EFFECT OF mums METHOD AND mums DATE ON THREE VARIETIES 0F LETTUCE (LACTUCA SATWA L.) - ' Thesis for the Degree MM. 8. MEMGAN STATE UNIVERSITY RAMACHANBRA SUBRAMANYA £973 ‘ + ABSTRACT EFFECT OF PLANTING METHOD AND PLANTING DATE ON THREE VARIETIES OF LETTUCE (LACTUCA SATIVA L.) BY Ramachandra Subramanya Transplants are successfully used in Michigan for the production of greenhouse lettuce (Lactuca sativa L.), but field lettuce is direct seeded and later thinned to a desir- able stand. Experiments reported herein with transplanted head lettuce resulted in increased yields and earlier maturity of the crop, which is very important in Michigan in order to make best use of the short growing season° This investiga- tion compared the effects of transplanting and field seeding on the horticultural characteristics of head lettuce° Three varieties of crisphead lettuce were planted in the field by tranSplanting plants growing in peat pots, bare- root plants, and by sowing seed directly° Three planting dates were used. The lettuce from each planting method was harvested at maturity and the following measurements were made: head weight, head diameter, stem length, days to maturity (from field planting) and amount of disease bottom Ramachandra Subramanya rot (Rhizoctonia solani) and leaf drop (Sclerotinia sclero- tiroum). To ensure disease, the surface of the soil in half of the plots was kept moist throughout the growth period by sprinkler irrigation. These experiments were conducted in 1971 and 1972, but because of the low temperatures and excess rainfall in 1972 the differences in treatment effects were not as evident as in 1971. The irrigated plots had a higher incidence of disease than the non-irrigated plots and is consistent with the fact that these diseases on the muck soil are associated with high soil moisture. Other horticultural traits were not affected by irrigation. Varietal differences were evident in head weight, stem length and incidence of disease. Varietal interaction with planting date and/or with planting method varied with the trait. Planting date had a significant effect on all traits. Interaction effects of planting date with planting method and/or with variety were also evident for all traits° Planting method also had a significant effect on all traits. The transplants had a higher incidence of disease than those of direct seeded plants. Peat pot transplants had the largest head weight, head diameter, stem length and also matured earlier than the field sown plants or bare-root transplants. Increased stem length did not result in bolting Ramachandra Subramanya of the plants. Disease was not reduced by shortening the total time that the plant was in the field. This finding sug- gests a need for disease resistant varieties or a fungicide which can effectively control these diseases. All horticul- tural characteristics were affected by planting method x planting date, or variety interactions. EFFECT OF PLANTING METHOD AND PLANTING DATE ON THREE VARIETIES OF LETTUCE (LACTUCA SATIVA L.) BY Ramachandra Subramanya A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Horticulture 1973 ACKNOWLEDGMENTS The author expresses appreciation to Dr. Grant H. Vest for the suggestion of the problem, and his guidance during the course of this study. Thanks are due also to Drs. R. L. Corolus and M. L. Lacy, who served as guidance committee members and assisted in preparing the manuscript. ii TABLE OF LIST OF TABLES . . . . . . CONTENTS INTRODUCTION . . . . . . . LITERATURE REVIEW. . . . . MATERIALS AND METHODS. . . O 0 Design and Analysis of the Experiment Growth, Care and Harvest. Irrigation. . . . . . Harvesting. . . . . . Head Weight. . . Head Diameter. . Stem Length. . . Days to Maturity Disease. . . . . RESULTS 0 O O O O O O 0 0 0 Head Weight . . . . . Head Diameter . . . . Stem Length . . . . . Days to Maturity. . . Disease . . . . . . . DISCUSSION . C C O U C O . APPENDIX-~TABLES BIBLIOGRAPHY . . . . . . . iii Page iv 12 l3 l4 l4 l4 l6 l7 l7 l8 l8 l9 19 22 24 27 30 36 4O 47 LIST OF TABLES Summary of rainfall and irrigation, in centi- meters, for each planting regime . . . . . . . . Average head weight in kilograms of three lettuce varieties by three planting methods and three planting date in both irrigated and con- ventional plots. . . . . . . . . . . . . . . . . Average head weight in kilograms of three lettuce varieties by three planting methods and two planting dates in both irrigated and conven- tional plots . . . . . . . . . . . . . . . . . . Average head diameter in centimeters of three lettuce varieties by three planting methods and three planting dates in both irrigated and con- ventional plots. . . . . . . . . . . . . . . . . Average head diameter in centimeters of three lettuce varieties by three planting methods and two planting dates in both irrigated and conven- tional plots . . . . . . . . . . . . . . . . . . Average stem length in centimeters of three lettuce varieties by three planting methods and three planting dates in both irrigated and con- ventional plots. . . . . . . . . . . . . . . . . Average stem length in centimeters of three let- tuce varieties by three planting methods and two planting dates in both irrigated and conven- tional plots . . . . . . . . . . . . . . . . . . Average days to maturity of three lettuce varieties by three planting methods and three planting dates in both irrigated and conven- tional plots . . . . . . . . . . . . . . . . . . Average days to maturity of three lettuce varieties by three planting methods and two planting dates in both irrigated and conven- tional plots . . . . . . . . . . . . . . . . . . iv Page 15 20 21 23 24 26 28 29 31 LIST OF TABLES--Continued TABLE 10. 11. Average disease percentages of three lettuce varieties by three planting methods and three planting dates in both irrigated and conven- tional plots 0 O O O 0 O 0 O O O O O C O O 0 Average disease percentages of three lettuce varieties by three planting methods and two planting dates in both irrigated and conven- tional plots . . . . . . . . . . . . . . . . Air temperatures Michigan State University Muck farm 1971. O O O O O O O 0 O O O O O O O O 0 Air temperatures Michigan State University muck farm 1972. O O O O O O O 0 O 0 O O O O O O O Page 33 34 43 47 INTRODUCTION Cultural practices such as fertilization, irrigation, population density, planting date, bed shaping and direc- tion of rows are known to affect the yield and horticultural characteristics of field grown lettuce (21,22,27). In Michigan and other places where lettuce is grown on muck soils, the crop matures uniformly allowing a once over harvest, and the growers often harvest two crops a year if weather conditions are favorable. At