Pests and Diseases: Aphids

 

Happy Tuesday to everyone! I received a note from a reader that is just beginning her gardening journey and she wanted to know more about aphids. She was wondering if I could go over what exactly they were and why she needs to be concerned about them. That made me realize that sometimes I talk about things that beginning gardeners may not be familiar with. I need your help with recognizing when that happens! Send me an e-mail or comment below if you’re unsure about something I’ve mentioned. I’d be happy to re-visit the items that I may have unknowingly just skimmed over. With all of that out of the way, here we go!

AphidsAphids are insects which means they have six legs. That may seem elementary but lots of people think spider mites are insects too…they aren’t and that totally changes the way you control them chemically. Anyway, aphids are ravenous little suckers, literally. They suck the plant’s juices, primarily the phloem, and weaken the plant. The phloem is responsible for transporting the food that is made through photosynthesis by the leaves down to the rest of the plant. (As a side note, if you have trouble remembering which is which, remember that the xylem transports up [x and u are close together in the alphabet] and phloem transports down). OK, back on topic. So the aphids remove valuable resources from the plants by sucking on plant juices and thereby weakening the plant. It’s as if someone allowed you all the water you wanted (provided by the xylem) but never let you have any food (provided by the phloem). At some point, you would kick off too.

The main problem with aphids is that they pro-create so darn rapidly. Eggs that survive the winter generally produce females and these females in turn produce more and more offspring. Even though a typical adult will only live for around 30 days, she can pump out lots o’ live babies which in turn produce more live babies and so on. I’m sure you’ve seen the cat statistics in the vet’s office about how many cats can be produced by a pair of unspayed and un-neutered cats…it’s kind of like that but multiplied by a higher number as the mama aphid can produce hundreds of live babies at a time.

Aphids come in all kinds of colors, ranging from green to black to white to peach. There are over Aphid4000 species of aphids so you can imagine that they have adapted to fit in with their local surroundings. Once you learn what an aphid looks like, you’re unlikely to ever forget. One very distinguishing characteristic of aphids are the cornicles…these are two little projections that protrude from their lower back. If you see these, rest assured that you have aphids.

SO WHAT DO YOU DO IF YOU HAVE APHIDS?

It really depends on how bad the infestation is. If you only have a few here and there, just squish them between your fingers…they are only 1/10 of an inch long. More than likely, by the time you see them though, you’ll have quite the infestation on your hands. Here are some ways to control them:

  1. Give them a harsh spray with your garden hose. Sure you won’t kill them all but if you can knock out some of the females, you’ll be cutting your future population down.
  2. Avoid spraying pesticides. I know that sounds counterintuitive but nature has a predator
    Aphid controller - ladybug larvae

    Ladybug larvae - aren't they beautiful?

    for every pest and there are many that enjoy aphids. Lady bugs, lacewings and parasitic wasps will all work diligently to curb the population. Of course they can’t kill all the aphids because then they wouldn’t have anything to eat. Keep that in mind when you feel like the predators aren’t doing their jobs swiftly enough. To the right is a picture of an immature ladybug…I’m surprised by how many people don’t know what they look like. If you see these little guys crawling around, leave them be so that they can grow up and do your work for you.

  3. Cut back on your fertilizer. Aphids love, love, love fresh new succulent plant growth and will flock to your overfertilized plants like moths to a flame. Again, nature knows how fast a plant is supposed to grow and when we go and pour on the nitrogen to get them to grow at a quicker pace, we have upset a natural balance.
  4. If you have tried all of the above methods, you can spray a tomato leaf spray. That may sound peculiar but it has worked for many generations of folks and it doesn’t kill the predators. You can find the recipe here.

 

I hope that I’ve been able to shed some light on aphids and the problems they pose for plants and gardeners alike. I know that I rambled a bit today and I apologize for that even though it is my nature. Many of you have commented that you don’t mind my rambles so I won’t refrain from them quite yet. If you have any experience with controlling aphids in your garden, please leave a comment below or e-mail me at stacey@midatlanticgardening.com. Happy gardening!

