White Mulch Research Articles

White mulch and a south facing position favour strawberry growth and quality in high latitude tunnel cultivation

Polyethylene mulches with black or white surface were compared in seven strawberry (Fragaria × ananassa Duch.) genotypes in a 2-yr experiment. The plants were covered by an unheated walk-in tunnel at the beginning of the first harvest season. The effects of a south-west versus north-east position of plants within the double-row beds were also studied. Soil temperatures were higher under black mulch, especially mid-day temperatures on the bed surface in the southward position. White mulch favoured root and crown growth in the first year, and the southwest position increased plant growth in both years. With black mulch, lower carbohydrate reserves were observed after transplanting, and a decreased chlorophyll content of leaves was detected in the second year. Mulch colour did not affect yield quantity. The first-year harvest was advanced with black mulch, but in the second year, the harvest season was earliest on the south side of beds with white mulch. Black mulch decreased fruit size in the first year and the concentration of fruit soluble solids in both years. The results suggest that in northern latitudes white mulch improves strawberry plant growth and fruit quality over that obtained using black mulch, but enhanced yield is not to be expected when a double-row tunnel cultivation system is used. Key words: Fragaria × ananassa, mulch, plasticulture, polyethylene, strawberry, tunnel

Effects of Silver Reflective Mulch, White Inter-row Mulch, and Plant Density on Yields of Pepper in Maine

Bell peppers (Capsicum annuum) are an economically important yet difficult to grow crop in northern New England. Yields of bell peppers can be increased through the use of plastic mulches; however, refinements are needed to make bell peppers a more viable crop in regions with short, variable growing seasons. The objectives of this study were to (1) compare the effects of black mulch with white inter-row much, reflective silver mulch, and standard black plastic mulched beds on bell pepper yield and quality and (2) compare the effects of two in-row plant arrangements [single rows at 12-inch within-row spacing (7260 plants/acre) and double rows spaced 18 inches apart with 18-inch in-row spacing (9680 plants/acre)] on pepper yield and quality. Treatments were factorial combinations of three mulch treatments and two within-row planting arrangements. Double rows produced more fruit by number and weight than single rows; however, fruit harvested from the double-row plots tended to be smaller than fruit harvested from the single-row plots. Mulch treatments significantly influenced total marketable yield and yield of cull bell peppers grown in Maine. The plots receiving the inter-row white mulch or reflective silver mulch treatment produced significantly greater yield than standard black plastic mulch treatment. The reflective mulch treatment produced significantly more cull fruit per acre compared with the white inter-row mulch and black plastic.

Leaf Area Distribution of Tomato Plants as Influenced by Polyethylene Mulch Surface Color

The influence of polyethylene (plastic) mulch surface color (white versus black) on leaf area distribution of tomato (Lycopersicon esculentum) was investigated in simulated planting beds at two sampling periods: an early sampling with relatively young plants that had been in the mulch treatment for 22 days and a late sampling with relatively mature plants that had been in the mulch treatments for 50 days. At the early sampling period, tomato plants grown with white mulch had more axillary leaves than plants in the black mulch, resulting in a greater axillary:main leaf area ratio for the plants with white mulch. Leaf area for total leaves (main + axillary) and plant biomass was unaffected by mulch surface color at the early sampling period. Tomato plants grown in black mulch at the early sampling period had significantly more area of main leaves partitioned to node 3, whereas plants grown in white mulch had more area of main leaves in nodes 8 and 9. Plants grown in the white mulch treatment had significantly more axillary leaf area at nodes 1, 2, and 3, whereas plants in black mulch had more axillary leaf area at node 6. At the later sampling period, most of the leaf area from both mulch treatments was recorded in the axillary leaves and there was no effect of mulch surface color on the amount of total leaf area partitioned to main, axillary, or total leaves; to the amount of biomass of the measured top growth; or to the nodal distribution of leaf area among main leaves or axillary leaves. Tomato plants in white mulch had significantly more fruit on plants at the later sampling period than plants in the black mulch. Mulch surface color also affected the plant light environment and soil temperatures. These results suggest that the polyethylene mulch surface color can induce changes in the plant microclimate and affect leaf area distribution of young tomato plants (as recorded at the early sampling) and fruiting of relatively more mature plants (as recorded at the later sampling).