present head lettuce is sown directly in the field using pelleted seeds to obtain precision planting, to reduce the amount of hand thinning, and to achieve the desired stand. Because of the small size and irregular shape of the seed, precision planting has been difficult and many differ- ent approaches to solve the problem of singulation have been reported (16). One method of overcoming the problem of singulation and thinning is by the use of transplants, which is still done in some states in the United States. Little work has been done with transplants of field lettuce in Michigan. Information on the horticultural char— acteristics of head lettuce is of commercial as well as theoretical interest. Information on the horticultural traits will enable a plant breeder to determine the desirable traits not influenced greatly by environment, which can be genetically fixed in a variety. The knowledge of highly heritable traits would also be invaluable to research in developing a successful breeding program. The advantages of improved varieties in agriculture are well known. The objectives of the research presented here were to compare the horticultural characteristics of direct seeded lettuce with the transplants and to ascertain the advantages associated with either method if any. LITERATURE REVIEW Nearly all lettuce seed is planted in the field with a bulk metering device. Although hill-drop planters with holes in metal plates or rubber belts as the metering unit have been available for some time, these machines do not consistently and precisely singulate and space the seed in the row. Hence, the problem of hand thinning has not been completely eliminated. Because of the small size and irregular shape of the lettuce seed, singulation of the seed in the field for pre- cision planting has been difficult. Many different approaches to the problem of singulation have been described (16). One method is to coat the seed such that the size is increased and the shape made more regular so that the coated seed can be sown with conventional planting devices. Both clay coated and vermiculite coated seeds are available at the present time. Although coated seed can be accurately singu- lated and spaced in the row and seed depth fairly well con- trolled, this planting technique gives inconsistent germination under some conditions (19). Vacuum pick-up devices for precision planting of naked lettuce seed have been reported (13,10). Precision small seed plate planters have been developed for naked lettuce seed and are commercially available. All planters for naked lettuce seed have the problem of either producing misses or doubles depending on planter adjustments and operating speed. Accurate planting depth is also difficult to maintain because of the small seed size. A paper tape planting system for small seed has been described (12). In this system the seed is attached to a tape at a desired spacing and the tape is placed at the de- sired depth in the seed bed. A water soluble polymer tape planting system is now available. Generally, the tape plant- ing systems are expensive and have not had wide acceptance among lettuce growers. A system that is supposed to provide seed singulation, accurate spacing, precise depth control, and a uniform germination environment for each seed has been reported (20). This system uses compressed vermiculite tablets or wafers for seed distribution. A single seed is located at the center of each tablet. The tablets are planted on edge and remain exposed at the soil surface thus providing a non- crusting emergence area for the seedling. This system has many difficulties, is expensive and has not been used very widely. Heavy pre-thinning stand densities of head lettuce were reported (30) to.cause,stunting of pre-thinning plant growth, a decrease in post-thinning plant survival, a delay in maturation, and a decrease in harvest density. Delayed thinning of such stands additionally caused a suppression of pre-thinning plant growth. Delayed thinning of light stands did not significantly reduce pre- or post-thinning plant growth, or reduce harvest density, or total yield. The yields were about the same as when thinning was done by chemicals or by hoeing. A high amount of seed per acre resulted in a reduced size and number of blank spaces in the row, a high thinning cost, a high incidence of midrib cracking, a late date of maturity and low yields. A lower number of seeds per acre showed lower thinning costs and earlier maturity (22). Different plant spacings were reported (21), to cause changes in yields. Increased plant density resulted in an increase in total yield. However, at close Spacings the heads were small and were acceptable only for shredding and took a longer time to reach maturity. With wider spacing the total yield was less but the individual heads weighed more, matured earlier, and nearly all the heads were market- able. Solid method or square spacings resulted in uniform maturation as each plant had the same soil volume, sunlight exposure and water availability. The use of transplants was reported (4), to reduce the quantity of seed required per acre by 80%. Other advantages of transplants are the easier and better maintenance of seedlings in their early growth stage, and faster growth with less risk of herbicide injury. It was also reported (15,16) that plants raised in soil blocks or pots in the greenhouse before transplanting, matured earlier and had a higher top quality lettuce than direct seeded plants. A reduction in plant-to-plant variation with transplanted cabbage and lettuce has also been reported (2). Transplants are of two types: 1) Plant is grown in soil blocks, peat pots, paper pots, clay pots, etc., where the plant continues to grow at the same rate if not more, even after transplanting to the field, i.e., there is no shock or setback of the roots, and 2) Transplants grown in medium or a combination of media best suited for germination and later lifted from the germination media and transplanted onto the soil. Here the root system is disturbed and the plants undergo a period of shock or setback. Hence, it takes a period of time for the roots to re-establish and perform their normal functions. The shock of lifting these bare- root plants can be reduced by transplanting at an early stage of development (30). Lettuce, cabbage, tomato, and capsicum seedlings grown in peat pots were reported to mature earlier than plants in other types of pots and in soil blocks prior to trans- planting (9). With field head lettuce, seedlings grown in peat pots, multi-pots and Japanese paper pots, it was found that peat encouraged earlier maturity of the crop. An interaction between different pot types and