'Windshield' scouting is not enough
Get in there and take a close look. If you have a large block of the same crop, walk in a z or a w through the field to get a good sense of the whole field. For many diseases experts recommend looking at 50 leaves in a field. On small patches you may want to look at every plant. Make sure you turn the leaves over. Protected, damp areas under plants are often insect and disease's favorite homes. Wet areas or other troubled spots should definitely be on your list of places to look.
Items needed to scout include:
- plastic bags for plant samples
- permanent marker to write on the bags
- 10 or 15X hand lens
- shovel to dig up plants
- clipboard to write down observations
- digital camera (optional)
Look for symptoms as well as the pests and diseases themselves
Good scouts will note patterns when they find a problem. Are symptomatic plants only near the edge of the field? Is the problem affecting only one variety? Does the problem start in one spot and radiate out through the field? Many pests and diseases you will learn to identify on site. For those you are unfamiliar with, here are a few questions to ask yourself when you find a problem: When did you notice the problem? Was the damage sudden or gradual? How old are affected plants? What percentage of the plant is affected? What is the degree of injury? Make sure you also note the cultural practices associated with that planting, for example irrigation and fertilization and recent environmental conditions, recent rainfall, etc.
Armed with your list of notes, it may be possible to discover your problem by consulting a good field guide or website. Penn State's publication " Identifying Diseases of Vegetables" is available through your local Extension Office. Another great source of information about Vegetable Diseases is Cornell's website. To see picture of some of the most common insects that attack vegetable crops, try Vegetable Insect Identification, or contact your local extension office.
If possible, take a fresh sample to your county's Extension office. Many times a county educator will be able to identify the problem. If the county office needs extra help or lab tests to diagnose the problem, they can send your sample on to the Penn State plant diagnostic clinic. Your county extension office can also help you if you decide you need to ship your sample directly to the clinic at Penn State. It is best to do this early in the week, to avoid having your sample sit in the mail over a weekend.
A few more hints
Never pull a plant out of the ground for diagnostic purposes. Dig the plant up carefully, wrap the above-ground foliage separately from the roots and their associated soil. Don't bring in the worst plant in the field. Bring a plant that has symptoms that are just beginning to show. Dead plants tell no tales.
Make a point to set aside some time, say once a week, in a regular schedule to scout your fields. Identifying a problem before it balloons out of control is well worth the time spent.