ARMYWORM, STINK BUG AND LEAFMINER CONTROL ON FRESH MARKET TOMATOES, SPRING 2006

Transplants were set 21 Mar, 18 inches apart within the row on 8-inch-high and 32-inch-wide beds of Myakka fine sand covered with white polyethylene mulch. Each plot consisted of a single 18-ft long row with rows spaced 5 ft apart and 7 ft end to end. Treatments were replicated four times in a randomized complete block design and were applied with a 2.5 gal, hand-held CO2-powered sprayer at 60 gpa on 25 Apr, 10 and 23 May, and at 90 gpa on 6 Jun (Table 1). The sprayer was fitted with a D-5 disk and #45 core and was operated at 60 psi. The number of Liriomyza trifolii leafmines ≥ 0.5 inch long were counted on 25 May and 8 Jun during a 1 min search of each plot by two individuals, and the numbers were totaled for analysis. On 10 May, the middle 10 plants of selected plots were shook and the numbers of beneficial insects dislodged were counted. Fruit were harvested on 31 May and 21 Jun from the middle 10 plants of each plot and the number and weight of non-damaged fruit and the number of fruit damaged by armyworm larvae and stink bugs were determined.

SILVERLEAF WHITEFLY AND LEAFMINER MANAGEMENT ON SQUASH, SPRING 2006

Transplants were set 28 Mar, 1.5 ft apart within the row on 8-inch-high and 32-inch-wide beds of Myakka fine sand covered with white polyethylene mulch. Each plot consisted of a single 21 ft-long row spaced 11 ft end to end and 10 ft apart. Treatments were replicated four times in a randomized complete block design. Treatments were made as soil drenches in 4 ozs of water per plant on 28 Mar. The number of whitefly adults was counted weekly on one top leaf of the middle 10 plants in each plot. The numbers of eggs, and first instar and second to fourth instar whitefly nymphs were counted weekly on each of 4, 3.5 cm leaf disks per each of 10 leaves per plot. The number of Liriomyza leafmines was counted by each of two persons during a one minute search of each plot on 1 and 10 May.

AFFECTS OF INSECTICIDES APPLIED FOLIARLY TO FRESH MARKET TOMATOES ON ARMYWORMS AND PREDATORS, FALL 2005

Transplants were set 8 Sep, 18 inches apart within the row on 8-inch-high and 32-inch-wide beds of Myakka fine sand covered with white polyethylene mulch. Each plot consisted of a single 18-ft long row with rows spaced 5 ft apart across the beds and 6.5 ft down the beds. Treatments were replicated four times in a randomized complete block design and were applied with a 2.5 gal, hand-held CO2-powered sprayer at 60 gpa on 30 Sep, 14 Oct, 10 Nov, and 1 Dec. The sprayer was fitted with a D-5 disk and #45 core and was operated at 60 psi. The numbers of armyworm larvae and predators were evaluated on the middle 10 plants of each plot by either examining all leaves of each plant or by shaking the plants and counting dislodged insects on the soil mulch. Sampling was conducted 3-4 days after treatments (DAT) for selected treatments and 6-14 DAT for all treatments. Fruit were harvested on 21 Nov and 7 Dec. The number and weight of undamaged fruit and the number of fruit damaged by armyworm larvae were determined and were totaled over both harvest dates.

