Q. I have been trying to make sense of mildew. What it is and how it occurs. I searched it on the internet and when I saw pictures it seemed like spots were in the leaves and not on it. It is contrary to what I experienced on my papaya and okra plants. The powdery stuff was on the leaves of my plants and could be easily removed by a sponge. I thought this is what mildew is but it seems that mildew discolours the leaf with its white spots and cannot be cleaned with a sponge and what I experienced was some other disease which shows up on the leaves and can be easily removed by a sponge. What exactly is mildew and what is the disease that is on my plants?

A. Mildew is a fungal disease, multiplied by spores and is particularly prevalent when humidity is high. There are two types of mildew: powdery mildew and downy mildew. Powdery mildew is mostly on top of the leaves and can be washed off using one tablespoon bicarbonate of soda and one teaspoon liquid soap mixed with four litres of water. Spray sponge down the leaves around sunset, never when the sun is up as that would further damage the leaves.

Downy mildew tends to appear as fuzz underneath the leaves, progressing to form the spots that you mention, it cannot be washed off and heavily infected plants should be removed and sensibly disposed of well away from your garden area. The most effective way of preventing mildews is to ensure free air flow in between and around plants — it is important to avoid overcrowding of plants for this reason — and to keep the garden and soil surface free of any plant debris which may harbour the spores. Also, take care not to overwater.

Plus, stick to an evening watering regime, watering the soil without wetting the plants, as this helps keep humidity to a minimum. Our climate being as it is, however, humidity cannot be totally prevented.

Q. What is the best way to store vegetable, fruit and flower seeds and how long can they be kept?

A. Fully ripe and dry seeds should be stored in dark coloured (to exclude light), airtight containers, labelled with the name of species and date harvested. These should be stored in a dry, cool and dark place. The salad drawer of a refrigerator is ideal but, as that may not be possible, you can put all the seed containers together in a waterproof bag/sealable box, adding some sachets of silica gel for extra safety, and keep them in the freezer. Some seeds can only be kept for a very short time, others can be stored for years. For full information you need to research the seed viability of the specific varieties you intend to store.

All your gardening queries answered here

Q. I planted some Jacaranda mimosifolia seeds in pots and they are now about two inches tall. I am planning to make bonsai out of them. Can you please tell me what kind of fertiliser I should use, specifically what the NPK (nitrogen, phosphorus and potassium) ratio should be. I reside in Karachi.

A. No fertiliser at all please. Fertiliser is known to prevent jacaranda trees from flowering, especially fertiliser containing nitrogen. They grow and flower best in poor soil.

Q. Having read your article about Opuntia stricta I have decided to grow them for animal fodder. Where, within Pakistan, can the seeds be obtained?

A. Opuntia stricta is usually multiplied from the pads of an existing plant. These pads are cut off the mother plant at their joints, left to dry in the sun for a few days and then simply stuck into well-draining, preferably light/sandy soil and will root and grow quite quickly. I suggest that you search out a few plants from nurseries and take the pads from these — wearing gloves of course. This will be far quicker than struggling to grow them from seed.

Q. My Kungni palm is infested with hard whitish stuff on its leaves. What is it and how to get rid of it?

A. Armoured scale insects are the bane of Kungni palms these days and are almost impossible to get rid of. You can try coating them with good quality vegetable oil/olive oil to suffocate them; you may have to do this a number of times as there are always a few different generations of these nasty insects present on the leaves and in the soil around the plant at the same time. Repeatedly spreading coffee grounds (left from freshly ground not instant coffee) on the soil around the base of the palm also works — or so it is claimed — as this kills off any eggs and larvae present in the soil. If the palm is heavily infected, it is, unfortunately, best to dispose of and grow something else in its place.

Please continue sending your gardening queries to zahrahnasir@hotmail.com. Remember to include your location. The writer does not respond directly by email. Emails with attachments will not be opened.

Published in Dawn, EOS, April 12th, 2020