the substrate used was also reported (24). The size of the pot or the soil block used in raising the seedlings is very important as the plants can experience root restriction in smaller pots or blocks (26). Increasing the pot or block size is also associated with increased head weight, steady unchecked quick growth, fewer losses from damping off and a shorter period of time to harvest (17,29). Because of the nature of growth and the habitat of head lettuce it is very difficult to control any disease which develops at the base of the plant and which is not seen until the parasite has completely invaded the plant. Diseases such as bottom rot and leaf drop ordinarily do not appear in Open fields until lettuce plants have attained a size sufficient that wrapper leaves touch the soil. This is usually about two weeks before harvest. Because of the sporadic and scattered nature of these two diseases and fluctuation in market value of lettuce, it is difficult to establish a dollar value on the losses caused by these diseases. Both diseases are more severe and frequent in muck grown head lettuce than lettuce grown on mineral soils and a need for practical means of control is generally recognized. Symptoms of leaf drop or the drop, caused by Sclerotinia sclerotiorum (Lib.) de Bary can be easily recognized. The older leaves wilt to the soil leaving only the heart leaves erect, and the entire plant has a pale color. Eventually the aerial parts of the plant become flattened, brown and mummi- fied (1,25). Many attempts have been made to control leaf drOp with varying degrees of success. Rotation with crOps not suscept- ible to leaf drop was reported to reduce the disease inci- dence (1,3). Use of black polyethylene mulch to prevent the contact of lettuce head with the soil was reported (15) to be effec- tive in controlling lettuce leaf drop, but an increase in this disease was also reported with the use of polyethylene mulch (11). Studies at Michigan State University also showed increased disease with the use of polyethylene mulch (unpub- lished data). Soil sterilants have been used with some success, but the method is applicable only to smaller growing areas. Many chemicals have been reported to reduce the amount of leaf drop (3,8,23), but none of these chemicals tested seem to control the disease completely, and many of the chemicals used were phytotoxic (1,23). The type of soil on which chemicals were applied was not indicated. Lettuce varieties of upright growth in which the leaves are more or less elevated above the soil exhibit less drop than varieties, where leaves are horizontal and close to the ground (1). None of the commercial varieties grown in Michigan are resistant to leaf drop. Like lettuce drop, symptoms of bottom rot caused by Rhizoctonia solani Kfihn., do not manifest until the plants have headed and are nearly mature. Most bottom rot results from infection which occurs late in the life of the plant, but plants may become slightly affected at the 'rosette' stage of growth and may develop bottom rot symptoms later (27). The disease is characterized by the decay of basal parts of the lettuce head. Sharply defined necrotic lesions appear on the petioles and the midribs of the leaves. These lesions vary in size from the area of a few cells up to the entire surface of the petiole. While lesions are forming, drops of an amber liquid ooze from lettuce tissue. If the disease is checked before the entire head has been destroyed, the lesions dry out and become sunken chocolate brown spots. The leaf blade of the lower leaves close to the ground is entirely destroyed by the fungus. Under conditions favor- able for its develOpment, the fungus works upward and inward passing from leaf to leaf until the entire head of lettuce has become decomposed. A head so affected wilts down and becomes a shiny brown mass of disorganized tissue which finally dries and darkens. Blackened mummies of once solid 10 heads of lettuce are sometimes produced within ten days of the initial development of symptoms (27). In areas where head lettuce is grown on muck soil, bottom rot is an economically important disease. The losses each year are estimated to be as much as 25% of the crop. In periods of wet humid weather it is not uncommon for growers to lose more than 50% of their mature crop (27). Rotation with other crops, green manure crOps and sani- tation were reported to be beneficial in reducing bottom rot (28), however, most of these operations are not used under a vast single cropping system. There was less disease on plants growing on a ridge (27), than in plants grown on level culture, probably due to better air and soil drainage around the plants. Since growing plants on ridges is sup- posed to reduce the number of plants that can be grown on an acre, this is not considered an economical practice. The use of black paper as a mulch also failed to control the disease (11,27). Soil applications with sulfur, sulfur and lime, lime- sulfur, Bordeaux mixture, cyanide and other chemicals with a fungicidal action were found ineffective in controlling bottom rot (6). Among several experiments with different fungicides to control bottom rot, a successful program with 90% control of the disease was developed by using certain mercury compounds (27). Mercury compounds, however, are now ll banned for the use of agricultural products. Many other fungicides have been tried without much success in controlling bottom rot (5,18). Differences in varietal resistance and disease escape of the upright growing habit was reported (27). The disease escaping tendencies of romaine lettuce were united with the butter head type of lettuce desired in the market, but the hybrid was not resistant to bottom rot. This should have been expected, since both parents of the hybrid were suscept- ible when inoculations were made with the fungus (6). MATERIALS AND METHODS Three varieties of crisphead lettuce--Ithaca, Fulton, and Spartan Lakes were used in this study. Seed of trans— plants was sown in the greenhouse in either 4 cm. peat pots or in flats. In both cases, vermiculite was used as the germinating medium. At the time the seedlings were trans- planted to the field, seed of each variety was directly sown in rows in the plots. The seedlings varied from 8-25 days old at planting. Unfavorable weather conditions delayed some plantings. The seedlings in the peat pots were thinned to one plant per pot and planted one foot apart in the row. Two to three bare-root seedlings were planted in each hill one foot apart, these were later thinned to one plant per hill. The direct seeded plots were thinned to one plant per foot at the 2-3 leaf stage. The final stand for all three planting methods was 53 cm (21") between the rows and 30 cm (12") within the row. There were 4 replications of each planting. Each replication consisted of 9 rows (3 varieties x 3 planting methods) of 20 plants each. All replications were bordered. 