EFFECTS OF COLORED MULCHES ON “B” SIZE POTATOES

The small, B size potatoes (<2 inches but ≥1.25 inches in diameter) represent a keen interest in new, specialty food items. Exotic shapes and color shades of the specialty varieties are also known for intense flavors and variations in textures in firmness and fiber that consumers are looking for today in an ever increasing health consciousness among consumers. In 2006, the varieties `French Fingerling' (West Edmonton, Alberta, Canada), Villetta Rose (Univ. of Wisconsin) and B1145-2 (USDA, Beltsville, Md.) were planted in a double row 8 inches between tubers and 18 inches between rows in a replicated trial using colored mulches. The mulch color included red, white, black, blue, green, and silver foil. These plastic mulches were laid on 6-ft centers. The mulches were shown to affect the microclimate of soil temperature, as expected, and therefore affecting yield. These temperature differences were measured with a Campbell CR 10X weather station (Logan, Utah) probes at a 2 inches above the soil surface and 4 and 6 inches below the soil surface. Plant stands were excellent with all mulches, however, blue mulch caused early emergence while white and silver delayed emergence. Just the opposite effect happened when it came to yields. The highest individual tubers per plant came from the white mulch with the green having the lowest tuber yields. Cultivar differences were also seen in there ability to produce marketable tubers. `Villetta Rose' had the highest plant vigor and also the most marketable tubers per plant. B1145-2 produced most of its tubers >2 inches in diameter with the tubers nonuniform in shape. French Fingerling produced a very uniform oblong tuber with few defects. Yields and quality were above normal for all cultivars when grown on either the silver reflective mulch or the white mulch.

Seasonal Variation of Paraquat Photodegradation Rate on Polyethylene Mulch

Field studies were conducted to determine the effect of season of the year, sunlight exposure time, and mulch color on paraquat photodegradation rate on polyethylene mulch. Experiments were established in winter, spring, and summer, with white and black polyethylene mulch, and paraquat-applied films were exposed to sunlight for 1, 4, 8, 24, 30, 48, 72, or 96 h after herbicide application. There was significant effect of the season by mulch color by time of exposure interaction on paraquat concentration recovered from mulch eluants. Winter paraquat photodegradation was lower than during the other seasons. At 48 h of sunlight exposure, predicted photodegradation on white mulch was 67, 83, and 88%, during winter, spring, and summer, respectively, whereas these values were 66, 82, and 84% on black mulch. The difference in paraquat photodegradation in winter with respect to the other seasons may be attributed to reduced ultraviolet radiation in winter, when solar radiation has to penetrate a larger atmosphere mass. In practical terms, transplanting on paraquat-applied mulch requires a minimum of 96 h during the spring and summer seasons, when concentrations were 5% or less, whereas a longer waiting period might be necessary in the winter.

HIGH TUNNEL PRODUCTION OF TOMATOES AND SNAPDRAGONS IN SOUTHEAST ALABAMA

Production of high tunnel tomatoes and snapdragons was evaluated over a 2-year period at the Wiregrass Experiment Station, in southeastern Alabama. `BHN 640', `Florida 91', `Sunleaper', and `Carolina Gold', were evaluated in early Spring 2004. Results indicated that `BHN 640' outperformed `Florida 91' and `Carolina Gold' in early production of high tunnel grown tomatoes. A late Fall 2005 study examined `BHN 640' and `Florida 91'. Results indicated that `BHN 640' was superior to `Florida 91' in total marketable fruit. Season extension of both spring and fall tomato production were accomplished. A planting date study was completed in the early Spring 2005. The following four planting dates were evaluated: 31 Jan., 17 Feb., 4 Mar., and 25. Mar 2005. Wind damage to the high tunnel caused some mortality; however, the two earliest planting dates (31 Jan. and 17 Feb. 2005) produced over 10 lbs. of marketable tomatoes per plant. These were both superior to the last planting date of 25 Mar 2005. Cut snapdragons were evaluated for suitable colored mulch (red, white, or blue) and varieties for summer (`Opus Yellow', `Opus Rose', `Monaco Red', and `Potomac Early White') and fall (`Apollo Purple', `Apollo Yellow', `Monaco Red', `Monaco Rose', and `Potomac Early Orange') production. Results indicated that inflorescence length was affected by the color of mulch. The red mulch had increased inflorescence length compared to the white in Summer 2005. The Fall 2005 study revealed that white mulch had longer inflorescence length than the red or blue mulch. Some varietal differences were observed. The `Apollo Purple' had longer stem lengths than all other varieties for the fall study. The summer study revealed that `Opus Yellow' had longer inflorescence lengths than all others but stem lengths were all similar.

