Dale I.M. Riggs
Former Area Vegetable Specialist
D. Riggs Consulting, Stone Wall Hill Farm, LLC

Pumpkins are an increasingly important crop throughout New York State as well as the rest of the country. Since 1995, trials have been conducted to determine ways growers can maximize yield through various cultural inputs and methods. This presentation will focus on the questions we tried to answer over the past four seasons.
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1. What effect does varying nitrogen levels have on yield of pumpkins?

Trials conducted at two locations in 1995 demonstrated that there was little difference in the yield of two pumpkin varieties (Howden and Wizard) as nitrogen rates were increased from 60 to 140 lbs/A. There was a trend towards slightly larger fruit size with higher rates of N but this was not consistent. These tests were conducted on silt loams with relatively good nutrient holding capacity so greater amounts may be useful on sandy or gravely soils. Higher amounts may lead to more foliage which could lessen fruit set. Based on these tests, 60 to 100 pounds N/A seems to be adequate.
One reason for a lack of effect due to nitrogen may be due to the timing of application. Typically, pumpkins are sidedressed just as they begin to run. Unfortunately, this is the same time when female flowers are being produced and fruit set is occurring. With pumpkins, it is impossible to sidedress later in the season since this would entail running over vines and fruit. One possible way to get around this would be to use trickle irrigation and fertigate later in the season after fruit set. A study is planned for 1999 to examine this method.

2. Can in-row spacing affect yield?

Grower practices vary in terms of spacing to optimize pumpkin yields. With cucumbers and watermelons, closer spacing has led to an increase in fruit per acre along with a smaller fruit size. The effect on tons/A seems to vary, resulting in either no effect or a significant increase. This trial was conducted to determine the effect of spacing on two pumpkin varieties, Howden, a large vining type, and Wizard, a semi-bush type.
Pumpkins were planted on 6 foot centers with in-row spacings of 1, 2, and 4 feet. Plants were thinned to a single plant per hill. At both locations, closer in-row spacings significantly increased the number of pumpkins/A while decreasing the average weight per fruit. At one location, despite the smaller fruit, the increase in fruit numbers resulted in a significant increase in tons/A while in the second location, the tons/A was not increased. Why the difference? The location in which we saw increased tons/A was irrigated while the other location was not. Apparently, to take maximum advantage of increased plant populations, growers need to ensure that water is not limiting.

3. What effect does between row spacing have on pumpkin yield?

Growers have two options when increasing plant populations: either within-row spacings or between row spacings can be decreased. From our previous trial, we know that changing in-row spacing significantly affects yield. For pumpkin growers, a wider between-row spacing may be better, allowing for easier access to fields for the purpose of cultivation, pesticide, or fertilizer applications. A trial was conducted comparing the same plant populations on 6 and 12 foot centers. For 6 foot centers, in-row spacings of 2, 4 and 6 feet were used. For 12 foot centers, in-row spacings of 1, 2, and 3 feet were used.
For both the 6 and 12 foot centers, we saw an increase in yield as within-row spacing decreased and population increased. Row width had little effect on any aspect of yield with the exception of the number of fruit /A. Six foot centers resulted in a significant increase in fruit numbers at both locations. The greater number of fruit did not result in increased tons/A as the average fruit size declined slightly with the narrow spacing.
The data indicate that row width may become more important at higher plant populations
tons/A. The effect is significant, however, only when spacing between rows is narrow. The narrow row width provides each plant a more square area of land than did wider spacings at the same population. Plants are spread out more evenly in the field and may be less likely to compete in this arrangement. The effect was seen for both a large vining variety (Howden) as well as a semi-bush type (Wizard). This effect may be more pronounced when yields are maximized with optimum inputs of fertilizer, irrigation, and pesticides.

4. Is there an advantage to having more than one plant per "hill"?

Some growers have traditionally kept two or three plants per hill in the belief that this increases yield. It is also good insurance in case a plant is lost to insect or disease. Based on previous studies, it would seem that two or more plants per hill would not increase yield. In 1997, a trial was conducted in which pumpkins were grown on six foot centers with 2, 4, or 6 foot in-row spacings. Each hill contained either one or two plants. As in the other studies, Howden and Wizard were the varieties grown.
Doubling the number of plants per hill had very little effect on yield. At one location, there was an increase in fruit number/A and a decrease in average fruit size with two plants. Most of the significant increase in yield was all due to the closer in-row spacings which resulted in more fruit/A and more tons/A, with a typical decrease in fruit size.
Although there was no advantage to having more than one plant per hill, there was also no yield "penalty". Growers may want to consider using 2 plants per hill to ensure that at least one healthy plant is available for yield.

5. What effect does irrigation have on pumpkin yield?

Form earlier trials, it seems that irrigation may be extremely important in determining the final size of a pumpkin. In 1995, two variety trials were conducted, similar in all ways except one was irrigated (overhead irrigation) and the other was not . The results indicate that irrigation can increase fruit size from 50-100%.
In 1998, a trial was conducted in which three levels of irrigation (using trickle) was maintained on pumpkin plots. There was no difference between the high and low irrigation treatments but when irrigation is compared to no irrigation, there was significant increase in fruit number per acre and tons per acre. Surprisingly, irrigation did not increase average fruit size.

What have we learned over the past four years?

NITROGEN FERTILIZER

• moderate amounts of nitrogen (60 to 100 pounds/acre) appear adequate on heavier soils
• excessive amounts may lead to a decrease in fruit set, increased foliage and a decline in yield
• timing of application may play an important role in yield effects

SPACING

• fruit number and tons/Acre can be increased by increasing the number of plants per acre
• pumpkin size will be smaller at higher populations
• growers are better off increasing populations through narrow between row spacing and wider in-row spacings - this more square arrangement seems to lead to less competition between plants
• the effect will be more pronounced when all inputs (fertilizer, irrigation, pest control, etc.) are maximized

NUMBER OF PLANTS PER HILL

• there is no advantage to having more than one plant per hill - two plants will essentially behave as a single plant
• there is also no real disadvantage to two plants per hill - growers may want to strive for two plants per hill to ensure at least one healthy plant

IRRIGATION

• irrigation will increase number and tons/acre but we're still not sure about the effect on individual fruit size

The overall effects seems to be true for both large vining varieties like "Howden" as well as semi-bush types like "Wizard". Competition for light, nutrients, and water would be increased in high density plantings. Close spacings could increase leaf wetness causing greater disease pressure. Growers who choose higher populations need to ensure that all inputs are optimized to reduce potential plant to plant competition. In addition, growers should only use varieties that are adapted to a particular region.

We wish to thank the Pennsylvania Vegetable Marketing and Research Program for their support of this study in 1995 and the NYS Vegetable Crops Statewide Program Committee for support in 1996-1997. Also, thanks to cooperating growers, Saulpaugh and Sons, Richard Ball, and Burton Metice.