Garden Word of the Day
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Today we will learn about an insect that smells things with its antennae, tastes things with its feet, and has no ears but can hear ultrasound. If all that was not odd enough, they also have a compass in their antennae.
Monarch butterflies (Danaus plexippus) are fascinating uber-travelers. And they are struggling in our modern age.
You might think it impossible, but delicate monarch butterflies travel 50 to 100 miles daily when migrating. Researchers recorded one overachiever clocking in with 265 miles in a single day!
And it takes four generations to reach their destination. You read that correctly - four generations.
While some western variety monarchs have North American overwintering sites, eastern monarch butterflies migrate more than 3,000 miles to get from their winter homes in Mexico to their summer homes elsewhere. Monarch butterflies have also been raised on the International Space Station. I can only imagine what their internal navigational systems had to say about that.
Traditionally, easter monarch butterfly populations have been measured by how many acres of land they cover when they overwinter in Mexico. In 1996-97, they covered more than 18 acres, which translates into approximately 1 billion butterflies. By 2014, that number dropped to only 1.6 acres. In simple terms, this indicates a 96% drop in population. Before jumping to conclusions, it is important that we understand there have not been comparable drops in summer populations, and scientists do not know why.
Monarch butterfly feeding and breeding grounds
Monarch butterflies lay their eggs on certain types of milkweed because those are the only plants the larval/caterpillar stages can eat. Popular rhetoric blames herbicides for killing these particular types of milkweed, but many regular monarch habitats are flush with milkweed - and there have been no monarchs. There are mixed opinions on why this is and what it means.
As monarch numbers dropped, people became worried and started planting milkweed and nectar plants to provide global food and habitat corridors for the lovely monarch butterfly. In less than one year, news agencies announced that monarch populations had risen from 1.6 acres to 2.8 acres as a direct result of these actions. Sounds great, but it is not that simple.
More monarch populations are appearing in previously unused areas. Some Monarchs are not migrating at all. Instead, they stay where they are and feed on popular tropical milkweeds that grow year-round. Sounds great, right? Well, it is, and it isn’t.
In “normal” eastern monarch cycles, winters are spent in a state called “reproductive diapause” which means the butterflies are not sexually active. Since native milkweed plants go dormant in the winter, everything was in balance. The tropical milkweed (Asclepias curassavica) does not go dormant in winter, so monarchs can stay in the same place year-round and forego the migration. The only problem with this is that continuous feeding has led to the emergence of a microbial parasite, called OE for short, that can weaken significant numbers of an already stressed species.
What is a gardener to do?
If you would like to help the monarch butterfly on its road to recovery, you can plant milkweed and nectar plants in your yard or on your balcony. Cosmos, marigolds, and zinnias are very easy-to-grow flowers that provide nectar, but you will still need to provide the proper type of milkweed to support monarch caterpillars. When shopping, look for native milkweed plants, not tropical varieties. If you already have tropical milkweed plants, you have two choices: rip them out and replace them, or trim them back 3 or 4 times a year, to interrupt the parasite’s lifecycle.
UPDATE (3/6/2016): Due to conservation efforts, the 2015-16 winter count of monarch butterflies reached 10 acres.
UPDATE (11/20/2016): I added milkweed to my garden and now have half a dozen monarch butterfly caterpillars munching away on the leaves and what looks like a few more eggs getting ready to hatch - and all that is on a single plant!
UPDATE (1/3/2017): Frost has killed the aboveground portion of my milkweed and there is no sign of Monarch caterpillars or chrysalis.
UPDATE (4/13/2019): The milkweed is coming in strong!
Soft scale insects are easy to miss as they suck the life out of your plants. Like their more heavily armored cousins, soft scale insects spend their adult lives protected under a dome.
The only real difference between armored and soft scales is that the bodies of armored scale insects are not attached to the dome, whereas soft scale insects are firmly attached. Soft scale domes are usually made of a more cottony, waxy, or powdery material, than the hard plating of armored scale. There are other types of scale insects, but we will leave those for another day.
Types of soft scale insects
There are hundreds of types of soft scale. These are the most common soft scale insects found in California gardens and landscapes:
Soft scales are so successful that several other insects mimic their appearance. These copycats include certain species of aphids, psyllids, mealybugs, and whitefly nymphs. There is even a fungus, called Diamond scale, that copies this successful arrangement.
Soft scale lifecycle
Soft scale has one of nature’s stranger life cycles. One thing that makes soft scales so interesting is that they are mobile only as infants. The initial development stage, or instar, has functional legs, whereas the adults are attached to the inside of a shell, where they feed and lay eggs pretty continuously, until the weather gets too cold or the host plant dies.
In the photo above, you can see a large number of established hemispherical soft scales. They suck sap from the twigs and leaves of the plant and then excrete a sugary honeydew that ants love. In fact, heavy ant traffic was what notified me of this very subtle, but potentially deadly infestation. As it was, I had to remove several branches.
The problem with infestations such as these is that the excreted honeydew provides a perfect growth medium for fungal diseases, such as sooty mold, and bacterial disease. As ants collect the honeydew and move from plant to plant, they can quickly spread disease throughout your garden.
Symptoms of soft scale infestation
One of the more inconspicuous insects, soft scale can build up a big infestation without anyone noticing. At first, you may simply see what looks like water-stress, leaves may turn yellow and drop earlier than normal, or leaves may die and stay attached.
To avoid the use of chemical treatment against soft scale, regularly monitoring woody plants and stripping any visible vermin away from twigs and leaves by hand are your best bet. You can also use a sticky barrier around the trunks of trees and shrubs to prevent the mobile first instars from establishing themselves on your plants and removing the protection provides by ants.
