UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY 4, CALIFORNIA SWEET CORN SUCKERING TRIALS IN CALIFORNIA P. A. MINGES," BERNARR J. HALL, 1 HILTON B. RICHARDSON, 3 D. N. WRIGHT, 4 and JOHN H. MacGILLIVRAY' Pruning of the corn plant has been customary for a good many years. The practice of removing secondary, or side, stems (shoots) of sweet corn or field corn at the base is known as "suckering." For field corn there has been developed, in some states, a practice of removing the portion of stalk above the mature ear. This has been called it improves production sufficiently to pay a profit above the cost of the operation. To justify suckering, the yields would have to be significantly greater to compensate the grower for the labor involved. The tests herein reported have been conducted for several years at Davis, and in various impor- Fig. 1. — Young sweet corn plants before and after the suckers were removed. Left, non suckered plants; right, the same plants after suckering. Approximate height for early suckering, as in test two. Background ruled off in 1-foot squares. "topping." Both suckering and topping are prun- ing operations and therefore may reduce growth and leaf area; this curtailment of leaf surface lessens the manufacture of carbohydrates. The number of ears is reduced somewhat through the removal of suckers. Suckering of sweet corn has been practiced throughout California, except in a recently de- veloped area in the deltas of the Sacramento and San Joaquin rivers. The benefits claimed by growers are: (1) a larger yield of corn, (2) a higher percentage of marketable corn, (3) in- creased earliness, and (4) larger individual ears. Obviously the practice is not justified unless Specialist in Agricultural Extension (Truck Crops) . Specialist in Agricultural Extension (San Diego County). 'Specialist in Agricultural Extension (Riverside County). Specialist in Agricultural Extension (Fresno County) . B Associate Professor of Truck Crops and Olericulturist in the Experiment Station. tant sweet corn producing counties through the cooperation of the Farm Advisors. Those most active in this work are listed as joint authors. Physiology of the Problem Suckering is a pruning operation that reduces the leaf area of the plant . In the test conducted in San Diego County in 1942, the number of leaves per plant for each treatment was recorded at the time of harvest. The averages were 25 leaves per plant when nonsuckered; 21 leaves when suckered once early; 12 leaves when suckered twice; and 11 leaves when given a single late treatment. The popular opinion is that this reduction of plant size will lower the water and nutrient require- ments of the plant , and thus encourage larger individual ear growth. On the other hand, prun- ing reduces the leaf area available for the manu- facture of sugars and carbohydrates, which make up the organic material found in the sweet corn ear. A larger supply of carbohydrates should in- crease root growth so that nutrients and water may be obtained from a larger volume of soil. The response to pruning is not always uniform with different crops, soil, or the climatic TABLE 1 Yields of Sweet Corn under Suckering Treatments Yields of unhusked marketable ears, in pound s per plant f Test nearest Variety- Harvest No Early Weekly Late no . city period suck- ering suck- ering suck- ering suck- ering 1 Davis Golden Bantam July 17— Aug. 2, 1940 0.65 0.45 0.39 0.36 2 Davis Golden Cross Bantam July 25— Aug. 7, 1941 1.38 1.50 1.32 1.16 3 Davis Oregon Evergreen Aug. 5— Aug. 11, 1941 1.06 1.18 1.07 1.05 4 Los Angeles Golden Cross Bantam July 21, 1941 0.86 0.76 0.74 0.60 5 Los Angeles Oregon Evergreen August 1, 1941 0.36 0.47 0.50 0.43 6 Los Angeles Oregon Evergreen Aug. 3— Aug. 8, 1941 1.20 1.03 .... 7 Davis Golden Cross Bantam July 17— July 29, 1942 0.80 0.94 0.80 0.84 8 Davis Oregon Evergreen July 28— Aug. 3, 1942 0.80 0.97 0.96 1.02 9 San Diego Golden Cross Bantam Aug. 10— Aug. 18, 1942 0.81 0.85 0.75 0.88 10 Indio Golden Cross Bantam June 1, 1942 0.98 0.98 0.92 0.90 11 Terminous Golden Cross Bantam Aug. 27— Sept. 8, 1942 1.28 1.10 1.04 0.97 12 Fresno Golden Cross Bantam Sept. 6, 1943 0.93 0.90 0.80 .... 13 San Diego Golden Cross Bantam July 2, 1943 0.72 0.72 0.70 0.64 14 Chino Golden Cross Bantam July 26— July 29, 1943 0.84 0.81 0.70 .... *Test 14 planted in three replications; all others in four. 'At odds of 19 to 1 , test 4 requires a difference of 0.05 for significance; test 11 requires 0.14. All other differences are not significant. TABLE 2 Effect of Sucker ing Treatments on Number of Marketable Ears* Location, nearest city Marketable ears, Marketable ears Test Year number per plant dozens ] per acre no. No Early Weekly Late No Early Weekly Late suck- suck- suck- suck- suck- suck- suck- suck- ering ering ering ering ering ering ering ering 1 ly40 Davis 1.88 1.48 1.08 1.01 1,175 925 675 631 2 1941 Davis 2.14 2.42 2.07 1.78 1,552 1,755 1,501 1,291 3 1941 Davis 1.36 1.49 1.38 1.31 986 1,080 1,001 950 4 L941 Los Angeles 1.28 1.10 1.04 0.92 1,280 1,100 1,040 920 5 1941 Los Angeles 0.48 0.69 0.67 0.57 360 518 503 428 6 1941 Los Angeles 1.29 .... 