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Controlling and Identifying Hornworms

August 9th, 2011

 Judy McFarland, Solano County Master Gardener, wrote an article in the Summer 2010 issue of Seeds for Thought, about how to identify and control pesky hornworms.

The tomato hornworm is closely related to the tobacco hornworm and both attack tomato plants. It is the larval (caterpillar) stage of the hornworm life cycle that does the damage. They are characterized by a large horn on the posterior end of the body. A tomato hornworm has seven white stripes, while the tobacco hornworm has eight white V-shaped marks, on their sides. These larvae reach about four inches in length.

Tobacco Hornworm Egg
 

The adult form is a large moth that lays her eggs on the tomato leaves (one egg per leaf), like the photo above. The moth generally flies after dusk and is therefore rarely seen.

Hornworm droppings

As soon as you see defoliation on your tomato plant, check the leaves and ground for small black droppings, similar to those in the picture above. If you find these you have active hornworms! To get rid of them cut them with garden shears or step on them, or have a little fun and toss them on your roof for the birds to eat! Beware that if you get rid of hornworms once, they will most likely come back again as they generally live two life cycles in one tomato growing season.

If you are unable to get rid of them by hand, you can try to gain control with Bacillus thuringiensis (or Bt for short), which is a naturally occurring bacteria that causes disease in only the larva of moths and butterflies. That does mean if you use Bt, you will also put whatever butterflies come to your garden at risk.

Hornworm pupa

After tomato season, it is very helpful to dig up the soil around the plants to locate and dispose of any hornworm pupae which migrate underground only to reemerge the following summer as moths and start the cycle over again. The pupae are hard shelled, brown, and shiny and can be 2.5″ in length. They also have a curved appendage at one end that resembles that handle of a pitcher.

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Getting Rid of Squash Bugs and Stink Bugs

August 8th, 2011

Stink and squash bugs can ruin a perfectly good summer crop, but we have tips on how to prevent that from happening. Elaine Haire, Placer County Master Gardener, wrote an article for the Summer 2001 issue of The Curious Gardener on how to prevent, identify, and remove the pesky critters from your vegetable garden. Click here to see the full article.

STINK BUGS

Consperse stink bug

Named for the strong odor they give off when disturbed. stink bugs are shield-shaped with a large triangle on their backs. Consperse stink bugs are speckled grey and brown and prefer fruits and vegetables. Infested pears or peaches will develop “dimples” or depressions around the feeding sites, while infested tomatoes will have a smooth skin but with green or yellow discolorations on the fruit.

Harlequin stink bug

The harlequin stink bug has very distinctive black and red markings and prefers broccoli, cabbage, or radishes. This bug will leave yellow or white blemishes on the leaves where they feed.

Photo of two-spotted stink bug.

One of the good guys! Two-spotted stink bug.

There are two stink bugs that are actually beneficial to your garden, so watch out for the two-spotted stink bug and the rough stink bug as you want to leave these guys alone!

Rough stink bug

SQUASH BUGS

Squash bug

These bugs are grey/brown with orange around the edge of their bodies. They feed on squash and pumpkins. The first sign of damage is small brown specks on the leaves, which left untreated will eventually cause the plant to turn yellow and die.

CONTROL METHODS

For the squash bug, try to plant resistant varieties of the crops they like, for example: the butternut, royal acorn and sweet cheese squashes are all squash bug resistant. Consider planting nasturtiums or marigolds as they will attract squash bugs away from your crops. For further prevention, apply and remove row covers before the first bloom. Also look for shiny brown egg masses on the underside of leaves and destroy them.

To control the stink bug, look on leaf surfaces for clusters of barrel-shaped eggs to smash. Take a second to inspect these egg masses for darker colored parasitized eggs. Be sure not to destroy them unless there is a jagged emergence hole. If they are not parasitized, go ahead and squash them. Pheromone traps are also available for the detection of stink bug migration.

For prevention of both bugs, consider planting insectary plants near the susceptible crops which will provide nectar and pollen to attract natural eneimes such as the tachinid fly to prey on squash bugs or the parasitic wasp to kill stink bugs. Attracting birds to your garden is another helpful way to get rid of both bugs. Garlic based materials can be used as repellents.

During the growing season, remove weeds, dead leaves and garden debris to deprive these bugs of a place to hide.

After the growing season, reduce overwintering hiding places by removing all debris, and destroying crop residue by disking or composting.

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Fighting Pests with…Pests!

