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Irrigation and Cultivar Selection for Cucurbit Pollination and IPM

Cucurbit growers can use resistant varieties and proper irrigation to manage insect pests, protect pollinators, and improve crop resilience under drought and other environmental stresses.

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Updated:

September 29, 2026

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Rainout shelter during the experiment with cucurbit varieties planted inside. Photo by Jaydyn Isiminger, Penn State.

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Cucurbit crops such as pumpkins and squashes are a valuable component of Pennsylvania’s agricultural economy. In 2025, over 5,000 acres of Pennsylvania farmland were planted with pumpkins, with a production value of $27 million. Damage by insects such as striped cucumber beetles (Acalymma vittatum), squash bugs (Anasa tristis), and melon aphids (Aphis gossypii) can significantly impact production by directly killing plants and reducing marketable fruits. Regular applications of pyrethroid or neonicotinoid insecticides are typically recommended to keep pest levels below economic thresholds. However, applications during peak flower production are highly detrimental to pollinators (for more details, access Pollination Services in Curcubits). Also, weather conditions may influence pest pressure in different ways. In Pennsylvania, there have been seven instances over the past 25 years where 50% or more of the total land area was in a stage of at least moderate drought, and 3/7 of those instances have occurred in the last 5 years. These conditions indicate that summer droughts continue to occur even with an increased likelihood of severe rainfall events in the region (Drought.gov 2026). To sustainably manage insect pests while protecting pollinators under variable environmental conditions, one of the best tools growers have is to implement a combination of resistant varieties and trap cropping to ensure crop resilience under various environmental stressors, such as drought.

Cultivar variation in pest pressure

We compared insect pest abundance on 8 different varieties of cucurbits from the three main cultivated species of Cucurbita (Table 1). These varieties were selected to represent a variation in appearance, size, and maturation date. For more information about these varieties, see the Mid-Atlantic Fruit and Vegetable Production Guide (Table 1).

Table 1: Varieties screened for pest resistance with the type of fruit produced, the species, and the seed supplier.
Variety	Type	Cucurbita Species	Supplier
Blue Ballet	Hubbard	C. maxima	Johnny's Seeds
Boston Marrow	Hubbard	C. maxima	Seed Saver's Exchange
Butterbaby	Butternut	C. moschata	Johnny's Seeds
Waltham Butternut	Butternut	C. moschata	Johnny's Seeds
Green Machine	Zucchini	C. pepo	Johnny's Seeds
Multipik	Summer squash	C. pepo	Harris Seeds
Lil' Ironsides	Carving pumpkin	C. pepo	Harris Seeds
Small Sugar	Pie pumpkin	C. pepo	Territorial Seed

All seeds used in the study were untreated. One-month old plants were transplanted into raised beds covered with black plastic and irrigated with drip tape. We surveyed insects for one month and found significant differences in pest abundance across varieties. Aphids were most abundant on the varieties "Green Machine" and "Multipik", which are both early producing summer squashes. Cucumber beetles were most abundant on: "Boston Marrow" and "Blue Ballet" (both C. maxima cultivars) and squash bugs were most abundant on "Multipik" and "Boston Marrow". Butternut cultivars "Waltham Butternut" and "Butterbaby" had the lowest pest abundance across all three pest species. Between the two pumpkin varieties, there was no difference in insect pest abundance for any of the three pest species (Figure 1). Growers should consider purchasing insecticide-treated seeds of the more susceptible varieties to provide early-season beetle control, or try an "attract and kill" strategy by planting a border with an attractive C. maxima cultivar and then treating the border with foliar insecticide applications.

Different colored points representing mean insect counts of different cucurbit varieties with standard error bars — Figure 2: Relative susceptibility of each cultivar to the three different cucurbit pests and mean insect counts of all three major pests surveyed weekly on 8 different cucurbit varieties in July of 2025.

Effects of drought on pest pressure

To examine how drought affected pest abundance, pollinator visitation, and yields, we covered half of the varietal plots (below) with a rainout shelter to prevent environmental rainfall (Figure 1). We also ceased irrigating the drought plots after a one-week establishment period following planting.

We found that aphids and cucumber beetles were more abundant on drought-stressed plants, while squash bugs were abundant on plants regardless of the watering treatment. Squash bugs laid more eggs on well-watered plants, likely because the plants are healthier and provide better food for emerging nymphs. Therefore, during drought years, additional pesticide applications may be necessary to control aphids and cucumber beetles.

Effects of drought on flowers and pollination

Cucurbits produce both male and female flowers (Figure 3). When pollinated, female flowers eventually set fruit, so female floral abundance is a key factor for yields. If plants look healthy but produce no female flowers, yields will be zero. Our data shows that under drought conditions, plants produced more male flowers with a reduction in the average number of female flowers by 40% in comparison with well-watered plants.

Two squash flowers, one male and one female — Figure 3: Male squash flower (left) and female squash flower (right). Photos by Lauren Sandberg, Penn State.

Regarding pollination, we found that drought significantly reduced visitation by bees (honey bees, squash bees, and bumblebees). Plants under drought stress received an average of 0.3 bee visits per flower, while well-watered plants received an average of 1 bee visit per flower across 5 minutes of observation (Figure 4).

Boxplot showing the median bee visits per flower in drought and well-watered plants. The median line for the drought is below the median line for the well-watered treatment. — Figure 4: Bee visits per flower on drought-stressed and well-watered plants across all varieties. Bees were surveyed between 6:00 and 9:30 AM.

Ultimately, drought had a pronounced negative effect on yields across all varieties. The variety most tolerant of drought stress was "Blue Ballet", while "Small Sugar" and "Boston Marrow" had the largest reductions in yield (Table 2).

Table 2: Average yield of well-watered plants (in lbs/acre) and percent reductions in yield due to drought stress in all 8 tested varieties.
Variety	Average yield (lbs/acre)	Percent yield reduction
Blue Ballet	4,316	43%
Boston Marrow	9,781	73%
Waltham Butternut	11,022	64%
Butterbaby	7,957	71%
Green Machine	19,471	66%
Multipik	16,419	63%
Small Sugar	8,312	73%
Lil' Ironsides	7,418	65%

Summary of recommendations

We recommend growers irrigate their pumpkins and squashes at least 3x/week during rain-free periods for optimal plant health. Drip irrigation is preferred over rain guns and sprinklers because excess moisture on the leaves can accelerate the growth of diseases such as powdery mildew. Growers cultivating multiple species or varieties of Cucurbita should consider the differences in pest susceptibility when planting their fields and planning for pest management. More susceptible varieties may require more frequent monitoring and management. Regular scouting remains an important part of implementing integrated pest management approaches that restrict pesticide applications to only when pests are above economic threshold levels. Striped cucumber beetles have seasonal peaks and adults are most abundant in mid to late June and late July/early August. Growers may want to consider administering a neonicotinoid pesticide through the irrigation system between late June and late July to kill developing larvae in the soil before they emerge as adults to avoid foliar sprays during peak pollinator activity. Decisions regarding squash bug management should be made based on nymphal counts rather than the number of egg masses, because the eggs are often parasitized later in the season, and the number of egg masses does not accurately predict future squash bug abundance (Boyle et al. 2025). Scouting during peak insect activity will help optimize the timing of insecticide applications to prevent excessive yield loss while preserving pollination benefits.

This work was funded by the Pennsylvania Department of Agriculture Award #C940001869, USDA-Applied Research and Development Program project no. 2025-70006-45152 and USDA National Institute of Food and Agriculture and Hatch Appropriations under project no. PEN04923 and accession no. 7006440.