Economic Aspects of Fumigation in Southern Forest Nurseries

William A. Carey, Auburn University Southern Forest Nursery Management Cooperative

A Technical Report in the last issue (vol. 5, no. 3) summarizes some $4 million in USDA-Forest Service research on fumigation alternatives in bareroot nurseries. Reported by region, the section on the South indicates some nurserymen there waste fumigation. Forest Service researchers never observed disease in southern trials and despite persistent weeds always considered that “seedling quality and quantity in the control (non-fumigated) plots were acceptable.”

The Auburn University Southern Forest Nursery Management Cooperative has conducted fumigation studies similar to those of the Forest Service across the South since 1993. Although both research efforts report persistent weeds and little mortality from disease, the Co-op’s focus on economics leads to a radically different conclusion about the value of fumigation to seedling quality and quantity. To support our position, some costs and values for our seedlings is needed.

As the Forest Service reported, about 1.2 billion forest tree seedlings, or 80% of the US total, are produced in the South each year. About 90 percent of these are produced by members of our Co-op, in just over 50 nurseries with average nursery productions of about 20 million seedlings. Through mechanization and economies of scale, most of these seedlings sell for an average price of only $ 0.035 each. Nevertheless, with about 29,000 square foot of bed surface per production acre, that price makes each seedling/ft2 represent $1,006 in potential sales. An average seedbed density of about 24 seedlings/ft2 makes an acre of seedlings valuable indeed. Fumigation costs could be paid for by only 1.2 to 1.5 more seedlings/ft2. Although Forest Service researchers considered their non-fumigated plots acceptable, they report an average increase of 2.2 seedlings/ft2 in Methyl Bromide (MBr) plots over four years of a Florida study. Those 2.2 seedlings should be worth about $30,000 each year to the nursery above the cost of fumigation. In a recent Co-op study, the average increase at three nurseries was seven more plantable seedlings/ft2 for the best fumigant. Fumigation associated reductions in weed control costs and the associated labor relief, along with the insurance against soil-born disease, need not be speculated on.

Forest tree seedlings are not an end-use product. The nursery-gate-price is a minimum valuation and their value for forest production can and should be considered. Historically, bareroot southern pine seedlings are classed as one of three grades based on root collar diameter (RCD). Grade 1’s have RCD’s greater than 4.8 mm, grade 2’s are smaller down to 3.2 mm, and smaller seedlings are considered culls. On average, grade 1’s survive and grow better than grade 2’s. If, for example, grade 2’s and 1’s have average RCD’s of, respectively, 4.5 mm and 6.5 mm, the grade 1’s will be about one year ahead (in a 20-yr rotation) and have perhaps 5% greater initial survival. These considerations, in an analysis of published studies (in 1984), suggested the present value of grade 1’s, on average, exceeded grade 2’s by $ 0.10 per seedlings.

So many seedlings are now produced per nursery that grading and physically removing small and or diseased seedlings after harvest is no longer practical. However, an appreciation for the improved performance of larger seedlings is indicated by the trend to produce fewer seedlings/ft2 and in the availability of low-seedbed-density seedlings at a higher price. For example, one corporation sells seedlings grown at 20/ft2 at a 66% increase compared to those grown at 25/ft2. The tacit assumption is that lower seedbed density seedlings are larger.

In Co-op studies, fumigation has increased both average seedling size and the number of seedlings. Increases in size and in numbers should be multiplied to estimate the real impact of treatment. For example, in the recent three study comparison, chloropicrin plus metham sodium (CMS) was the best fumigant (MBr was not tested). Compared to non-fumigated plots, CMS increased total seedlings (including culls) by only 3/ft2 but increased grade 1 seedlings by 6.5/ft2. If all those seedlings were sold, sales would increase $3,000/ac and present values, estimated as above, would increase $26,000/ac. Nursery reputations rise or fall in time with product quality so there is value to the nursery beyond the sale price. However, the present value of the seedlings is the value beyond the nursery. Should this value concern the Forest Service?

The Forest Service’s research priorities remain the development of non-chemical technologies. For example, to forecast disease based on soil assay, to manage disease by organic amendments or barefallow treatments or the containerization of some bareroot production. Estimates for practical availability and cost are avoided. A cost estimate for containerization is simple; in the South it adds about $0.10 per seedling compared to bareroot production and so would add $100 million to seedling costs.

In The Biologic and Economic Assessment of Methyl Bromide (NAPIAP 1993) the largest estimated economic return per pound of MBr was $109/lb in forest tree nurseries. That equals $30,000 per nursery acre. Is that realistic? The production /ft2 in a 1998 Georgia study was 11.5 grade 2 plus 2.5 grade 1’s in control plots and 5.4 grade 2 plus 14.0 grade 1’s in CMS fumigated plots. Increasing the present value of grade 1’s for expected growth makes the value in control plots and in fumigated plots, respectively, $21,500 and $59,300. Evaluating fumigation in bareroot nurseries requires more than disease associated mortality.

Last Updated: October 1, 1999