Scouting Your Vegetable Crops for Pests and Disease

pests on produce

As you are transitioning from summer to fall crops it is a good time to scout your fields for pests and disease. This also applies to transplants that might not yet be planted in the field. The last thing you want to do is to introduce disease to your field through infected seed. Scouting is an integrated pest management (IPM) strategy that systematically assesses the health of your crops and the threat of pest outbreak without having to inspect every plant in the field. By monitoring and scouting your plants routinely you are better able to detect early threats from either pests or disease and implement proper management strategies.

When scouting for disease, monitor your crop for symptoms, such as leaf discoloration, and signs, such as powdery mildew. Scouting for pests requires you to scout your field for insect activity including the presence of eggs on the underside of foliage, entry holes, or frass (insect excrement). It is equally important to monitor and record the scale of damage and pest population size. This data will be critical in deciding how best to manage the problem. Routine and detailed record keeping is essential to ensuring proper management of pest and disease pressure.

Essential Tools:

  • Hand lens for inspecting small insects, mites, insect eggs or feeding damage.
  • Small tally counter to keep insect counts accurate.
  • Traps of various forms that may or may not include lures to attract insects.
  • Camera for taking quality pictures. (You could probably use your phone for this)
  • Sweep net for collecting insects from foliage.
  • Shovel or spade and containers (paper bags, cups) for collecting plant, disease and insect samples.
  • Cooler for transporting and preserving samples.
  • Permanent marker to label containers with pest samples.
  • Diagram of your fields made by hand or graphing program.
  • Crop-pest scouting sheets for data collection.

 

Methods

There are four main methods to consider for scouting your field. These methods include visual observation, sweep net sampling, trapping and environmental monitoring.  Visual observation of crops and environmental monitoring should occur routinely to identify an early presence of pest or disease. Sweep net sampling and trapping apply mostly to pest pressure monitoring.  Before you begin to scout your fields develop a scouting plan that will divide your fields into manageable portions that can be organized by crop variety, size, and location.

Visual Observation:

This method works well when monitoring exposed feeding insects. Through this method you are able to observe the presence on beneficial insects or any beneficial parasites that might be present on pest insects. In addition to assessing pest levels this method allows you to observe any signs of plant disease, environmental damage, or any improper field management practices that could lead to an increase in pest or disease levels.

 

Visual signs that indicate insect damage or disease:

  • Cupped, chlorotic, spotted or malformed foliage.
  • Discolored, damaged, swollen or sunken areas in plant tissues.
  • Insect feeding, entrance holes in stems, chewing or rasping damage, or frass.
  • Aggregation of insects.
  • Pockets of less vigorous or dying plants.
  • Anything out of the ordinary.

Since visual observations can be subjective it is important to have the same person walk the fields routinely to monitor pest or disease levels. When walking the field, select a path that will allow for observing a random selection of crop. One common method is walking a “W” route through the field and selecting random leaves for inspection. It is important to inspect both sides of the leaf, looking for signs of potential pests. Don’t forget to record both your route and any observations made while in the field. Follow this same procedure each time that you scout your field, but remember to vary your path in order to cover different areas. Field areas with high levels of pest and/or disease should be scouted frequently.

Sweep Net Sampling:

This method is used to monitor the presence of small pests over a large area. Sweep net sampling works best in areas with low growing, flexible crops such as: carrots, peas, leafy greens, and onions. Pests that are easy to monitor with this method are pea aphids, flea beetles, and adult potato leafhoppers. An effective method for sweep net sampling requires you to swing the net in front of your body in a 180° arc from right to left and back again as you walk through the field. A sweep net made of muslin is preferable because it is lighter, more flexible, and dries quicker than nets made of other materials.

 

Trapping:

There are various trapping methods when it comes to pest pressure management. Two common methods are the use of attractants, such as pheromones, and the use of visual cues, such as soapy water. Pheromone traps are pest specific and are generally used for non-beneficial butterflies and moths. This particular trap will emit a sex pheromone produced by the female of a specific species to attract a mate, luring the mate to the trap. Traps that use visual cues act as a decoy for pests often mimicking plants, leaves, or fruit. Filling a bright colored dishpan with soapy water and placing it on the ground will attract aphids and other adult flies. The purpose of either one of these methods is to lure pests away from crops, while monitoring first catch, emergence, and tapering of the pest. Recording these observations will be important to have as a reference for future grow seasons.

 

General guidelines to follow when trapping:

  • Place traps in field about 2 weeks before the anticipated emergence of the targeted insect.
  • Refer to manufacturer or extension recommendations for trap placement and spacing.
  • Check and clean the traps weekly. Consider checking the traps more often until you notice the first pest emergence of the season.
  • Replace attractant lures as recommended and store in freezer to preserve.

 

Remember, scouting is the routine monitoring of pest and disease pressure in a crop. It is important to establish an action threshold for each of your crops. An action threshold is the point that you determine that you will experience economic loss if control measures are not taken to subdue the presence of disease or pest. Through this process, you are better able to detect and manage a problem within the field before it gets out of control and results in crop loss.

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