1.09 .... 1,076 909 7 1942 Davis 1.54 1.68 1.43 1.40 1,194 1,302 1,108 1,085 8 1942 Davis 1.16 1.34 1.37 1.47 928 1,072 1,096 1,176 9 1942 San Diego 1.44 1.48 1.23 1.54 1,410 1,413 1,190 1,386 10 1942 Indio 1.73 1.69 1.65 1.67 1,677 1,646 1,537 1,592 11 1942 Terminous 1.94 1.75 1.70 1.53 1,594 1,438 1,397 1,257 12 1943 Fresno 1.49 1.46 1.30 .... 1,458 1,500 1,313 13 1943 San Diego 1.20 1.16 1.10 1.10 744 693 673 681 14 1943 Chino 1.25 1.12 0.97 .... 1,165 1,148 983 *Test numbers correspond with years, areas, and varieties given in table 1. At odds of 19 to 1, test 11 requires a difference of 0.25 for significance; test 14 requires 0.16. All other differences are not significant. conditions. Further study is being made of the relation of irrigation and spacing to the effect of suckering on yield. The pruning of greenhouse tomatoes or sweet potato vines has caused reduced yields, as have also extended harvestings of as- paragus . Sweet corn is often grown by persons familiar with the production of tree fruits. Since prun- ing is extremely important for orchards, its effects on tree fruits should be compared with its effects on sweet corn. The pruning of tree fruits is considered essen- tial, but the method and severity vary with the different species and also with different soil and climatic areas. Of the five reasons enumerated by Tufts 6 for pruning trees, only the objective of securing good size and quality of fruit would apply to sweet corn suckering. Practically all pruning of mature trees is performed in the dor- mant season — a schedule that will not apply to an annual plant. Summer pruning is not recom- mended on mature fruiting trees because it will cause the production of smaller fruits. Summer pruning of young trees "at any time is devital- izing, and midsummer cutting is more weakening than cutting done early in the season." Thus it would seem that the pruning (suckering) of sweet corn and deciduous trees must have simi- lar effects, namely, possible reduced yield and size of fruit. Trials in Other States Suckering experiments have been conducted in three eastern states on field corn and in three TABLE 3 Size of Sweet Corn Ears under Different Suckering Treatments* Husked or Average size of ear, pounds 1 No Early Weekly Late Test unhusked suck- suck- suck- suck- no. ear ering ering ering ering 1 Husked 0.22 0.20 0.21 0.23 2 Husked 0.42 0.40 0.41 0.41 3 Husked 0.51 0.51 0.50 0.51 4 Unhusked 0.68 0.69 0.71 0.65 5 Unhusked 0.74 0.68 0.74 0.77 6 Unhusked 0.64 .... 0.64 .... 7 Unhusked 0.34 0.35 0.33 0.36 8 Unhusked 0.43 0.46 0.44 0.44 9 Unhusked 0.56 0.58 0.62 0.56 10 Unhusked 0.56 0.58 0.56 0.54 11 Unhusked 0.46 0.43 0.44 0.44 12 Unhusked 0.64 0.63 0.62 .... 13 Unhusked 0.59 0.62 0.62 0.59 14 Unhusked 0.66 0.68 0.71 .... *Test numbers correspond to years, areas, and varieties given in table 1. f At odds of 19 to 1, there were no signifi- cant differences. states and Canada on sweet corn. McCrory has reported on this practice with sweet corn grown under conditions of heat and drought; he also gives a summary of other corn suckering tests. Although these experiments were all conducted east of the Rocky Mountains, they clearly indi- cate that this practice does not increase yield and, in some cases, may even be detrimental. These previous studies have been instrumental in causing eastern growers to abandon sweet corn suckering as an essential operation. The present study was designed to test the applicability of the eastern data to California conditions. Labor Required and Cost of Suckering Cost-accounting studies were conducted in 1941 in two important sweet corn producing counties, namely Alameda and Los Angeles. In both areas the growers' corn was suckered an average of 2.2 times. In Alameda County this operation required an average of 32 man-hours per acre; it cost $13.18, or 11 per cent of the total costs, and was more expensive than any other item except fertilizer. In Los Angeles County, suckering re- quired 36s man-hours per acre; it cost $12.89, or 10 per cent of the total costs, and was more ex- pensive than any other material or operation. TABLE 4 Weights of Air-dry Plants in the Various Sucker- ing Treatments Averag plant e pounds of air per plot (1/30C -dry acre)* Tear Variety No suck- Early suck- Weekly suck- Late suck- ering ering ering ering 1940 Golden Bantam 50.4 36.9 17.1 13.3 1941 Golden Cross Bantam 29.7 22.1 14.9 14.1 1941 Oregon Ever- green 36.8 25.2 21.1 19.5 1942 Golden Cross Bantam 27.0 21.6 15.8 15.7 1942 Oregon Ever- green 37.5 28.9 26.0 26.3 *At odds of 19 to 1, these tests require a difference of 7.2 pounds for significance. "Tufts, W. P. Pruning deciduous fruit trees. California Agr . Ext. Cir. 112:1-68. 