THE EFFECT OF PLANTING SYSTEM ON THE YIELD OF STRAWBERRY GROWN OUT-OF-SEASON

Production system for out-of-season summer harvest of strawberry were examited in teh temperature climate of Republic of Croatia. The aim was to prolong the harvest season. Two new prospective shor-day cultivars Madeleine and Raurica were grown with two different plastic mulch system (black and white) using drip irrigtion. A one row bed systemwas used. Plants were spaced 0, 2 m apart and rows were 1, 2 m apart, creating a planting density of 40, 000 plants per hectare. The highest yield was obtained from raurica in combination with white plastic mulch using cold-stored runner plants. The quality of fruit was good, with higher total soluble solids in comparasion with the same cultivars grown in season. By using new cultivars with higher yield potential and excellent quality nursery plants, it might be possible to extend the strawberry production season.

Effects of Living and Synthetic Mulch on the Population Dynamics of Whiteflies and Aphids, Their Associated Natural Enemies, and Insect-Transmitted Plant Diseases in Zucchini

Living and synthetic mulches were evaluated for control of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, and aphids in zucchini plantings. Two living mulches, buckwheat, Fagopyrum esculentum Moench, and white clover, Trifolium repens L., and two synthetic mulches (reflective and white) were evaluated during the fall of 2002 and 2003. Results from pan-traps, yellow sticky traps, and foliar counts showed that reflective and buckwheat mulches consistently had fewer numbers of adult whiteflies and aphids compared with the standard white mulch treatments. In 2003, a significant increase in the abundance of natural enemies was recorded in all treatments. Living mulch treatments had higher natural enemy populations than synthetic mulch and bare-ground treatments. However, there were no differences in the species diversity of natural enemies found between treatments. The effectiveness of mulches for controlling immature whitefly numbers and the incidence of squash silverleaf disorder were inconsistent between years. Additional data taken at the end of the 2003 season revealed that two viral strains (PRSV-W and WMV-2) were present in the field. However, visual symptoms associated with these viral diseases did not occur until the end of the season.

(183) Effects of Colored Plastic Mulches on Tomato Growth and Yield

Different colored plastic mulches can influence tomato (Lycopersicon esculentum L.) growth and yield. A study was carried out to compare the effects of different colored plastic mulches and bare ground on growth and yield of tomato. Ten treatments, namely, control (bare ground), and plastic mulches (black smooth, red, black embossed, blue, olive, yellow, clear, white, and reflective) were replicated four times in a randomized complete-block design. Tomato variety `Sunstart' seeds were planted in flats filled with Jiffy Mix in a greenhouse in late Apr. 2004 and seedlings transplanted in early June 2004. The seedlings planted in white and reflective plastic mulches were taller than seedlings planted in black smooth, black embossed, clear, blue, red, and olive mulches by 24 July 2004. Weeds were growing underneath clear, yellow, and red plastic mulches, and squash bugs were observed in yellow plastic mulch treatment on 2 July. Cumulative marketable tomato yield was highest in plants grown in reflective and white plastic mulches, and lowest in plants grown in yellow plastic mulch. Marketable fruits from plants grown in reflective and white mulches were larger than fruits from other treatments. In comparison with black embossed plastic mulch, plants grown in reflective and white plastic mulches had 2 and 1.2 tons/acre higher marketable yields, respectively, than plants grown in black embossed plastic mulch.

Responses of cucumbers to mulching in an unheated plastic greenhouse

SummaryPlastic greenhouses have become widespread in recent decades, predominantly as low–cost structures. Those using plastic houses often adopt techniques developed for more sophisticated glasshouses without prior studies to see if it is necessary to adapt them. White plastic mulching is used widely in heated glasshouses to increase available light during periods of low radiation, and thus benefit plant growth. A 2-year study was conducted to determine the response of a soilless cucumber crop to white plastic mulching, compared with an unmulched treatment, in unheated plastic greenhouses in southern Spain. The reflection of solar radiation by the plastic mulch reduced the mean substrate and air temperatures by up to 3.0ºC and 1.5ºC, respectively, during the early stages of canopy development. When substrate and air temperatures are sub-optimal, small temperature differences can be detrimental to crop growth and yield.The increase in available photosynthetically-active radiation (PAR) in mulched cucumbers could not compensate for the delay in growth in unheated greenhouses, and so yields were less than for unmulched cucumbers.

