Sunny Slope Orchard

Sunny Slope Orchard
In the coast range foothills overlooking the Sacramento Valley

Wednesday, May 16, 2012

Good bugs, bad bugs


A lady bug feasting on green aphids

When the subject of organic agriculture comes up people often ask, "But what do you do about bugs?" My answer starts with, "well, there are good bugs and there are bad bugs. We do everything we can to encourage the good bugs so they will help us to control the bad ones."

 

 
It’s a basic fact of nature that all life is interdependent and is generally in balance until we humans come along and upset things. Where there is a crop damaging pest there is usually a predator present that feeds on that pest. The photos above and below are examples.

Eggs from the green lacewing (on stalks), a
major predator of aphids, laid among the aphids
So the conventional approach of indiscriminately using broad spectrum pesticides kills not only the pests but the predators that help to keep pest numbers from exploding. That often causes a more serious problem by upsetting nature’s equilibrium. In the worst case this can lead to worsening pest outbreaks requiring ever more powerful pesticide applications, leading to a host of problems from toxic residues on the crop to environmental pollution to pests developing immunity.

 
A more natural approach of working with, rather than against, nature can yield the best results. This means identifying the pest, learning its life cycle and natural enemies, and then creating conditions that make life difficult for the pest and favorable for the beneficial insects that prey upon the pests. Most importantly this means accepting a certain amount of pest damage, since without pests there would be no reason for their predators to stick around and help to control them.
 
A case study
Tools of the trade, a microscope and loupe for
identifying the pest curling these plum leaves
So how does one go about this type of natural pest control? Here is one example. One of the most common springtime pests are aphids, and over the past couple of years we have had a serious outbreak of the Leaf Curl Plum Aphid on our Santa Rosa plum trees. Last year the infestation reached the point of weakening the trees and reducing fruit size and quality, so this year we launched a "shock and awe" campaign, deploying every available strategy against this pest.

First, following the admonition to "know your enemy," I researched its life cycle and consulted with the county ag commissioner, a supplier of beneficial insects, and UC Davis resources. Eliminating ants is essential to controlling aphids since they "farm" aphids just as humans farm cows, so when ants are present any aphid control effort will have limited success. We had carpenter ants in the plum trees, so step one was to set out ant bait stations to gradually kill the colonies but also to band the trees with sticky Tanglefoot as a barrier to crawling insects.

This particular aphid lays eggs near plum tree buds in the Fall, so step two was to apply two dormant season sprays of an organic mineral oil to smother the over-wintering aphid eggs.

Strips of legume and mustard cover crop left
unmowed as habitat for beneficial insects
The aphids begin to hatch around bloom time, so step three was to maximize predators that feed on aphids. We always grow a winter cover crop that attracts and nurtures lady bugs, lacewings and other beneficials. It needs to be mowed down in the Spring to conserve soil moisture, but I leave unmowed strips as beneficial insect habitat as long as possible. But this year I went a step further by doing three releases of lacewings and a predator midge (a tiny fly with a voracious appetite for this particular aphid), purchased from an insectary as eggs.
Pheromone lures hung in plum trees
to attract beneficial insects

Step four was to hang pheromone lures in the trees that attract beneficial insects, as well as cards painted with beneficial insect food - a mixture of soy flour, nutritional yeast, and calf milk replacer - to keep the beneficials as healthy as possible. In addition I have found a pheromone attractant to draw the aphids to a sticky card trap.

Even with all these efforts we have had some spot outbreaks, but they are very minor compared to past years. I am currently employing a final step of clipping off the worst aphid infested shoots, dousing them in a bucket of soapy water and discarding in the trash. And here I need to grit my teeth and remember the principle of nature’s balance: there have to be some pests present in order to keep the pest’s predators around. So when I reach to clip off an aphid infested shoot and see lady bugs or lacewings present, I am reminded that in this instance "zero tolerance" is not the best approach. My hope is that the benefits of all these efforts will compound in future years, as the life cycle of the pest is disrupted and the beneficials gain the upper hand.

Toads live under cover during the day,
come out and eat slugs at night
Once you start thinking in terms of maintaining nature's balance, many pest control strategies become obvious. Those spiders that build webs in your potted plants? They are ferocious hunters of many plant damaging insects so it is best to leave their webs alone. That toad hanging out under your garden stepping stone? He comes out at night to eat slugs and snails, so it's helpful to install more toad housing in the yard. And that pest control guy that comes and sprays all around the house? He's ensuring job security for himself by killing pest and predator alike, making it easier for the pests to rebound.

Some information and products for natural pest control can be found here:
  • Your county Ag Commissioner’s office can help identify plant pests and diseases and suggest remedies
  • UC Davis has excellent online pest & disease information at http://www.ipm.ucdavis.edu/
  • Cornell University has a great guide to biological controls at http://www.biocontrol.entomology.cornell.edu
  • There are a number of online suppliers of natural pest control products, here are two:
http://www.rinconvitova.com
http://www.arbico-organics.com

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