August 2nd, 2011

Thanks to an article written by Peggy Tharp, Nevada County Master Gardener, in the Summer 2003 issue of The Curious Gardener, we now know of two insects that are on our side! Both the lady bug and green lacewing help keep our gardens pest-free. Read on to find out why.

COCCINELLIDS

Adult Ladybug

More commonly known as ladybugs, coccinellids are shiny and often brightly colored, with black, red or orange markings. The ladybug larvae are alligator shaped, meaning broad in the middle and tapering to the tail. They are black or grey with red, orange, yellow or white spots and many have spines or are covered with wax.

Ladybug Larvae

No plant-feeding ladybugs are considered pests in California. The young larvae usually pierce and suck the contents of their victims, while the older larvae and adults chew and consume the entire prey. A ladybug’s insect of choice includes: aphids, mealy bugs, mites, scales, and whiteflies. Adult ladybugs can consume up to 100 aphids a day!

Fortunately many ladybugs can make it through the winter as adults by nesting in protected spots on or near the host plant. Plants that attract ladybugs are buckwheat, corriander, dill, fennel, marigold, sunflower, tansy, yarrow, and calendula.

LACEWING

Adult Green Lacewing

Lacewing have slender, green bodies, lacy wings and golden eyes. The adults are night flyer’s and attracted to light. Lacewings particularly love nectar and pollen but also feed on aphid honeydew. The larvae which are sometimes called aphid loins, gorge themselves on various small, soft-bodied insects such as aphids, scale crawlers, mealy bugs, whiteflies, leafhoppers, psyllids, small caterpillars and insect eggs.

Lacewing Larvae

The adult female lacewings make it through winter on leaf litter, while laying their eggs on slender white stalks on the leaves or twigs in the vicinity of the prey. The larvae then arrive in 3-6 days and are tapered at the tail and flattened with distinct legs and long mandibles used for snatching up prey.

Plants that attract lacewings are: angelica, caraway, coreopsis, cosmos, dill, fennel, Queen Anne’s lace, sunflower, sweet alyssum and yarrow.

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Give those pests a run for their money and I.D. them before they get started!

May 31st, 2011

Pests can move in and take over in the blink of an eye!  Fortunately for us, Placer County Master Gardener Gay Wilhelm has some amazing tips for early recognition and removable of pests in the Summer 2010 issue of The Curious Gardener. Before the summer is over, pests can reproduce hundreds of generations, which is why recognizing them and taking control now is an integral part of keeping them at bay throughout the end of the season.

aphids

Heard a rumor that these guys can fly? Well, its kind of true. Generally adults are wingless but some are able to fly, usually around the spring and fall.

Aphids (left) are a fairly common pest in gardens of all kinds, as they are found on lettuce, apples and squash, just to name a few. They are green, yellow, brown, or red, and pear-shaped with long legs and antennae.   If aphids are your gardening nightmare, then you want to look for a influx of ant activity around the plant you think might be in jeopardy.  Ants are a warning sign for aphids because aphids excrete a sweet honeydew, which draws the ants toward the plant. Be wary of using fast acting nitrogen fertilizers as they increase aphid reproduction; instead use slow release fertilizer and use it in small amounts.

adult hornworm

Next one on the list: the hornworm!  If you plan on growing tomatoes this season or have already planted them, this is your enemy.  These guys are small brown or cream-colored grubs, and they grow into a long green worm with a horn on their tail, eventually turning into the sphinx moth, which is about five inches across and seen in the early evening. If you have hornworm visitors, you’ll start to see black droppings or denuded leaves.  Look for the young larvae around midsummer. Once you’ve seen them the best method for eradication is to hand pick them off the plant, but as this can be time consuming, we also suggest Bt spray. Bt, standing for Bacillius thuringiensis, will effectively destroy the larvae but if you choose this method do take into consideration that Bt will also kill any native caterpillars and butterflies that the spray comes into contact with.

hornworm with wasp eggs

The hornworm photo above is what you’ll see if you have adult hornworms running around. The photo on the right is also of a hornworm but this one may not be such a bad sign. In this instance a wasp has laid its own larvae into the worm’s back. Being a host to wasp larvae will not only kill the hornworm carrying the eggs but wasps are natural hornworm predators, so if you let the wasp larvae continue on their cycle you will decrease your need for Bt spray because the wasps will help in your hornworm eradication.

For more information, on pest like scales, cabbage maggots, earwigs and squash bugs, click here to see the rest of the article.
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