Leaf yield of Amaranthus hypochondriatus L. (Imbuya), affected by irrigation systems and water quality

Family scale vegetable production should be enhanced in rural areas in order to prevent vitamin A deficiencies. A soil-less water-use-efficient ‘Ebb-and-Flood’ production system, developed for areas with limited water resources, was compared with two conventional soil irrigation systems, using Amaranthus hypochondriatus L., locally known as Imbuya. The soil-grown plants were flood- and drip irrigated once every week, using nutrient solutions at two electrical conductivity (EC) levels of 1.80 mS cm−1 and 3.60 mS cm−1. The same volumes of nutrient solution were applied to these soil-irrigated plots as was used in the preceding week by the soil-less ‘Ebb-and-Flood’ system. With the soil-less ‘Ebb-and-Flood’ system, plants were fertigated five times per day and the containers were randomly allocated between the soil-grown field plots. Leaf yield as well as water use efficiency was highest when the high EC nutrient solution was drip irrigated. As part of the drip treatment, the dripper lines were covered with white plastic soil mulch to limit soil moisture losses. Due to rain before transplanting, the field-grown drip- and flood-irrigated treatments received extra water from the soil. In spite of this, the ‘Ebb-and-Flood’ system out yielded the flood treatment, when the nutrient solution with an EC of 3.60 mS cm−1 was used, probably due to insufficient root aeration in the flooded soil or due to better water uptake by the ‘Ebb-and-Flood’ system under saline conditions.

Butterbean Seed Yield, Color, and Protein Content Are Affected by Photomorphogenesis

Yield and nutrient content of edible beans are important to growers and consumers. Our objective was to determine whether some colors of light reflected to growing bean plants could affect photomorphogenesis enough to result in greater seed yield. Speckled butterbean (Phaseolus lunatus L.) was used as the test crop because it is a popular food crop, and the speckled areas contain anthocyanins, which function as antioxidants. The plants were grown in drip-irrigated rows that were covered with plastic mulch to conserve water and to reflect morphogenic light. Black served as the control; and red, green, and white mulch surface colors were used to reflect different quantities of blue (BL), red (R), and far-red (FR) light to the plants from emergence to ripening of seed. Seed yield over red was significantly greater than over black, green, or white. The area of seed coat covered by dark speckles was highest over red and lowest over black and green. Protein concentration on a seed weight basis did not differ among colors, but significantly more seed protein per plant was found in beans that developed over red than over black, green, or white surfaces. We conclude that altering the amounts of BL, R, and FR reflected to developing speckled butterbean plants can alter physiological processes enough to affect seed yield, anthocyanin-containing area on seed coats, and amount of seed protein per plant.

Onion Development and Yield in Response to Manual Cultivation, Herbicides, or Colored Mulches

ABSTRACT The extent of onion (Allium cepa L.) bulb and seed production varies with different production management practices. Field experiments were conducted during the 2000–2001 and 2001–2002 growing seasons to evaluate bolting and yield in onion grown with blue, red or white mulch in comparison to those grown with manual cultivation or chemical weed control treatment without mulch. The role of low temperature at the post-juvenile growth stage in bolting induction was also examined. Bolting was sometimes higher under mulch as compared to plots receiving manual hoeing or herbicide treatments. No particular mulch color appeared to consistently favor bolting. There was an inverse relationship between bolting and yield. Treatments did not affect germination of harvested seeds. Onion plants which were exposed to low temperature after attaining the critical growth stage for vernalization produced more inflorescences.

