Pollination Problems

Overview

Flowering plants such as cucumbers, melons, peppers, squash, and tomatoes will not produce fruit or will produce deformed fruit when pollination has been inhibited. 

Symptoms and Diagnosis

Tomatoes & Peppers

Tomatoes have both male and female parts in the same flower but sometimes pollination fails to occur. The result is that the plants may appear to be healthy, growing well, and flowering, but many or all of the blossoms drop from the plant failing to form fruit. Plants grown outdoors are generally self-pollinating as long as there is a breeze or other mechanism for moving pollen from anthers to pistil.

Cucurbits

Cucurbits (cucumbers, melons, & squash) are monoecious; there are separate male and female blossoms on the same plant. The male flowers tend to open first, followed by the female flowers. It is only when both the male and female flowers are open that pollination can occur. The female flower is open for only one day and is most receptive between the hours of 9 AM and 4 PM. During this time the flower must receive about 15 bee visits for maximum pollination. Unfertilized or poorly fertilized flowers fall from the vine. The plants may appear to be healthy, growing well, and flowering, but many or all of the blossoms drop from the plant. Fruits may appear to start developing but become incomplete or die entirely.

Life Cycle

Weather conditions are key factors in successful pollination. High daytime temperatures or low nighttime temperatures will diminish pollination in tomatoes, which causes flowers to drop and fruit not to form. High humidity creates sticky pollen which does not transfer well (this is the problem with most cucurbit pollination issues). Excessive use of nitrogen fertilizer can also result in copious leaf production at the expense of flowering and fruit development. Dry soil can also result in fruit drop and high humidity can create sticky pollen which does not transfer well. 

For tomatoes, daytime temperatures between 70 - 80^oF. and night temperatures between 60 and 70^oF are ideal. Temperatures below 50^oF. or over 90^oF. can prevent pollination from taking place., which results in flower drop. The use of a hormone spray; such as Blossom Set, can improve the chances of successful pollination and fruit set during periods when night temperatures are below 60 degrees F.  At temperatures above 90^oF hormone sprays are not effective. Temperature ranges and the use of hormone sprays are very similar for peppers.

Integrated Pest Management Strategies

1. Follow planting guidelines for your time zone. Tomatoes planted too early or too late are more likely to have pollination problems. Early and late varieties may be more fruitful if weather is an issue.

2. Hormone sprays. The use of a blossom set hormone may increase fruit production if the cause is cool, cloudy weather, but not if the temperatures are too high. Follow label directions. To be effective each flower must be treated. Avoid spraying the whole plant.

3. Provide good culture. Minimize stress on your plants with proper spacing, watering, and pest management.

4. Fertilize properly. Avoid excess nitrogen which will promote foliage growth at the expense of blossom formation.

5. Plant recommended varieties. Select varieties that are recommended for your area of the country. Recommended varieties may have been selected to better tolerate your temperature variations.

Organic Strategies

Strategies 1, 3 and 5 are strictly organic approaches. Using an appropriate organic fertilizer would be a viable organic approach to Strategy 4.