Amcotone plant growth regulator (PGR) in the production of seepage irrigated tomato.

C.S. Vavrina
Vegetable Horticulturist

Introduction

In 1998-99, over 37,000 acres of tomatoes were grown in Florida. Acreage has declined over the past several years due to expanding competition, poor markets, increasing regulations, and environmental constraints. However, the 1997-1998 season was a lucrative one and hence acreage was increased the following production season. To remain competitive, FL growers must increase yields and offset production costs.

Amcotone (Amvac Chemical Corp., Newport Beach, CA) is a product with physiological action to induce fruit set and to stimulate plant growth in critical stages. It consists of 1.2% naphthylacetamide, 0.45% naphthylacetic acid, and 98.35% inert ingredients. Naphthylene acetic acid (NAA) has been used in agriculture as a thinning agent and sprout inhibitor for sucker control in fruit crops. The objective of this study was to apply Amcotone in accordance with an Amvac Corp. protocol on seepage irrigated tomatoes to test the hypothesis of enhanced crop growth and yield.

Methods

A trial was established at the Southwest FL Research and Education Center of the University of Florida in Immokalee, FL. A standard methyl bromide fumigated (320 lbs./A, broadcast), dry granular fertilized (208N-96P-300K), plastic mulched (white on black, 0.3 mil), 32" wide bed was prepared on Aug. 15, 1998 allowing two weeks for fumigant action.

Tomato holes were punched in a single row, 18" in-row pattern on 6' centers on Sept. 2, and transplants of `Solar Set’ (Asgrow Seed, Kalamazoo, MI) fresh market, hot set, tomato cultivar were planted. No starter fertilizer was applied at setting, but the transplants were watered in. Twenty plants were set per treatment in 30-foot plots. Admire (Bayer, Corp.) was applied on Sept. 15 to reduce the possibility of Tomato Yellow Leaf Curl Virus (TYLCV). The plants were not pruned, but staked and tied, all in accordance with IFAS recommendations. Manzate plus copper and Bravo fungicide applications given weekly prevented the advancement of routine fungal diseases and bacterial spot. Various Bt's were also applied to reduce worm pressure.

Amcotone treatments were applied according to a schedule that centered on first flower. Early flowering was defined by when most of the plants had one open flower. Mid, late, and early fruit set applications were applied, in general, on a sequential 7-day schedule following first application. The rate by timing experiment imposed on the crop appeared as follows:

* 60 grams of Amcotone in 100 liters of water = 10 ppm

Amcotone sprays were applied on 10/2, 10/9, 10/16, and 10/23. Samples (1 plant per plot) of plant dry weight (DW) and fruit development were taken 47 and 60 days after planting (DAP). Generally, 30 and 60 day samples are taken, however under the conditions of this test no treatments had been applied 30 DAP. Ten tomato plants were harvested per treatment and yield was separated into red/breaker fruit and mature green. Each color category was further subdivided into medium, large, and extra-large size. Three harvests were obtained in all.

The six replications of the randomized complete block design were employed and analyzed by ANOVA (SAS) with mean separation via Fisher's Protected LSD at p<0.05 and 0.1.

Results

Tomato Plant Dry Weight & Fruit Development

Amcotone treatment showed no significant effect at any rate on tomato shoot (leaves and stems) dry matter accumulation at either 47 or 60 DAP when analyzed at p<0.05 or p<0.10 (Table 1). While no particular trend for shoot dry weight was established, the 20 ppm Amcotone treatment applied early and mid flower posted the greatest shoot dry weight at both sampling periods.

Fruit development at 47 and 60 DAP similarly showed no significant treatment effect for either number, weight or average fruit weight (Table 2). Again, however, Amcotone at 20 ppm treatment applied early and mid flower posted the largest number of fruit set at both sampling periods and this translated to the greatest overall fruit weight at 60 DAP. Amcotone at 20 ppm applied at early, mid and late flower attained the greatest average preharvest fruit weight at both sample periods.

Tomato Yield

Amcotone had no effect on tomato maturity or yield in 1998 when statistically analyzed at p<0.05 (Tables 3 and 4). A few minor treatment differences were noted however, when the data were analyzed at p< 0.10:

a.) Treatments 3, 4, and 6 produced more (number) red medium fruit at second harvest than treatments 1 and 2 (p<0.10).

b.) Treatments 3 and 4 produced more (weight) large green fruit at second harvest than treatments 6 and 8 (p<0.09).

Further effects on overall tomato fruit size grade or average fruit weight were not apparent (Table 5). An incidence of target spot brought on by Tropical Storm Mitch may have affected photosynthetic partitioning enough to mask fruit sizing effects. However, this trial resulted in 10 - 11 lbs./plant, reflecting yields typical of efficient commercial producers in south FL which fall in the 10 – 12 lbs./plant range.

Discussion

Amcotone application, regardless of rate or timing, had no effect on tomato fruit yield in this trial. However, if one follows the trend established in the early DW and fruit set parameters a pattern, of sorts, develops specifically for the Amcotone treatment at 20 ppm applied at early and mid flower. This treatment had the greatest DW 46 and 60 DAP and the greatest number of fruit as well. Furthermore, Amcotone at 20 ppm applied at early and mid flower posted the greatest number and weight of overall fruit in the trial.

Conversely, Amcotone treatment at 20 ppm applied at early and mid flower seemed to slow fruit maturity producing among the least red/breaker and total fruit at first harvest. Maturity is generally defined by the expression of color and plays the most important role when noticed at first harvest. The 20 ppm treatment applied at early and mid flower then produced more medium red/breaker fruit than the identical timing at 10 ppm and significantly more large green fruit (p<0.09) than the control, at second harvest. This is an excellent example of compensatory development (i.e., low at first harvest, high at second harvest.)

Similar comments can be made about treatment #3 (Amcotone @ 10 ppm, early/mid/late flowering and fruiting) except the early plant DW and fruit set increases were not present. Treatment #5 (Amcotone @ 20 ppm, early/mid/late flowering) exhibited the greatest preharvest fruit weight, but then never figured prominently in the yield aspects.

The results noted here are fairly typical of PGR trials. In general, numerical differences may exist (not always to the benefit of the PGR), but statistical differences are elusive. This essentially exhibits the great amount of variability inherent in crop growth and how a product would have to make a significant contribution to register a difference.

If application scheduling is so crucial for the efficacy of this product, large acreage, sequential planting growers may find it difficult to use. While growers are generally tuned into to the development of the crop, subtle nuances such as first open flower are often missed in the grander scope of production. The definition of mid and late flowering alone caused concern for this researcher. Granted fruit thinning and sprout retarding are also timing issues, but these issues generally offer a broader application spectrum and a more specific mode of action.

Table 1.  Field sample dry plant top - Amcotone, Fall, 1998

Table 2. Preharvest fruit number and weight with respect to treatment application.

Table 3. The effect of Amcotone on tomato yields in number of fruit per plot (10 plants per plot at 18 in. spacing.

Table 4.  The effect of Amcotone on tomato yields in pounds per plot (10 plants per plot at 18 in. spacing.