Light Transmission Through Colored Polyethylene Mulches Affects Weed Populations

Weed control is one of the benefits associated with the use of plastic mulches used for vegetable production. The mulches decrease light transmission and prevent development of most weed species. Plastics chemistry has developed films varying in their ability to reflect, absorb, and transmit light. Laboratory and field experiments were conducted to 1) measure light transmitted through colored mulches, 2) evaluate weed populations under each mulch type, and 3) determine if light transmission could be used as an indicator for weed populations in the field. The polyethylene mulches were black, gray, infrared transmitting brown (IRT-brown), IRT-green, white, and white-on-black (co-extruded white/black). On average, 1%, 2%, 17%, 26%, 42%, and 45% light in the 400 to 1100 nm range was transmitted through the black, white/black, gray, IRT-brown, IRT-green, and white mulches, respectively. In field experiments, density and dry biomass of weeds growing under the mulches were evaluated. The white mulch had the highest weed density with an average of 39.6 and 155.9 plants/m2 in 2001 and 2002, respectively. This was followed by the gray mulch, with 10.4 and 44.1 weed seedlings/m2 in 2001 and 2002, respectively. Weed density was <25 plants/m2 with the other mulches in both years. Weed infestation was correlated with average light transmission for white, black, white/black, and gray mulches. However, both light quantity and quality were necessary to predict weed infestations with the IRT mulches. Weed infestation under the IRT mulches was better estimated when only wave lengths in the photosynthetically active radiation range (PAR; 400 to 700 nm) were considered. Low weed pressure and high light transmission with the IRT mulches would make them appropriate for use in areas where both weed control and soil warming are important factors.

TOMATO PLANT GROWTH DURING ESTABLISHMENT AS AFFECTED BY ROOT ZONE TEMPERATURE UNDER COLORED MULCHES

Soil warming is one of the benefits associated with the use of plastic film mulches. However, under high temperature and intense solar radiation, further warming of the soil may negatively affect plant growth during establishment. Greenhouse-grown tomato seedlings were transplanted to the field and exposed to a range of root-zone temperatures (RZTs), resulting from growing the plants in different seasons and by utilizing colored mulches that differed in their soil-warming ability. The objective was to determine the relationship of RZT to plant growth during the first 28 days after transplanting (DAT). Experiments were carried out in Fall 1999, Spring 2000, and Fall 2000. Black (n = 2), gray, red, silver (n = 3), and white (n = 2) mulches, and unmulched soil were used. RZT under mulch was measured with copper-constantan thermocouples placed 10 cm below the soil surface. Irrespective of the season, the highest mean RZT (from planting to 28 DAT) occurred under black mulch, and the lowest under white mulch. The mean RZT under black mulch was 4°C greater than under white mulch. In the spring season, vegetative top dry weight (DW) at 28 DAT was higher with increasing mean RZTs. In the fall seasons, vegetative top DW at 28 DAT decreased with increasing mean RZTs. Pooling data from fall and spring seasons, vegetative top DW at 28 DAT was found to fit a quadratic relationship with RZT. From this relationship, optimal RZT for vegetative top growth was calculated to be 25°C. Vegetative top growth during the first 28 DAT was correlated with subsequent vegetative top growth and fruit yield. In conclusion, RZT under colored mulches significantly affected tomato plant growth during the establishment period. INTRODUCTION In the United States, commercially produced fresh market tomato (Lycopersicon esculentum Mill.) are commonly grown on plastic film mulch (Lamont, 1993). The benefits associated with use of plastic mulches include higher yields, earlier harvests, improved weed control, and increased efficiency in the use of water and fertilizers. Increased plant growth, yield and earliness have been attributed to the soil-warming effect of mulches at northern latitudes (Lamont, 1993; Wien and Minotti, 1987). Colored plastic film mulches influence plant growth and yield through modification of the light environment around the plant. Red mulches reflect far red light, resulting in a modified red:far red ratio in plants (Decoteau et al., 1988; Kasperbauer, 1992). Thus, in addition to the light effects of mulches, possibly colored mulches modify RZT in ways that may influence plant growth during the establishment period. Colored mulches have also been shown to affect plant growth and yield by modifying insect behaviour (Schalk and Robbins, 1987; Csizinszky et al., 1995). Under conditions of high ambient temperature and high solar radiation, plants often grow poorly and produce low yields because mulches warm the soil to temperatures that may be deleterious to plant growth (Miller, 1986; Tindall et al., 1991; Diaz-Perez et al., 2002). Root-zone temperature is important in plant growth and development because it affects physiological processes in roots such as uptake of water and nutrients (Cooper, Proc. XXVI IHC – Transplant Production and Stand Establishment Eds. C.S. Vavrina et al. Acta Hort. 631, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA) 12

