A common problem affecting otherwise healthy tomato and capsicum plants during heat waves is blossom end rot, where partly formed fruit develops a dark, sunken patch furthest from the stem.
This is caused by calcium deficiency, and is not a disease. Like us, plants need a good supply of calcium to form a strong structure. Hot and very windy days increase transpiration (water loss) from plants in the same way we perspire to keep cool, and calcium can only be absorbed by plants as water-soluble, electrically-charged ions. This problem can also affect zucchini, pumpkin and melon plants.
During heat waves, daily watering rarely solves the problem. A deep watering a couple of times a week is more beneficial. If soil around plants is mulched to keep roots cooler and reduce water loss, an efficient way to water quickly is to place juice or soft drink bottles, neck down, beside plants. See: Watering in drought conditions
Other causes of blossom end rot are:
• Erratic watering
• Soil is too acidic (soil pH less than 6)
• Poor fertilising routine
• Overuse of fertilisers high in nitrogen or potassium, including some seaweed fertilisers
• Rarely, in very alkaline soil where calcium becomes insoluble.
The squash or Cucurbit family that includes chokoes, cucumbers, grammas, gourds, pumpkins, rockmelons, squash, watermelons, and zucchinis, produce both male and female flowers on the same plant, and rely on insects, such as bees, to pollinate the female flowers and produce fruit. (Although we eat many of this family as vegetables, in gardening terms, their produce is fruit.)
If bee activity is low, flowers of this family remain unpollinated, and fruit is unable to form. When this happens you may have to hand pollinate your plants to reap the benefits of your hard work. This is quite a simple procedure.
First identify the the female flowers on your vine or bush. At the base of each female flower you will find a miniature version of the mature fruit of that particular species. For example, cucumber vines produce what looks like a tiny gherkin at the base of each female flower while watermelon produce a watermelon miniature, often complete with stripes. The bases of male flowers, on the other hand, join directly onto a vine stem. See examples below.
Cucumber flowers – Male on the Left, female on the right.
Zucchini flowers – Male on the left, female on the right.
To hand pollinate, take a clean, dry, soft-bristled paint brush and ‘tickle’ the centre of a male flower to collect pollen on the tips of the bristles, then gently transfer the pollen to the stigma at the top of the style in the centre of female flowers, making sure that it is well-covered with pollen. (Image shows hand pollination of female cucumber flower.)
Or, you can remove a male flower from the vine, and carefully peel back the petals so that the pollen bearing part in completely exposed. Then dab the centre of the male flower into the centre of a female flower. Repeat this process, replacing the male flower as pollen is removed. Then stand back, and allow nature to take its course. If you can only find male flowers on your cucurbit vine, the problem takes a little longer to overcome. Pinch off the end of each long runner. This will stimulate the plant to produce side shoots called laterals. Some members of this family tend to produce female flowers on laterals. Once female flowers form, proceed with hand pollination if there are not many bees around.