12 13 Design and Analysis of the Experiment The experiment in 1971 was a modified split plot design. There were two sections, one irrigated and one non-irrigated, each having a total of 27 treatment combinations with three varieties, three planting methods and three planting dates. The 27 treatment combinations were replicated four times in each section. Each planting date, a total of 36 rows, con- sisted of 9 treatments and 4 replications. The blocks (replications) and the treatment within blocks were random- ized. One section was irrigated at regular intervals in order to keep the soil surface wet. This was done to give optimum conditions for the two soil borne diseases, bottom rot and leaf drop, to develop. This section was called the irrigated plot and the other section which was not irrigated at regular intervals was called the conventional plot. In 1972 the design of the experiment was a classical split plot design with two replications and two planting dates. A third planting date was eliminated by frost. Analysis of variance of the treatments were calculated for each observation. The significant treatment means from the analysis of variance table were compared using Duncan's New Multiple Range Test. Simple correlations among the horticultural traits were also computed. 14 Growth, Care and Harvest A 5-10-3- + 2% manganese fertilizer at the rate of 454 kilograms (1000 lbs) per acre before planting and urea at the rate of 23 kilograms (50 lbs) per acre 4-5 weeks after plant- ing were applied to the field plots. All weeding was done with either a hand hoe or a wheel hoe. Fungicides were not applied in order to obtain disease. Insecticide Carbaryl (Sevin) at the rate of 0.7 kilograms of 80% wettable powder per acre was applied every two weeks until the heads were harvested. Irrigation All newly planted plots were irrigated with rotating sprinklers at the rate of 0.3 cm (.1") per hour daily to prevent loss of transplants and to maintain a moist soil sur— face to facilitate uniform germination in the seeded area. This irrigation was stopped when the germinating seedlings appeared above the soil. The total rainfall and irrigation in each planting are shown in Table 1. Harvesting Maturity was based on head firmness. One person made this determination both the years at all planting dates to 15 Table 1: Summary of rainfall and irrigation, in centimeters, for each planting regime. Planting Conventional Irrigated Dates Rain Sprinkled Total Rain Sprinkled Total 5-13-71 13.49 7.24 20.73 13.49 11.81 25.30 6-18-71 16.13 6.73 22.86 16.13 12.83 28.96 7-16-71 18.87 7.37 26.24 18.87 12.95 31.82 5-18-72 20.96 5.08 26.04 20.96 7.37 28.32 6-21-72 49.35 1.91 51.26 49.35 1.91 51.26 16 avoid variation of maturity due to individuals. Eight to 10 heads were selected and harvested and the following measure- ments were taken on each: 1. Head weight in kilograms. 2. Head diameter in centimeters. 3. Stem or core length (from the first true leaves to the tip of the growing point) in centimeters. 4. Days to maturity (from field planting). 5. Percentage of disease (bottom rot and leaf drop were recorded as one, because of the difficulty in dis- tinguishing between the diseases at the time of harvest). Air temperatures were also recorded during the growth period (Appendix A). Head Weight: Lettuce head weight or the yield is a very important character since at a given plant density, yield can be im- proved only by increasing head weight. Some crops such as the cereal grains adjust to wide variations in plant density through changes in branching patterns, but head lettuce has limited adaptability and must be planted in precise patterns for maximum utilization of space. Varietal differences in head weight exist under a given set of conditions. The total yield per acre is dependent on the number of plants, but the individual head weight decreases, after a point, with increase 17 in number of plants (22). Small, light weight heads of lettuce are not economical for fresh market use. Head Diameter: Head diameter is closely related to head weight. Head diameter varies with the variety. Some varieties have large dead diameter, but they may have a very soft head with a few loose wrapper leaves. The soft heads have the disadvantages of leaf tearing during handling, short maintaining quality during transportation and easy bolting. Soft heads also limit the total yield (weight) in an acre compared with firm heads. Crispheads break if not handled prOperly. Head diameter is also very important since too small a head is not economical for fresh market (21). Head size is not as important as the head weight if the heads are used for shredding purposes. Like the head weight, the individual head size also depends on the spacing and total number of plants in an acre (21). Stem Length: Stem length is associated with bolting. Head lettuce varieties with soft heads usually have long stem lengths and bolt very easily. A head with a short stem and tightly wrapped leaves is required in a variety, to increase head weight and to reduce bolting. Varietal differences in the stem length suggest a genetically controlled trait. 18 Days to Maturity: Days to maturity in head lettuce varieties grown in Michigan approximates 60 days varying with variety and grow- ing conditions and date of planting. Head lettuce is a sensitive crop with rather precise nutrient and environmental requirements. Minor variations of temperature and moisture results in a change in the growth rate which alter the days to maturity. Days to maturity is a very important character in order to make best use of the available growth period. Disease: Disease here refers to both bottom rot caused by Rhizoctonia solani and leaf drop caused by Sclerotinia sclerotiorum which are serious diseases of head lettuce grown on muck soil. Both diseases have similar environmental requirements for their development. Because of the nature of growth and the habitat of head lettuce, they are very difficult to control since both diseases develop at the base of the plant late in the growth period just before harvest, and are not seen until the parasite has invaded the plant. There are no chemicals or resistant varieties of head lettuce to prevent these diseases. It is not uncommon on muck soil to lose 50% or more of the crop during a wet year or heavy rains a few weeks before harvest. RESULTS Head Weight: In 1971, significant differences in head weight were associated with variety, planting date