Research report from OSU's North Willamette Research and Extension Center
Delbert Hemphill
OSU Dept of Horticulture, NWREC
Pruning and training methods are known to affect yield and quality of tomato fruit. However, specific data for Willamette Valley conditions and varieties have been lacking. The trial reported here grew out of observations on the effect of staking and single-leader pruning vs. no staking or pruning on the variety Early Girl. In a 1977 tomato variety trial, some plants of the indeterminate Early Girl were allowed to grow and spread along the ground unchecked by pruning or training. Other plants were pruned to a single leader and tied to a stake. This severe pruning and training resulted in earlier fruit ripening on the first three trusses and slightly larger fruit size, but decreased yield and increased splitting and cracking during a heavy rainfall period. The 1978 trial was designed to more closely examine these effects.
Methods
Seeds were planted on April 13 in Jiffy Pots containing a mix of sandy loam:peatmoss:perlite (1:1:1) and placed in a heated greenhouse. Seedlings were fed 1/2 cup weekly of 10-30-20 (1 ounce/gallon) after appearance of the first true leaf. Just prior to first bloom, the plants were moved to the field and grown on 42 inch raised beds covered with black plastic mulch. Fertilizer consisted of 1,000 pounds/acre of 10-20-10 and 1,000 pounds/acre dolomite incorporated into the Willamette sandy shot loam before bed shaping. All plants received one cup of 1 ounce/gallon 10-30-20 at transplant. Viaflo tubing was used for irrigation. No pesticides were used.
Four replicates of three plants each were pruned to a single leader (vine) and tied to 6-foot stakes. An equal number of plants were neither pruned nor staked. Plant density in each case was one plant/square yard or about 4,800 plants/acre. Fruit was harvested weekly after August 1. In an attempt to induce blossom end rot (BER) and cracking, the beds were flooded on July 26 and then dried until plants were visibly wilted. The flooding was repeated on August 16 and the beds again allowed to dry. Water was given as needed after September 1. All fruit was picked at pink to red-ripe stage except that the last two harvests were at breaker stage.
Results
In 1978, with intentional induction of BER and cracking, the 1977 results were confirmed and, indeed, magnified. Fruit size was considerably larger (29 percent) for the more lightly cropped staked plants and earliness was again promoted, with 53 percent ripened by August 31 for staked plants vs. 35 percent for nonstaked plants (Table 21). Total yield was more than halved on staked plants while marketable yield was reduced by nearly half (Table 22). Incidence of BER was nearly 8-fold higher on staked plants and misshapen fruit and radial cracking were 3 to 4-fold greater on staked plants. Concentric cracking was not significantly different between the treatments. However, late blight affected over five times as many fruit on nonstaked as on staked plants.
The sugar/acid ratio or apparent ripeness of the fruit after three days at room temperature was not consistently affected by pruning method (Table 21). Three unblemished red-ripe fruit per replicate per harvest period were used for these measurements. Sugar was estimated by a refractometer reading of expressed juice while acid was estimated by titration against standard base assuming 100 percent citric acid. There was less seasonal variation in sugar/acid ratio in nonstaked fruit.
The lowered yields for staked plants are to be expected since sucker removal greatly reduces the number of flower clusters/plant. But since the trained plants require less space, a greater plant population is easily attainable and can correct the yield difference, although at a higher cost for seed, other materials, and transplanting. The increased fruit size and earlier ripening of the staked plants may be explained by reduced competition for photosynthate, minerals, etc.
Early Girl is an early, rather small-fruited variety and increased fruit size might improve marketability when competing against later, larger-fruited varieties. The increased BER and cracking with alternate flooding and drying suggests that fruit on staked plants are more susceptible to changes in water or nutrient availability. However, control of both water and nutrient status should normally be no problem with plastic mulch and drip irrigation. Staking appears to offer some disease protection, possibly because of better air movement, remoteness from soil-borne pathogens and greater spatial separation between clusters.
In summary, severe pruning and staking of the popular hybrid tomato cultivar Early Girl will produce earlier ripening, increased fruit size, and possibly some disease protection at the cost of decreased yield/plant, possible BER or cracking problems when moisture and nutrients are inadequately controlled, and increased expenditures for materials and labor.
Table 21. Effect of Pruning Method on Earliness, Fruit Size, and Sugar/Acid Ratios of Early Girl Tomato at Various Harvest Periods Pruning Harvest period Season method 7/31- 8/09- 9/01- 9/21- 10/12- average 8/08 8/31 9/20 10/11 10/24 Percent ripened Staked 13 40 12 19 16 - during period Nonstaked 3 32 45 14 6 - ------------------------------------------------------------------------- Fruit size Staked 137a 159a 176a 117a 106a l4laY (grams) Nonstaked 94b 124b 113b 85b 60b 109b ------------------------------------------------------------------------- Sugar/acidZ Staked 5.7a 6.3a 5.9a 4.9a - 5.8a ratio Nonstaked 5.2a 5.3b 5.9a 5.5a - 5.5a ZSugar/acid ratio is the percent by weight soluble solids/percent by weight titratable acidity. YMeans in same column followed by different letters are significantly different at 95 percent confidence level. Table 22. Effect of Pruning Method on Yield, Incidence of Blossom-end Rot, Concentric Circular Cracking, Radial Cracking, Rough Fruit, and Susceptibility to Late Blight of Early Girl Tomato Pruning Total Market- BER Conc. Radial Rough, Late method yield ableZ cracking cracking misshapen blight ton/ yield acre ton/acre % % % % % Staked 24a 15a 19.0a 15a 18a 14a 7a Nonstaked 55b 29b 2.4b lla 5b 4b 40b ZMarketable yield is the total yield less any fruit which were severely cracked, split, blighted, severely misshapen, or blossom-end rotted. Many individual fruits had a combination of two or more defects.