Plastic mulches and row covers for early and midseason crisphead lettuce produced on organic soils

Plastic mulches and row covers for early and midseason crisphead lettuce (Lactuca sativa L. ‘Ithaca’) grown on organic soils were investigated over 2 yr. For early production, four mulch treatments (infrared transmitting, silver-on-black co-extruded polyethylene, white-on-black co-extruded polyethylene and a bare soil control) with and without an agrotextile low tunnel were tested. For midseason production, the same mulch treatments were evaluated in combination with normal and high planting densities (54 400 plants ha-1 and 65 200 plants ha-1). Low tunnels combined with mulches accelerated early growth and maturity by 10 d for infrared-transmitting mulch, 7–8 d for silver mulch and 3–5 d for white mulch, relative to production on bare soil control without a low tunnel. Infrared-transmitting mulch alone increased plant biomass early in the season and produced a lettuce head of heavier or similar weight relative to that from bare soil, even if harvested 3–4 d earlier. Lettuce heads grown on silver and white mulches were harvested 1–3 d earlier, and were 22% heavier in the first year and 29% heavier in the second year than when grown on bare soil. Head weights of lettuce under the low tunnels were higher than those from control plots in the first year only, and head size was similar in both years. For midseason production, infrared-transmitting and silver mulches accelerated the early growth of lettuce, but resulted in heads with long cores at maturity, particularly with infrared-transmitting mulch. Silver mulch increased the percentage of marketable heads in the first year and head weight and size at maturity in the second year, and reduced the incidence of aphids in both years, relative to plots without mulch. White mulch resulted in larger and heavier heads than those produced without mulch in the second year, and produced heads with shorter cores than those produced with other mulches in both years, even during particularly hot growing conditions. The percentage of marketable heads was similar for both the high- and low-density plantings and, as a result, the former produced more marketable heads per hectare. However, lettuce plants grown at the higher density were smaller in the second year. During conditions conducive to disease development in the first year, higher density plantings were more susceptible to downy mildew. Key words: Lactuca sativa, iceberg lettuce, muck soils, plasticulture, mini-tunnel, physiological disorder, planting densities

Suppression of Watermelon Mosaic Virus in Summer Squash with Plastic Mulches and Rowcovers

Plastic mulches and rowcovers were evaluated in southern Illinois to determine their influence on watermelon mosaic virus (WMV) disease incidence and symptom severity in susceptible and tolerant summer squash (Cucurbita pepo). The use of either black or white mulch produced greater early and total marketable yields than no mulch (bare soil) on `Dividend' and `Multipik'. More fruit had WMV symptoms with no mulch than with mulch, regardless of cultivar. However, more severe WMV symptoms developed on the fruit of susceptible `Multipik' compared to tolerant `Dividend'. The use of plastic mulches provided greater and longer protection to `Dividend' compared to `Multipik'. However, `Dividend' fruit did eventually develop virus symptoms as disease incidence in production fields increased. Rowcovers reduced the number of alate aphids landing on plants which resulted in fewer plants with WMV symptoms and suppression of symptoms on squash plants regardless of mulch type. Rowcovers had a greater influence on reducing the incidence of WMV and the severity of symptoms on `Dividend' compared to `Elite'. Rowcovers did not reduce WMV on `Elite' by the end of the season and were more effective when used with white mulch compared to black mulch. Rowcovers suppressed the incidence and severity of WMV symptoms that developed on a virus tolerant squash cultivar for a greater length of time compared to a susceptible cultivar, which related to increased yields and fewer culls with virus symptoms on the tolerant cultivar.