and planting method. Irrigation did not have any effect on the head weight. Ithaca had the highest head weight followed by Fulton and Spartan Lakes respectively. The second planting produced the heaviest heads followed by the third and first plant- ings respectively. Peat pot transplants produced the heaviest head followed by bare-root and field sown plants in that order (Table 2). In 1972, differences in head weight were associated only with variety. Again Ithaca had a heavier head than either Fulton or Spartan Lakes which did not differ from each other (Table 3). Head weight differences in 1971 were also due to the interaction effects of planting date x planting method and variety x planting method x planting date. The planting method x planting date interaction was due to head weights in the second planting which did not differ. The three-way interaction was also due to head weight differences in the second planting where Ithaca pot transplanted weighed less than its field sown plants or bare-root transplants. l9 Average head weight in kilograms of three lettuce varieties by three planting methods and three planting dates in both Table 2. ted and conventional plots. irriga PLANTING METHOD Conventional Field Peat Bare Pot Irrigated Field Peat Bare Sown Overall Mean Planting Date and Variety Root Field Peat Bare Pot SOWD Root Sown Root Pot 5—13-71 Ithaca 1.0 1.0 1.0 0.9 0.9 1.1 0.9 0.8 0.9 . 0.9 0.9 Fulton 0.9 0.8 Spartan Lakes 6-8-71 1.5 1.5 Ithaca Fulton 1.3 1.4 . 1.4 1.2 Spartan Lakes 1.5 1.4 1.4 . 1.4 1.5 1.4 1.5 7—16-71 Ithaca 1.2 l 1.4 1.2 1.3 . 1.2 1.1 1.3 1.3 1.2 1.4 1.2 l 1.3 L 1.0 Fulton 1.2 . 1.1 . 1.3 1.2 1.2 1.1 Spartan Lakes 1.2 1.3 1.4 1.2 1.2 1.2 1971 Means Ithaca 1.3 1.2 1.1 1.3 1.2 1.4 1.2 1.3 1.4 1.4 1.2 1.3 1.3 1.3 1.2 1.3 1.1 1.2 1.4 Fulton 1.1 1.1 1.1 1.0 Spartan Lakes 1.2 1.2 . 1.1 21 5.0 0.0 5.0 0.0 5.0 0.0 0.0 0.0 0.0 0.0 5.0 .W 5.0 5.0 0.0 0.0 5.0 0.0 5.0 5.0 5.0 0.0 0.0 0.0 mmxmq cmuummm 5.0 5.0 0.0 5.0 0.0 5.0 0.0 5.0 5.0 5.0 0.0 5.0 COUHSh 0.0 0.0 0.0 0.0 0.0 0.0 m.0 0.0 0.0 0.0 0.0 0.0 monggH wcmmz N50H 5.0 5.0 5.0 0.0 0.0 5.0 0.0 0.0 5.0 0.0 0.0 0.0 x 5.0 0.0 5.0 5.0 5.0 5.0 0.0 5.0 5.0 0.0 5.0 5.0 mmxmq cmuummm 5.0 5.0 5.0 0.0 0.0 5.0 0.0 0.0 5.0 5.0 0.0 0.0 COHHSh 0.0 5.0 5.0 0.0 0.0 0.0 5.0 0.0 5.0 5.0 0.0 0.0 MOMSUH N5IHNI0 0.0 0.0 0.H 5.0 0.0 5.0 0.H 0.0 0.0 0.0 0.H 5.0 .M 5.0 5.0 0.0 0.0 5.0 5.0 0.0 0.0 5.0 0.0 0.0 0.0 mwxmq Cmuummm 0.0 5.0 0.H 5.0 0.0 0.0 0.H 0.0 0.0 5.0 0.H 5.0 GOMHSW 0.0 0.0 0.H 0.0 0.0 0.0 0.H 0.0 0.H 0.0 H.H 0.0 MOMSHH N5l0lm X poom Dom G300 x HOOK uom C300 X HOOK HOW C300 I. mumm umwm waoflm .l mumm ummm UHme I. wumm ummm UHon humflum> was smwz Hamuw>o HMQOHucm>COU pmuwmwuuH - eczema ozHezfim mama mafiusmHm 03» van muonuwa msflucmam wows» an mmflumfium> mosuuwa mmunu mo mfimumoaflx CH unmwmz cams mmmnm>¢ .muon HMGOHusm>c00 0cm woummfiunfl anon CH mounp msflusmam .m magma 22 The head weights of Fulton were not affected by planting methods. With Spartan Lakes pot transplants weighed more than either the field sown plants or bare-root transplants (Table 2). In 1972, at the first planting, pot transplants weighed more than either field sown plants or bare-root transplants, which did not differ from each other, head weights resulting from three planting methods in the second planting did not differ from one another (Table 3). Head Diameter: in 1971, head diameter differences were associated with planting date and planting method. Head diameters were not affected by irrigation, neither were there diameter differ- ences among the varieties. Head diameters did not differ in the second and third plantings, however, both of these plant- ings produced larger heads than the first planting. Head diameters, of the pot transplants were larger than either bare-root plants or field sown plants in 1971 (Table 4). In 1972, head diameter was not significantly affected by irrigation, variety, planting date and planting method.CTable 5). In 1971, interaction effects on head diameter were associated with variety x planting date, variety x planting method and planting method x planting date. Ithaca in the first planting had a smaller head than either Fulton or Spartan Lakes, whose head diameters did not differ from each other. In the second planting, head diameters of Ithaca and 23 N.MH 5.MH N.MH m.MH v.MH m.MH N.MH v.MH H.MH 5.mH N.MH m. mama. o.MH 0.MH N.MH MJmfl N.MH 0.MH N.MH m.MH m.NH 5.MH N.MH mmxma cmuummm m.MH N.MH 0.MH m.MH 0.mH v.ma 0.VH v.MH m.ma m.NH 5.mH 0.MH couadm vama v.ma 5.MH m.NH m.ma 0.ma m.ma 0.MH m.MH v.MH 0.MH m.NH downgH mama: H5mH 0.0H 0.MH 5.¢H H.MH 0.MH 5.MH 5.¢H m.NH m.ma 0.MH 5.VH m.ma m. o.ma q.mH ~.v~ H.mH m.ma «.ma m.vH m.~H e.mH m.ma m.vH v.mH mmxmq cmuummm m.mH 0.MH m.va N.mH m.MH 5.MH m.VH 0.MH o.vH m.ma m.vH v.MH COUHDM mama 0.MH 0.mH m.NH mzma m.ma m.vH m.NH 0.va 0.MH H.ma 0.MH momnuH H5I0HI5 0.MH 5.MH 5.MH 5.MH 0.vH 0.MH 5.MH m.MH m.ma 0.MH 0.MH N.VH .W m.mH «.ma n.ma m.MH o.MH m.ma n.ma m.ma q.ma H.ma h.mH m.ma mmxmq :muummm oova 5.MH m.ma v.va 0.MH 0.MH 0.MH H.vH N.va 0.MH N.VH 5.VH couasm oowa v.vH 0.MH H.vH H.VH 5.vH 0.MH 5.MH oava H.VH m.MH m.vH MUMSUH H5I0I0 m.NH m.NH 0.NH m.NH 0.NH m.NH N.ma 5.NH m.NH N.NH m.NH m.mH .W 0.NH m.NH H.MH 0.NH m.NH 0.NH H.MH m.NH 0.NH m.NH H.MH m.NH mmxmq cmuummm 0.NH m.NH 0.NH 0.NH 0.MH 0.NH V.MH m.NH mama H.NH m.HH 0.NH Gouaflm N.NH H.NH 5.NH 5.HH m.NH H.NH 0.MH v.NH m.HH N.NH ¢.NH H.HH moman H5Imalm x #000 uom G300 x Hoom pom G300 x “Com uom G300 I. mumm umom pamflm .I mumm umom @Hon I. mumm ummm paoflm >uwaum> paw cmmz Hamnm>o Hmsoflucm>coo pmummHHuH mumo mcflusmam - nomemz 02525.” cam mvocuofi mcflucmflm manna >3 mmfluoflum> wosuuoa omunu mo mnmumfieucoo Ga Houmsmflc cum: womuo>¢ .muon HMCOflucm>soo cam woummwuhfl Anon Ga mount msflusmHm woman .v manna 24 o.HH «.ma m.HH A.HH v.HH m.HH m.HH «.ma m.HH m.mH H.NH .m o,~a m.HH m.mH o.HH A.HH m.HH o.mH A.HH m.ma H.~H H.ma m.HH mmxmq cmuummm m.aa m.HH o.ma H.~H o.HH m.oa o.mH o.mH o.mH >.HH H.~H ~.ma couasm o.~H m.HH o.mH «.ma >.Ha m.HH o.HH m.HH m.NH m.HH v.mH m.NH momnuH mammz mums H.~a A.HH H.NH m.mH o.ma m.HH m.ma m.~H N.~H m.HH H.ma A.ma .m «.ma H.NH h.ma m.mH m.NH m.HH s.ma «.ma o.ma m.mH m.~H o.NH mmxmq cmuummm m.HH m.HH m.HH m.mH m.HH m.oa m.mH o.mH m.HH A.HH m.HH m.mH couasm o.NH o.HH m.HH m.ma m.HH A.HH m.HH o.mH N.NH m.HH H.NH H.mH momruH mundane m.HH o.HH m.ma m.HH v.HH m.HH m.HH N.HH m.mH o.mH o.MH m.HH .m o.HH o.HH m.ma m.HH e.HH m.HH m.HH N.HH «.ma o.mH v.mH v.oa mmxmq cmuummm A.HH N.HH m.mH m.HH m.HH m.oH A.HH v.HH H.NH m.HH m.mH m.HH couasm o.mH H.~H m.ma w.HH m.aa o.