Thursday, July 26, 2012

Pest Identification

Often people have pests or weeds they want identified so that they can find out how to control them. Sometime it is difficult to describe the pest or weed in words. A picture paints a thousand words and so I often ask people to send me some photographs. But photographs sometimes do not show the detail that is needed for identification.

Here are a few guidelines on how to take photographs for identification.

Most cameras (compacts or reflex) are capable of taking good photos. Even many phones and other electronic equipment with image capture capability can give sufficiently good photos for identification purposes.

The most important thing is focus – blurred images are of little use.
  • Many cameras have a macro function for focusing close up on small objects.
  • Take more than one image.
  • In order of importance take an image of:
    1. The whole weed/pest/object
    2. Specific parts of the weed/pest/object. e.g. flower, leaf, seed, legs, teeth, droppings, damage.
    3. The situation in which the weed/pest/object is found.
  • If possible compose the photos with a neutral uncluttered background. A grey road is a good background. Do not use a white or black background as this will affect the camera’s exposure and the weed/pest/object will be too dark or too light.
  • Avoid harsh sunlight and images with bright areas and shadows. If it is a sunny day take the photograph in a shaded place.
  • Avoid camera shake, use a fast shutter speed if possible; faster than 1/30th of a second. For slower shutter speeds brace the camera against a solid object or use a tripod.
  • Most cameras will display the image and may have an enlarge function. Check your photo for clarity. Take another one if necessary.
  • For small objects and when using a camera with the ability to change the aperture use as small and aperture as the light allows. This give a better depth of field so more of a 3 dimensional object will be in focus. Use f16 or smaller (the bigger the f number the smaller the aperture).

Sending in samples for identification

For identification it is often necessary to send a sample of the weed/pest/object. There are some basic points to remember:

  • Include all available parts of the plant e.g. leaf, flower, seed, berry, bark.
  • Take a note (write it down, don’t rely on memory) of where the plant was situated and what size it is and other details.
  • Place the samples in a plastic bag and seal.
  • Keep the samples cool. Avoid leaving the samples in a hot car.
Insects or other
  • Try to avoid damaging the subject.
  • Ideally put the insect in 70% alcohol to preserve it.
  • Seal in a jam jar or other airtight container.
  • Keep the sample refrigerated.
  • Take notes of where the subject was found and when.
Pack the samples well before sending. Samples can be sent by post but they are better taken in person or sent by courier.

There are many organisations in New Zealand that will provide identification of plants, insects or other material depending on what it is. These would include CRIs such as Landcare Research, universities, museums, MPI (ex MAF) Biosecurity and pest controllers. I will be happy to receive and try to identify pests, weeds, plant diseases etc. But please contact me prior to sending.

A biology student did an experiment on a grasshopper. If its legs were taken off what would happen?
He pulled off one of its legs and yelled “hop!”, and the grasshopper hopped. 
Then he took another leg and yelled “hop!” and the grasshopper hopped. 
Then he took all of its legs and yelled “hop!” but the insect did not hop. He yelled again, but the insect did not hop.    
So he came to the conclusion that when all the legs of a grasshopper are removed, it becomes deaf.

He was right! Long-horned grasshoppers and crickets have ears in the knee-joints of their front legs.