Tuesday, 3 January 2017

Poor Pollination

Corn Pollination

Pollination? It just happens right? Not necessarily, there are many variables in successful pollination. 

For instance corn is susceptible to pollination problems as it is pollinated by wind and therefore should be planted in blocks of at least four for adequate cross-pollination to occur. 

Corn anthers - male part of corn plant

Pollen from the male part of the plant falls onto the wispy immature heads of the corncobs. 

Poor pollination results in 'skips' or missing kernels and poorly filled ears. Inadequate watering can also affect the ability of the corn plants to pollinate properly. 

 Cucurbitaceae Family

Female squash blossom with a small, immature fruit
 at the base of the yet-to-be pollinated flower.

Crops in the Cucurbitaceae family, for instance cucumber, squash, pumpkin and watermelon, require cross-pollination to produce their fruits. 

They often suffer from poor pollination. 

Within a day of the flower opening and insects
have pollinated it the fruit begins to expand
and its supporting stem begins to strengthen
to support it on the vine as it ripens.
Separate male and female flowers are produced on the same plant. Pollinator insects move pollen from the male flowers to the female flowers where the pollen can fertilise the ovules (tiny seeds) inside the ovary (the very small fruits that appear below the female flowers).  

If the flower isn't well pollinated, the fruit will begin to yellow
and shrivel quickly, sometimes turning brown or black at
the flower end over time.

Blooms will often also simply drop off the plant if they are not pollinated. This can be caused by low bee/insect activity.
In the image (right) examples of a successful and unsuccessful pollination of a zucchini. 

Encouraging insect pollination

To encourage good pollination by insects we need to entice them to our gardens. Flowers which are particularly good at attracting insects to the vegetable garden and these can be grown as companion plants to our crops. Some good plants to grow would be comfrey, geranium, lupin (good as a nitrogen 'fixer' too), borage, buddleia, lavender, sunflower and alyssum to name but a few.

We need to be quite circumspect with the use of sprays in our vegetable gardens. Read the labels very carefully before use to see if it will be harmful to beneficial insects too.

Insects will always be the top pollinators in our vegetable gardens, so to encourage them is perhaps the best way to facilitate the process.

For the dedicated - hand pollinating

Hand pollination is not normally necessary if there are plenty of insects around. However certain vegetables (such as eggplant and kiwi fruit) can be a bit tricky to pollinate, so hand pollination may be necessary.

Pollinating by hand also avoids cross-pollination which can be useful if you want to save seeds. Cross-pollination occurs when pollen from one vegetable variety fertilises a different variety of the same (or similar) species. For example if a bee pollinates a pumpkin flower with pollen from a butternut squash flower, the resulting fruit could be an inedible hybrid of the two!

The method you use to pollinate your crop should depend on the type of flower you are pollinating. Plants in the squash family have male or female flowers. Female flowers have an immature fruit just behind the flower and male flowers have just a long stem with no swelling at the base. Simply pick an open male flower and strip off the petals to expose its stamens and pollen then rub them against the stigma of a female flower (the flower with a swelling below it) until you see the pollen has rubbed onto it.

You can also dislodge the pollen in self-pollinating flowers by shaking the plant gently. A more reliable method however is to use a soft paintbrush. Gently brush the inside of each flower. You will see the pollen transfer onto your brush; if you transfer pollen between the flowers you will mimic the natural movements of insects.

If you feel there has been insufficient wind to pollinate your corn crop, hand pollinating could be the go for you. 

The best supply of fresh, high-quality pollen is shed from mid to late morning, so that's the best time to assist in the pollination process. 

Take a broad, dry pan as as a pie tin and hold it beneath the tassels and give them a tap to shake out pollen. Free-floating pollen will likely land on many of the silks and some will accumulate in your pan. Sprinkle pinches of the powdery pollen over the silks of ears on the edges of your planting, as well as those on the upwind side of your plot.

Snip off a few anther-bearing branches from the tassels that look like they are freshly opened. The days new anthers often appear yellowish because they are full of fresh pollen (one dangling anther can hold 2500 grains of pollen). Gently tough the tassels to waiting corn silks, as shown here.

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