~H m.HH o.HH v.mH m.ma A.NH ~.mH momnuH . msumum x uoom pom czom .m poem pom csom x poem pom czom I. mumm ummm vamflm mnmm ummm paoflm W. mumm ummm camflm mumflum> can cam: Hamum>o Hmcoausm>coo omummHHHH mama msflucmam .momBME UZHBZflAm can mponumfi msflucmHm mmnnu 5Q mmfluwHHm> moduuma mmufiu mo muwuofiflusmo CH kumEMHU 0mm: mmmuo>€ .muOHQ Hmsofluso>coo cam Umummfluufl Anon Ga mmpmp mswucmHm 03» .m magma 25 Fulton were nearly the same, but both varieties had a larger head than Spartan Lakes. Head diameters of all three varie- ties did not differ from one another in the third planting. Head diameters resulting from different planting methods varied with variety. Field sown Ithaca was significantly smaller than its transplants. The head diameter of Fulton was not affected by the planting method. The head diameter of Spartan Lakes pot transplants were larger than the field sown plants. Head diameters resulting from the three plant- ing methods did not differ from one another within the first and second plantings but in the third planting pot trans- plants were significantly larger than either field sown or bare-root transplants (Table 4). Stem Length: In 1971, differences in stem length were associated with variety, planting date, and planting method. Irrigation did not have any effect on stem length. Ithaca had the longest stem length followed by Fulton and Spartan Lakes respectively. Stem length of plants in the second and third plantings were not different from each other, but both were longer than plants from the first planting. Peat pot transplants had longer stem lengths than either bare-root or field sown plants, which did not differ from each other (Table 6). Average stem length in centimeters of three lettuce varieties by three planting methods and Tafle6. 1 plots. 1011a ted and convent irriga three planting dates in both PLANTING METHOD Planting Date and Variety Overall Mean Conventional Irrigated Field Peat Bare Pot Root Field Peat Bare Pot Sown Field Peat Bare Pot Root Sown 3? Root Sown 5—13—71 Ithaca 6.7 6.0 6.6 7.1 6.8 6.2 6.1 6.6 7.1 5.4 6.1 6.7 6.0 5.8 6.3 5.2 6.1 Fulton 5.8 6.3 5.4 5.8 5.3 5.2 Spartan Lakes 5.7 6.4 5.9 6.0 5.6 Ix 6-8-71 7.3 Ithaca 26 . 6.8 . 6.1 7.4 6.6 6.4 6.4 6.9 7.2 6.4 6.6 Fulton 6.6 Spartan Lakes 7.]. 7.4 7.3 7.6 6.7 7.2 6.7 Ix 7-16-71 Ithaca 7.3 . 7.3 7.1 6.1 7.7 6.7 6.8 6.7 6.4 6.1 Fulton 6.5 6.6 6.4 5.9 6.8 6.8 6.1 Spartan Lakes 6.9 6.9 7.2 6.7 6.7 6.9 6.4 IX 1971 Means 7.1 6.5 7.3 7.5 7.5 7.0 7.3 7.5 6.9 7.2 6.9 Ithaca 6.7 6.7 6.6 6.2 6.8 6.7 Fulton 6.5 6.0 6.2 6.6 5.8 6.2 604 6.4 6.1 Spartan Lakes 6.7 6.8 7.0 6.4 6.7 6.7 . 6.5 6.7 6.6 Ix 27 In 1972, effects of irrigation, variety, planting date and planting method on stem length were not statistically different. In 1971, interaction effects on stem length were associ- ated with planting date x planting method. In the first planting pot transplants had a longer stem length than either field sown or bare-root transplants. In the second planting, bare-root transplants, had a shorter stem length than the plants from the other two planting methods, but in the third planting stem lengths resulting from three planting methods did not differ from one another (Table 6). In 1972, in the first planting, pot transplants had a longer stem length than either field sown or bare-root transplants, but in the second planting stem lengths resulting from three planting methods did not differ from one another (Table 7). Days to Maturity: In 1971, differences in days to maturity were associated with planting date and planting method. Irrigation had no effect on maturity. Plants in the second planting matured 4 days earlier than plants in the first planting and twelve days earlier than plants in the third planting. Peat pot transplants matured 6 days earlier than either bare-root or field sown plants (Table 8). 0.v o.m 5.v 0.v m.v o.m m.v 0.v 0.v o.m 5.v .M 28 m.v m.v m.v H.v m.v m.v m.v o.v m.w v.4 m.v H.v mmxmq :mpummm 5.v m.v m.v m.¢ m.w H.v H.m m.m 0.v v.v 0.¢ 0.v souasm H.m m.v m.m N.m o.m m.v m.v m.m m.m o.m 5.m H.m momcuH mammz m5mH 5.v 0.v m.v m.v m.v 5.v 5.v o.m o.v 0.v m.v m.v .M m.v v.v H.w m.v v.v v.v v.v m.v N.v v.v m.m m.v mmxmq smuummm m.v m.v o.v o.m w.v m.v v.v H.m m.v m.v 5.m o.m couasm m.m m.v H.m m.m m.m 5.v N.m m.m m.m m.m o.m m.m momcpH m5leI© m.w m.v 0.m m.v w.v v.v m.m 5.v o.m 5.w m.m v.v .m 8.4 m.v o.m m.m v.4 8.4 v.m m.m n.v m.v m.m m.m mmxmq cmuummm m.v H.v 5.m m.v m.v m.m m.m v.m m.v 5.v 0.m m.m souasm Ham m.v m.m w.v m.¢ o.m 5.v m.v v.m m.v v.0 m.v momnuH N5Imlm x uoom pom :30m x I poem pom ssom x uoom pom ssom I. mumm umwm pamflm .I mnmm umom vawflm I. wumm ummm pamflm mumflum> cam :mmz Hamuw>o Hmsoflucm>cou pmummHuHH oumo msflusmam QOEBMZ QZHBZNHQ .muon Hmsowuso>soo paw woummfiunfi suOQ cw mmpmc mcaucmHm 03» wow mposums msflucmHm mousu an mmflumflnm> monuuoa wwunu mo mnmvoaflpsmo cw npmsma Baum mmmwmbd .5 magma 29 M0 50 m0 H0 M0 50 v0 H0 v0 5m 00 .W H0 m0 5m m0 H0 M0 50 v0 H0 M0 50 v0 mmxmq CMHHQO H0 M0 50 m0 H0 M0 50 v0 H0 m0 50 v0 COHHHK N0 M0 50 v0 N0 v0 5m v0 H0 M0 50 v0 MOMHHH mammz H50H 00 N5 H0 N5 00 N5 H0 N5 00 N5 N0 N5 .M 00 N5 H0 N5 00 N5 H0 N5 00 N5 N0 N5 mmxmq GMHHQO 00 N5 H0 N5 00 N5 H0 N5 00 N5 N0 N5 GOHHSK 00 H5 H0 N5 00 H5 N0 N5 00 N5 N0 N5 momnHH H5I0HI5 00 mm 0m 0m 0m 00 om 00 mm 0m 0m 0m .M 0m 00 00 0m 0m 00 om 00 mm 0m 00 00 mmxmq EmHHQO mm 0m 00 0m 00 mm 00 00 mm 0m 0m 0m GOHHDK 00 mm Om 0m 0m 00 om 00 mm 00 00 00 mUMSHH H5I0I0 00 00 00 H0 00 00 00 H0 00 00 00 H0 M. 00 00 00 H0 00 00 00 H0 00 00 00 H0 mmxmq GMHHQO 00 00 00 H0 00 00 00 H0 00 00 00 H0 COHHDK 00 00 00 H0 H0 00 00 N0 00 00 00 H0 mUMSHH H5IMHIm X HOOK HOK 2300 X HOOK HOK C300 X HOOK HOK E300 I. oumm ummm waoflm .I mumm ummm pawflm I. wumm umom wamwm mumfium> can saw: Hamuw>o stowucwbcou - oomemz 6232..qu kunmfluuH muma msflusmam .muoam HMCOHHG¢>G00 cam wmummfluufl anon 2H mmuwc mswucmam owns» new moonuma msfiusmam omnsu Sn mmflumflum> mosuuma mmunu mo auwusums on what mmmnm>¢ .m manna 30 In 1972, differences in maturity were associated with planting method only. Peat pot transplants matured earliest followed by bare-root transplants and field sown plants, respectively (Table 9). Days to maturity in both years were affected by inter- actions between planting date x planting method. In 1971, in the first planting both peat pot and bare—root transplants matured earlier than field sown plants. In the second plant- ing, pot transplants matured earliest followed by the field sown and bare-root tranSplants. In the third planting, pot transplants matured earlier than either field sown or bare- root transplants, which did not differ from each other (Table 8). In 1972, the trend was similar to that of first year in the first planting, where both transplants matured earlier than field sown plants; however, in the second planting pot transplants matured earlier followed by bare- root transplants and field sown plants