If you have a citrus tree, you may want to take a closer look for signs of purple scale in late spring and early summer, and again in autumn.
Purple scale insects suck the sap from citrus trees and they look like miniature mussels. Also known as mussel scale, orange scale, and comma scale, purple scale (Lepidosaphes beckii) are a type of armored scale that attach to banana, bay laurel, citrus, fig, mango, pear, and stone fruit trees and grapevines. These pests have several ornamental hosts that bear inspection:
Purple scale damage
Like other scale insects, purple scale feed predominantly on leaves and young fruit, but they will attack all parts of a tree. You may see tiny yellow halos on the leaves. Purple scale feeding can weaken branches, disfigure fruit, and reduce productivity. Heavy feeding can lead to defoliation and twig dieback. In extreme cases, the tree can die.
Populations of purple scale are usually low and found mostly in coastal regions, but mild temperatures, high humidity, and overcast skies can provide the conditions needed for a population explosion. You can find these pests in the cooler, shaded areas of trees.
Purple scale identification
Purple scale insects aren’t actually purple. That sure would make them easier to find! Instead, they are dark brown and may have tan edges with a slight purplish tinge.
Male purple scales are smaller and narrower than females. In both cases, you may see a slight bend at the narrow end of the scale. Male purple scales are 1/10” long and females are slightly larger. Male purple scale insects are tiny and they fly around in search of immobile females.
Purple scale lifecycle
Females lay 40 to 80 eggs under their protective covers. After the eggs hatch, crawlers emerge and scuttle to nearby fruit, leaves, and twigs, where they begin forming their own covers. At first, purple scale crawlers are covered with a mass of waxy threads. When they are about half-grown, their purplish-brown covers begins to develop. Once a female attaches herself, she stays put.
Purple scale management
Temperatures above 80°F are hard on purple scale, so their numbers are greatly reduced by the time summer is in full swing. But a second generation may appear in autumn and, in some years, a third generation may occur before winter cold brings them to a halt.
Natural predators, such as parasitic wasps, twicestabbed lady beetles, and Australian lady beetles, take a big bite out of these pests. We can help them do their job by avoiding broad-spectrum pesticides and applying sticky barriers to the trunks of trees. Argentine ants are known to protect scale insects, so sticky barriers remove that protection.
Purple scale prefer dusty conditions, so giving your citrus trees a quick shower with the hose can help.
Rather than steamy backseat interludes, frenching describes the way leaves can become discolored or distorted.
Frenching most commonly occurs in cotton and tobacco, but it may also be seen in citrus, sorrel, squash, and tomatoes. Peppers seem to be exempt from this condition, but no one knows why.
Is frenching a disease?
Well, yes, and no, and maybe. Since frenching is not entirely understood by botanists, its causes are currently referred to as “frenching factors”. These factors include predominantly fungal diseases, insufficient iron, poor drainage, alkaline soils, and temperatures above 95°F. [It sounds like I just described my yard!]
In some cases, frenching is caused by specific bacteria commonly found in the soil (Bacillus cereus, Macrophomina phaseolina), the latter being one cause of damping-off disease. Frenching is also more likely when plants are grown in soil that stays moist during a drought. [I guess this means I should back off on watering my heavy clay soil quite so much in summer…]
How to identify frenching
While there are many ways that leaves can turn the wrong color or take on an abnormal shape, frenching has some consistent characteristics:
*Apical dominance refers to some plants’ natural tendency to have one main shoot that actively inhibits the growth of other shoots.
These symptoms can be mistaken for aster yellows at first, but roots are not affected. This condition, regardless of its cause, starts out as tiny pinheads of chlorosis. New leaves are narrower than normal with wavy edges. As these leaves grow, only the midrib gets longer, pulling the leaves into strap-like shapes that end up looking more like stiff strings than leaves.