1939. 7 McCrory, S. A. Heat and drought tolerance of sweet corn as influenced by tillers. Amer. Soc. Hort. Sci. Proc. 40:424-28. 1942. "Sullivan, W. , and T. 0. Morrison. Market sweet corn production costs and efficiency ana- lysis. California Agricultural Extension Service leaflet. (Mimeo.) 4 p. 1941. (Issued by office of Alameda County Farm Advisor, Federal Bldg. , Hayward, California. ) "Gillette, A. F. , and W. Sullivan. 1941 pro- duction costs of market sweet corn. California Agricultural Extension Service leaflet. (Mimeo.) 4 p. 1941. (Issued by office of Los Angeles County Farm Advisor, 808 North Spring St., Los Angeles 12, California.) Sometimes the suckers from sweet corn are used for livestock feed. This practice may be justi- fied under conditions of extreme feed shortage but, even then, it is probably uneconomical. Suckering Treatments The plots used in the experiments conducted by the present writers consisted of two rows each, and ranged in length from the minimum of 25 feet to a maximum of 180. They were replicated as given in table 1. The treatments were as follows: (1) not suckered; (2) suckered early once, when the stalk was 12 to 18 inches high (fig. 1); (3) suckered early, and the suckering repeated once or twice; and (4) suckered late once, when plants began to tassel (fig. 2). All trials were con- ducted on irrigated plots. Fig. 2. — Plants before and after suckering at tassel stage of growth, as in test 4. Left, nonsuckered; right, same plants after suckering. Description of Experimental Areas Davis: The crops were grown on the University Farm and were planted in early spring. The rows were 3 feet apart, with plants 16 to 18 inches apart in the row. Los Angeles County: Tests 4 and 5 (table 1) were made at the County Farm under the direction of A. F. Gillette, formerly Assistant Farm Ad- visor, and I. C. Ibergj Farm Superintendent. There was some pilferage and wireworm damage on the Oregon Evergreen test plot (test 5)« Test 6 was located on the ranch of J. W. Spencer, near Artesia. San Diego County: Test 9 was made in Mission Valley on the C. S. Bond ranch. Test 13 was at El Cajon on the L. H. Saunders ranch. Both tests were conducted by Bernarr J. Hall. Riverside County, Coachella Valley: This ex- periment was on the Whittier Ranch near Indio, with Robert Bowlin as the cooperator and Hilton B. Richardson supervising the test. San Joaquin County: This test was made in a field of corn grown near Terminous for the San Francisco market, on the Richmond Chase Ranch. Fresno County: The test was conducted on the ranch of Roy Phillips near Sanger, under the supervision of D. N. Wright. San Bernardino County: This test, made on the ranch of Charles Pierce near Chino, was con- ducted by Paul Moore, formerly Assistant Farm Advisor. Results and Discussion Tables 1 to 4 give the data collected in seven different areas of the state over a period of four years. In these fourteen tests there was not a single case where suckering gave sig- nificantly better production. With regard to pounds of unhusked ears pro- duced per plant (table 1), in eight of the tests the highest average yield was obtained on the non- suckered plants. Two of these yields were signifi- cantly greater. In all cases except three, the late suckering produced the lowest yields. Table c shows two cases where the number of ears per stalk was significantly increased by the nonsuck- ering treatment. In the remaining tests the dif- ferences were not significant, but in eight of these the nonsuckered plants showed the best average yields. Suckering did not significantly affect the ear size, as is shown by table 3. It did result in a decreased size of plant (table 4), and usually this reduction was proportional to the severity of pruning. In these tests, suckering failed to hasten maturity; in ten out of eleven trials there was no significant increase in early yields from the suckered plots. In the Oregon Evergreen experi- ment at Davis in 1941, significantly higher early yields were obtained from the early and repeated suckering treatment . Further studies are to be made upon the effect of irrigation and planting distance under this practice. One advantage of suckering that has been ob- served is greater ease of harvesting, especially where favorable conditions have produced lux- uriant stalk growth. However, the cost of suck- ering cannot be justified on this basis alone, since the actual saving in cost of harvesting is usually slight. Conclusions According to tests conducted on irrigated sweet corn in seven counties, over a period of four years, neither the yield, nor the number of ears per plant, nor the ear size is improved by suck- ering. Therefore, suckering appears to be an un- justified practice which adds considerably to the cost of production without giving a commensurate return to the grower.