Posts Tagged ‘bacillus thuringiensis’

Parsleyworm Normally, when an insect attacks the vegetable garden a gardener’s revenge is swift and decisive. Although we don’t mind sharing, some bugs take more than their portion, stripping plants to the point where we have to show them the door – or the neighbor’s garden – and order them to leave.

But this summer a beloved insect is back on the plants, nibbling on members of the carrot family and delighting everyone who sees them. Blaring their presence with a striping of black, white, and yellow, the parsleyworm (Papilio polyxenes) is one visitor you might want to let stick around.

When little, this caterpillar’s coloration has it dressed up like bird droppings, something that makes predators think twice before eating it. If the predator is determined to chomp them, the parsleyworm has another trick up its sleeve: they push a pair of orange, smelly “horns” from their head. As long as you’re not sniffing their head when they do this, it’s an endearing trick.

Yes, they’re eating the parsley. And the dill, fennel, and carrots. This is a small price to pay for nurturing the Black Swallowtail butterfly, which is what these very hungry caterpillars grow into. Should you want to control them, pick them from the plant or spray with Bacillus thuringiensis (Bt), an organic insecticide.

But if you choose to let these lovely creatures live to become adults, don’t worry if your caterpillars disappear from the plants. After stuffing themselves, the caterpillars roam about, looking for a place to spin their chrysalis in which to pupate. You’ll see your parsleyworm again, this time as an adult, a large black butterfly with yellow and blue spots.

 Flitting through the garden, sipping nectar and visiting flowers, this butterfly and its two close relatives, Tiger Swallowtails, are as welcome as fireworks on the Fourth of July. Attracting them to your garden is simple: plant food for the caterpillars to eat, such as parsley, carrots, or dill for Black Swallowtails and willow, green ash, or chokecherry for Tiger Swallowtails. Don’t forget to add in flowers to give adults nectar to sip, particularly butterfly bush (Buddleia spp.), geraniums, butterfly weed (Asclepias spp.), or zinnia.

After all, you don’t mind sharing, do you?

This post was previously published in the Longmont Ledger.

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As the cold recedes from the orange groves and Floridians thaw, the country begins to assess the damage done by freezing weather in the sunshine state.  Though concern is high for the future of fruit, the real blow delivered by the cold snap was to the egos of states far, far away.

Up until now, we thought we had pest problems.  But one look at the iguanas dropping from the trees and our problems seem paltry in comparison.  After all, it’s hard to get pity for a plague of fungus gnats when others are contending with a rain of giant, cold-stunned lizards.   As temperatures plummeted below 40 degrees, the lizards grew comatose, losing their grip on branches.

Yet a pest is a pest, be it large or small, and there’s no need to feel inadequate if what’s bugging you is smaller and less impressive than your neighbor’s.  A closer look at both of these beasts reveals the threats they both pose to our peace of mind.

The Green iguana (Iguana iguana), the Mexican spiny-tailed iguana (Ctenosaura pectinata), and black spiny-tailed iguana (C. similis) in Florida are invasive, non-native animals that escaped from captivity or were released into the wild by people who didn’t want to care for them anymore.  Like any tourist who spends time in the warmth and sun of this subtropical state they thrived, finding mates, raising families, and settling into the landscape.

Fungus gnats (Bradysia species) in Colorado are native insects that are released into the home when people bring potted plants indoors.  Basking in the temperature-controlled climate of a house, fungus gnats breed, fly about, and make themselves comfortable in houseplant soil.

As large plant eaters, iguanas pose problems for landscape plants, gnawing on trees, shrubs, and ornamentals like it’s an all-you-can-eat buffet.   After their meals, they enjoy lazing in the sun on sidewalk, stone walls, and other flat stone surfaces, where their droppings collect in an unsightly, smelling mess.

Fungus gnats are dainty eaters, preferring to dine on soft algae, fungi or decomposing plant parts in houseplant soil.  Occasionally they nibble plant roots, but are rarely problems for plant health.  Egg to adult takes a mere three weeks, at which point the adults fly free from the soil and spend a week (or 10 days) looking for love, laying eggs, and driving homeowners crazy.

As iguanas have become entrenched in Florida, alarm has risen over their increasing numbers and damage to yards.  But control is difficult.  These lizards bite and scratch to defend themselves, but it’s their tail you have to watch:  a blow from this mighty muscle is a slap you’ll never forget.

Here’s where fungus gnats measure up to their larger competitor.   Flying lazily about the room, the gnats seem drawn to human faces, setting the people to flailing their arms to drive off the insect.  Often the attempts at swattage end in tragedy, when an innocent bystander – family member, friend or pet – is smacked by the wildly waving hands.

Exclusion with strong screens may keep iguanas at bay and using plants they don’t like to eat will have them looking elsewhere for fodder.  Experts recommend accessorizing trees with sheet metal to stop iguanas from climbing, cementing in their burrows, or encouraging beneficial predators like raccoons, vultures, or feral pigs.  Of note is that experts draw the line at shooting iguanas, since discharging firearms in areas where people live is frowned upon.  Slingshots are encouraged as a harassment tool, provided you’re careful to have a solid backstop.

Fungus gnats can be a mighty big problem to overcome.  But because they are a bigger problem in homes where houseplants are overwatered, try allowing the soil to dry between watering.  In general, the gnats live in the top two inches of soil; letting the soil dry in this area kills eggs and larvae. 

There are several pesticides with pyrethroids available for those who would like a stronger control.  Look for those that are persistent, active for several days after application.  Or, if you prefer, Bacillus thuringiensis strain israelensis (Bti) is helpful when applied as a soil drench when you water.  But Bt is tough to find as a homeowner.  Try searching for Gnatrol or Knock Out Gnats.

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The first sign of trouble on the kale really didn’t look like much compared to the havoc on the beets and spinach nearby.  Those were getting tunneled by leaf miners, making them inedible; that obvious loss to my salads absorbed my attention. 

 The kale seemed indestructible in comparison – immune to insects and disease.  After all, the nibbling of the leaf was just a light scoring of the surface, and, lulled by the belief that the kale wasn’t as sissified as the tender spring greens, I ignored it.

Oh, how foolish can a gardener be?  Those early signs were the key to staving off the destructive juggernaut of the Imported Cabbageworm.   cabbageworm larvae

These one inch-long, velvety green caterpillars are munching down on every kale leaf in the bed and where they haven’t gnawed, they’re leaving deposits of frass, which is an entomologist’s way of talking nicely about poop.  My dinner prep the other night consisted of hand picking the worms and sluicing off their leavings (we weren’t having guests for dinner – honestly, I’d never serve them this). 

 The worst part of this latest assault on my garden isn’t the bugs – they’re easily dealt with by a spritz of Bacillus thuringiensis (Bt).  This organic pesticide made from soil-borne bacteria will give those bugs a killer bellyache.  No, the bigger problem is that I know better than to let the early signs of an oncoming problem be ignored.

You see, most garden problems don’t require pesticides if the gardener is alert and scouts their plants.  In the early stages, a pest can be controlled with a bit of pruning, hand picking or row covers.  Most plants can take a small amount of damage, but if left to mushroom out of control, small bugs become big pests and people either abandon their crops or break out the chemicals. 

 Hence my guilt for ignoring my training.  Yes, I have an organic solution, and once under control, the kale will recover – fortunately there is enough growing season for the plant to size up.   As for other, more serious pests on the horizon, my lesson is learned and I’ll pay attention to the early warning signs.

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