Scientists have found that autoclaving soil eliminates the frenching effect, but I’ll bet none of us have that option. There isn’t much we can do about the weather, either, but there are things we can do that will reduce the chance of frenching in our home gardens. Those actions include improving drainage, monitoring and maintaining a good soil pH, and feeding and irrigating plants regularly should do the trick.
Have you seen frenching in your garden? Which plants were affected?
Today, we are learning about the Krebs cycle. Wait! Come back!
The Krebs cycle is how plants get energy from their food. Also known as the citric acid cycle, it won’t tell you how to grow bigger tomatoes or sweeter melons, but understanding the Krebs cycle gives you a better understanding of how plants grow and what they go through to make all those delicious things we eat.
We’ve already discussed the nitrogen cycle, the carbon cycle, and the water cycle. Those cycles describe how things needed by plants become available (and unavailable) as they change forms, moving through the environment.
We’ve also discussed the Calvin cycle, which is part of photosynthesis. In the Calvin cycle, several anaerobic chemical reactions occur that allow plants to transform the carbon from CO2 into sugars. After those sugars are formed, the Krebs cycle begins.
Messrs. Krebs and Johnson
In 1937, a man by the name of Albert Szent-Györgyi was studying pigeon muscles. Stay with me, now! He received a Nobel Prize for his efforts, part of which was discovering several aspects of what later became known as the citric acid cycle. His discoveries were taken further that same year by Hans Adolf Krebs and William Arthur Johnson. [I guess they decided the Johnson cycle didn’t sound as impressive.] Krebs received the Nobel Prize for Physiology in 1953 for that work. [I don’t know why Johnson didn’t. Maybe he was too difficult to work with. I don’t know.] The Krebs cycle is part of the aerobic respiration process plants use to produce usable energy.
Respiration, not what I expected
When I hear “aerobic respiration” I start thinking about increased heart rates and time spent on a treadmill, but that’s not it. Aerobic respiration refers to one way that usable energy is formed. That usable energy is adenosine triphosphate or ADT. ATP is a molecule that carries usable energy around within a cell, taking it wherever it is needed. ADT is created when food (sugar) is burned with oxygen. I don’t know how plants burn anything but I keep getting images of little campfires in plant cells, so that’s kinda fun.
Sugar as plant food
I always thought plants simply drank sugar solution as food, but that’s not exactly how it works. Let’s put our steampunk magnifiers on and see what’s really going.
How plants convert sugar into energy is far more complex and amazing than my little campfire, especially when you think of the scale at which all of this is happening. Plant cells are 10 to 100 micrometers across, depending on the species. This means you could put approximately 180 to 1,800 plant cells across the top of an American dime. [Human and animal cells are even smaller and they do similarly impressive things.] Now back to converting sugar.
To start, you need to know that sugar molecules are relatively large. To use them, plant enzymes go to work, breaking down those acidic glucose molecules into energy and pyruvic acid. That process is called glycolysis. More reactions occur, breaking the remaining bits down into carbon dioxide. As energy is released through these processes, it is moved to other molecules, called electron carriers. Electron carriers are like tiny cargo trucks. They form a chain called the electron transport chain. This transport chain creates ATP. As a side benefit, the processes also create the building blocks of several other molecules, such as amino acids.
For perspective, let’s say that a plant cell is the size of Arizona and the mitochondria are Phoenix. Arizona has a railway system that transports food. All the food comes from Texas and is too big to be packaged. This giant-sized food is taken to Phoenix where it goes through a 9-step process that converts the giant food into snack-sized portions that are small enough to fit on the trains. The trains take the food wherever it is needed. Put simply, that’s the Krebs cycle.
But what does all this have to do with your garden?
The bottom line, healthy plants produce bigger, tastier crops with less effort on our part. They are better able to defend themselves against pests, diseases, and weather extremes. All you have to do is make sure they get the right amount of water regularly and that the soil they are growing in contains the correct range of nutrients.
Have you had your soil tested yet? What did you learn?