respectively (Table 9). This differed from that of second planting in 1971 where the field sown plants matured earlier than baresroot transplants. Disease: In 1971, differences in incidence of disease were associated with irrigation, variety, planting date and plant- ing method. Incidence of disease in the irrigated plots was higher than in conventional plots. Spartan Lakes had twice 31 m0 H0 50 v0 m0 H0 50 v0 m0 H0 50 .W v0 m0 H0 50 v0 m0 H0 50 we m0 H0 50 moxmq :munmmm «0 m0 H0 50 v0 m0 N0 50 «0 m0 H0 00 souasm m0 m0 00 50 v0 m0 00 50 v0 m0 00 50 momzHH mcmwz N50H H0 00 5m 00 N0 N0 0m 00 H0 H0 5m 00 X H0 H0 5m 00 N0 N0 0m 00 H0 H0 5m 00 mmxmq CMHHme N0 00 mm 00 N0 N0 00 00 N0 H0 0m 00 COHHDK H0 00 m0 00 H0 H0 0m 00 H0 00 0m 00 momnHH N5samww 50 50 mm mm 50 50 m0 mm 50 50 m0 mm m. 50 50 mm mm 50 50 m0 mo 50 50 m0 m0 mmxmq cwuummm 50 50 m0 00 50 50 m0 00 50 50 m0 00 COHHDK 50 50 m0 00 50 50 m0 00 50 50 m0 m0 MUMLHH N5Imlm X HOOK HOK £300 .M HOOK HOK C300 X HOOK HOK G300 I. wumm umom UHmHm oumm ummm paofim I. mumm ummm UHon humflum> paw cmmz Hamuw>o Hmcoflusm>cou pmummHMuH oumo msausmam DOmBmE OZHBZKAK .muoam HMGOHHGm>soo 02m Umummfiunfl AHOQ cw mmump msflucmHm 03» can mUO£umE mcflucmHm mmhgu NA mwflumflum> muduuma mmunu mo huflusumfi ou mhmp mmmum>¢ .m magma 32 as much disease as either Fulton or Ithaca. Plants in the first planting had six times, and plants in the late plant- ing had 10 times as much as the plants in the second planting. The percentage of disease in pot transplants was higher than either the bare-root transplants or field sown plants (Table 10). In 1972, differences in incidence of disease was associ- ated only with variety. Spartan Lakes again had a higher percentage of disease than either Ithaca or Fulton (Table 11). In 1971, differences in incidence of disease were also associated with interaction effects of variety x planting date, variety x planting method, and planting date x planting method. The variety x planting date interaction was due to differences in the second planting where incidence of disease was not different for the three varieties. There was a general trend across varieties for disease to be highest in the third planting followed by first and second plantings reSpectively. The variety x planting method interaction was due to differences in incidence of disease with transplants of Spartan Lakes whose peat pot transplants had a higher per- centage of disease than did the bare-root transplants. The planting method x planting date interaction was due to the absence of disease in the second planting with pot and bare- root transplants, and the incidence of disease was the same irrespective of the planting method (Table 10). 33 m.0 0.HH 5.v H.5 H.0 m.0H 0.m 0.0 0.0 0.NH 0.0 X 0.HH 0.HH 5.0a 0.m 0.0H N.HH 0.5a 5.m 5.NH 0.0a m.ma 0.5 moxmq cmHhomm m.0 5.5 m.5 0.N v.0 0.5 v.m 0.N m.5 m.5 m.0 0.0 COHHDK mo0 v.0 m.0 m.v H.m v.0 m.5 m.N 0.5 0.5 0.0 5.0 moonuH mcmoz H5WH v.vH N.0H m.5H 0.0 0.NH N.0H 5.MH N.0 5.0H N.0H N.HN 0.NH X momH 0.0N H.0N 0.0a 0.5H 5.MN m.NN m.5 N.HN m.5H 5.mm m.NH moxoq CMHHmmm 0.HH m.vH 0.HH H.0 mom 5.MH 5.0 N.0 5.MH N.0H 0.0a 0.0H COHHDK 0.NH H.MH m.NH 0.0a 5.0 N.HH 0.0a 0.m vomH 0.0a 0.0a N.0H MOMSHH H5I0HI5 v.H 0.0 0.H 0.H 0.0 0.0 v.0 0.0 N.N v.0 m.m 0.N X N.N m.o e.m m.m w.o m.H N.H o.o n.m o.o m.m o.m moxmq cmuummm 0.0 0.0 0.0 N.H 0.0 N.H 0.0 N.H 0.0 0.0 N.H N.H COHHSK N.H 0.0 N.H 0.H v.0 0.0 0.0 N.H 0.N N.H m.N 0.N MOMSHH anamam 0.0 m.0 v.mH 0.N 5.0 m.5 5.0a 0.N 0.0 H.m H.VH 5.m .W 5.MH 0.HH m.VN v.v H.VH 5.0 0.0m 5.0 m.ma 0.0a 5.0a N.0 moXMQ CMHHmmm 0.0 v.5 0.0H 0.N 0.0 5.0 0.5 N.H 0.5 N.0 m.NH 5.m GOHHDK 0.0 0.m 0.HH N.H N.0 0.m m.NH N.H N.0 N.0 N.HH N.H oomnHH H5IMHIm X HOOK HOK G300 X HOOK HOK C300 X HOOK HOK G300 .l oumm umom paoflm .I ouom umom paowm I. owmm umom oaoflm muoflum> 0cm coo: Hamuo>o Hoseauco>sou UoHomHHHH QOKBKZ OZHBZsoo tam woummflwufl anon CH moump msflusmam oounu cam moonpos msflusmam oounu an moHuoHHo> oosuuoa oonnu mo momousoouom ommomflp ommmo>4 .oa oanme 34 m.mH m.mn o.mH n.4n m.vn m.mH m.en m.en H.6n «.mn ¢.HH x m.mn m.nm m.mH m.mn m.om o.mn o.mm n.mn m.nn o.mm o.on k.mn moxmq cmnummm m.mn m.vn o.mn o.HH v.nn o.mn o.m o.HH m.vH o.vn o.mn o.HH connsm m.mn m.on o.mn o.mn m.mn o.m o.mn o.an m.ma o.mH o.mn o.on womanH memos mama o.nn m.m m.on H.mn H.mn o.oH m.mn n.mn o.m m.m o.m m.m x m.nn o.mn o.m m.mn m.mn o.vn o.mn 0.0m m.m o.mn o.m o.n moxmq connmmm 0.0 0.5 0.5 0.NH 5.0 0.0 0.0 0.NH 0.0 0.0 0.0 0.NH aonasm m.mn o.m o.mn o.vn m.ma o.on o.mn o.mn 0.0a o.m o.mn o.oa moman Nuanmsm v.mn o.nm m.nm m.ma m.mH m.mn o.mn m.mn 8.0m m.mm n.4m m.mn m. m.mm o.mm 0.0m m.mn o.mm o.vm 0.8m o.na 0.0m o.vm o.mm 0.0m moxmq connmmm 0.5H o.mm o.mn o.on o.va 0.8m o.m o.on 0.0m 0.0m 0.0m o.oH connsm m.~n 0.NH o.mn o.on o.on o.m o.mH o.on m.vn o.mH o.mn o.on momnnH megmum x noom nom czom x noom now 230m x noom nom c3om I. onmm nmom paonm I. onom nmom paoflm I. oumm nmom paoflm Xnoflnm> Cam coo: Hamuo>0 Hoseanao>aou ConomHHnH onoo maflnaoam DOEBMZ UZHBZKAK .mnon Hmaonnao>aoo can wonmmnuun anon on monmw mannamHo an 0am mvoanoE maflnaoam oouan ma moHnoHHm> oosnnoa oouan mo mommnaoonom ommomHU ommno>a .HH oHQoE 35 In 1972 interaction effects on disease were associated only with variety”x planting date. In the first planting Spartan Lakes had a higher disease than either Fulton or Ithaca, but in the second planting the varieties did not differ in the incidence of disease (Table 11). DISCUSSION Although two year results were reported, the results of 1972 were greatly affected by excess rainfall and low temperatures, and differences were not as evident as in 1971. Because of this, the discussion is limited to the re- sults of the 1971 season. The heavier head weight of tranSplants can probably be attributed to early rapid growth during the seedling stage in the greenhouse. Bare-root transplants weighed more than the field sown plants but they did not differ in their head diameter. This density might have been due to transplanting shock on the bare-root plants. Peat pot transplants, which did not undergo a shock at transplanting, continued to grow, resulting in heavier and larger heads. Varietal variations in traits and their variations in different planting regime was expected since lettuce is a sensitive crop, with rather precise environmental requirements. The longer stem length of peat pot transplants could have resulted from any one or a combination of factors, such as heavier heads and larger head diameter and/or the early rapid growth during the seedling stage. From the correla- tion studies of this experiment the longer stem length of peat pot transplants appear to be a part of the increased 36 37 head weight and size. Heavier head weight, head diameter, and