Easily recognized by their unusually large size (up to 4”) and horn-shaped tail, tomato hornworms (Manduca quinquemaculata) can strip your tomato plants of foliage and fruit in short order.
Distinguished from their tobacco-loving cousins, Manduca sexta, by displaying white V-shaped markings, rather than single slash marks, both varieties are difficult to see until the damage is done. To learn more about the differences between these two agricultural pests, the University of Florida Extension Office has an excellent resource.
The first sign of hornworm infestation is usually stripped leaves and missing smaller stems on tomato plants. Hornworm caterpillars will also eat peppers, potatoes, eggplant and even jimsonweed ~ all members of the nightshade family. They prefer younger, new growth, but they tend to hide under larger leaves. Their bright green coloration provides excellent camouflage.
Once they eat their fill of your garden delectables, hornworm caterpillars will return to the soil where they develop a hard-shelled pupal covering. Within their winter chalet, hornworms undergo a complete metamorphosis from worm to moth. In spring, the large (4-5”), heavy-bodied brown Sphinx moth will emerge to lay light green, oval eggs on upper and lower leaf surfaces. These eggs hatch and tiny caterpillars emerge, and the cycle continues. In some cases, a second generation can occur in a single year.
So what can you do if you find hornworm damage on your plants?
Handpicking hornworms from your plants is the best defense. They can be dropped in soapy water, tossed in a trash bag or, my favorite, fed to the chickens! Plants should be inspected at least twice a week through summer. If you happen to be lucky enough to discover a hornworm covered with little white packets, do yourself and your garden a favor: place the hornworm in a container covered with hardware cloth and leave it alone. The little white packets are the eggs of predatory braconid wasps. These beneficial wasps are too tiny to cause humans any problems, but they are your friends in the garden. As they hatch, they will feed on the hornworm body, as nature intended.
Since hornworms also feed on weeds in the nightshade family, you can reduce hornworm populations by keeping your garden weed free. Also, in the fall, till the soil where susceptible plants were grown to kill pupae and burrowing caterpillars.
Green lacewings and lady beetles also prey on eggs and new caterpillars, so keep your garden predator-friendly with water, plants from the Allium family, and little or no pesticide use.
Walking my dogs this morning, I was surprised to see a light dusting of frost on neighborhood rooftops. As all gardeners must do, I made a mental note to adjust my garden tasks as the risk of frost increases.
Frost, by itself, isn’t necessarily bad for your plants. The real problem is that frost tends to exist in the same conditions that lower a plant’s internal temperature to the point that cell walls break down. If you’ve ever left a crop of tomatoes, melons or zucchini out in the cold, you have probably woken to a dismal scene of brown wilted leaves and mushy fruit.
Farmers and gardeners in the NE and the Midwest don’t even try to grow the more delicate natured plants in the winter, but we Californians have the luxury of at least trying. We can protect our crops by using the USDA Hardiness Map to determine your planting zone (I’m in 9b) and learning when to expect frost to occur. According to the Cornell Cooperative Extension office, “Cool, clear nights with low humidity, often following a cold front, are signs of an impending frost.”
UC Davis provides a helpful table that estimates when various areas of California can expect frost in the fall. Keep in mind that these are only educated guesses and that Mother Nature tends to kick our butts whenever we get careless or complacent. If you live outside of California, you can check with your local Cooperative Extension office or Master Gardener office for your first and last frost dates. Armed with this valuable information, you can determine which plants will need protection. You can also follow these helpful tips to reduce the negative impact of lower temperatures:
How do you prepare your garden for winter?
Good drainage is crucial to plants, both containerized or in the ground, to avoid things like root rot, fungus gnats and, well, drowning.
So, how do you know if you have a drainage problem?
If you see pooling, puddling, or muddy spots, you may have a drainage problem. Water will either be held in the soil or it will go someplace else. Now, soil is pretty amazing. Picture the spaces between grains of sand. Water passes through those spaces easily. Loamy soil has medium-sized spaces that slow water movement a bit. Clay soil is made of really tiny bits that create lots and lots of tiny pockets for water to hang out in. If you have mostly clay soil, poor drainage can be a real threat to plant health.
How can you correct a drainage problem?
Adding organic material to your soil is the best way to improve drainage. Period. It doesn’t matter what type of soil you have. Adding compost improves soil structure, increases the level and variety of nutrients available to plant roots and, hey, it reduces the amount of stuff in landfills! As long as it isn’t diseased, you can compost just about any plant material and use it to improve your soil’s health and drainage. By adding compost to sandy soil, you provide smaller bits of stuff that help hold water and nutrients in place. Loamy soil is already rock star material, but adding compost just makes it even better. When you add compost to clay soil, you create bigger pockets that allow air and water to move more freely, keeping the soil and your plants healthier.
Really big drainage problems can be resolved with swales, ditches, or French drains. Quite simply, you dig a trench that gets progressively deeper as you move away from the problem area. Gravity and surface tension pull the water away and deposit it in areas better able to handle that much water. Rain gardens are another option.
One thing to keep in mind when considering drainage is what is in the water that is draining away. When water drains out of or away from your yard or garden, it’s not going out alone. Every drop of that water contains precious nutrients and microbes. When people use fertilizers, pesticides, herbicides or fungicides, those chemicals are also leached away. This nutrient soup is usually dumped into nearby creeks, rivers, lakes or oceans, disrupting the natural cycles of growth that take eons to evolve (and repair). Just sayin’…
You can grow a surprising amount of food in your own yard. Ask me how!
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