Jour – Spotted Spurge

For years I’ve been dealing with a weed that appears every summer during the hottest time of the year. I’ve pulled it, hoed it and sprayed it but I never knew what it was. Now I do – spotted spurge (Euphorbia maculata).

Sap from Spotted Spurge Stem

I was fascinated when I found out that this weed is a Euphorbia. The genus Euphorbia is a strange and diverse group of plants that includes the crown of thorns house plant (Euphorbia milii), a number of different succulent species and, most surprising of all, the poinsettia (Euphorbia pulcherrima). One of the characteristics of a Euphorbia is that if you cut the stems, they exude a milky sap. This is one way to help identify spotted spurge – break a stem and you’ll see the sap.

Small Spotted Spurge Plant – almost ready to blossom

Spotted spurge is a summer annual that grows in a prostrate manner and forms a mat that can reach the size of a dinner plate. The small leaves are opposite one another and oblong in shape with a maroon blotch on them. A closely related and very similar weed is prostrate spurge (Euphorbia humistrata). The primary difference between the two is that prostrate spurge will develop roots along its stems; spotted spurge does not.

I consider this weed to be a master of camouflage. The plants are difficult to detect when they’re small, especially if they’re growing on bark or stone mulch. The bad news is that spotted spurge starts to set seed when the plants are only a couple of weeks old. So all of those little plants that are overlooked until they get big have more than enough time to set a lot of seeds. No wonder this weed just keeps coming back year after year.

Mature Spotted Spurge Plant

The good news is that spotted spurge is easy to control. The plant has a shallow root system and, since it doesn’t root along the stems, it’s very easy to remove by simply pulling the plant out of the ground.

Spotted spurge is one of those weeds about which I can’t get too concerned. It’s an annual so it dies with the first frost; it’s not noxious; it’s not terribly invasive and it’s easy to pull. I wish all weeds were like the spotted spurge!

Mid-July Photos

Every week I take a lot of pictures of the various flowers in the garden. Even with the heat and dry weather that we’ve been having, there are plenty of things in bloom. Here are some the latest pictures. You can click on the pictures to see them full-sized.

Zinnia

Black Eyed Susan (Rudbeckia)

Portulaca

Daylily

Tuberous Begonia

Knock Out Rose

Knock Out Rose

Knock Out Rose Close-Up

Hibiscus

Hibiscus Close-Up