The water cycle is a global phenomenon, but something similar is happening in your garden.
In its simplest terms, the water cycle describes how water moves around on the Earth’s surface. It might be moving very slowly as ice in a glacier, whipping around on the wind as a gas, or flowing across the soil surface to water your bean plants. Regardless of its form, the mass of water on Earth stays relatively unchanged. The same is not true of your garden.
Unless you water exclusively from a rain barrel, the water for your garden probably comes from a spigot. If you’ve ever experienced a water main break or a flood, you know just how devastating too much water can be.
Let’s compare the basic aspects of the water cycle from global and gardening perspectives.
The water cycle starts when the sun heats the surface of the planet. Water on the surface is converted to a gas that rises into the atmosphere. The soil of your garden, your driveway and house, and the concrete of your patio also act as heat islands, absorbing the sun’s heat and causing nearby water to evaporate. This is why it’s a good idea to give potted plants sitting on a concrete patio feet that raise them off the surface enough to allow air to flow. This will keep them cooler and reduce the amount of water they need.
Water held within plants is also released. As they perform photosynthesis, gas exchanges must occur. Water is released into the atmosphere as this happens. The combination of evaporation by heat and transpiration by plants is called evapotranspiration.
As water vapor moves around in the atmosphere, the bits of water vapor bump into each other and grab on. Those clusters of water vapor keep getting bigger, condensing into fog, mist, and clouds. If you’ve ever been to Disney World in August, you know exactly what I mean.
Some plants thrive in misty, foggy, humid environments. Others end up with fungal diseases. If humidity is causing problems in your garden, be sure to prune your plants in ways that provide good airflow.
Water falling to the ground is precipitation. Globally, precipitation may mean rain, snow, hail, or sleet. In your garden, that precipitation may be rain, sprinklers, or a garden hose. As precipitation passes through the atmosphere, it collects particles along the way. Those particles are often car fumes, factory pollution, and dust, and those particles reach your soil right along with the water.
Water passing from the surface into the ground is called infiltration. Once the water has been absorbed by the soil, it is known as groundwater or soil moisture. Just because water is in the ground does not mean it is available to plants. Compacted soil has poor infiltration rates. And water does not spread smoothly through the soil in all directions.
A fellow gardener called me with a zucchini problem. Her plant kept wilting, even though she was watering it regularly. I asked her if the water was reaching the roots. The phone was silent for a moment before she replied, saying she thought so. I had her go check. She called me back a few minutes later astounded. Even though she had been laying the hose next to her zucchini plant, the water was all veering away in another direction once it infiltrated the soil. I had her create an irrigation ring around her zucchini and it grew much better.
Speaking of growing well, infiltration is how minerals get in the water that feeds our plants. As water enters the soil, some minerals are caught in solution. That solution is then absorbed by plants to provide both food and water. Now, some plant nutrients are more mobile than others. Immobile nutrients aren’t actually immobile, they just need a lot more water to move around. Blossom end rot is an example of irregular irrigation causing what looks like a nutrient deficiency. Most gardens on the West Coast of the US have abundant calcium, but may not be watered regularly enough. [Of course, a lab-based soil test is the only way you can learn what’s really in your soil.]
Water moving across the land is called runoff. Surface runoff, or urban drool, is wasteful and potentially dangerous. As suburban sprinklers miss their mark and water streets and sidewalks instead of lawns, they also carry oil, excess fertilizer, trash, and pollutants into waterways. Please make sure your sprinklers water where you think they do and adjust them as needed.
As you can see, the water cycle is a series of steps that pass through various filters along the way. I once had a student create a variety of natural filtering systems for a science project. She used rocks, leaves, sand, and soil in separate containers to filter muddy water. Which material do you think did the best job of cleaning the water?
I thought it would be the rocks, but I was wrong.
It was the soil.
You can grow a surprising amount of food in your own yard. Ask me how!
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