stem length observed in the peat pot transplants was probably due to peat pot treatment itself which allowed a better growth of the seedlings in both the greenhouse and the field. Increased stem length of peat pot transplants did not cause in bolting. Shorter stem lengths and smaller head diameters of bare-root transplants appears to be associ- ated with the shock of transplanting. Earlier maturity of peat pot transplants was not unex- pected since the seedlings were older than field sown plants. Bare-root transplants, however, do not appear to offer any advantage over direct seeded plants in any trait which was studied including days to maturity. The higher disease incidence of irrigated plots was also expected and agrees with the already well-known fact that bottom rot and leaf drOp are associated with high soil moisture content. The high disease in transplants has not been reported previously. These findings indicate a need for disease resistant varieties of crisphead lettuce or a fungicide which either prevents or controls the disease In addition to reduction of seed required per acre, transplanting offers other advantages. Since there are no selective herbicides on crisphead lettuce grown on much soils, and the pre—emergent sprays are known to affect seedling count and final yield of direct seeded lettuce, use of 38 transplants could overcome this problem as they are not affected by the application of pre- or post-emergent herbi- cides (28). Maintenance and care of plants in the early stage of growth are also made easier with transplants as they occupy a minimal area (14,7). In areas where the growing season is short, bare-root transplanting would have no advantage over the direct seeded crop, since it is not possible to reduce the total growth period in the field. However, peat pot transplants could be successfully used in such areas. In Michigan, growers usually plant two crops a year. Our studies at MSU with three plant— ing dates indicated that plants grown during mid-summer had a maximum head weight, head diameter, with a minimum of disease, this increase was probably due to higher temperatures (Appendix A). Since total growth period of lettuce plants in the field could be reduced by using peat pot plants, it allows one to concentrate the two crops in mid-summer, where the environ_ mental conditions are best suited to rapid growth. By manipu- lating the size of peat pot, further reducing the growth period in the field, it appears that one could possibly grow an addi- tional crop, i.e., a total of three crOps. As there are no selective herbicides on lettuce, frequent cultivation to prevent weed competition is necessary. Reduc- ing the number of cultivations at a later growth stage is very important to avoid leaf tearing and root damage. 39 It appears that this reduction in cultivation could be accom- plished by using peat pot transplants in combination with a preemergent herbicide at a stage where the plants after trans- planting cover the soil surface in a short period, thus shad- ing the weed seedlings. The idea that bottom rot and leaf drop could be reduced by reducing the growth period in the field was not substan- tiated. It may be possible to overcome the disease by an application of a fungicide, which has a residual action for the period the peat pot transplants occupy the field or which is systemic. Major disadvantages of using transplants are the cost of raising seedlings, transplanting equipment and hot house space. Size of pot and stage of plant for transplanting to obtain best results, and the economics and feasibility of using transplants in the production of head lettuce in Michigan are still to be determined. APPENDIX TABLES 40 Table A-I. Air temperatures Michigan State University muck farm 1971. Temperature (°F) High Low lst Planting--May 13 68 34 14 69 49 15 79 57 16 78 38 17 82 62 * 18 87 67 19 82 41 20 65 39 21 60 29 22 64 33 23 71 57 24 78 55 25 55 47 26 53 42 27 64 33 28 68 26 29 75 39 30 81 48 31 69 48 June 1 64 55 2 73 49 3 81 50 4 88 60 5 90 65 6 85 65 7 87 54 2nd Planting 8 64 39 9 68 36 10 75 47 ll 81 65 12 87 66 13 82 60 14 79 51 15 82 52 16 85 54 17 87 58 18 88 63 19 89 71 20 91 63 21 76 52 22 80 57 23 82 55 continued Table A-I--Continued 41 Temperature (°F) High Low June 24 86 71 25 85 59 26 84 65 27 96 66 28 97 69 29 94 69 30 92 69 July 1 82 52 2 74 43 3 80 54 4 83 65 5 78 64 6 85 55 7 88 61 8 83 65 9 84 58 10 82 62 ll 80 44 Harvest lst 12 83 70 Planting Average 79.1 54.1 Y 66.6 13 84 54 14 82 48 15 77 54 3rd Planting 16 82 56 17 75 40 18 78 60 19 68 43 20 78 46 21 81 66 22 86 67 23 80 65 24 78 57 25 85 68 26 74 43 27 74 43 28 70 44 29 74 56 30 74 44 31 72 48 August 1 79 54 2 82 51 continued Table A-I--Continued 42 Temperature (°F) High Low August 3 73 58 4 73 38 5 79 44 6 84 44 7 86 50 8 86 55 9 85 72 10 90 61 ll 72 44 Harvest 2nd 12 77 61 Planting Average 81.4 56.5 X 69.0 13 85 67 14 82 56 15 74 45 16 82 43 17 86 46 18 86 51 19 87 68 20 88 68 21 88 50 22 88 46 23 73 38 24 79 62 25 83 61 26 75 60 27 70 60 28 77 47 29 84 49 30 86 59 31 69 55 September 1 79 63 2 82 65 3 84 70 4 86 72 5 89 70 6 68 7 86 71 8 91 70 9 84 64 10 86 66 continued 43 Table A-I--Continued Temperature (°F) High Low September 11 -- -- 12 70 50 13 74 55 14 83 46 15 71 58 16 70 48 17 70 52 18 66 40 19 64 52 20 62 21 68 35 22 70 38 23 64 45 24 64 31 Harvest 3rd 25 54 32 Planting ' Average 77.9 53.9 X 65.9 44 Table A-II. Air temperatures Michigan State University muck farm 1972. Temperature (°F) High Low lst Planting--May 18 82 46 19 77 50 20 80 44 21 81 -- 22 80 50 23 84 48 24 84 50 25 80 44 26 76 41 27 78 44 28 —- -- 29 84 65 30 65 44 31 47 40 June 1 70 40 2 79 46 3 84 62 4 77 62 5 78 40 6 77 52 7 78 40 8 82 45 9 69 52 10 60 38 11 68 29 12 62 56 13 79 61 14 87 68 15 75 57 16 59 37 17 68 42 18 74 40 19 83 70 20 83 62 2nd Planting 21 55 48 22 60 46 23 53 46 24 61 50 25 73 57 26 73 54 27 80 55 28 79 55 continued 451 Table A-II--Continued Temperature (°F) High Low June 29 7O 58 30 80 58 July 1 83 55 2 77 61 3 71 46 4 65 41 5 69 37 6 76 37 7 75 48 8 75 54 9 80 52 10 85 58 ll 92 59 12 89 65 13 77 68 14 85 69 15 79 67 16 81 55 17 81 53 18 77 66 19 83 65 20 90 69 HarVest lst 21 89 73 Planting ' Avepage 75.9 52.2 X 64.0 22 . ‘90 69 23 87 72 24 84 62 25 75 52 26 65 45 27 71 54 28 74 48 29 78 46 30 81 48 31 83 52 August 1 80 59 2 75 65 3 69 58 4 68 45 5 74 42 6 76 53 7 63 56 continued 46 Table A-II--Continued Temperature (°F) High Low August 8 61 49 9 66 46 10 71 38 ll 69 49 12 -- -- 13 -- -- 14 85 61 15 72 51 16 74 44 17 85 68 18 85 62 19 79 61 20 81 62 21 83 67 22 85 66 23 80 66 24 77 58 Harvest 2nd 25 81 54 Planting __ ' Avegage 75:47 54.8 X 65.1 10. 11. 12. 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