University of Florida

Field Scouting Procedures

Tomato Field

Fields are visited by scouts twice a week. It is a good idea to gather background information for each field scouted. Information of this sort may include previous crops, irrigation method, cultivar of tomato, fumigation practices, etc. These and other factors can have a direct bearing on the status of pests in the field throughout crop development. Record stage of growth each time the field is visited (see stage of growth description in Appendix 4).

At least one 6 row-ft sample for every 2.5 acres of tomatoes should be taken. Fields less than 20 acres in size may require one sample per acre and may prove less economical to scout than larger fields. Samples should be selected "at random". That is to say, every 6-ft sample for data collection should be selected without previous bias. For instance, there has been a tendency for some scouts to select sampling sites in those areas where plants look particularly bad. Others might use large weeds sighted at a distance as spots for sampling sites. Both these approaches are obviously biased. A better, more bias-free method is to predetermine the number of rows to be stepped off before selecting a row to be sampled and then stepping off a predetermined number of paces in the row before stopping at plants to be sampled. The predetermined numbers of rows and paces should be reselected randomly for each sample date.

Sample Grid MapA "grid system" has been chosen to spread the samples more or less evenly throughout the field (see Grid Map in Appendix 8). In the field represented by the map, a 6-ft sample is selected "at random" in each 2.5 acre section (areas 1,2,3, and so on), ensuring that all parts of the field will be visited on each trip and that pest outbreaks can be pinpointed in certain areas of the field.

The first procedure is to make a visual inspection of the 6-ft sample for identification of flying insects. Several important insects quickly fly away when approached and must be counted as best one can while approaching the sample.

The populations of leafminer larvae (living and dead), aphids and insect eggs are counted on the whole plant (up to two true leaves present on the tomato plants), of the terminal three leaflets (trifoliolates) of the third fully expanded leaf from the top of the leafminer larvaemain stem (three true leaves to bloom), or the terminal trifoliolate of the seventh fully expanded leaf from the tip end of any branch (after blooming to end of crop). Live leafminer larvae appear yellow; dead ones are dark brown to black. Use six plants or six trifoliolates per six-foot sample. Express leafminer densities for that sample on the basis of an average for one trifoliolate. To do this, divide the total count from the six subunits by six to arrive at the estimate of number of leafminer larvae per plant or per trifoliolate. For example, if nine live larvae are counted on six trifoliolates, results should be reported as 1.5 live larvae per trifoliolate. Inspections for caterpillar larvae, with the exception of the tomato pinworm, are concentrated in areas of the sample where there may be evidence of feeding (including plant damage and frass). Tomato pinworm populations are determined by counting the number of larvae on the foliage of whole plants (up to the seventh true leaf stage) or on one leaf selected from the lower canopy of each plant (eight true leaves to end of crop). Pheromone traps may also be used to monitor pinworm adult activity in order to time applications of pheromones for mating disruption.

After fruit set, 10 fruit per sample are inspected for damage from disease, caterpillars, and stink bugs. Thrips populations are estimated by gently exhaling on each of 10 flowers in the six-foot sample and counting the number of thrips that are disturbed (seen coming out of flowers).

Silverleaf whitefly NymphWhen sampling for silverleaf whitefly nymphs use the same six trifoliolates as are used for leafminer sampling and count pupae and nymphs of silverleaf whitefly on each terminal leaflet. Count adult whiteflies on the whole plant (up to three true leaves present) or the terminal leaflet of the third leaflet from the top of a stalk.

Observations on foliar disease incidence are made at each sample site using the Horsfall-Barratt rating system (see Appendix 5). Examples of diseases sampled in this manner are bacterial spot, late blight, leaf mold, and early blight. Diseases that attack the entire plant (their presence causes whole plant debilitation, rather than partial loss of photosynthetic surface) are recorded as percent plants infected in the sample. Examples of diseases of this type are Sclerotinia stem rot, bacterial wilt, southern blight, and potato Y virus.

Record the counts (number of individuals, percent damage, etc.) for each pest at each sample site on the field sheet (see field sheet sample in Appendix 6). Calculate the average level of each pest and beneficial in the field. This average is your estimate of the true population average for the field. On the grower report sheet (see Scouting Results Summary sheet in Appendix 10) report the average counts just taken, the past week's counts, and comments (any additional specific information that would benefit the grower). Do not make specific recommendations. Record weed situations and any other pertinent information in the "comments" section of the report sheet. Growers especially appreciate any additional information you can provide. Depending on your understanding of the needs of your client you may want to use the comments section to point out nonpest problems like windburn, herbicide damage, etc. The final treat/no-treat decision-making obviously is a job for the farm manager. He can contact his county vegetable crops agent or the state specialist for specific recommendations.