January 17, 2012Permalink 3 Comments

Pests and Diseases: Spider Mites

 

Since I touched on spider mites in my organic vs. conventional gardening article, I thought it would be wise to expand on them a bit more. Many people believe that spider mites are insects but they aren’t. At the fear of offending an entomologist, I’ll just say that insects have 6 legs whereas arachnids have 8 legs. Guess how many legs a spider mite has…if you guessed 8 you would be correct.

When viewed up close, as in the picture to the left, the spider mite is a ferocious beast to behold. I have observed them under a microscope and you can just see them ripping and tearing into the plant tissue to obtain their dinner. They use their needlelike mouthparts to literally suck the life out of your plants. They are very small and can build to damaging populations very quickly; spider mites can develop from an egg to an adult in a week’s time. They are only about as big as the period at the end of this sentence so they often go unnoticed until their damage is evident.

Their damage is usually seen as stippling on the upperside of the leaves. With a heavy or prolonged infestation, the leaves will turn brown and drop off. The damage may be apparent on the tops of the leaves but the villains reside on the undersides of the leaves where they can be protected from weather extremes and predators…and pesticides. While I don’t advocate the use of conventional pesticides, anything that kills (-cide) pests is a pesticide in my eyes. That includes some of the control methods that we’ll discuss later.

WHAT CONDITIONS FAVOR SPIDER MITE DEVELOPMENT?

Spider mites are usually at their worst when it is hot and dry. When I say hot and dry, I’m not only talking about when the temperatures are high and the humidity is low. You can have an average summer where it rains periodically but if you site a plant that is susceptible in an area that is hot and dry, such as by an asphalt drive or against a brick wall, that microclimate is hot and dry even though the surrounding area isn’t.

Plant stress also triggers spider mite development. Plants produce all kinds of hormones in reaction to stress and plant pests are wise enough to be able to detect them. If a plant is located in an area that is not conducive to growth, such as large shade trees planted in small parking lot islands, spider mites and all types of plant pests will move right in. Think of it as the plant posting on its Facebook wall that dinner is served.

HOW CAN YOU BE SURE THAT SPIDER MITES ARE THE CULPRIT?

The best investment that you can make in terms of combating pest and disease issues is a good quality hand lens. The 10X magnification is sufficient to cover 90% of the pests you will encounter. Equipped with a hand lens, you can easily see the spider mites on the undersides of the leaves.

Another trick you can use is to hold a white piece of paper under the plant and then tap on the leaves…the spider mites should show up on the paper as little crawling specks.

The most obvious ID tactic is to look for webbing…now it won’t look a Halloween display but it should be readily visible when the critters are present.

WHAT CAN YOU DO IF YOU HAVE SPIDER MITES?

  • If your infestation is particularly bad, you may have to count your losses and remove the plant. Dwarf Alberta Spruce are notorious for spider mites and if your plant looks like this, you may be better off pitching it. There is a saying in the nursery industry: “if in doubt, throw it out”.
  • You can keep the plants showered with water and that will usually be enough to send the mites running. Now I’m not talking about a continuous shower…I mean spraying them 1-3 times per day for about a week with a garden hose. This could open you up to other issues such as fungal diseases so be sure to allow enough time for the plant to dry before the sun sets for the evening.
  • Mix up a potion of soap and water and spray the little monsters. You have to make sure that you are spraying them on the undersides of the leaves, not just the top of the leaves. That’s what makes controlling them and many other pests difficult…they know exactly where to hide.

 

The long and short of spider mites is that they are a pest whose population can quickly explode into damaging populations. But if you consider where you site your plants before installing them, it can dramatically lower your chances of having an infestation of epic proportions. And if you do see them wreaking havoc on your plants, give your plants a cool shower a couple times of day…chances are the spider mites will decide that your landscape is inhospitable to uninvited guests and move on. If you’ve had any issues with the eight-legged critters we discussed today, post your experience in the comments below. And remember that I am here to help you, so don’t hesistate to e-mail me with any questions or concerns you may have at stacey@midatlanticgardening.com. Happy gardening!

December 13, 2011Permalink 1 Comment

Organic Gardening vs. Conventional Gardening

 

Sorry that I didn’t post yesterday…my son had a birthday party to go to and we didn’t make it home until late. I thought that I would make it up by posting today instead.

