Scouting to manage pests

CEW-MR-1-Scouting Pests669by Tamara Scully
Pest management means scouting for pests. If you don’t know what is out there, or if they are out there en masse or just at a tolerable level, any control program is going to be more costly and less effective than a targeted approach. Whether a young farmer, just learning the ropes, or an experienced grower needing to intensify pest management strategies, scouting more effectively, and learning how to use the results, is good practice.
Doug O’Brien, an agricultural consultant and adjunct professor at Cabrillo College, in California, teaching organic farming, and Helen Attowe, a farmer, organic farm consultant and former horticultural extension agent, recently addressed a web-based audience, providing scouting information, tips, tools and procedures.
“It all sounds really easy, but it isn’t,” O’Brien said.
The best time to scout? High noon. Row covers, staked plants and tall plants can all make proper scouting difficult. Moving along rows is not the best way to scout. Row covers should be crawled through, and tall plants can be nearly impossible to move amongst to get an accurate sampling. Scouting involves moving through fields in an organized manner, observing all parts of the plants as well as all sections of the field, and statistically sampling in order to produce an accurate record of the pest pressures in the field, he said.
“It’s really important to observe from different distances,” O’Brien explained, as color variations, density, height changes and other discrepancies can point to problem areas in the field. “It’s a very active process.”
Looking from a distance, seeing many plants at a time, one can observe these changes. But it’s up-close where the pests will actually be seen. The pattern of scouting should involve edge plants, plants 20 feet in the row, and the biggest and the smallest plants in an area. A diagonal pattern across the field being sampled should be made.
On a small farm, a more intensive pattern of scouting may be manageable. Planned movement through the field, as well as varying entry points with each scouting foray, can go a long way towards getting an accurate look at pest activity. Between 10 and 20 plants out of every 100 should be observed closely for a statistical sample. In some cases, as many as 50 plants might be examined, depending on the concern. Fields should be scouted as often as possible in mid-summer, when pressures are high.
“We are talking about farms who have too much crop” to do end-to-end field scouting, O’Brien said. “To get a statistical sample, we have to look at enough of the crop, of the plants, to be reasonable sure that it is representative of the whole group. Putting a number on things is really important.”
Having accurate sampling allows one to factor in how much risk is acceptable, and helps to determine when treatment techniques need to be implemented.
Pest pressure
Thresholds are “levels which trigger some sort of action,’ O’Brien explained. “The threshold varies with the field, and the time of the year, and the crop. Everything happens faster in warm weather and increasing soil temperatures.”
Atthowe spoke of thresholds as a way to determine “whether we’ve gotten to a level that’s going to cost.” She emphasized that the threshold can vary from farm to farm. A direct-market small grower can have a much higher threshold than a large wholesaler, where there is little tolerance for imperfection from buyers.
Predators and parasites should also be included when determining a threshold for a particular pest. Atthowe considers it important to do so in order to determine whether or not there is enough predator and parasite load to actually make a difference” in the pest pressure. If there is a high predator/parasite load, there may not be a need to treat, even if the pest load is also higher than desired. The threshold will change depending on predator load.
It is also critical to know when these beneficials are most active. Models of degree days in relation to pest activity can help to more accurately paint a picture of when beneficials may be able to handle the threat, or when more intervention migh be needed. Attowe gave an example of how “aphids have become almost a non-pest” on one of her farms, because there is such a high predator/parasite load. Predatory activity is not static, either. There are “different peaks for predatory activity,” and knowing when to expect the most activity from a given predatory is important in determining thresholds as well.
O’Brien pointed out that accurate records help to determine patterns of pest pressure. Farmers can avoid planting a crop at certain times, when pest activity is too high. For example, planting a specific crop in June may coincide with increased pest damage. Skip that planting, and plant at other times, when the pest threshold for problem pests is lower.
Start scouting
Atthowe posed the questions: “If you have a pest and you want to set up a scouting program, where do you start? How do you start doing that?”
Her answer: get looking; get educated about what you are looking at; learn to identify pests at all of their life stages; know your predators; and use information from the experts on thresholds. Start monitoring as soon as the crop is planted, and keep records.
A hand lens is needed for scouting. A notebook, a knife, and shovel should also be a part of a scouting routine. Buds, roots, internal leaves, growing tips and the underside of leaves should all be examined. Young and old plants are the first ones to be impacted by a pest or disease issue, O’Brien said.
“The more records you keep, the better,” Atthowe said. “The key to good scouting is to look regularly and keep consistent records.”
After scouting
The National Young Farmers Coalition recently sponsored a pest management segment, with pest management expert Mike Dimock. Dimock answered farmers’ questions on treating various insect problems. Users of the Young Farmers Coalition Forum (www.youngfarmers.org) had questions on management of particular pests. Growers on the forum expressed concerns about harlequin bugs, tomato russet mite, imported cabbage worm, and potato leaf hoppers.
Dimock recommends that small growers hand-pick pests when practical. Environmentally-sensitive products, such as neem oil, pyrethrin-based insecticidal soap, BT and beneficial insects are all a part of the pest management arsenal available to growers. Planting trap crops, leaving unmowed cover crop strips to attract beneficial insects, immediately mowing down old crops, and leaving natural vegetation buffers outside of fields are all measures for keeping pest populations in check.
The first step in controlling pests is knowing where they are. Scouting a field properly can help to determine if and when pest issues reach a level where damage control needs to occur. Having the tools to keep pest levels from becoming an issue, as well as the right tools to use when they do get out of hand, requires smart pest management techniques.

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