The first instalment of the Root Awakening column was published last Saturday on 5 Sep 09 on Straits Times Life! As usual, answers to three gardening questions were given answers.
The first question dealt with mealy bugs on chilli plants and how one can use white summer oil or neem oil to eradicate them. White summer oil is a contact pesticide derived from petroleum oil that works only on small sucking insects such as mealy bugs, aphids and spider mites by suffocating them. It has no effect on chewing insects such as grasshoppers and caterpillars.
Neem oil, on the other hand, is a botanical pesticide that is obtained from the kernels of neem tree seeds. When sprayed onto small sucking pests, it kills them by suffocation. Unlike white summer oil, neem oil also deters chewing insects from damaging plants. According to some reports, neem oil is also absorbed into the plant and may work like a systemic pesticide.
Remember to spray at the right time in a day. Beneficial insects are most active during the day. The best time to spray pesticides is very early in the morning (around 7 am), so the spray can dry before the beneficial insects become active. Also a good time is the late afternoon or evening.
White summer oil (tradename – Acalineum) and neem oil or its extract (active ingredient – azadiractin) can be purchased from Ang Mo Kio Floral & Landscape Pte Ltd and HortMart.
The second question asked how one can treat leaf spot disease on yam plants. Leaf spot disease can be caused either by pathogenic bacteria or fungus but it may be difficult to distinguish the two.
Leaf spots caused by bacteria are often initially light green and look “water-soaked”. These leaf spots will eventually turn brown or black and may have definite margins. Fungal leaf spots appear as brown or black spots that are randomly scattered across the leaf. They may or may not have the appearance of concentric rings and the margins of the spot may be a different color than the center of the spot.
For non-chemical control, cut away all affected leaves and discard diseased material in the garbage bin and not into the compost heap. Give plants enough sunshine and air circulation to grow and avoid soil splashes on the leaves. Use sterilized cutting tools to prune your plants the next time. The use of a fungicide warranted only when the disease is ascertained to be caused by pathogenic fungi. Because some fungicides can damage plant foliage – test on a small area before treating the whole plant.
The last question was about germination failure of wheat grass seeds. One of the reasons that could have caused the problem is infected compost mix that was used to sprout them. The organic compost used may not be sterile and pathogenic organisms such as bacteria and fungi may have attacked your wheat seeds and led to the germination failure. One may want to sterilize small amounts of compost by heating a tray of the material in a baking or microwave oven.
Another reason for the seed germination failure could be due to excessive moisture in the compost. Compost can retain too much water in itself that makes it far too wet for wheat seeds to sprout. Consider mixing equal parts of washed fine sand and compost to help improve drainage and aeration.