I’ve been thinking quite a bit about organic gardening versus the conventional way of using chemical fertilizers and pesticides. My personal philosophy revolves around working with the natural cycles that Ma Nature has laid down well before my existence on this planet. I am an environmentalist with a little e, not an Environmentalist with a big E. To me, the difference between the two is that the big E folks tend to treat the earth almost like a religion. I prefer to put my belief system in God and his Son Jesus Christ. If you’re thinking that perhaps I’ve gone off on a tangent, you’re right…the more you get to know me, the more you’ll understand that’s a tendency of mine. My environmental stance is that we should leave the world a better place than we found it for our children and grandchildren. That means that we shouldn’t carelessly apply fertilizers and chemicals without realizing their repercussions.

Many gardeners will apply nitrogen based fertilizer in the spring and then wonder why they have aphids literally sucking the life out of their plants. Or they’ll treat their plants with imidacloprid and then wonder why they have an explosion of spider mites. The answer to both of these problems is that there is an imbalance. In the fertilizer example, the plants are growing at such a fast rate that they invite aphids to take them over. Aphids love fresh new succulent growth and by applying high nitrogen fertilizer, you have pushed the plants past their normal level of growth which triggers the aphid infestation. With the imidacloprid, you have successfully killed off the insects (six legs) that were troublesome but you have opened Pandora’s box for spider mites (eight legs) because there are no longer any natural predators to keep the mite population in check.

What would have happened if you wouldn’t have put down any more nitrogen in the spring? Unless you have very poor soil, the plants would have flushed out from their winter dormancy and probably done very well. If there was a nutritional deficiency, there’s a magic soil amendment that would have taken care of it…COMPOST! If we as gardeners would focus more on feeding the soil instead of feeding the plants, our results would be amazing. But instead, we see that the plant looks a little yellow so we put down fertilizer on everything. Or worse, we fertilize every spring because that’s what we’ve always done. Another thing that we could do instead of fertilizing is take a soil sample and determine the pH of the soil. Many nutrients, including iron, are unavailable at certain pHs and that can make your plants look chlorotic.

What would have happened if you didn’t apply imidacloprid to your willow oaks to treat for scale? If you noticed the problem before the temperatures were above 80 degrees, you could have applied dormant horticultural oil which would have smothered the scale. One of the attractive features of imidacloprid is that it has residual activity since it is taken up by the tree into the phloem. If an insect feeds on it after the chemical has been applied, then the insect is also consuming the insecticide. But on the flip side of things, can you see the problem that this presents? All of the predatory insects are also killed and as a result, you have an explosion of spider mites that you now have to contend with.

Now I have to admit, I spray glyposhate based products such as RoundUp or RazorPro to deal with weeds and I’ll use MiracleGro on plants that are showing nitrogen deficiencies. But I only do these things after I have determined that the real problem isn’t something else that is manifesting itself as a deficiency. And I’ll add compost to the soil to try to fix the real problem…soil fertility. Again, it’s not a plant fertility problem, it’s a soil fertility problem.

I’ve been learning a lot about permaculture lately and Jack Spirko from The Survival Podcast has been my primary source of education. For those of you who don’t know, it’s a daily podcast that he produces on a wide array of topics from gardening to food storage to prepping. The founder of permaculture, Bill Mollison has described permaculture as “a philosophy of working with, rather than against nature; of protracted and thoughtful observation rather than protracted and thoughtless labor; and of looking at plants and animals in all their functions, rather than treating any area as a single project system”. I think that’s a pretty accurate description of how we should see any gardening that we do. Whether you enjoy vegetable gardening, woody plants, herbaceous perennials or annuals, we need to see the system as a whole, instead of just its parts. By doing this, we can ensure that our children and grandchildren are left with a planet that can sustain them and many generations to come.

I’d love to hear how you’ve incorporated organic gardening principles into your landscapes. Or perhaps you haven’t and can’t see a reason to start doing so…I love a good debate and I’d love to hear your thoughts. Leave them in the comment section below or e-mail me at stacey@midatlanticgardening.com. Happy gardening!

December 10, 2011Permalink 2 Comments